tag:theconversation.com,2011:/us/topics/new-horizons-3395/articlesNew Horizons – The Conversation2020-02-14T11:26:09Ztag:theconversation.com,2011:article/1317972020-02-14T11:26:09Z2020-02-14T11:26:09ZWhy the most distant object ever visited looks like a snowman – flyby delivers results<figure><img src="https://images.theconversation.com/files/315286/original/file-20200213-11017-106p6rx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Arrokoth.</span> <span class="attribution"><span class="source">Quapan/Flickr</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>Just over a year ago, courtesy of <a href="https://theconversation.com/new-horizons-is-an-old-spacecraft-but-it-will-transform-our-knowledge-of-pluto-44524">NASA’s New Horizons mission</a>, we were treated to images of <a href="https://www.space.com/32049-kbo-2014-mu69.html">2014MU69</a>, a small object 6.6 billion kilometers from the sun – making it the most distant object to have ever been visited by a spacecraft. It was described, variously, as a snowman, a bowling pin or a peanut. What we were seeing was a picture of one of the oldest and most primitive bodies in the solar system.</p>
<p>New Horizons took only a handful of minutes to <a href="https://theconversation.com/fly-by-missions-what-is-the-point-when-we-have-the-technology-to-go-into-orbit-44622">fly past the object</a> at its closest approach of about 3,500km – but those minutes were well spent, recording a huge amount of information. It has taken many months to download the data from the spacecraft because of its distance from Earth and slow rate of data transfer. </p>
<p>Now, though, a series of papers from the mission team, published in Science (see <a href="https://science.sciencemag.org/lookup/doi/10.1126/science.aay3999">here</a> and <a href="https://science.sciencemag.org/lookup/doi/10.1126/science.aay3705">here</a>), illustrate what can be learnt with a few minutes of carefully planned and coordinated recording time. The papers give a detailed description of the object. It hasn’t changed in shape – but now we know why it has the shape it does. And the explanation will help us understand more about the most unaltered objects in the solar system.</p>
<p>The object resides in the <a href="https://theconversation.com/there-are-missing-objects-at-the-fringe-of-the-solar-system-new-study-puzzles-astronomers-112436">Kuiper Belt</a>. “Kuiper Belt Objects” form a belt of small bodies that extends way out beyond the orbit of Neptune. They are the cold and rocky remnants of solar system formation. The body in question is dark and a bit reddish in colour. Its double-lobed appearance resembles <a href="https://theconversation.com/building-blocks-of-life-found-among-organic-compounds-on-comet-67p-what-philae-discoveries-mean-45379">comet 67P/Churyumov-Gerasimenko</a>, the target of ESA’s <a href="https://theconversation.com/emotion-and-tears-in-mission-control-as-rosetta-comes-to-a-silent-end-66343">incredibly successful Rosetta mission</a>. </p>
<p>But before we get into what the 36km-long body can tell us, we should know how to refer to it correctly. What is it called? Its official name is still 2014MU69, but, as is common with important astronomical objects, it has been given a more memorable label. For many months following the fly-by, 2014MU69 was referred to as “Ultima Thule”, meaning a far distant land – and 2014MU69 certainly was (and is) a far distant land. </p>
<p>But this nickname was <a href="https://gizmodo.com/new-horizons-scientists-double-down-on-ultima-thule-nic-1831439791">rather controversial</a>, as it has links to Nazism, with “Thule” referred to as the original origin of the “Aryan race” according to far-right mythology. The New Horizons team also wanted something more specific. In November 2019, the International Astronomical Union (the organisation that oversees the naming of astronomical objects) agreed to name 2014MU69 “Arrokoth”. </p>
<p>Why Arrokoth? The beauty of the night sky has inspired generations of poets and songwriters; it is the backdrop for myths and legends and is a “free-to-view” panorama of celestial entertainment. The sky is, of course, a boundless horizon – which is why, when the New Horizons mission team was searching for a name for their latest target, they turned to the sky for inspiration. </p>
<p>Arrokoth is a Native American term meaning “sky” – and as Alan Stern, the principal investigator of the New Horizons mission <a href="https://www.nasa.gov/feature/far-far-away-in-the-sky-new-horizons-kuiper-belt-flyby-object-officially-named-arrokoth">explained:</a>: “The name ‘Arrokoth’ reflects the inspiration of looking to the skies and wondering about the stars and worlds beyond our own.”</p>
<h2>Gentle merger</h2>
<p>Back then, to what Arrokoth has shown us. It is described as a contact binary – which means that it has two lobes that are stuck together. We have known that since the flyby, but now that higher-resolution images have been received, we can see that the surface of Arrokoth is quite smooth and has very few craters. </p>
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<img alt="" src="https://images.theconversation.com/files/315285/original/file-20200213-11011-15iyvjo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/315285/original/file-20200213-11011-15iyvjo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=857&fit=crop&dpr=1 600w, https://images.theconversation.com/files/315285/original/file-20200213-11011-15iyvjo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=857&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/315285/original/file-20200213-11011-15iyvjo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=857&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/315285/original/file-20200213-11011-15iyvjo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1077&fit=crop&dpr=1 754w, https://images.theconversation.com/files/315285/original/file-20200213-11011-15iyvjo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1077&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/315285/original/file-20200213-11011-15iyvjo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1077&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Arrokth image.</span>
<span class="attribution"><span class="source">NASA</span></span>
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<p>One of the most important aspects, though, is the way the two lobes are joined. The neck between the two lobes is well defined, but now also seen to be smooth – there is no indication of any fracturing. This is important, as fracturing would be the case if the two lobes had smashed together in an energetic impact or were collisional fragments from a larger body. </p>
<p>The implication is that the individual lobes were already bound to each other by gravity, rotating slowly before coming together in a gentle collision at a velocity of only a few metres per second. At the time of the collision, there would still have been sufficient gas present to slow down the rotation and help to move the bodies together – hence the gentle impact.</p>
<p>Even though the lobes are thought to be single bodies, and not accretion of smaller units, they can still be mapped into different terrains marked by changes in colour, slope and smoothness. We do not have sufficient information to determine whether these units have differing mineralogies, but data show that even though the changes in colour are quite subtle, they can be distinguished. </p>
<p>Deposits of methanol ice and complex organic compounds cover Arrokoth’s surface. The organics are likely to be material derived directly from the primordial cloud from which the sun was born, mixed with more complex compounds produced by radiation-driven reactions on the surface. Although water and ammonia ices have not been identified, they might be present below the surface layer of dust and organics. However, given the freezing temperatures in the Kuiper Belt, Arrokoth is very unlikely to host any life. </p>
<p>Arrokoth’s two lobes would each have formed by aggregation of dust in the primordial cloud. This makes Arrokoth a first-generation occupant of the solar system, having been little disturbed for 4567 million years. </p>
<p>The sky is not the limit for the New Horizons mission – even though the data from Arrokoth have not yet all been downloaded, planning is in progress for the spacecraft’s next target. I wonder what shape that might turn out to be – snowman, bowling pin or peanut?</p><img src="https://counter.theconversation.com/content/131797/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Monica Grady receives funding from the UK Space Agency and the STFC. She is a member of the Liberal Democrats, Research Fellow of the Natural History Museum and Chancellor of Liverpool Hope University</span></em></p>Meet Arrokoth – one of the first generation of solar system objects.Monica Grady, Professor of Planetary and Space Sciences, The Open UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1155672019-04-23T20:12:49Z2019-04-23T20:12:49ZWhy Pluto is losing its atmosphere: winter is coming<figure><img src="https://images.theconversation.com/files/269935/original/file-20190418-28113-wpxk2p.jpg?ixlib=rb-1.1.0&rect=138%2C81%2C2898%2C1714&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The spectacular layers of blue haze in Pluto's atmosphere, captured by NASA's New Horizons spacecraft.</span> <span class="attribution"><a class="source" href="https://solarsystem.nasa.gov/resources/637/blue-rays-new-horizons-high-res-farewell-to-pluto/?category=planets/dwarf-planets_pluto">NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute</a></span></figcaption></figure><p>The ominous warning – “winter is coming”, popularised by fantasy series Game of Thrones – applies equally well to Pluto.</p>
<p>The dwarf planet’s tenuous atmosphere appears to be on the verge of a stunning collapse due to a change in the seasons and approaching colder conditions, according to <a href="https://arxiv.org/abs/1903.02315" title="Pluto's lower atmosphere and pressure evolution from ground-based stellar occultations, 1988-2016">research to be published in the journal Astronomy & Astrophysics</a>.</p>
<p>Discovered in 1930, it was only around 1980 that astronomers began to suspect Pluto might have an atmosphere. <a href="https://solarsystem.nasa.gov/planets/dwarf-planets/pluto/in-depth/#atmosphere_otp">That atmosphere</a> was <a href="http://www.cbat.eps.harvard.edu/iauc/04000/04097.html#Item2">tentatively discovered</a> in 1985 and fully <a href="https://www.space.com/29885-pluto-atmosphere-to-be-revealed-by-nasa-new-horizons-spacecraft.html">confirmed by independent observations in 1988</a>.</p>
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Read more:
<a href="https://theconversation.com/ive-always-wondered-how-do-we-know-what-lies-at-the-heart-of-pluto-101327">I've Always Wondered: How do we know what lies at the heart of Pluto?</a>
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<p>At the time, astronomers had no way of knowing what dramatic changes were in store for the little world’s thin envelope of nitrogen, methane and hydrocarbons.</p>
<h2>A cosmic coincidence</h2>
<p>By a cosmic coincidence, the last decades of the 20th century and first decades of the 21st also saw a lucky alignment of Earth, Pluto and the dense stellar fields of the distant centre of the Milky Way.</p>
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<img src="https://cdn.theconversation.com/static_files/files/563/pluto_through_years_full.gif?1555809969" width="100%">
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<span class="caption">This animation combines various observations of Pluto over the course of several decades.</span>
<span class="attribution"><span class="source">NASA</span></span>
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<p>This coincidence means Pluto passes relatively often between us and a background star. When this happens, its shadow falls on Earth, an event astronomers refer to as an <a href="https://www.space.com/33946-occultations.html">occultation</a>.</p>
<p>During an occultation, any observatory that happens to lie within the path of the shadow can watch the star seem to disappear as Pluto passes in front of it, and then to reappear as the planetary alignments shift. For any given place on Earth’s surface, a Pluto occultation lasts a couple of minutes at most. </p>
<p>The technique of occultations has been widely used to study the orbits, rings, moons, shapes and atmospheres of the worlds of the outer Solar System, including asteroids, comets, planets and dwarf planets.</p>
<p>By comparing what observers see at different locations on Earth, the size and shape of the occulting world can be worked out. If the object has an atmosphere, then for a few brief seconds as the starlight winks out and then comes back on, the starlight can be altered by absorption and refraction as it passes through the planetary atmosphere.</p>
<p>Since the first successful occultation measurements in the 1980s, a succession of observations have established increasingly precise measures of Pluto’s radius, as well as continually sharpening our understanding of the temperature and pressure of its atmosphere.</p>
<h2>Long orbit and seasons</h2>
<p>Like Earth, Pluto has a seasonal cycle due to the <a href="https://solarsystem.nasa.gov/planets/dwarf-planets/pluto/in-depth/#orbit_and_rotation_otp">inclination of its poles</a> to the plane of its orbit. Over the course of Pluto’s long year – equivalent to 248 Earth years – first the north pole and then the south pole are angled toward the distant Sun.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/270196/original/file-20190421-28090-1me0otf.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/270196/original/file-20190421-28090-1me0otf.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/270196/original/file-20190421-28090-1me0otf.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=337&fit=crop&dpr=1 600w, https://images.theconversation.com/files/270196/original/file-20190421-28090-1me0otf.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=337&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/270196/original/file-20190421-28090-1me0otf.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=337&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/270196/original/file-20190421-28090-1me0otf.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=423&fit=crop&dpr=1 754w, https://images.theconversation.com/files/270196/original/file-20190421-28090-1me0otf.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=423&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/270196/original/file-20190421-28090-1me0otf.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=423&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">A drawing of the Solar System shows Pluto’s tilted orbit, which is also more elliptical than that of the planets.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/audience/forstudents/5-8/features/nasa-knows/what-is-pluto-58.html">NASA (modified)</a></span>
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<p>But unlike Earth, Pluto’s orbit is stretched into an extreme elliptical shape. Its orbit is so elongated that its distance from the Sun varies from 4.4 to 7.4 billion kilometres (30 to 50 times as far as the Earth-Sun distance).</p>
<p>By contrast, Earth’s distance from the Sun varies by only 3.4% over a year. Pluto’s atmosphere was discovered just before Pluto reached its closest approach to the Sun, which happened in 1989. </p>
<p>Since 1989, Pluto has been retreating from the Sun. The temperatures have been decreasing accordingly. </p>
<h2>Under pressure</h2>
<p>At the time Pluto started moving away from the sun, astronomers expected that this would cause its atmospheric pressure to drop, in much the same way that the pressure in an automobile tyre decreases with cold weather and increases in the heat. On the contrary, observations from 1988-2016 have shown a steady increase in the atmospheric pressure. </p>
<p>Immediately before the arrival of <a href="https://www.nasa.gov/mission_pages/newhorizons/main/index.html">NASA’s New Horizons probe</a> in 2015, occultation measurements <a href="https://iopscience.iop.org/article/10.3847/2041-8205/819/2/L38/meta">discovered</a> the atmospheric pressure on Pluto has tripled since 1988 (the equivalent on Earth would be to compare the pressure at the top of Mt Everest to that at sea level).</p>
<p>What is the cause of the discrepancy? Any thought that the occultation measurements were in error was banished by the Radio Science Experiment (<a href="https://www.nasa.gov/mission_pages/newhorizons/spacecraft/index.html">REX</a>) aboard New Horizons, which returned direct measurements in agreement with the Earthbound observers.</p>
<p>The new research has solved the mystery using a seasonal model for the transport of gas and ice around the surface of the planet.</p>
<p>Even though Pluto is moving farther from the Sun every year, its north pole is continuously sunlit during this part of its orbit, causing its nitrogen ice cap to revert to the gas phase. </p>
<p>This explains the rapid increase of atmospheric pressure over the past three decades. </p>
<p>But the climate modelling shows this trend will not continue.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/270193/original/file-20190421-28087-1ll5i3g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/270193/original/file-20190421-28087-1ll5i3g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/270193/original/file-20190421-28087-1ll5i3g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=370&fit=crop&dpr=1 600w, https://images.theconversation.com/files/270193/original/file-20190421-28087-1ll5i3g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=370&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/270193/original/file-20190421-28087-1ll5i3g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=370&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/270193/original/file-20190421-28087-1ll5i3g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=465&fit=crop&dpr=1 754w, https://images.theconversation.com/files/270193/original/file-20190421-28087-1ll5i3g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=465&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/270193/original/file-20190421-28087-1ll5i3g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=465&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">The frozen canyons of Pluto’s north pole captured by NASA’s New Horizons spacecraft.</span>
<span class="attribution"><a class="source" href="https://solarsystem.nasa.gov/resources/639/the-frozen-canyons-of-plutos-north-pole/">NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute</a></span>
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<h2>Winter really is coming</h2>
<p>Pluto will continue to move farther from the Sun until the year 2113, and the weak sunlight will not be sufficient to similarly warm the southern polar regions.</p>
<p>During the long northern autumn and winter, Pluto’s atmosphere is expected to collapse, frosting out onto the surface like ice on a car windscreen on a clear and cold winter night.</p>
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Read more:
<a href="https://theconversation.com/planet-or-dwarf-planet-all-worlds-are-worth-investigating-74682">Planet or dwarf planet: all worlds are worth investigating</a>
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<p>At its lowest ebb, the atmosphere is predicted to have less than 5% of its current pressure. The combination of Pluto’s close approach to the Sun and northern hemisphere spring won’t recur until the year 2237.</p>
<p>Until then, it will be of critical importance to test our understanding of planetary atmospheric models under extreme low-temperature and low-pressure conditions through continued occultation measurements.</p>
<p>But these opportunities will become less frequent as <a href="https://theskylive.com/pluto-tracker">Pluto’s orbit</a> takes its apparent position farther from the dense starfields of the galactic centre that helped us make the observations.</p><img src="https://counter.theconversation.com/content/115567/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Andrew A. Cole receives funding from l'Agence Nationale de la Recherche. The University of Tasmania Greenhill Observatory is supported in part by contributions from the SearchLight Observatory Network and Dr David Warren. </span></em></p>The dwarf planet Pluto is heading away from the Sun and that’s having a devastating impact on its atmosphere.Andrew A. Cole, Senior Lecturer in Astrophysics, University of TasmaniaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1120302019-02-22T09:44:16Z2019-02-22T09:44:16ZWhat’s the weather like on Uranus and Neptune? New images give important clues<figure><img src="https://images.theconversation.com/files/260425/original/file-20190222-195867-tbkvkc.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Uranus (left) and Neptune (right) seen by Hubble.
</span> <span class="attribution"><span class="source">NASA, ESA, A. Simon (NASA Goddard Space Flight Center), and M.H. Wong and A. Hsu (University of California, Berkeley)</span></span></figcaption></figure><p>The outer region of the solar system may be the least explored, but scientists have managed to unravel several of its mysteries in recent weeks. On New Year’s Day, the NASA spacecraft New Horizons <a href="https://solarsystem.nasa.gov/news/807/new-horizons-successfully-explores-ultima-thule/">encountered the icy object Ultima Thule</a> for the first time, shedding light on how it formed. Astronomers <a href="https://www.nature.com/articles/s41586-019-0909-9">have also just discovered</a> a previously unknown moon orbiting Neptune, which has been dubbed “Hippocamp”.</p>
<p>Another discovery, thanks to <a href="http://hubblesite.org/image/4320/news_release/2019-06">new images</a> from the <a href="https://theconversation.com/telescopes-on-the-ground-may-be-cheaper-but-hubble-shows-why-they-are-not-enough-40724">Hubble Space Telescope</a>, is that there’s a variety of intriguing weather patterns in the atmospheres of both Neptune and Uranus. So what would it be like to go there?</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/260211/original/file-20190221-195892-1cgrhm9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/260211/original/file-20190221-195892-1cgrhm9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=360&fit=crop&dpr=1 600w, https://images.theconversation.com/files/260211/original/file-20190221-195892-1cgrhm9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=360&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/260211/original/file-20190221-195892-1cgrhm9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=360&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/260211/original/file-20190221-195892-1cgrhm9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=452&fit=crop&dpr=1 754w, https://images.theconversation.com/files/260211/original/file-20190221-195892-1cgrhm9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=452&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/260211/original/file-20190221-195892-1cgrhm9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=452&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Artist’s impression of Neptune and Hippocamp.</span>
<span class="attribution"><span class="source">ESA/Hubble</span></span>
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<p>Having four times the diameter of the Earth, we typically refer to Uranus and Neptune as “ice giants”. Unlike the gas giants, Saturn and Jupiter, Neptune and Uranus are lower in hydrogen and helium and higher in concentrations of heavier material such as methane, water and ammonia.</p>
<p>Uranus is especially interesting as it is also the only planet in the solar system that <a href="https://theconversation.com/how-did-uranus-end-up-on-its-side-weve-been-finding-out-109894">rotates on its side</a>. A northern summer on Uranus lasts 21 years with the north pole receiving constant sunlight, while the south pole sees continual darkness.</p>
<p>This tilt to the Uranian axis is believed to be the result of an early solar system collision with an <a href="https://www.space.com/41076-uranus-weird-til-icy-rock-crash.html">object at least as large as the Earth</a>. Such a collision would either have released the internal heat reserves of the planet or created a layer of particles which effectively insulate the interior of the planet – <a href="http://iopscience.iop.org/article/10.3847/1538-4357/aac725/meta">preventing heat flow</a> to space. Neptune, having avoided such an encounter, still has an <a href="https://theconversation.com/curious-kids-how-does-heat-travel-through-space-if-space-is-a-vacuum-111889">outward heat flow</a>. As such, both planets are almost the same temperature (within a few degrees) despite Uranus being 33% closer to the sun.</p>
<h2>Weather on Uranus</h2>
<p>The <a href="https://planetaryweather.blogspot.com/2013/05/why-does-uranus-emit-very-little-heat.html">absence of any significant internal heat flow</a> on Uranus means that this planet’s atmosphere is distinctly less active than Neptune’s. In fact the Uranian atmosphere in winter is the coldest planetary atmosphere in the solar system. When Voyager 2 flew past Uranus in 1986, the planet appeared as a largely featureless green-blue disc. In the years since, however, scientists have realised that even this apparently cold, dead world has a surprisingly dynamic atmosphere. </p>
<p>But the new images from the Hubble Space Telescope show a previously unseen huge white cloud likely composed of ammonia or methane ice enveloping the north pole (see top image). Clearly visible at the edge of this huge cloud system is a smaller cloud of methane ice which rotates around the larger cloud edge. These cloud structures may be seasonal, resulting from the current constant sunlight at the north pole. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/260201/original/file-20190221-195873-21rioa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/260201/original/file-20190221-195873-21rioa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=480&fit=crop&dpr=1 600w, https://images.theconversation.com/files/260201/original/file-20190221-195873-21rioa.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=480&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/260201/original/file-20190221-195873-21rioa.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=480&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/260201/original/file-20190221-195873-21rioa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=603&fit=crop&dpr=1 754w, https://images.theconversation.com/files/260201/original/file-20190221-195873-21rioa.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=603&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/260201/original/file-20190221-195873-21rioa.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=603&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Uranus.</span>
</figcaption>
</figure>
<p>Around the equator of Uranus we can also see a thin band of cloud (top image), though how this cloud band remains so narrow is not currently understood. Wind speeds on Uranus are so high that they can blow clouds along at up to 560mph, which would spread clouds outwards over a large area. All planetary atmospheres possess a <a href="https://theconversation.com/beast-from-the-east-the-science-behind-europes-siberian-chill-92385">latitudinal circulation system</a> which should, in theory, also distribute this cloud band over wider latitudes. It could be that these methane clouds are somehow constrained by these circulation patterns, due to altitude or chemical instability. </p>
<p>If we could visit Uranus, the winds at a depth equivalent to the atmospheric pressure of Earth’s surface could reach up to 250 metres per second, or roughly three times as fast as a category five hurricane. Be sure to bring your coat, too, as temperatures at this depth are a frigid -200C.</p>
<h2>Weather on Neptune</h2>
<p>As strong as the winds of Uranus are, they are nothing compared to those found on the other ice giant. Neptune boasts supersonic wind speeds of over <a href="https://media.giphy.com/media/d2W6sksZ9o3qopUc/giphy.gif">1,300mph</a>, and numerous storm systems. The most famous of these features was the <a href="https://www.nasa.gov/content/25-years-ago-voyager-2-captures-images-of-neptune">Great Dark Spot</a> which was observed in close up by Voyager 2 in 1989. This huge storm system covered an area roughly equivalent to one sixth of the surface area of Earth. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/260204/original/file-20190221-195876-q3t31n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/260204/original/file-20190221-195876-q3t31n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=599&fit=crop&dpr=1 600w, https://images.theconversation.com/files/260204/original/file-20190221-195876-q3t31n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=599&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/260204/original/file-20190221-195876-q3t31n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=599&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/260204/original/file-20190221-195876-q3t31n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=753&fit=crop&dpr=1 754w, https://images.theconversation.com/files/260204/original/file-20190221-195876-q3t31n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=753&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/260204/original/file-20190221-195876-q3t31n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=753&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Neptune with Great Dark Spot.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>In the latest Hubble images, a different storm system is visible near the North pole, accompanied by bright clouds of methane ice crystals. The reason these features appear darker than their surroundings is because they are holes offering a view into deeper layers of the Neptunian atmosphere, much like the eye of a hurricane on Earth allows you to see the surface from space. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/260199/original/file-20190221-195861-l5t3qp.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/260199/original/file-20190221-195861-l5t3qp.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=300&fit=crop&dpr=1 600w, https://images.theconversation.com/files/260199/original/file-20190221-195861-l5t3qp.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=300&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/260199/original/file-20190221-195861-l5t3qp.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=300&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/260199/original/file-20190221-195861-l5t3qp.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=377&fit=crop&dpr=1 754w, https://images.theconversation.com/files/260199/original/file-20190221-195861-l5t3qp.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=377&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/260199/original/file-20190221-195861-l5t3qp.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=377&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Neptune seen by the Hubble Space Telescope.</span>
<span class="attribution"><span class="source">NASA/ESA/M.H.Wong/A.I. H</span></span>
</figcaption>
</figure>
<p>Like on Jupiter and Saturn, these gigantic storm systems are believed to be powered by heat flowing out of the planet, left over from the planet’s birth some 4.5 billion years ago. Once again, a visit here would be problematic, with similar temperatures to Uranus but double the wind speed. In fact, Neptune is the windiest planet in the solar system.</p>
<p>The ice giants are the <a href="https://www.sciencedirect.com/science/article/pii/S0032063314002955">most commonly observed type of “exoplanet”</a> – planets orbiting stars other than our sun. If we know more about Uranus and Neptune, we can therefore understand more about planets throughout the universe. </p>
<p>Of course, the ideal plan would be to travel to these worlds. Sadly, apart from the great distance involved, the exceptionally cold temperatures, massive storms and strong winds make them particularly unsuitable for a human visit. So for now, we shall just have to rely on telescopes like Hubble to tell us about our local ice giants.</p><img src="https://counter.theconversation.com/content/112030/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The Hubble Space Telescope has spotted clouds and storms on the solar system’s ice giants.Gareth Dorrian, Post Doctoral Research Associate in Space Science, Nottingham Trent UniversityIan Whittaker, Lecturer, Nottingham Trent UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1083622018-12-31T10:32:41Z2018-12-31T10:32:41ZFrom volcanoes on Mars to scarps on Mercury – how places on other worlds get their names<figure><img src="https://images.theconversation.com/files/250012/original/file-20181211-76977-m3q7mc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The solar system's largest volcano Olympus Mons on Mars, seen by Viking 1.</span> <span class="attribution"><span class="source">NASA/JPL</span></span></figcaption></figure><p>The <a href="https://theconversation.com/new-horizons-is-an-old-spacecraft-but-it-will-transform-our-knowledge-of-pluto-44524">New Horizons</a> spacecraft, which <a href="https://theconversation.com/new-horizons-finally-gets-up-close-with-pluto-for-15-minutes-44603">flew past Pluto</a> in 2015, successfully <a href="http://pluto.jhuapl.edu/">completed a flyby</a> of “Ultima Thule”, an object in the <a href="https://www.universetoday.com/107598/what-is-the-kuiper-belt/">Kuiper belt</a> of bodies beyond Neptune on January 1, 2019. The name Ultima Thule, signifying a distant unknown place, is fitting but it is currently just a nickname pending formal naming. The official names of the body and of the features on its surface will eventually be allocated (this could take years) by the <a href="https://www.iau.org/">International Astronomical Union (IAU)</a>, which celebrates its centenary in 2019. </p>
<p>The IAU’s achievements during its first few decades include resolving contradictory sets of names given to features on the Moon and Mars by rival astronomers during the previous few centuries. The nomenclature working group’s task would then have been largely over, had the space age not dawned – allowing space probes to send back images revealing spectacular landscape details on planets and their moons. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/249245/original/file-20181206-128214-199hss7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/249245/original/file-20181206-128214-199hss7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=774&fit=crop&dpr=1 600w, https://images.theconversation.com/files/249245/original/file-20181206-128214-199hss7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=774&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/249245/original/file-20181206-128214-199hss7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=774&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/249245/original/file-20181206-128214-199hss7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=973&fit=crop&dpr=1 754w, https://images.theconversation.com/files/249245/original/file-20181206-128214-199hss7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=973&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/249245/original/file-20181206-128214-199hss7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=973&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Map of the Moon by Michael van Langren (1655).</span>
<span class="attribution"><span class="source">wikipedia</span></span>
</figcaption>
</figure>
<p>Planetary scientists would find life difficult without names for at least the largest or most prominent features on a body. If there were no names, the only ways to be sure that other investigators could locate the same feature would be by numbering them or specifying map coordinates. Either option would be cumbersome and unmemorable.</p>
<h2>The rules</h2>
<p>Building on some of the already entrenched lunar and martian names, the IAU imposed order by establishing themes for the names of features on each body. For example, large craters on Mars are named after deceased scientists and writers associated with Mars (there’s an Asimov and a Da Vinci), and craters less than 60km across are named after towns and villages on Earth (there’s a Bordeaux and a Cadiz).</p>
<p>Apart from craters, most names are in two parts, with a <a href="https://planetarynames.wr.usgs.gov/DescriptorTerms">“descriptor term”</a> of Latin origin added to denote the <em>type</em> of feature that has been named. On Mars we find neighbouring valleys called Ares Vallis, Tiu Vallis and Simud Vallis, in which the descriptor term “Vallis” is Latin for valley. This is preceded by the word for “Mars” in a different language – in these examples Greek, Old English/Germanic and Sumerian respectively. Among other descriptor terms are Chasma (a deep, elongated depression), Mons (mountain), Planitia (a low lying plain) and Planum (a high plain or plateau).</p>
<p>Descriptor terms are chosen to avoid implying that we know how any particular feature formed. For example, there are many scarps on Mercury that are currently interpreted as <a href="https://en.wikipedia.org/wiki/Thrust_fault">thrust faults</a> (where one region of a planet’s surface has been pushed over another). However, a neutral descriptor term – in this case <em>Rupes</em> (Latin for scarp) – is used so they would not have to be renamed if we were to realise that we’d been misinterpreting them. Similarly, none of the giant mountains on Mars that are almost certainly volcanoes has volcano as a formal part of its name.</p>
<p>The largest volcano on Mars, <a href="https://www.esa.int/Our_Activities/Space_Science/Mars_Express/Olympus_Mons_-_the_caldera_in_close-up">Olympus Mons</a>, coincides with an ephemeral bright spot that can sometimes be discerned through telescopes. Though this was initially dubbed Nix Olympica (meaning “the snows of Olympus”) by the 19th-century observer, <a href="http://www.phys-astro.sonoma.edu/bruceMedalists/Schiaparelli/index.html">Giovanni Schiaparelli</a>, space probes have since shown that the temporary brightness is not snow but clouds that sometimes gather around the summit. The IAU decided to keep the Olympus part of the name, qualified by the more appropriate descriptor <em>Mons</em> (mountain in Latin).</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/249243/original/file-20181206-128217-m4v1uu.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/249243/original/file-20181206-128217-m4v1uu.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=212&fit=crop&dpr=1 600w, https://images.theconversation.com/files/249243/original/file-20181206-128217-m4v1uu.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=212&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/249243/original/file-20181206-128217-m4v1uu.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=212&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/249243/original/file-20181206-128217-m4v1uu.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=266&fit=crop&dpr=1 754w, https://images.theconversation.com/files/249243/original/file-20181206-128217-m4v1uu.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=266&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/249243/original/file-20181206-128217-m4v1uu.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=266&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Approved names on global topographic map of Mars.</span>
<span class="attribution"><a class="source" href="https://astrogeology.usgs.gov/search/map/Docs/Globes/i2782_sh1">USGS</a></span>
</figcaption>
</figure>
<p>On the Moon, the IAU retained <em>Mare</em> (Latin for sea) as a descriptor term for dark spots, even though it is clear they have never been water-filled as was once thought. However, Michael van Langren’s Mare Langrenianum, which he immodestly named after himself on his 1655 map, is now <a href="https://en.wikipedia.org/wiki/Mare_Fecunditatis">Mare Fecunditatis</a>.</p>
<h2>Cultural balance</h2>
<p>The IAU is rightly sensitive to achieving cultural and gender balance. The names of lunar craters that the IAU inherited commemorate famous past scientists, which for historical reasons are dominantly male and Western. In partial compensation, the IAU decided that all features on Venus, whose surface was virtually unknown because of its global cloud cover until we got <a href="https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA00205">radar spacecraft</a> into orbit, would be named after females (deceased or mythical). For example, there is a <a href="https://en.wikipedia.org/wiki/Nightingale_Corona">Nightingale Corona</a>, a large oval-shaped feature named after Florence Nightingale. The only non-female exceptions are three features that had already been named after being detected by Earth-based radar.</p>
<p>Prior to the first detailed images of Jupiter’s moons by <a href="https://voyager.jpl.nasa.gov/">Voyager-1</a> in 1979, the IAU planned to use names from the myths of peoples in Earth’s equatorial zone for the moon Io. It would use mythical names from the European temperate zone for Europa, names from near-Eastern mythology for Ganymede and names from far northern cultures for Callisto.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/249340/original/file-20181206-128205-xwxhpi.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/249340/original/file-20181206-128205-xwxhpi.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/249340/original/file-20181206-128205-xwxhpi.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=339&fit=crop&dpr=1 600w, https://images.theconversation.com/files/249340/original/file-20181206-128205-xwxhpi.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=339&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/249340/original/file-20181206-128205-xwxhpi.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=339&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/249340/original/file-20181206-128205-xwxhpi.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=425&fit=crop&dpr=1 754w, https://images.theconversation.com/files/249340/original/file-20181206-128205-xwxhpi.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=425&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/249340/original/file-20181206-128205-xwxhpi.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=425&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A map of part of Io, with names added.</span>
<span class="attribution"><span class="source">USGS</span></span>
</figcaption>
</figure>
<p>They stuck to the latter three, and so Europa has Annwn Regio (a region named after the Welsh “Otherworld”), and Ganymede and Callisto have craters named Anubis (Egyptian jackal-headed god) and Valhalla (Norse warriors’ feast hall). </p>
<p>However, because Io was revealed to be undergoing continual volcanic eruptions, the original naming theme was deemed inappropriate and was replaced by the names of fire, sun, thunder/lightning and volcano deities from across the world’s cultures. For example, the names Ah Peku, Camaxtli, Emakong, Maui, Shamshu, Tawhaki, and Tien Mu (which occur on the map above) come from fire, thunder or Sun myths of the Mayans, the Aztecs, New Britain, Hawaii, Arabia, the Maoris, and China, respectively.</p>
<h2>Captain Cook and the Maoris</h2>
<p>The IAU has struggled to achieve cultural balance for some features. For example, the <a href="https://planetarynames.wr.usgs.gov/Page/Categories">theme</a> for Rupes on Mercury is “ships of discovery or scientific expeditions”. By the nature of world history, there is a preponderance of Western ship names. For example, we find Adventure, Discovery, Endeavour, and Resolution – all four ships from <a href="https://en.wikipedia.org/wiki/James_Cook">Captain Cook’s</a> 18th-century voyages to the Southern Ocean and Pacific.</p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/mysterious-red-spots-on-mercury-get-names-but-what-are-they-95114">Mysterious red spots on Mercury get names – but what are they?</a>
</strong>
</em>
</p>
<hr>
<p>Personally, I am content that these were <a href="https://theconversation.com/discovery-settlement-or-invasion-the-power-of-language-in-australias-historical-narrative-57097">primarily journeys of scientific discovery</a> rather than of conquest or colonisation. Cook’s first voyage was undertaken to observe a rare <a href="https://theconversation.com/transit-of-venus-a-tale-of-two-expeditions-7246">transit of Venus</a>, and his second voyage reached further south than ever before. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/249440/original/file-20181207-128211-17o18kk.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/249440/original/file-20181207-128211-17o18kk.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/249440/original/file-20181207-128211-17o18kk.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=480&fit=crop&dpr=1 600w, https://images.theconversation.com/files/249440/original/file-20181207-128211-17o18kk.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=480&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/249440/original/file-20181207-128211-17o18kk.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=480&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/249440/original/file-20181207-128211-17o18kk.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=604&fit=crop&dpr=1 754w, https://images.theconversation.com/files/249440/original/file-20181207-128211-17o18kk.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=604&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/249440/original/file-20181207-128211-17o18kk.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=604&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Endeavour Rupes, the shadowed escarpment in the middle of a 400km wide view of Mercury.</span>
<span class="attribution"><span class="source">NASA/JHUAPL/CIW</span></span>
</figcaption>
</figure>
<p>That said, it would be nice to redress the balance. In connection with a European <a href="https://planmap.eu/">planetary mapping project</a>, one of my PhD students and I hope to get at least one of Mercury’s as yet unnamed Rupes named after a canoe in which the Maoris arrived in New Zealand. </p>
<p>Ultimately, space exploration is for all of humanity.</p><img src="https://counter.theconversation.com/content/108362/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Rothery is co-leader of the European Space Agency's Mercury Surface and Composition Working Group, and a Co-Investigator on MIXS (Mercury Imaging X-ray Spectrometer) that is now on its way to Mercury on board the European Space Agency's Mercury orbiter BepiColombo. He has received funding from the UK Space Agency and the Science & Technology Facilities Council for work related to Mercury BepiColombo, and is currently funded by the European Commission under its Horizon 2020 programme for work on planetary geological mapping (776276 Planmap). He is author of Planet Mercury - from Pale Pink Dot to Dynamic World (Springer, 2015), Moons: A Very Short Introduction (Oxford University Press, 2015) and Planets: A Very Short Introduction (Oxford University Press, 2010). He is Educator on the Open University's free learning Badged Open Course (BOC) on Moons and its equivalent FutureLearn Moons MOOC, and chair of the Open University's level 2 course on Planetary Science and the Search for Life.</span></em></p>Naming features on other worlds is a trickier issue than you might think.David Rothery, Professor of Planetary Geosciences, The Open UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1022012018-09-13T14:10:27Z2018-09-13T14:10:27ZWhy NASA chose Senegal to find out more about an asteroid in outerspace<figure><img src="https://images.theconversation.com/files/236025/original/file-20180912-133904-dh0kpm.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A telescope pointed at the skies above Senegal to capture the stellar occultation.</span> <span class="attribution"><span class="source">François Colas, Observatoire de Paris, Insititut de Mécanique Celeste et de Calcul des Ephémérides</span></span></figcaption></figure><p><em>Dozens of scientists from NASA and France, along with five tons of astronomical equipment descended on Dakar, Senegal in August 2018. They joined 21 Senegalese scientists in an important mission: collecting precious data in preparation for the flyby of an asteroid called Ultima Thule on January 2019. The <a href="https://www.nasa.gov/mission_pages/newhorizons/main/index.html">project</a> marked the first time Senegal was involved in a space mission to explore our solar system. Natasha Joseph from the Conversation Africa asked the chairman of the <a href="http://africapss.org">African Initiative for Planetary and Space Sciences</a>, David Baratoux, about the mission.</em></p>
<p><strong>What was the purpose of the mission to Senegal?</strong></p>
<p>NASA’s New Horizon spacecraft has become famous for revealing <a href="https://www.nasa.gov/feature/new-horizons-top-10-pluto-pics">Pluto’s amazing icy landscapes</a> to the world. Now it’s pursuing its journey to the edge of the solar system – and to Ultima Thule, an asteroid from the Kuiper Belt Object (that’s a small chunk of rock or dirty ice which orbits the sun). This will be the most distant object ever explored by a man-made spacecraft. </p>
<p>It orbits around the sun and is an unknown world. So was Pluto, before New Horizon’s flyby.</p>
<p>Preparing a flyby requires precise knowledge about the size and shape of this object. However, Ultima Thule is usually not visible using ground-based telescopes; it is too far away and too small. </p>
<p>Figuring out how far New Horizons must travel to reach Ultima Thule has been one of the big challenges. This is where something a phenomenon called stellar occultations – and Senegal – came in.</p>
<p>A stellar occultation involves an asteroid and a star: the light from a star is blocked by the asteroid from reaching an observer. They’re similar to a solar eclipse. It’s generally a very short event. When Ultima Thulé is involved, it only lasts around a second.</p>
<p>Ultima Thule has already been involved in one stellar occultation, captured in 2017 from sites in Patagonia. That event helped NASA to calculate the trajectory New Horizons must follow to reach the asteroid. </p>
<p>New Horizons scientists predicted a new stellar occultation for August 2018, which would be visible in Colombia, Senegal, Mali, and Algeria. </p>
<p><strong>So why was Senegal chosen?</strong></p>
<p>A few factors were taken into consideration. These included security conditions, climatic conditions at that time of year, the existence of potential scientific partners, and what facilities were available. </p>
<p>Senegal has made great strides in astronomy and planetary sciences in recent years. That’s been largely driven by the <a href="https://www.facebook.com/astronomiesenegal/">Senegalese Association for the Promotion of Astronomy</a>, led by Maram Kaire. Some Senegalese researchers are also involved in the <a href="http://africapss.org">African Initiative for Planetary and Space Sciences</a>, which I head up.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/236048/original/file-20180912-133880-d4e4fp.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/236048/original/file-20180912-133880-d4e4fp.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/236048/original/file-20180912-133880-d4e4fp.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/236048/original/file-20180912-133880-d4e4fp.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/236048/original/file-20180912-133880-d4e4fp.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/236048/original/file-20180912-133880-d4e4fp.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=504&fit=crop&dpr=1 754w, https://images.theconversation.com/files/236048/original/file-20180912-133880-d4e4fp.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=504&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/236048/original/file-20180912-133880-d4e4fp.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=504&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Scientists at work in Senegal.</span>
<span class="attribution"><span class="source">Jean-Luc Dauvergne, Journaliste at Ciel et Espace</span></span>
</figcaption>
</figure>
<p>And so, NASA focused its efforts in Senegal. It sent 21 teams to the country, and six to Colombia, which had less favourable climatic conditions. One team, composed of Algerian astronomers from the <a href="https://www.craag.dz">Centre de Recherche en Astrophysique et Géophysique</a>, also attempted to observe the occultation in the south of Algeria.</p>
<p><strong>So was the mission a success?</strong></p>
<p>Three nights were dedicated to preparation and training. The 21 teams in Senegal were composed of Senegalese, French and US scientists. Participants were selected based on experience, their ability to work in a team, and how quickly they could pick up skills.</p>
<figure>
<iframe src="https://player.vimeo.com/video/289489785" width="500" height="281" frameborder="0" webkitallowfullscreen="" mozallowfullscreen="" allowfullscreen=""></iframe>
<figcaption><span class="caption">A time lapse video shows the training sessions in the new city of Diamniadio, near Dakar. François Colas, Observatoire de Paris.</span></figcaption>
</figure>
<p>Each team was responsible for a telescope and data acquisition system. During the first two nights of training, they oriented the telescope, placed the star that would be occulted by Ultima Thumé in the field of view and recorded 10 or 20 minutes of images. </p>
<p>We dealt with technical problems as they arose, and rearranged the teams as needed. On the third night the teams set up at the 21 pre-identified sites, training in real conditions, in rural and remote areas. People in the villages close to the observation sites were very welcoming and friendly – even when, in some cases, they found three strangers with a large telescope in their fields in the middle of the night.</p>
<p>The stellar occultation happened on the fourth night. Our teams were in place. Some weren’t able to collect any data because their view was obscured by clouds. Others recorded images 10 minutes before and after the predicted time of occultation. The data are now being processed by the New Horizons team.</p>
<p><strong>How will Senegalese science benefit from the August mission?</strong></p>
<p>This experiment was much more than a short-term visit of researchers from prestigious scientific institutions to a developing country. It was an inspiring example of scientific and international cooperation. </p>
<p>But such initiatives are only really valuable if they’re integrated into a country’s long-term scientific plans. That’s exactly what Senegal has done. The government recognised that this work fits in with some of its broader plans for higher education and research. </p>
<p>We were even granted an audience with Senegal’s President, </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/236019/original/file-20180912-133892-53y3ur.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/236019/original/file-20180912-133892-53y3ur.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=376&fit=crop&dpr=1 600w, https://images.theconversation.com/files/236019/original/file-20180912-133892-53y3ur.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=376&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/236019/original/file-20180912-133892-53y3ur.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=376&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/236019/original/file-20180912-133892-53y3ur.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=473&fit=crop&dpr=1 754w, https://images.theconversation.com/files/236019/original/file-20180912-133892-53y3ur.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=473&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/236019/original/file-20180912-133892-53y3ur.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=473&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">In front of the Presidential Palace with Macky Sall, President of the Republic of Senegal. The group photo includes Senegal, French, and US researchers, and French and US diplomatic representation.</span>
<span class="attribution"><span class="source">Courtesy Ministry of Research, Higher Education and Innovation of Senegal</span></span>
</figcaption>
</figure>
<p>The Minister of Higher Education, Research and Innovation, Mary Teuw Niane, and his team organised a <a href="https://africapss.org/nasa-observation-of-stellar-occultation-by-mu69-public-activities/">public outreach programme</a> before and after the observation. </p>
<p>Scientists, some of them local and others from France and the US, delivered public lectures. We were all struck by the incredible questions and discussions these sparked. People asked us about the science itself, but also about how planetary science research and related technologies like telecommunications could benefit Senegal’s economic and scientific development.</p>
<p>Marc Buie, the chief of the experiment in Senegal and Colombia, commented to me that he had never seen such a thirst for knowledge among non-scientists. What’s really exciting is that many young people attended these sessions, so that may inspire a new generation of scientists.</p><img src="https://counter.theconversation.com/content/102201/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Baratoux a reçu des financements du CNES (Centre National d'Etudes Spatiales) et de l'ERC grant Lucky Star (Bruno Sicardy, Observatoire de Paris) et de l'Uranoscope de France pour soutenir la participation française et sénégalaise à l'observation de l'occultation stellaire par Ultima Thulé.</span></em></p>Senegal has made great strides in astronomy and planetary sciences in recent years.David Baratoux, Geologist, Institut de recherche pour le développement (IRD)Licensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/688782016-11-17T10:28:55Z2016-11-17T10:28:55ZWhy Pluto may have a large ocean beneath its icy surface<figure><img src="https://images.theconversation.com/files/146359/original/image-20161117-18113-isgo9a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Pluto seen by New Horizons.</span> <span class="attribution"><span class="source">NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute</span></span></figcaption></figure><p>It may have been more than a year since NASA’s New Horizon spacecraft <a href="https://theconversation.com/new-horizons-finally-gets-up-close-with-pluto-for-15-minutes-44603">whizzed past Pluto</a>, but the data it captured is still helping space scientists make important new discoveries about the enigmatic dwarf planet. Now two <a href="http://nature.com/articles/doi:10.1038/nature20120">new studies</a>, <a href="http://nature.com/articles/doi:10.1038/nature20148">published in Nature</a>, have shed light on Pluto’s past and present structure by investigating an impact crater located in Pluto’s heart-shaped “Tombaugh Regio” area.</p>
<p>The solar system formed from a spinning cloud of material that collapsed under gravity. Most of the planets in the solar system spin approximately in the same direction as a result of that initial spin. Differences from this simple picture – such as Uranus orbiting the sun on its side – are produced by collisions and the force of gravity. Changes in the surface and interior of <a href="http://www.nature.com/nature/journal/v531/n7594/abs/nature17171.html">planets</a> and <a href="http://www.nature.com/nature/journal/vaop/ncurrent/full/nature19846.html">moons</a> can also reorient them, heating the interior and cracking surfaces as they happen. </p>
<p>The new studies show that this might have been at work in “Sputnik Planitia”, a large basin in Tombaugh Regio, on Pluto. Sputnik Planitia is named after Earth’s first artificial satellite and is about 1,000km wide and 2-3km deep. It’s believed that it was produced by a meteor impact, similar to <a href="http://neo.jpl.nasa.gov/images/meteorcrater.html">Meteor Crater</a> in Arizona, US. Since this putative impact, the basin has filled with nitrogen and methane ice, and traces of carbon monoxide ice.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/146264/original/image-20161116-13515-537om.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/146264/original/image-20161116-13515-537om.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=389&fit=crop&dpr=1 600w, https://images.theconversation.com/files/146264/original/image-20161116-13515-537om.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=389&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/146264/original/image-20161116-13515-537om.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=389&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/146264/original/image-20161116-13515-537om.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=489&fit=crop&dpr=1 754w, https://images.theconversation.com/files/146264/original/image-20161116-13515-537om.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=489&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/146264/original/image-20161116-13515-537om.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=489&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">High resolution image of Sputnik Planitia captured by the New Horizons spacecraft.</span>
<span class="attribution"><span class="source">NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute</span></span>
</figcaption>
</figure>
<h2>Wandering poles</h2>
<p>The presence of this impact basin acted to change the “balance” of Pluto. Imagine what would happen if you spun around and someone suddenly put a heavy shopping bag in one of your hands. Your balance would be changed and how you spin would change. The formation of Sputnik Planitia changed the distribution of mass inside Pluto; described by a quantity known as the moment of inertia. When the moment of inertia changes the body reorients itself, tipping over until a new equilibrium is reached. The poles of the planet thus “wander”, in Pluto’s case by about 20 degrees. But how can we know that this really happened? The smoking gun for this process is the location of an anomaly near the equator, which is exactly what Sputnik Planitia represents. So its mere existence is proof.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/146273/original/image-20161116-13530-15fz78a.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/146273/original/image-20161116-13530-15fz78a.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=204&fit=crop&dpr=1 600w, https://images.theconversation.com/files/146273/original/image-20161116-13530-15fz78a.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=204&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/146273/original/image-20161116-13530-15fz78a.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=204&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/146273/original/image-20161116-13530-15fz78a.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=256&fit=crop&dpr=1 754w, https://images.theconversation.com/files/146273/original/image-20161116-13530-15fz78a.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=256&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/146273/original/image-20161116-13530-15fz78a.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=256&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Simplified illustration of true polar wander. With the addition of a new load (the purple circle), for example an impact basin or volcanic rise, the moment of inertia of the body is altered. To reach a minimum energy state the orientation of the body changes.</span>
<span class="attribution"><span class="source">Chris Arridge/Lancaster University</span></span>
</figcaption>
</figure>
<p>An impact basin is known as a “negative” topography feature – a dip in the landscape – and so might be thought of as a negative mass anomaly. But polar wander can also be caused by a “positive” topography feature – like a mountain, or a mountain range. However, where the poles wander depends on whether the anomaly is positive or negative. In reality, a planet or moon is not a perfect sphere and tides also play a role in the reorientation process. This can tell us more about the Sputnik Planitia anomaly.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/146358/original/image-20161117-18108-5dy1ok.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/146358/original/image-20161117-18108-5dy1ok.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=472&fit=crop&dpr=1 600w, https://images.theconversation.com/files/146358/original/image-20161117-18108-5dy1ok.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=472&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/146358/original/image-20161117-18108-5dy1ok.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=472&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/146358/original/image-20161117-18108-5dy1ok.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=593&fit=crop&dpr=1 754w, https://images.theconversation.com/files/146358/original/image-20161117-18108-5dy1ok.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=593&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/146358/original/image-20161117-18108-5dy1ok.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=593&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Sputnik Planitia formed northwest of its present location, and reoriented to its present location as the basin filled with volatile ices.</span>
<span class="attribution"><span class="source">Illustration by James Tuttle Keane.</span></span>
</figcaption>
</figure>
<p>In the Earth-moon system a line can be drawn through the Earth, moon, and the high-tide points: the tidal axis. During true polar wander, positive mass anomalies tend to line up with the tidal axis and negative mass anomalies with the rotational axis of the planet. The fact that <a href="http://www.nature.com/nature/journal/vaop/ncurrent/full/nature20120.html">Sputnik Planitia is also on the Pluto-Charon (Pluto’s moon) tidal axis shows that it is a positive mass anomaly</a> – the result of volatile ices filling the basin.</p>
<h2>An ocean below the cracked surface?</h2>
<p>During this process of changing shape, the surface can crack, producing characteristic tectonic patterns. These have also been seen in the surface of Pluto, supporting Sputnik Planitia’s role in producing Pluto’s current orientation. Future studies of these cracks, and how they are changed by the ongoing geological activity on Pluto, <a href="http://www.nature.com/nature/journal/vaop/ncurrent/full/nature20120.html">may help us to eventually determine the age of Sputnik Planitia</a>.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/146279/original/image-20161116-13534-hd426k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/146279/original/image-20161116-13534-hd426k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=238&fit=crop&dpr=1 600w, https://images.theconversation.com/files/146279/original/image-20161116-13534-hd426k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=238&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/146279/original/image-20161116-13534-hd426k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=238&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/146279/original/image-20161116-13534-hd426k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=299&fit=crop&dpr=1 754w, https://images.theconversation.com/files/146279/original/image-20161116-13534-hd426k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=299&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/146279/original/image-20161116-13534-hd426k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=299&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Water ice in surface cracks (extensional faults) that support the reorientation of Pluto.</span>
<span class="attribution"><span class="source">NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute</span></span>
</figcaption>
</figure>
<p>The story doesn’t end here. Even if an ancient impact carved out a 7km deep basin which subsequently filled with nitrogen and methane ice, the <a href="http://www.nature.com/nature/journal/vaop/ncurrent/full/nature20148.html">researchers argue</a> that it wouldn’t produce a positive anomaly large enough to cause Pluto’s 20 degree reorientation. The nitrogen ice layer would have to be an implausibly thick 40km. </p>
<p><a href="http://science.sciencemag.org/content/340/6140/1552">Studies of our moon</a> show that during collisions, uplift of the mantle can make such positive anomalies. This is unlikely at Pluto since the rocky mantle is at great depth. But the impact with an icy crust over a sub-surface ocean, <a href="http://www.nature.com/nature/journal/vaop/ncurrent/full/nature20148.html">and subsequent uplift of that ocean</a>, could produce an anomaly large enough to explain Pluto’s current orientation and Sputnik Planitia’s location. The ocean would probably contain ammonia due to ammonia’s low freezing point.</p>
<p>This adds to the growing list of bodies in the outer solar system (including for example Europa, Ganymede, Enceladus, Titan) where evidence for subsurface oceans has been presented. Subsurface oceans may be ubiquitous in the solar system and hint at what might be found at Uranus and Neptune, or further out in the Kuiper belt. <a href="http://www.nature.com/nature/journal/v409/n6823/full/4091092a0.html">Extremophilic organisms</a> are found to thrive wherever there is liquid water. So although the presence of life in these oceans is open for debate, the probability is high enough for us to try to look for it.</p><img src="https://counter.theconversation.com/content/68878/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Arridge receives funding from the Royal Society. He advises the Science and Technology Facilities Council and the UK Space Agency on solar system research in the UK.</span></em></p>Astronomers are excited about sub-surface oceans in the solar system, as they may support life. Now Pluto joins the club.Chris Arridge, Research Fellow/Lecturer, Lancaster UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/651942016-09-14T17:01:29Z2016-09-14T17:01:29ZMordor mystery: scientists solve puzzle of the strange, dark north pole on Pluto’s moon Charon<figure><img src="https://images.theconversation.com/files/137256/original/image-20160909-13383-8s9jru.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Charon's north pole, imaged by New Horizons.</span> <span class="attribution"><a class="source" href="http://pluto.jhuapl.edu/Multimedia/Science-Photos/image.php?page=6&gallery_id=2&image_id=323">NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute</a></span></figcaption></figure><p>Had <a href="https://theconversation.com/stunning-crystal-clear-images-of-pluto-but-what-do-they-mean-47517">Pluto itself</a> not proved to be so spectacular when NASA’s <a href="http://pluto.jhuapl.edu/">New Horizons</a> probe flew past last year, there can be no doubt that its large moon <a href="https://theconversation.com/images-of-plutos-moon-charon-show-huge-fractures-and-hints-of-icy-lava-flows-48533">Charon</a> would have won more admirers.</p>
<p>The remarkable moon has a mysterious dark-red stain over its north pole, called “Mordor Macula” by the New Horizons team – where Macula means “dark spot” and Mordor refers to the “black land” in Tolkien’s The Lord of the Rings. While many bodies in the solar system have polar caps or hoods of some sort, these are typically bright, due to reflective ice or frost of some kind, rather than dark. So what’s going on at Charon? A new study, <a href="http://nature.com/articles/doi:10.1038/nature19340">published in Nature</a>, has proposed an answer.</p>
<p>One of Charon’s most interesting features is a vast chasm system, which cuts across the middle of Charon’s Pluto-facing hemisphere and reaches a maximum depth of 7.5km. This speaks of an era of upheaval when slabs of Charon’s icy crust were ruptured, tilted and then partially flooded by a type of lava produced by icy volcanism.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/137272/original/image-20160909-13359-1ka8fv0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/137272/original/image-20160909-13359-1ka8fv0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/137272/original/image-20160909-13359-1ka8fv0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=269&fit=crop&dpr=1 600w, https://images.theconversation.com/files/137272/original/image-20160909-13359-1ka8fv0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=269&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/137272/original/image-20160909-13359-1ka8fv0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=269&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/137272/original/image-20160909-13359-1ka8fv0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=338&fit=crop&dpr=1 754w, https://images.theconversation.com/files/137272/original/image-20160909-13359-1ka8fv0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=338&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/137272/original/image-20160909-13359-1ka8fv0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=338&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Charon’s vast equatorial chasms. The most obvious ones are unofficially named Macross Chasma (on the left) and Serenity Chasma (on the right).</span>
<span class="attribution"><span class="source">NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute</span></span>
</figcaption>
</figure>
<p>Charon’s surface is mostly dirty, grey water-ice, and the red stain around the north pole looks to be a thin film, coating but not burying the underlying topographic features such as craters.</p>
<p>Mordor Macula resembles the red-stained areas of Pluto. This led to early suggestions that they share a similar origin. However, Pluto’s red stuff is understood to be tarry molecules called <a href="http://www.planetary.org/blogs/guest-blogs/2015/0722-what-in-the-worlds-are-tholins.html">tholins</a>, which form in the atmosphere when sunlight strikes molecules and makes them sufficiently reactive to link together. This forms haze particles, which eventually settle to the ground. Unlike Pluto, however, Charon has no trace of an atmosphere, so how can tholins form there?</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/137277/original/image-20160909-13345-lykp9c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/137277/original/image-20160909-13345-lykp9c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/137277/original/image-20160909-13345-lykp9c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/137277/original/image-20160909-13345-lykp9c.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/137277/original/image-20160909-13345-lykp9c.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/137277/original/image-20160909-13345-lykp9c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/137277/original/image-20160909-13345-lykp9c.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/137277/original/image-20160909-13345-lykp9c.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Pluto’s hazy atmosphere, made visible by scattered sunlight seen by New Horizons.</span>
<span class="attribution"><span class="source">NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute</span></span>
</figcaption>
</figure>
<h2>Molecules of Mordor Macula</h2>
<p>The researchers behind the new study think they have the answer. The New Horizons probe detected two sorts of molecules <a href="http://www.nasa.gov/feature/science-papers-reveal-new-aspects-of-pluto-and-its-moons">leaking away from Pluto</a>: methane and nitrogen. Although nitrogen is the most abundant gas in Pluto’s atmosphere, methane is lighter and is being lost about 500 times faster. Tholins and their precursors are far too heavy, and cannot escape Pluto in the same way, so Charon’s tholins must be somehow made from methane arriving from Pluto.</p>
<p>Charon orbits very close to Pluto, and quite a lot of Pluto’s escaped methane falls onto its surface. If a methane molecule strikes the night side of Charon it will stick, particularly near the winter pole where the temperature is lowest (less than 30 degrees above absolute zero). This is because at lower temperatures surface molecules vibrate more slowly, and atmospheric molecules travel more slowly, so collisions are gentle. However, if a methane molecule hits a sunlit part of the surface, it will tend to bounce off and fly away into space because of Charon’s weak gravity (which has long since allowed it to lose any atmosphere that it may once have possessed). </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/137265/original/image-20160909-13348-1asb0nw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/137265/original/image-20160909-13348-1asb0nw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/137265/original/image-20160909-13348-1asb0nw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=502&fit=crop&dpr=1 600w, https://images.theconversation.com/files/137265/original/image-20160909-13348-1asb0nw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=502&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/137265/original/image-20160909-13348-1asb0nw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=502&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/137265/original/image-20160909-13348-1asb0nw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=631&fit=crop&dpr=1 754w, https://images.theconversation.com/files/137265/original/image-20160909-13348-1asb0nw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=631&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/137265/original/image-20160909-13348-1asb0nw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=631&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Charon (left) and Pluto (right) at the same scale. Charon is 1,212 km in diameter, Pluto 2,370 km.</span>
<span class="attribution"><span class="source">NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute</span></span>
</figcaption>
</figure>
<p>Ultraviolet sunlight shining on methane molecules coating Charon’s surface could stimulate photochemical reactions to link them into progressively longer molecular chains, to form tholins. However, the “Catch 22” is that a methane molecule on the cold night-side surface ought to be able to break free in the daytime, when the temperature rises to the giddy heights of -220°C – allowing it to float away into space and become permanently lost. And as there is no sunlight at night, methane molecules can’t link together (making them too massive to float away) before the dawn of a new day.</p>
<p>In a surprising result the new study shows that, even by night, Charon’s poles receive enough ultraviolet light to allow methane molecules to link together. This is because interplanetary dust in the region scatters sunlight in all directions, including onto the night side of Charon. Once a molecule is a chain of two or three methanes linked together (with or without the occasional nitrogen for good measure) it is probably heavy enough to stay bound to the surface even during the daytime. Normal daytime sunlight can then take over to complete the process of forming tholins.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/137292/original/image-20160911-13345-18fsxlt.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/137292/original/image-20160911-13345-18fsxlt.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=180&fit=crop&dpr=1 600w, https://images.theconversation.com/files/137292/original/image-20160911-13345-18fsxlt.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=180&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/137292/original/image-20160911-13345-18fsxlt.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=180&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/137292/original/image-20160911-13345-18fsxlt.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=226&fit=crop&dpr=1 754w, https://images.theconversation.com/files/137292/original/image-20160911-13345-18fsxlt.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=226&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/137292/original/image-20160911-13345-18fsxlt.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=226&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">An example of a tholin molecule. This is a molecule proposed to form in the atmosphere of Saturn’s moon Titan. Tholins on Charon probably have less nitrogen.</span>
<span class="attribution"><span class="source">after Ehrenfreund et al., 1996</span></span>
</figcaption>
</figure>
<p>But what about the south pole? Could Mordor Macula’s location at Charon’s north pole, where the temperature is low enough for cold-trapping of methane, be just a fluke? Apparently not. Although it was winter in Charon’s southern hemisphere when New Horizon made its flyby, keeping its south pole in darkness, the researchers were able to study the south pole by “Pluto shine” (sunlight reflected off Pluto). The spatial resolution of these data is poor, but it is sufficient to demonstrate that Charon’s south pole has similarly dark red material at its surface. So there is not just one Mordor on Charon, but two.</p><img src="https://counter.theconversation.com/content/65194/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Rothery is author of Planet Mercury - from Pale Pink Dot to Dynamic World (Springer, 2015), Moons: A Very Short Introduction (Oxford University Press, 2015) and Planets: A Very Short Introduction (Oxford University Press, 2010). He receives funding from the UK Space Agency and the Science & Technology Facilities Council for work related to Mercury and the European Space Agency's Mercury orbiter BepiColombo. He is Educator on the Open University/FutureLearn Moons MOOC <a href="https://www.futurelearn.com/courses/moons">https://www.futurelearn.com/courses/moons</a></span></em></p>Trapped gas could be tainting the north pole of Pluto’s moon Charon dark red.David Rothery, Professor of Planetary Geosciences, The Open UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/562612016-03-17T18:01:55Z2016-03-17T18:01:55ZPicture of Pluto further refined by months of New Horizons data<figure><img src="https://images.theconversation.com/files/115335/original/image-20160316-30211-mjo9qb.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">New Horizons continues to help unravel the icy dwarf planet's secrets.</span> <span class="attribution"><span class="source">NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>When the New Horizons spacecraft made its <a href="https://theconversation.com/a-team-members-view-of-all-the-work-on-earth-it-took-to-get-new-horizons-to-pluto-44696">flyby of Pluto</a> on July 14, 2015, there was worldwide celebration that we’d finally gotten <a href="https://theconversation.com/in-focus-new-horizons-crisp-images-shed-new-light-on-the-origins-of-pluto-and-its-moons-44451">our first detailed look</a> at this completely new type of planet in the outer reaches of our solar system.</p>
<p>But for those of us on the <a href="http://pluto.jhuapl.edu/Mission/The-Team.php">New Horizons science team</a>, that day and those first images were only the beginning. Since then, I’ve been watching with amazement as the New Horizons spacecraft has transmitted spectacular images back that reveal surprises all over the place. We’ve been making discovery after discovery about the dwarf ice planet Pluto and its moon Charon, and this is likely to continue as we get more data back from the spacecraft. Here’s a summary of just a few of our scientific results to date. </p>
<h2>What do we see on Pluto’s surface?</h2>
<p>Perhaps one of the biggest surprises that was obvious from the very first images was that Pluto has a <a href="http://dx.doi.org/10.1126/science.aad7055">surface that is incredibly diverse</a>. </p>
<p>Some surface areas, such as those that are heavily cratered from asteroid impacts, seem to date back to just after Pluto formed, about 4.5 billion years ago. Other regions show evidence of geological activity that may have lasted throughout Pluto’s billions of years of history. Enormous ice volcanoes (cryovolcanoes) must have taken a large fraction of Pluto’s history to form. These volcanoes are driven by warm underground liquids, such as, perhaps, water and ammonia, instead of liquid rock-magma that we have on Earth, and their rough, crusty surface is made of stuff that has erupted from deep within Pluto’s interior. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/115326/original/image-20160316-30206-h27pf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/115326/original/image-20160316-30206-h27pf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/115326/original/image-20160316-30206-h27pf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=608&fit=crop&dpr=1 600w, https://images.theconversation.com/files/115326/original/image-20160316-30206-h27pf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=608&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/115326/original/image-20160316-30206-h27pf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=608&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/115326/original/image-20160316-30206-h27pf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=764&fit=crop&dpr=1 754w, https://images.theconversation.com/files/115326/original/image-20160316-30206-h27pf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=764&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/115326/original/image-20160316-30206-h27pf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=764&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Pluto’s Sputnik Planum captured hearts here on Earth.</span>
<span class="attribution"><span class="source">NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Other areas, such as the informally named Sputnik Planum – the heart-shaped, Texas-sized nitrogen ice glacier – show no evidence of asteroid impacts at all, suggesting continual surface activity, such as convection of ices from underground. This surface can’t be more than 10 million years old – a blink of the eye on a geological time scale! </p>
<p>Pluto is geologically active! I doubt there’s a single person on Earth who would have expected to see that!</p>
<h2>What’s Pluto made of?</h2>
<p>The diverse chemical compositions we’ve seen on Pluto are giving us some important clues to understanding <a href="http://dx.doi.org/10.1126/science.aad9189">Pluto’s geological history and climate</a>.</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/115458/original/image-20160317-30244-bwwkck.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/115458/original/image-20160317-30244-bwwkck.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/115458/original/image-20160317-30244-bwwkck.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=546&fit=crop&dpr=1 600w, https://images.theconversation.com/files/115458/original/image-20160317-30244-bwwkck.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=546&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/115458/original/image-20160317-30244-bwwkck.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=546&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/115458/original/image-20160317-30244-bwwkck.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=687&fit=crop&dpr=1 754w, https://images.theconversation.com/files/115458/original/image-20160317-30244-bwwkck.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=687&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/115458/original/image-20160317-30244-bwwkck.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=687&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Pluto’s rugged, icy cratered plains.</span>
<span class="attribution"><a class="source" href="http://pluto.jhuapl.edu/Multimedia/Science-Photos/image.php?page=2&gallery_id=2&image_id=385">NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>The high-resolution images from the New Horizons cameras show diverse ice reservoirs across Pluto’s surface. By studying the reflected spectra from the surface, we’ve identified several different types of ices: in particular, nitrogen, methane and carbon monoxide. The locations and characteristics of these ice reservoirs mean that there have been long epochs of ice transport across the dwarf planet’s surface.</p>
<p>A darker veneer on top of the ices is probably tholin material – organic compounds processed by solar radiation. These are produced slowly in Pluto’s atmosphere and gently rain down, even now, onto the surface. An enormous darker region, informally named Cthulhu Regio, has a meters-thick layer of this organic tholin material that has built up over billions of years. Frozen water is one of the strongest solids at the low temperatures we see on Pluto. We believe that the ice mountains that extend several miles above the surface are made of water ice – the biggest ice cubes in the solar system. </p>
<p>Charon, too, had some major surprises in store for us. Pluto’s largest moon has an extended equatorial region of smooth plains that may also be due to material that erupted from Charon’s interior via ice volcanoes that then flowed over its surface about four billion years ago. We suspect that was when Charon’s subsurface water ocean froze, causing global fractures as the moon expanded in size (water expands when it freezes).</p>
<p>Charon has dark poles that may be related to volatile gases that escaped from Pluto’s atmosphere only to be captured by the moon’s cold poles. These gases trigger chemical reactions on the surface that, we believe, produce the darker color of the poles. </p>
<h2>How does Pluto’s atmosphere work?</h2>
<p>The <a href="http://www.boulder.swri.edu/palice/">spacecraft’s Alice instrument</a> made observations of sunlight passing <a href="http://dx.doi.org/10.1126/science.aad8866">through Pluto’s atmosphere</a>. We see absorption features that indicate an atmosphere made up of nitrogen (like Earth’s) with methane, acetylene and ethylene as minor constituents.</p>
<p>Pluto’s small size and low gravity cause it to hold onto its atmosphere much more weakly than larger planets like the Earth (which has 16 times stronger gravity than Pluto). Prior to the New Horizons’ encounter, we expected this would produce an atmosphere that was greatly extended and rapidly escaping to space. But it turned out the upper atmosphere is much colder than we thought it would be and so more compact – the atmosphere does not extend nearly as far into space as we expected and the escape rate of atmospheric gases is extremely slow. But why the atmosphere is so cold is still a complete mystery.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/115334/original/image-20160316-30231-etsjv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/115334/original/image-20160316-30231-etsjv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/115334/original/image-20160316-30231-etsjv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=256&fit=crop&dpr=1 600w, https://images.theconversation.com/files/115334/original/image-20160316-30231-etsjv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=256&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/115334/original/image-20160316-30231-etsjv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=256&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/115334/original/image-20160316-30231-etsjv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=322&fit=crop&dpr=1 754w, https://images.theconversation.com/files/115334/original/image-20160316-30231-etsjv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=322&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/115334/original/image-20160316-30231-etsjv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=322&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Pluto’s haze is a photochemical smog.</span>
<span class="attribution"><span class="source">NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>As an atmospheric scientist, I found the most amazing discovery to be the brilliant, light blue, globally extensive haze that we can see because large numbers of small atmospheric particles scatter sunlight. This haze extends hundreds of kilometers into space, and embedded within it are over 20 very thin, but far brighter, layers. We suspect the thin layers are produced by some type of atmospheric wave that causes localized regions of condensation of some as-yet-unknown gas. The largest moon of Saturn, Titan, shows similar layering of haze in its upper atmosphere. So there may be some interesting comparative planetary studies that come out of the analysis of the Pluto data.</p>
<h2>Where did Pluto’s moons come from?</h2>
<p>The origin of <a href="http://dx.doi.org/10.1126/science.aae0030">Pluto’s five moons</a> has been a long-standing question. But the flyby observations have given us some critical data that we needed in order to develop convincing explanations.</p>
<p>We believe that Charon is just about as old as Pluto, having formed when Pluto was very young. An impact between Pluto and another large Kuiper Belt object early in their history ejected an enormous amount of debris into orbit around Pluto. As time went on, this orbital debris coalesced into Charon.</p>
<p>Previous speculation was that the four smaller moons are actually asteroids captured by Pluto’s gravity as they passed too near the dwarf planet. But the New Horizons observations showed that these four moons have an unusually high reflectivity – much different than the extremely dark materials that we see on asteroids in the outer solar system. This has led to a compelling argument that the smaller moons are also made of debris from the same impact that formed Charon.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/115333/original/image-20160316-30241-1ca6h5c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/115333/original/image-20160316-30241-1ca6h5c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/115333/original/image-20160316-30241-1ca6h5c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=329&fit=crop&dpr=1 600w, https://images.theconversation.com/files/115333/original/image-20160316-30241-1ca6h5c.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=329&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/115333/original/image-20160316-30241-1ca6h5c.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=329&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/115333/original/image-20160316-30241-1ca6h5c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=413&fit=crop&dpr=1 754w, https://images.theconversation.com/files/115333/original/image-20160316-30241-1ca6h5c.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=413&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/115333/original/image-20160316-30241-1ca6h5c.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=413&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Pluto’s atmosphere is buffeted by protons and electrons streaming from the sun as the solar wind.</span>
<span class="attribution"><span class="source">H.A. Weaver et al. / Science (2016)</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>How does Pluto interact with its space environment?</h2>
<p>As the New Horizons spacecraft approached Pluto, there was some concern that a small amount of debris might still remain in orbit around the dwarf planet. A collision between New Horizons and even one particle of debris the size of a grain of sand could cause considerable damage to, or possibly destroy, the spacecraft.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/115341/original/image-20160316-30234-1ehh95s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/115341/original/image-20160316-30234-1ehh95s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/115341/original/image-20160316-30234-1ehh95s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=603&fit=crop&dpr=1 600w, https://images.theconversation.com/files/115341/original/image-20160316-30234-1ehh95s.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=603&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/115341/original/image-20160316-30234-1ehh95s.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=603&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/115341/original/image-20160316-30234-1ehh95s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=758&fit=crop&dpr=1 754w, https://images.theconversation.com/files/115341/original/image-20160316-30234-1ehh95s.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=758&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/115341/original/image-20160316-30234-1ehh95s.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=758&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Student Dust Counter is one part of the science payload New Horizons’ been carrying for a decade.</span>
<span class="attribution"><a class="source" href="http://pluto.jhuapl.edu/Mission/Spacecraft/Payload.php">NASA/New Horizons</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>But the student-built Dust Counter, which measures small micrometer size dust particles in space, detected only a single particle during the flyby – and it was much too small to cause spacecraft damage. This means Pluto’s environment is now largely devoid of debris – all of it likely swept up by the moons early in the system’s history.</p>
<p>The <a href="http://dx.doi.org/10.1126/science.aad9045">New Horizons spacecraft also carried instruments</a> to study what happens to the <a href="http://solarscience.msfc.nasa.gov/SolarWind.shtml">solar wind</a> when it encounters Pluto’s atmosphere. The detailed way in which solar wind particles from the sun interact with a planet’s atmosphere provides important clues about the nature of that atmosphere, particularly how far it extends into space and the escape rate of atmospheric gases. The interaction region between Pluto and the solar wind was observed to be much smaller than expected, only about 12 Pluto diameters across. This means that the atmosphere is smaller than expected, and so these results confirm the Alice observations that the upper atmosphere is much colder than expected. </p>
<h2>So much more yet to come</h2>
<p>These are just a few of the many exciting, and unexpected, results from the New Horizons flyby of Pluto and Charon. The discoveries we’ve already made will mean that textbooks on planetary science must be rewritten. And yet this sampling of the New Horizons results is just from the tip of an ice mountain of data that we’ll be analyzing and writing papers about for many years, perhaps decades. The data are so rich in things we’ve never seen before that I’m sure there are many more surprises yet to come.</p><img src="https://counter.theconversation.com/content/56261/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Mike Summers receives funding from NASA. </span></em></p>After last summer’s Pluto flyby, the New Horizons spacecraft started sending data back to Earth – at 2 kilobits per second. Here’s some of what scientists have learned so far from that rich, slow cache.Mike Summers, Professor of Planetary Science and Astronomy, George Mason UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/519822015-12-24T19:39:18Z2015-12-24T19:39:18ZSpace in 2015 was out of this world<figure><img src="https://images.theconversation.com/files/105637/original/image-20151214-29732-ik2juz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A highlight of 2015 was the number of weird and wonderful exoplanets that were found.</span> <span class="attribution"><span class="source">NASA/JPL-Caltech</span></span></figcaption></figure><p>This was a golden year for planetary exploration thanks to all of the NASA and European Space Agency missions that were planned and implemented decades ago. Not since Apollo and the epic space race of the Cold War has space featured so heavily in the public eye. </p>
<p>So here are the top ten space events that I got most excited about in 2015:</p>
<h2>1. Pluto Flyby by New Horizons</h2>
<p>For me the biggest scientific result of the year, if not the decade, was the revelation by <a href="https://theconversation.com/au/topics/new-horizons">New Horizons</a> that the frozen distant world of Pluto was as active and varied as any we had yet explored. </p>
<p>Organic material staining the surface orange, kilometres high water-ice mountains plunging into freshly resurfaced nitrogen-ice sheets and a collapsing atmosphere all made this dwarf planet astoundingly exciting and well worth the almost decade long journey to reach.</p>
<p>While this world is definitely not a planet (having a system of moons almost as massive in total as it is) the distant frozen dwarf planet is truly King amongst the new class of Plutoids that represent a distinct phase of planet formation.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/B0xkupKwjfM?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The sharpest views of Pluto that NASA’s New Horizons spacecraft obtained during its flyby.</span></figcaption>
</figure>
<h2>2. Water (but no atmosphere) on Mars</h2>
<p>The <a href="http://www.abc.net.au/news/2015-09-28/nasa-to-share-'major'-mars-science-discovery/6808612">announcement</a> that Mars has <a href="https://theconversation.com/nasa-streaks-of-salt-on-mars-mean-flowing-water-and-raise-new-hopes-of-finding-life-48182">flowing water</a> on its barren surface was of huge importance as (at least on Earth), where there’s flowing water, there’s life. It meant we need to reassess the conditions under which water can exist and hence the possibilities for life. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/105023/original/image-20151209-3288-1qfxhw2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/105023/original/image-20151209-3288-1qfxhw2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/105023/original/image-20151209-3288-1qfxhw2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=312&fit=crop&dpr=1 600w, https://images.theconversation.com/files/105023/original/image-20151209-3288-1qfxhw2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=312&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/105023/original/image-20151209-3288-1qfxhw2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=312&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/105023/original/image-20151209-3288-1qfxhw2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=392&fit=crop&dpr=1 754w, https://images.theconversation.com/files/105023/original/image-20151209-3288-1qfxhw2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=392&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/105023/original/image-20151209-3288-1qfxhw2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=392&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">There’s water in them hills.</span>
<span class="attribution"><span class="source">NASA/JPL/University of Arizona</span></span>
</figcaption>
</figure>
<p>The red planet made the list because of the incredible discovery by NASA’s <a href="https://www.nasa.gov/mission_pages/maven/main/index.html">MAVEN spacecraft</a> that the <a href="https://theconversation.com/how-did-mars-lose-its-habitable-climate-the-answer-is-blowing-in-the-solar-wind-50258">Sun was responsible</a> for stripping the Martian atmosphere away, turning a water-rich world nearly four billion years ago into the inhospitable desert it is today. </p>
<p>The atmosphere isn’t locked away in rocks underneath the surface, a la <a href="http://www.imdb.com/title/tt0100802/">Total Recall</a>, but instead has been lost to space meaning future colonists may well have to bring more of their supplies than thought.</p>
<h2>3. Philae called home (and more Rosetta discoveries)</h2>
<p>The idea that there’s a <a href="https://theconversation.com/au/topics/rosetta">spacecraft</a> sitting on a comet still astounds me. </p>
<p>That #WakeUpPhile came true (briefly) in 2015 is a great reason to feature Rosetta again this year and explore the scientific discoveries from the comet, such as how the iconic <a href="https://theconversation.com/rosetta-scientists-unveil-the-source-of-ice-and-dust-jets-on-comet-67p-48122">tail forms from comet ice</a> as well as the <a href="https://cosmosmagazine.com/space/what-rosetta-found-comet-67p">discovery of organic material</a>. These compounds are the precursors to several different amino acids as found in organisms on Earth, meaning objects like Comet 67P could have brought the ingredients for life to the planet’s earliest days.</p>
<p>One of the big surprises is that the water in this comet has three times more “heavy” water (where hydrogen is replaced with its heavier isotope deuterium) than in the oceans of Earth. Wherever the water came from that made life possible on Earth it <a href="https://theconversation.com/rosetta-is-making-a-splash-again-but-results-show-comets-water-not-the-same-as-earths-35411">wasn’t from comets like this</a>.</p>
<h2>4. Alien worlds discovered by Kepler</h2>
<p>NASA’s <a href="http://kepler.nasa.gov">Kepler spacecraft</a> continued to search for <a href="https://theconversation.com/au/topics/exoplanets">exoplanets</a> around stars in our Milky Way, even after the f<a href="https://theconversation.com/the-tools-needed-to-seek-out-new-worlds-out-there-in-space-33481">ailure of critical gyroscope stabilisers</a>, bringing the total to 1,030 confirmed worlds (with thousands more candidates to be followed up). </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/105026/original/image-20151209-3266-lmlhi8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/105026/original/image-20151209-3266-lmlhi8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/105026/original/image-20151209-3266-lmlhi8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=337&fit=crop&dpr=1 600w, https://images.theconversation.com/files/105026/original/image-20151209-3266-lmlhi8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=337&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/105026/original/image-20151209-3266-lmlhi8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=337&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/105026/original/image-20151209-3266-lmlhi8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/105026/original/image-20151209-3266-lmlhi8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/105026/original/image-20151209-3266-lmlhi8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">There are many more exoplanets out there.</span>
<span class="attribution"><span class="source">ESO/M. Kornmesser</span></span>
</figcaption>
</figure>
<p>One of the most exciting discoveries was of a rocky world similar in size to Earth orbiting a Sun-like star, <a href="https://theconversation.com/exoplanet-kepler-452b-offers-a-glimpse-into-the-future-fate-of-our-earth-45144">Earth’s “cousin”</a>. Although this is far from saying it’s <a href="https://theconversation.com/why-it-is-misleading-to-compare-exoplanet-kepler-452b-to-earth-45192">Earth-like</a>. We don’t know if <a href="https://www.nasa.gov/press-release/nasa-kepler-mission-discovers-bigger-older-cousin-to-earth">Kepler-452b</a> is habitable yet as we can’t measure its atmosphere. </p>
<p>However, a rocky world orbiting in the “<a href="https://theconversation.com/alien-worlds-most-stars-have-planets-in-the-habitable-zone-38964">goldilocks zone</a>” suitable for liquid water to exist was a huge step forward in our ultimate search for Earth 2.0 and finding life beyond Earth.</p>
<h2>5. Breakthrough Listen to hunt for ET</h2>
<p>An incredible <a href="http://www.breakthroughinitiatives.org/News/1">US$100 million initiative</a> funded by Russian billionaire Yuri Milner to use two of the world’s largest radio telescopes including Australia’s <a href="http://www.parkes.atnf.csiro.au">Parkes</a> (aka <a href="http://www.imdb.com/title/tt0205873/">The Dish</a>) to search the closet million stars and 100 nearest galaxies for alien signals. Breakthrough Listen will also use the optical <a href="https://www.ucolick.org/main/index.html">Lick observatory</a> in the chance that aliens have upgraded from radio/TV signals to laser-based communications.</p>
<p>In the <a href="http://www.abc.net.au/news/2015-07-21/what-is-the-multimillion-dollar-breakthrough/6638164">decade-long search</a> astronomers will upgrade the telescopes to the <a href="https://theconversation.com/its-not-all-about-aliens-listening-project-may-unveil-other-secrets-of-the-universe-45031">benefit of astronomy</a> worldwide, and learn incredible things about the stars of our Milky Way. Most excitingly of all we may be able to answer one of the most important questions of all time: are we alone? </p>
<h2>6. The Martian</h2>
<p>Rarely does a film convey the science so well that it could be considered an <a href="http://pursuit.unimelb.edu.au/articles/an-astrophysicist-meets-the-martian">educational resource</a>, but <a href="http://www.imdb.com/title/tt3659388/">The Martian</a> managed it. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/105031/original/image-20151209-3269-17cm8sp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/105031/original/image-20151209-3269-17cm8sp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/105031/original/image-20151209-3269-17cm8sp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/105031/original/image-20151209-3269-17cm8sp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/105031/original/image-20151209-3269-17cm8sp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/105031/original/image-20151209-3269-17cm8sp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/105031/original/image-20151209-3269-17cm8sp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/105031/original/image-20151209-3269-17cm8sp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Science in science fiction?</span>
<span class="attribution"><span class="source">20th Century Fox</span></span>
</figcaption>
</figure>
<p>Exceptionally detailed consideration of the physics of orbital dynamics, life support systems, astro-biology and some poignant moments of the cost of space exploration to astronauts as much as their families left behind. </p>
<p>The initial sandstorm was more plot device than physical reality, as while global sandstorms occur, the air pressure is so low on Mars (and we now know why thanks to discovery 2 above) that a few air molecules at hurricane speed would only feel like a light breeze in the denser air of Earth.</p>
<h2>7. Super blood moon (lunar perigee eclipse)</h2>
<p>One of the most observed events of the celestial year, the lunar eclipse was also, in some circles, reported as being the <a href="https://theconversation.com/fact-over-fiction-on-the-apocalyptic-super-blood-moon-47916">harbinger of the apocalypse</a>. </p>
<p>This was because during a lunar eclipse the moon turns “blood” red as sunlight travelling through our atmosphere scatters onto the moon. Only longer, red, wavelengths of light make it through the atmosphere which is why the sun low on the horizon appears red. The result is that the “blood” is being illuminated by all the sunrises and sunsets of Earth. </p>
<p>This eclipse occurred when the moon was at its closest point to Earth (known as a perigee or “super” moon), making this a beautiful sight for most, and a terrifying one for some. If you missed it this year we won’t see a similar super lunar eclipse until 2033.</p>
<h2>8. Dawn exploration of Ceres</h2>
<p>NASA’s <a href="http://dawn.jpl.nasa.gov">Dawn</a> <a href="https://theconversation.com/after-eight-years-nasas-dawn-probe-brings-dwarf-planet-ceres-into-closest-focus-49274">mission to Ceres</a>, a dwarf planet and largest body in the asteroid belt, was overshadowed by the flashier, high speed flyby of Pluto by the New Horizons mission. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/105033/original/image-20151209-3288-1mjo9ea.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/105033/original/image-20151209-3288-1mjo9ea.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/105033/original/image-20151209-3288-1mjo9ea.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=313&fit=crop&dpr=1 600w, https://images.theconversation.com/files/105033/original/image-20151209-3288-1mjo9ea.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=313&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/105033/original/image-20151209-3288-1mjo9ea.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=313&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/105033/original/image-20151209-3288-1mjo9ea.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=394&fit=crop&dpr=1 754w, https://images.theconversation.com/files/105033/original/image-20151209-3288-1mjo9ea.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=394&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/105033/original/image-20151209-3288-1mjo9ea.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=394&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The intriguing bright spots in Occator crater on Ceres.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech/UCLA/MPS/DLR/IDA</span></span>
</figcaption>
</figure>
<p>Yet as <a href="https://cosmosmagazine.com/space/dawn-arrives-ceres">Dawn drifted towards Ceres</a> on the faintest of thrust from its ion engine it spotted a huge surprise. Ceres had <a href="https://cosmosmagazine.com/space/what-ceres-are-those-bright-spots">bizarre bright regions</a> shining out from an asphalt-dark world. These were so unexpected that NASA even created an <a href="http://www.jpl.nasa.gov/dawn/world_ceres/">online poll</a> so everyone could make a guess.</p>
<h2>9. Launch of LISA Pathfinder</h2>
<p>The race to test <a href="https://theconversation.com/where-are-the-missing-gravitational-waves-47940">Einstein’s final prediction</a> of gravitational waves heated up this year, and 2016 will only be more exciting.</p>
<p>The <a href="http://www.esa.int/ESA">European Space Agency</a> successfully <a href="http://sci.esa.int/lisa-pathfinder/56969-esa-pr--2015-lisa-pathfinder-en-route-to-gravitational-wave-demonstration/">launched LISA Pathfinder</a> in December meaning that, technically, it won’t begin its mission (orbiting between the Earth and Sun) until February. It still makes the list as this is a critical first step and technology demonstrator of the ultimate space-based gravitational wave detector, <a href="http://lisa.nasa.gov">LISA</a>, or as it is now called, the <a href="http://sci.esa.int/lisa/48728-mission-status/">New Gravitational wave Observatory</a>. </p>
<p>The spacecraft formerly known as LISA will consist of three satellites in space precisely measuring their respective distances with lasers. These can then measure the change in their separation as a ripple in spacetime itself, caused by the titanic collisions of distant blackholes, passes by. An audacious goal which is why checking the technology is even possible first with LISA Pathfinder is a smart move.</p>
<h2>10. Growing space lettuce</h2>
<p>Aboard the <a href="https://www.nasa.gov/mission_pages/station/main/">International Space Station</a> astronauts took their <a href="https://theconversation.com/first-ever-bites-of-space-grown-food-45958">first bite of space-grown lettuce</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/105032/original/image-20151209-3282-194u0r4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/105032/original/image-20151209-3282-194u0r4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/105032/original/image-20151209-3282-194u0r4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/105032/original/image-20151209-3282-194u0r4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/105032/original/image-20151209-3282-194u0r4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/105032/original/image-20151209-3282-194u0r4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/105032/original/image-20151209-3282-194u0r4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/105032/original/image-20151209-3282-194u0r4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A little piece of Earth floats on-board the ISS.</span>
<span class="attribution"><span class="source">NASA/Don Pettit</span></span>
</figcaption>
</figure>
<p>While the jokes write themselves – e.g. the astronauts were growing cos_(mos)_ lettuce but it tasted like <em>rocket</em> – the demonstration that we can grow our own food in space will be critical for our possible migration from Earth to the rest of the solar system. </p>
<p>In the future we may look back on this moment as the biggest reason why 2015 had a <em>bumper crop</em> of astronomical events. Sorry.</p><img src="https://counter.theconversation.com/content/51982/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Alan Duffy receives funding from Swinburne University of Technology.</span></em></p>From a flyby of Pluto to the search for extrasolar planets and gravitational waves, 2015 was a monumental year for space news.Alan Duffy, Research Fellow, Swinburne University of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/525312015-12-23T15:51:33Z2015-12-23T15:51:33ZThe magical Solar System discoveries we made in 2015<figure><img src="https://images.theconversation.com/files/106971/original/image-20151223-27875-10fe10l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Comet 67P/Churyumov-Gerasimenko, as seen from Rosetta.</span> <span class="attribution"><a class="source" href="http://www.esa.int/spaceinimages/Images/2015/11/Comet_on_17_November_2015_-_NAVCAM">ESA/Rosetta/NAVCAM</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>It has been a busy year for Solar System exploration – and particularly our galactic neighbourhood’s small icy bodies. Comets, asteroids, <a href="http://pluto.jhuapl.edu/Participate/learn/What-We-Know.php?link=The-Kuiper-Belt">Kuiper Belt Objects</a> and planetary satellites have all been in the news – from stunning images of comet <a href="http://sci.esa.int/rosetta/14615-comet-67p/">67P Churyumov-Gerasimenko</a> at the start of the year, to the recent close-up of Saturn’s moon, Enceladus, via Ceres and Pluto. </p>
<p>Early January was a continuation of the stream of data from <a href="http://www.esa.int/Our_Activities/Space_Science/Rosetta">Rosetta</a>, as comet 67P drew closer to the sun. Images were released of jets emanating from the <a href="http://www.esa.int/spaceinimages/Images/2015/01/Comet_activity_22_November_2014">sun-facing surface</a>, from which it could be seen that sublimation of water-ice increased during the daytime, and died down at night. But because the dark surface of the comet retained some heat, the comet was not completely inactive at night – it was possible that fluid might exist for very short periods, leading to sub-surface hydrous activity.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/106984/original/image-20151223-27880-1m1k3oh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/106984/original/image-20151223-27880-1m1k3oh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/106984/original/image-20151223-27880-1m1k3oh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/106984/original/image-20151223-27880-1m1k3oh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/106984/original/image-20151223-27880-1m1k3oh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/106984/original/image-20151223-27880-1m1k3oh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/106984/original/image-20151223-27880-1m1k3oh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Activity on Comet 67P.</span>
<span class="attribution"><a class="source" href="http://www.esa.int/spaceinimages/Images/2015/01/Comet_activity_22_November_2014">ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>One of the other significant results from Rosetta was recognition from magnetic measurements that the two lobes of the comet had been separate bodies, presumably brought together by collision. </p>
<p>Closest approach to the sun was in mid-August, a few weeks after the <a href="http://blogs.esa.int/rosetta/tag/philae-2/">Philae lander</a> signalled that it had woken up after its enforced hibernation. Unfortunately, communication between Rosetta and Philae could not be established reliably, leaving a certain amount of frustration that additional data could not be acquired from the surface. </p>
<h2>Welcome to Pluto (and Charon)</h2>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/106974/original/image-20151223-27863-s0qf68.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/106974/original/image-20151223-27863-s0qf68.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/106974/original/image-20151223-27863-s0qf68.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/106974/original/image-20151223-27863-s0qf68.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/106974/original/image-20151223-27863-s0qf68.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/106974/original/image-20151223-27863-s0qf68.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/106974/original/image-20151223-27863-s0qf68.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Composite image of Pluto and Charon.</span>
<span class="attribution"><a class="source" href="http://www.nasa.gov/image-feature/charon-and-pluto-strikingly-different-worlds">NASA/JHUAPL/SwRI</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>July brought us a close-up of Pluto. The images have been tremendous, turning Pluto from a fuzzy grey blob into a fascinating body of mountains, plains and valleys. Pluto’s closest, and largest, moon, Charon was also captured by the New Horizon mission cameras in similar detail. <a href="https://www.nasa.gov/image-feature/charon-and-pluto-strikingly-different-worlds">The two worlds are very different</a> in their characteristics. Parts of Pluto’s icy surface are crumpled into <a href="https://www.nasa.gov/image-feature/plutos-incredible-diversity-of-surface-reflectivities-and-geological-landforms">mountains and ridges</a>. The “heart” of Pluto, around 1500km across, is a flat and featureless plain, presumably resurfaced relatively recently, showing that Pluto is more active than anticipated.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/106975/original/image-20151223-27851-10v23di.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/106975/original/image-20151223-27851-10v23di.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=541&fit=crop&dpr=1 600w, https://images.theconversation.com/files/106975/original/image-20151223-27851-10v23di.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=541&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/106975/original/image-20151223-27851-10v23di.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=541&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/106975/original/image-20151223-27851-10v23di.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=679&fit=crop&dpr=1 754w, https://images.theconversation.com/files/106975/original/image-20151223-27851-10v23di.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=679&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/106975/original/image-20151223-27851-10v23di.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=679&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Dark areas on Pluto.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/image-feature/plutos-incredible-diversity-of-surface-reflectivities-and-geological-landforms">NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Charon, with approximately half the diameter of Pluto, is also a <a href="https://www.nasa.gov/feature/pluto-s-big-moon-charon-reveals-a-colorful-and-violent-history">world of contrasts</a>. The southern hemisphere is flat, relatively smooth and low-lying, broken mainly by impact craters, while the northern regions are fractured with much more topography. Separating the two halves of the moon is an extensive system of canyons, perhaps akin to the Valles Marineris on Mars, probably caused by tectonic stress. Mission scientists have suggested that the southern region is younger than the northern, and has been resurfaced by cryovolcanism – instead of lava, cryovolcanos eject substances such as water, methane or ammonia – implying a frozen ocean below Charon’s crust.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/106976/original/image-20151223-27880-1vw2axp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/106976/original/image-20151223-27880-1vw2axp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/106976/original/image-20151223-27880-1vw2axp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/106976/original/image-20151223-27880-1vw2axp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/106976/original/image-20151223-27880-1vw2axp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/106976/original/image-20151223-27880-1vw2axp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/106976/original/image-20151223-27880-1vw2axp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Charon.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/feature/pluto-s-big-moon-charon-reveals-a-colorful-and-violent-history">NASA/JHUAPL/SwRI</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>It should be remembered that the wealth of data now returning to Earth from the New Horizon’s spacecraft was acquired during a fly-by of Pluto that lasted a mere 15 minutes. Imagine what could be learnt with an orbiter.</p>
<h2>A new dawn</h2>
<p><a href="http://dawn.jpl.nasa.gov">The Dawn mission</a> to Asteroid (1) Ceres was a bright spot – literally – in the planetary exploration calendar. At the start of the year, the spacecraft began to orbit the dwarf planet, and images revealed several patches of <a href="http://dawn.jpl.nasa.gov/multimedia/images/image-detail.html?id=PIA20180">highly reflective material</a>. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/106979/original/image-20151223-27894-z2s7i6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/106979/original/image-20151223-27894-z2s7i6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/106979/original/image-20151223-27894-z2s7i6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/106979/original/image-20151223-27894-z2s7i6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/106979/original/image-20151223-27894-z2s7i6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/106979/original/image-20151223-27894-z2s7i6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/106979/original/image-20151223-27894-z2s7i6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Ceres from Dawn.</span>
<span class="attribution"><a class="source" href="http://dawn.jpl.nasa.gov/multimedia/images/image-detail.html?id=PIA20180">NASA/JPL-Caltech/UCLA/MPS/DLR/IDA</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>At first it was suggested that the patches may be of water-ice. This would be unexpected, since the surface of Ceres is too warm for water-ice to be stable at the surface. It is now thought that the bright spots might be salts remaining <a href="https://theconversation.com/dawn-breaks-over-distant-ceres-and-perhaps-reveals-signs-of-habitability-38967">following evaporation (or sublimation of water)</a>.</p>
<h2>A ball of mud</h2>
<p>Ceres is currently thought to be like a ball of compressed mud, possibly with a layer of water-rich slurry below a thin crust of mud – not an attractive description for the largest of the asteroids, but one which clearly shows that the minor planet has had a lengthy history of aqueous activity. </p>
<p>This is important because, like comets, asteroids have played a significant role in the delivery of water and other volatile compounds to Earth. The Dawn spacecraft spent most of 2015 orbiting Ceres at gradually decreasing altitudes – settling, at the beginning of December, in its lowest orbit about 400km above the surface. </p>
<p>Images have shown that Ceres is crossed by troughs and grooves reminiscent of those present on other (larger) <a href="http://dawn.jpl.nasa.gov/multimedia/images/image-detail.html?id=PIA20186">planetary bodies</a>. Some of the features are impact-related, but some seem to have been produced by stress fracturing of the crust, another example of Ceres’ puzzling and sometimes contradictory history.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/106981/original/image-20151223-27858-psoq2w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/106981/original/image-20151223-27858-psoq2w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/106981/original/image-20151223-27858-psoq2w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/106981/original/image-20151223-27858-psoq2w.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/106981/original/image-20151223-27858-psoq2w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/106981/original/image-20151223-27858-psoq2w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/106981/original/image-20151223-27858-psoq2w.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Ceres: time for your close-up.</span>
<span class="attribution"><a class="source" href="http://dawn.jpl.nasa.gov/multimedia/images/image-detail.html?id=PIA20186">NASA/JPL-Caltech/UCLA/MPS/DLR/IDA</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>The oceans of Enceladus</h2>
<p>Although the <a href="http://saturn.jpl.nasa.gov">Cassini mission</a> has been operational within the Saturnian system for over a decade, and is coming to the end of its life, it is still returning exciting data from the icy moon, Enceladus. In October, the spacecraft took a dive through the plume at the south pole, flying only about 50km above the surface. Then, only last week, Cassini completed its final close encounter with Enceladus, giving us pictures of <a href="http://www.ciclops.org/view_media/41440/Frozen-Fractures">frozen fractures and ridges</a>. We know that Enceladus has a sub-surface global salty ocean – placing it with Jupiter’s moon, Europa, as a possible host to an ocean-floor ecosystem.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/106985/original/image-20151223-27890-fagymy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/106985/original/image-20151223-27890-fagymy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/106985/original/image-20151223-27890-fagymy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/106985/original/image-20151223-27890-fagymy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/106985/original/image-20151223-27890-fagymy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/106985/original/image-20151223-27890-fagymy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/106985/original/image-20151223-27890-fagymy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The surface of Enceladus.</span>
<span class="attribution"><a class="source" href="http://photojournal.jpl.nasa.gov/catalog/PIA17209">NASA/JPL-Caltech/Space Science Institute</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>What next?</h2>
<p>The amazing images that have come from the missions to icy bodies have generated a great increase in public interest in Solar System exploration. A quick trawl through social media sites such as Twitter shows how avidly the missions are followed and results discussed, almost in real time. If 2015 was a Golden Age for the exploration of small icy bodies, we can only hope that among the legacies of the missions is a generation of students enthused to continue investigation of our neighbourhood. </p>
<p>But what may be in store for small icy bodies in 2016? Work has only just started for the cameras on board Dawn, as the spacecraft starts its mapping of Ceres. There will be more images and information from Pluto and its satellites, especially Charon. Cassini has made its final close fly-by of Enceladus, and the images will be returned throughout the coming year. Rosetta will watch 67P’s activity die down as the comet moves further and further away from the sun. But before we say a complete goodbye to comet Churyumov-Gerasimenko, maybe, just maybe, we will hear from Philae …</p><img src="https://counter.theconversation.com/content/52531/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Monica Grady receives funding from the STFC and is a Trustee of Lunar Mission One.</span></em></p>Prepare to be amazed …Monica Grady, Professor of Planetary and Space Sciences, The Open UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/522092015-12-20T19:55:02Z2015-12-20T19:55:02Z2015, the year that was: Science + Technology<figure><img src="https://images.theconversation.com/files/105373/original/image-20151211-8335-1tq3brf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">2015 saw us complete our exploration of all nine planets (including dwarf planet Pluto) in our solar system.</span> <span class="attribution"><span class="source">NASA</span></span></figcaption></figure><p>This year came and went almost as fast as NASA’s <a href="https://theconversation.com/au/topics/new-horizons">New Horizons</a> probe zipped past the distant dwarf planet, Pluto. Yet New Horizons managed to pack a lot into its <a href="https://theconversation.com/beyond-pluto-new-horizons-mission-is-not-over-yet-44520">flyby</a>, revealing <a href="https://theconversation.com/stunning-crystal-clear-images-of-pluto-but-what-do-they-mean-47517">astounding images</a> of Pluto that show it to be far from a static icy world. </p>
<p>And its mission isn’t over yet; New Horizons will now venture deep into the outer <a href="https://theconversation.com/beyond-pluto-new-horizons-mission-is-not-over-yet-44520">reaches of the solar system</a>, probing the expanse of the Kuiper belt and shedding light on this ancient and hitherto unexplored region of space.</p>
<p>Fuelling planet fever (dwarf or otherwise) was also one of the most scientifically accurate – and science-celebrating – films to emerge from Hollywood in recent times: <a href="https://theconversation.com/the-martian-review-science-fiction-that-respects-science-fact-48373">The Martian</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/105374/original/image-20151211-8297-166ktng.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/105374/original/image-20151211-8297-166ktng.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/105374/original/image-20151211-8297-166ktng.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/105374/original/image-20151211-8297-166ktng.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/105374/original/image-20151211-8297-166ktng.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/105374/original/image-20151211-8297-166ktng.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/105374/original/image-20151211-8297-166ktng.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/105374/original/image-20151211-8297-166ktng.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Being suck on Mars has never been so fun.</span>
<span class="attribution"><span class="source">20th Century Fox</span></span>
</figcaption>
</figure>
<h2>Eye in the sky</h2>
<p>Speaking of space, this year was the 25th anniversary of the Hubble Space Telescope, which has proven to be one of the most enduringly popular and <a href="https://theconversation.com/why-the-hubble-space-telescope-has-been-such-a-stellar-success-40312">most successful</a> scientific projects in history. </p>
<p>Besides its triumphs of discovery, Hubble has also generated a startling array of wonderous images of our universe. Best of all is when those images are both <a href="https://theconversation.com/hubble-in-pictures-astronomers-top-picks-40435">beautiful and richly informative</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/105375/original/image-20151211-8329-183atk1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/105375/original/image-20151211-8329-183atk1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/105375/original/image-20151211-8329-183atk1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=398&fit=crop&dpr=1 600w, https://images.theconversation.com/files/105375/original/image-20151211-8329-183atk1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=398&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/105375/original/image-20151211-8329-183atk1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=398&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/105375/original/image-20151211-8329-183atk1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=500&fit=crop&dpr=1 754w, https://images.theconversation.com/files/105375/original/image-20151211-8329-183atk1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=500&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/105375/original/image-20151211-8329-183atk1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=500&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Happy 25th Hubble!</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>And speaking of anniversaries, it was one hundred years ago that Albert Einstein altered the face of physics by publishing his <a href="https://theconversation.com/au/topics/general-relativity-centenary">general theory of relativity</a>. It’s hard to overstate the significance of this revelation about the nature of space and time. </p>
<p>It’s also difficult to fathom how <a href="https://theconversation.com/without-einstein-it-would-have-taken-decades-longer-to-understand-gravity-50517">just one man</a> was able to come up with a theory of such breathtaking accuracy, and such <a href="https://theconversation.com/the-art-and-beauty-of-general-relativity-51042">profound beauty</a>.</p>
<h2>Smart batteries, smart houses</h2>
<p>More down to earth were significant developments in battery technology. While we might not think of batteries as the glamorous vanguard of technology, they underpin the mobile technology we’ve become accustomed to, and they can also potentially transform the way we <a href="https://theconversation.com/tomorrows-battery-technologies-that-could-power-your-home-41614">generate, store and consume energy</a>.</p>
<p>At least, that’s what Tesla Motors CEO Elon Musk is banking on with the announcement of the company’s home battery offering, <a href="https://theconversation.com/the-winners-and-losers-in-teslas-battery-plan-for-the-home-41151">Powerwall</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/105376/original/image-20151211-8291-19mdkci.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/105376/original/image-20151211-8291-19mdkci.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/105376/original/image-20151211-8291-19mdkci.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=200&fit=crop&dpr=1 600w, https://images.theconversation.com/files/105376/original/image-20151211-8291-19mdkci.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=200&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/105376/original/image-20151211-8291-19mdkci.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=200&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/105376/original/image-20151211-8291-19mdkci.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=251&fit=crop&dpr=1 754w, https://images.theconversation.com/files/105376/original/image-20151211-8291-19mdkci.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=251&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/105376/original/image-20151211-8291-19mdkci.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=251&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Tesla Powerwall could make solar power work all day and all night.</span>
<span class="attribution"><span class="source">Tesla Motors</span></span>
</figcaption>
</figure>
<p>Another technology that promises (or threatens, depending on your perspective) to transform the world is <a href="https://theconversation.com/your-questions-answered-on-artificial-intelligence-49645">artificial intelligence, robotics and automation</a> more generally.</p>
<p>The first wave is likely to be in the form of <a href="https://theconversation.com/where-we-are-on-the-road-to-driverless-cars-50079">driverless cars</a>, which will not only be safer and more efficient than those driven by hairless primates, but also could change the way we think of things like <a href="https://theconversation.com/driverless-cars-will-change-the-way-we-think-of-car-ownership-50125">car ownership</a>. </p>
<p>But then, what will happen to all those people who currently make a living from driving? Like many, they may <a href="https://theconversation.com/could-a-robot-do-your-job-short-answer-yes-39569">lose their jobs</a> to increasing automation. We may need to <a href="https://theconversation.com/we-need-new-jobs-as-the-machines-do-more-of-our-work-38600">create new jobs</a> in the wake of the robot invasion, but even that might not be enough.</p>
<p>More menacing is the prospect of lethal autonomous weapon systems, colloquially called “killer robots”. There are already defensive weapon systems that can operate autonomously, but this year saw a call by many of the leading AI and robotics researchers to <a href="https://theconversation.com/open-letter-we-must-stop-killer-robots-before-they-are-built-44577">ban offensive autonomous weapons</a>. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/105378/original/image-20151211-31729-6ee31w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/105378/original/image-20151211-31729-6ee31w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=283&fit=crop&dpr=1 600w, https://images.theconversation.com/files/105378/original/image-20151211-31729-6ee31w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=283&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/105378/original/image-20151211-31729-6ee31w.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=283&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/105378/original/image-20151211-31729-6ee31w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=356&fit=crop&dpr=1 754w, https://images.theconversation.com/files/105378/original/image-20151211-31729-6ee31w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=356&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/105378/original/image-20151211-31729-6ee31w.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=356&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The robots are coming, although they probably won’t look like this.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<h2>Digital scapes</h2>
<p>This is not to say we don’t already have challenges to face in the digital world. Cybercrime is still a scourge, with it become more <a href="https://theconversation.com/how-cybercrime-has-changed-over-the-past-5-years-it-hasnt-got-any-better-47027">professional and businesslike</a> over the year.</p>
<p>Hackers have a growing <a href="https://theconversation.com/hackers-kit-bag-the-tools-that-terrorise-the-internet-37715">range of tools</a> at their disposal to steal your identity, extort you, pilfer your information or even penetrate business or <a href="https://theconversation.com/cyber-breach-at-the-bureau-of-meteorology-the-who-what-and-how-of-the-hack-51670">government</a>. They can even remain hidden in the “<a href="https://theconversation.com/explainer-what-is-the-dark-web-46070">dark web</a>”.</p>
<p>Ultimately, there may be no simple technological panacea, except for us each to <a href="https://theconversation.com/we-need-to-take-responsibility-for-our-own-safety-online-38368">maintain vigilance</a>. Although would be little solace to those exposed in the hack of dating website <a href="https://theconversation.com/what-if-the-ashley-madison-hack-was-an-inside-job-46404">Ashley Madison</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/105379/original/image-20151211-8291-1x1t3wj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/105379/original/image-20151211-8291-1x1t3wj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/105379/original/image-20151211-8291-1x1t3wj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/105379/original/image-20151211-8291-1x1t3wj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/105379/original/image-20151211-8291-1x1t3wj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/105379/original/image-20151211-8291-1x1t3wj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/105379/original/image-20151211-8291-1x1t3wj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/105379/original/image-20151211-8291-1x1t3wj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">They’re getting better at their business.</span>
<span class="attribution"><span class="source">Brian Klug/Flickr</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
</figure>
<h2>True or false?</h2>
<p>But you can’t believe everything you hear. This is especially if it sounds too good to be true, such as that <a href="https://theconversation.com/trolling-our-confirmation-bias-one-bite-and-were-easily-sucked-in-42621">eating chocolate helps you lose weight</a>. Or that <a href="https://theconversation.com/overcoming-the-social-barriers-to-climate-consensus-36889">climate change</a> is not real.</p>
<p>But there are things you can do to protect yourself – or <a href="https://theconversation.com/inoculating-against-science-denial-40465">inoculate yourself</a>, if you will – from anti-science and quackery. There are a few techniques you can use to help <a href="https://theconversation.com/busting-myths-a-practical-guide-to-countering-science-denial-42618">debunk science denial</a> when you see it.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/105380/original/image-20151211-8314-15lblrr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/105380/original/image-20151211-8314-15lblrr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/105380/original/image-20151211-8314-15lblrr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=387&fit=crop&dpr=1 600w, https://images.theconversation.com/files/105380/original/image-20151211-8314-15lblrr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=387&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/105380/original/image-20151211-8314-15lblrr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=387&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/105380/original/image-20151211-8314-15lblrr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=487&fit=crop&dpr=1 754w, https://images.theconversation.com/files/105380/original/image-20151211-8314-15lblrr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=487&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/105380/original/image-20151211-8314-15lblrr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=487&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Got to defend against the bad vibes.</span>
<span class="attribution"><span class="source">Bryan Rosengrant/Flickr</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>The Abbott government itself hit some bumps when it came to its support for science, particularly when it threatened to cut funding to the National Collaborative Research Infrastructure Strategy, or <a href="https://theconversation.com/explainer-the-national-collaborative-research-infrastructure-strategy-ncris-38837">NCRIS</a>. </p>
<p>Then Education Minister Christopher Pyne was hoping to hold NCRIS ransom to encourage researchers to back his proposed higher education reforms, but the scientific community was as one in its opposition to the cuts, arguing they’d hurt <a href="https://theconversation.com/research-infrastructure-cuts-harm-science-the-economy-and-the-nation-38478">science, the economy and the nation</a> at large.</p>
<p>The government eventually got the message and <a href="https://theconversation.com/pyne-backflips-on-research-infrastructure-funding-cut-38849">capitulated</a>, with Minister Pyne continuing funding in the short term, then solidifying that funding following the change of Prime Minister to Malcolm Turnbull – at which point Christopher Pyne switched to the Innovation, Industry and Science portfolio and changed his tune on research considerably.</p>
<p>In fact, the Turnbull government’s gushing appreciation of science and optimistic spirit when it comes to innovation – backed by <a href="https://theconversation.com/au/topics/innovation-statement">over A$1 billion in funding</a> for science and commercialisation – changed the way <a href="https://theconversation.com/expert-panel-what-the-national-innovation-statement-means-for-science-51902">many scientists felt</a> about the government.</p>
<p>2015 has been a year of milestones and triumphs for science and technology, although laced with a few cautionary messages. We’re now half way through the second decade of the 21st century, and it’s starting to feel like we’re genuinely living in the future – albeit not the future as envisaged by many in the 20th century.</p>
<p>With a new drive for innovation, greater appreciation of the role of science and the emergence of (dare we say) paradigm shifting technologies, such as automation and artificial intelligence, we may feel the lingering traces of the 20th century fall further into the past as 2016 takes over.</p>
<p><strong>Top ten Science + Technology stories by readership in 2015:</strong></p>
<ol>
<li><a href="https://theconversation.com/explainer-what-is-the-dark-web-46070">Explainer: what is the dark web?</a> by <a href="https://theconversation.com/profiles/david-glance-148">David Glance</a></li>
<li><a href="https://theconversation.com/four-easy-tips-to-make-your-batteries-last-longer-41172">Four easy tips to make your batteries last longer</a> by <a href="https://theconversation.com/profiles/valentin-muenzel-130702">Valentin Muenzel</a></li>
<li><a href="https://theconversation.com/its-often-the-puzzles-that-baffle-that-go-viral-40216">It’s often the puzzles that baffle that go viral</a> by <a href="https://theconversation.com/profiles/jonathan-borwein-jon-101">Jon Borwein</a></li>
<li><a href="https://theconversation.com/inskip-beach-collapse-just-dont-call-it-a-sinkhole-48241">Inskip beach collapse: just don’t call it a ‘sinkhole’</a> by <a href="https://theconversation.com/profiles/stephen-fityus-194631">Stephen Fityus</a></li>
<li><a href="https://theconversation.com/the-other-red-meat-on-the-real-palaeodiet-41272">The ‘other’ red meat on the ‘real’ palaeodiet</a> by <a href="https://theconversation.com/profiles/darren-curnoe-2101">Darren Curnoe</a></li>
<li><a href="https://theconversation.com/seven-myths-about-scientists-debunked-37148">Seven myths about scientists debunked</a> by <a href="https://theconversation.com/profiles/marguerite-evans-galea-5223">Marguerite Evans-Galea</a>, <a href="https://theconversation.com/profiles/jeffrey-craig-99410">Jeffrey Craig</a></li>
<li><a href="https://theconversation.com/european-invasion-dna-reveals-the-origins-of-modern-europeans-38096">European invasion: DNA reveals the origins of modern Europeans</a> by <a href="https://theconversation.com/profiles/alan-cooper-18427">Alan Cooper</a>, <a href="https://theconversation.com/profiles/wolfgang-haak-156711">Wolfgang Haak</a></li>
<li><a href="https://theconversation.com/the-verdict-is-in-feel-good-exercise-hormone-irisin-is-real-46082">The verdict is in: feel-good exercise hormone irisin is real</a> by Eliza Berlage</li>
<li><a href="https://theconversation.com/brain-to-brain-interfaces-the-science-of-telepathy-37926">Brain-to-brain interfaces: the science of telepathy</a> by <a href="https://theconversation.com/profiles/kristyn-bates-5106">Kristyn Bates</a></li>
<li><a href="https://theconversation.com/the-smell-of-rain-how-csiro-invented-a-new-word-39231">The smell of rain: how CSIRO invented a new word</a> by <a href="https://theconversation.com/profiles/howard-poynton-157622">Howard Poynton</a></li>
</ol><img src="https://counter.theconversation.com/content/52209/count.gif" alt="The Conversation" width="1" height="1" />
2015 was a year where we expanded our view of the universe, embraced new technologies and got a hint of the profound changes to come.Tim Dean, EditorLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/475172015-09-18T11:26:47Z2015-09-18T11:26:47ZStunning, crystal-clear images of Pluto – but what do they mean?<figure><img src="https://images.theconversation.com/files/95261/original/image-20150917-7534-11t5a81.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The best shot yet.</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/feature/pluto-wows-in-spectacular-new-backlit-panorama">NASA/JHUAPL/SwRI</a></span></figcaption></figure><p>The more we find out about Pluto, the more perplexing it seems. For several weeks after its <a href="https://theconversation.com/live-blog-new-horizons-flyby-of-pluto-44670">July 14 fly-by</a>, NASA’s probe <a href="https://theconversation.com/new-horizons-is-an-old-spacecraft-but-it-will-transform-our-knowledge-of-pluto-44524">New Horizons</a> was too busy doing science to transmit data to Earth. During that time we had to content ourselves with the few <a href="https://theconversation.com/historic-close-ups-of-pluto-and-its-moon-charon-present-puzzle-for-scientists-44615http://example.com/">“taster” images</a> that were beamed back immediately after it passed Pluto. </p>
<p>However the probe has now begun the year-long process of transmitting its vast haul of fly-by data, including images that are crisper and more reliable because they preserve original details that we couldn’t see in the compressed versions. A selection of <a href="http://pluto.jhuapl.edu/Multimedia/Science-Photos/">new images</a> is released every Thursday – with the latest revealing Pluto’s haze layers in stunning detail.</p>
<h2>Crazy haze</h2>
<p>The picture above is my favourite. It was captured just 15 minutes after closest approach, looking back sunwards across part of the southern edge of the bright area informally known as Tombaugh Regio. </p>
<p>The water-ice mountains adjoining and projecting up through it are wonderfully shadowed, and look at the incredibly complex haze layers that you can see above the distant horizon. These are probably a product of the solar ultraviolet light stripping hydrogen from molecules of methane, which then link together to form long chains of <a href="http://www.planetary.org/blogs/guest-blogs/2015/0722-what-in-the-worlds-are-tholins.html">tar-like substances</a> called tholins. These form tiny particles, and those that settle to the ground help to give it a reddish stain, but why there are so many layers in the atmosphere, we don’t know.</p>
<p>Below is a spectacular simulated view (compiled from several individual images) showing the Tombaugh Regio area to the north and the dark, heavily-cratered terrain to its south. These craters are prominent because of their bright rims, which could be nitrogen frost. What catches my attention in particular on this image are the curved and <a href="http://www.lpi.usra.edu/education/explore/shaping_the_planets/tectonism.shtml">branching fractures</a> that sweep across the terrain in the lower left and slice through several of the smaller craters, providing evidence of an episode of geological activity, maybe even within the past billion years.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/94676/original/image-20150914-4698-p0kjfw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/94676/original/image-20150914-4698-p0kjfw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/94676/original/image-20150914-4698-p0kjfw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=389&fit=crop&dpr=1 600w, https://images.theconversation.com/files/94676/original/image-20150914-4698-p0kjfw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=389&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/94676/original/image-20150914-4698-p0kjfw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=389&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/94676/original/image-20150914-4698-p0kjfw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=489&fit=crop&dpr=1 754w, https://images.theconversation.com/files/94676/original/image-20150914-4698-p0kjfw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=489&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/94676/original/image-20150914-4698-p0kjfw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=489&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Simulated view looking north-east from 1,800km above Pluto’s equator. Tombaugh Regio dominates the upper right.</span>
<span class="attribution"><span class="source">NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute</span></span>
</figcaption>
</figure>
<p>You can see the northern ends of a couple of these fractures in the lower left of the next image. More importantly, it shows a relationship between Pluto’s dominant landscape-forming material (water-ice) and the more <a href="https://www.nasa.gov/press-release/nasa-s-new-horizons-discovers-frozen-plains-in-the-heart-of-pluto-s-heart">volatile ices</a> (such as frozen nitrogen, methane and carbon monoxide) that make up the pale terrain of Tombaugh Regio. At the very low temperatures on Pluto’s surface (-225°) water-ice is as strong as rock on Earth.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/94685/original/image-20150914-4695-18jjpux.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/94685/original/image-20150914-4695-18jjpux.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/94685/original/image-20150914-4695-18jjpux.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=469&fit=crop&dpr=1 600w, https://images.theconversation.com/files/94685/original/image-20150914-4695-18jjpux.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=469&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/94685/original/image-20150914-4695-18jjpux.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=469&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/94685/original/image-20150914-4695-18jjpux.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=590&fit=crop&dpr=1 754w, https://images.theconversation.com/files/94685/original/image-20150914-4695-18jjpux.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=590&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/94685/original/image-20150914-4695-18jjpux.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=590&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Detail of part of the western edge of Tombaugh Regio. Image is 470km across.</span>
<span class="attribution"><span class="source">NASA/Johns Hopkins University Applied Physics La boratory/Southwest Research Institute</span></span>
</figcaption>
</figure>
<p>The landscape in the left third of this image is composed of water-ice. The very flat terrain in the right third, which is part of Tombaugh Regio, is weaker and cannot be frozen water. You can see it divided into slabs or cells. Some on the <a href="https://theconversation.com/a-team-members-view-of-all-the-work-on-earth-it-took-to-get-new-horizons-to-pluto-44696">New Horizons team</a> have suggested it might be traces of convection currents driven by heat from Pluto’s interior.</p>
<p>There’s a rugged mountain peak of water-ice, more than a kilometre high, piercing the exotic ice in the lower right. The middle third of this image reveals for the first time that all the water-ice around this edge of Tombaugh Regio has been disrupted into a jumble of giant, jagged blocks, of which that mountain is just a large example. As yet we have no idea how this happened, but it suggests that each cell in the interior of Tombaugh Regio might be sitting over its own block of disrupted water-ice.</p>
<h2>Layers of ice</h2>
<p>The next image is from a little further south-east around the edge of Tombaugh Regio. Here the water-ice terrain has been stained very dark, perhaps by particles of tar settling out from the nitrogen atmosphere. There’s a similar pattern of giant jumbled blocks, but there’s a new twist here. If you look carefully you can make out fine patterns of lines, in both the dark terrain and in some of the bright terrain.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/94686/original/image-20150914-4678-e2rbo0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/94686/original/image-20150914-4678-e2rbo0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/94686/original/image-20150914-4678-e2rbo0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=541&fit=crop&dpr=1 600w, https://images.theconversation.com/files/94686/original/image-20150914-4678-e2rbo0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=541&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/94686/original/image-20150914-4678-e2rbo0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=541&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/94686/original/image-20150914-4678-e2rbo0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=679&fit=crop&dpr=1 754w, https://images.theconversation.com/files/94686/original/image-20150914-4678-e2rbo0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=679&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/94686/original/image-20150914-4678-e2rbo0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=679&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">View, 350km wide, including a dark area at the south-western edge of Tombaugh Regio.</span>
<span class="attribution"><span class="source">NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute</span></span>
</figcaption>
</figure>
<p>One suggestion from the New Horizons team is that these are dunes composed of wind-blown ice grains, preserved from a time when Pluto’s atmosphere was denser. The present atmosphere is mostly nitrogen with a little carbon monoxide and methane, and there are signs that it is currently freezing out onto the surface as <a href="https://theconversation.com/pluto-and-its-collision-course-place-in-our-solar-system-43404">Pluto’s eccentric orbit</a> carries it further from the sun. I’m sceptical about the dunes, and wonder if instead the pattern records <a href="http://www.atacamaphoto.com/atacama/atacama45.htm">ablation of ice-like penitentes</a> on Earth – when snow formations at high altitudes are removed by melting or evaporation.</p>
<p>Next a view covering the northern edge of Tombaugh Regio. At the upper left, note the glacier-like flow of the weak exotic ice into the rugged water-ice terrain. The part of Tombaugh Regio on the right cannot be floored by weak ice; it is rugged terrain, no different to that seen elsewhere except that its surface is especially bright. This is probably nitrogen snow covering water-ice terrain, and there are signs that nitrogen-ice flows glacier-like from the bright rigged terrain into the flat area. Why here? How recent? We don’t know.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/95259/original/image-20150917-7507-gotyhe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/95259/original/image-20150917-7507-gotyhe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/95259/original/image-20150917-7507-gotyhe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=429&fit=crop&dpr=1 600w, https://images.theconversation.com/files/95259/original/image-20150917-7507-gotyhe.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=429&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/95259/original/image-20150917-7507-gotyhe.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=429&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/95259/original/image-20150917-7507-gotyhe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=539&fit=crop&dpr=1 754w, https://images.theconversation.com/files/95259/original/image-20150917-7507-gotyhe.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=539&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/95259/original/image-20150917-7507-gotyhe.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=539&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Pluto’s Tombaugh Regio.</span>
<span class="attribution"><span class="source">NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute</span></span>
</figcaption>
</figure>
<p>This next image, like the top one was taken just 15 minutes after the closest approach to Pluto. The mountains on the left are up to 3,500 meters high. The layers of haze in Pluto’s atmosphere are also visible.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/95263/original/image-20150917-7521-1o9pg86.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/95263/original/image-20150917-7521-1o9pg86.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=386&fit=crop&dpr=1 600w, https://images.theconversation.com/files/95263/original/image-20150917-7521-1o9pg86.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=386&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/95263/original/image-20150917-7521-1o9pg86.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=386&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/95263/original/image-20150917-7521-1o9pg86.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=485&fit=crop&dpr=1 754w, https://images.theconversation.com/files/95263/original/image-20150917-7521-1o9pg86.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=485&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/95263/original/image-20150917-7521-1o9pg86.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=485&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Area including the informally named icy plain Sputnik Planum, which is part of Tombaugh Regio.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/sites/default/files/thumbnails/image/nh-apluto-mountains-plains-9-17-15_0.png">NASA/JHUAPL/SwRI</a></span>
</figcaption>
</figure>
<h2>Charon</h2>
<p>And finally, Pluto’s large moon Charon. It’s not been getting much attention, but for me it too is a fascinating world. New Horizons found no trace of an atmosphere and the surface is mostly water-ice but it boasts the only dark polar cap in the solar system. Did tar particles from Pluto’s atmosphere somehow make it across to Charon? </p>
<p>Elsewhere there are plenty of impact craters, though probably fewer than on Pluto’s water-ice terrains, which poses a problem of why and how Charon has been resurfaced more recently than much of Pluto. Maybe there is some twist to the <a href="http://www.open.edu/openlearn/science-maths-technology/science/physics-and-astronomy/icy-bodies-europa-and-elsewhere/content-section-1.4">tidal-heating interaction</a> between Pluto and Charon that we have yet to fathom. Charon also boasts a globe-spanning system of kilometres-deep fractures, grander than anything seen on Pluto so far.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/94694/original/image-20150914-31151-ca21m4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/94694/original/image-20150914-31151-ca21m4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/94694/original/image-20150914-31151-ca21m4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/94694/original/image-20150914-31151-ca21m4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/94694/original/image-20150914-31151-ca21m4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/94694/original/image-20150914-31151-ca21m4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/94694/original/image-20150914-31151-ca21m4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The best global view of Pluto’s largest moon Charon (1,200km diameter). The dark north polar cap can be seen at the top.</span>
<span class="attribution"><span class="source">NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute</span></span>
</figcaption>
</figure>
<h2>Challenges ahead</h2>
<p>While the images tell us a lot about Pluto and Charon, they also raise a number of new questions. We simply don’t know what controls the localised nitrogen snowfall, the intricate haze layers or the old fractures that cut through the craters. We don’t know why Pluto’s surface is so diverse or its atmosphere so complex, or how much of this is driven by tidal interactions between Pluto and Charon. The list goes on. Scientists will be using New Horizons data to try to answer these questions for decades to come.</p><img src="https://counter.theconversation.com/content/47517/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Rothery is author of Planets: A Very Short Introduction (Oxford University Press, 2010) and Moons: A Very Short Introduction (Oxford University Press, 2015). He receives funding from the UK Space Agency and the Science & Technology Facilities Council for work related to Mercury and the European Space Agency's Mercury orbiter BepiColombo.</span></em></p>From a mysterious haze to strange nitrogen snowfall, the latest pictures of Pluto pose many new questions.David Rothery, Professor of Planetary Geosciences, The Open UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/448652015-07-24T04:33:36Z2015-07-24T04:33:36ZNew Horizons scientists were masters of the long haul – here’s how people stick with extremely long-term goals<figure><img src="https://images.theconversation.com/files/89517/original/image-20150723-22821-am24jj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">What keeps workers going when the goal isn't even in sight?</span> <span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-218527948/stock-photo-empty-blurred-asphalt-road-towards-the-setting-sun-concept-with-arrow-and-sign-start.html">Road image via www.shutterstock.com</a></span></figcaption></figure><p>It took almost a decade for NASA’s <a href="https://www.nasa.gov/mission_pages/newhorizons/main/index.html">New Horizons</a> spacecraft to navigate its way across the solar system to start taking and transmitting dramatic closeup photos of the dwarf planet Pluto. Another three and a half years passed before New Horizons performed the furthest flyby in history, zooming past a Kuiper Belt object nicknamed <a href="http://pluto.jhuapl.edu/Ultima/Ultima-Thule.php">Ultima Thule</a>. Initially turning funding into the reality of a launch <a href="http://www.nytimes.com/2015/07/19/us/the-long-strange-trip-to-pluto-and-how-nasa-nearly-missed-it.html">involved</a> another five years before all that. Was it worth the wait? One team member <a href="https://theconversation.com/a-team-members-view-of-all-the-work-on-earth-it-took-to-get-new-horizons-to-pluto-44696">calls it</a> “a once-in-a-lifetime opportunity” to participate in “a history-making event,” so apparently it was.</p>
<p>Lurking behind the scientific excitement are questions about the nature of work that involves goals with very long time horizons, goals that may never be reached in one person’s working lifetime. A Washington Post <a href="http://www.washingtonpost.com/local/for-one-of-its-developers-the-new-horizons-probe-crosses-eras-on-earth/2015/07/12/00d14162-2704-11e5-b72c-2b7d516e1e0e_story.html">profile</a> of New Horizons scientist Andy Cheng reminded us that life happened during the long wait. As New Horizons made its three-billion-mile way through the solar system, Cheng’s kids grew up, his father and a brother died, a daughter married, hair thinned, health changed.</p>
<p>What’s it like to do the kind of work in which the time horizon to accomplishment is so vast? Here’s what Cheng told the Post: “You just have to teach yourself: Wait. Just wait. Be patient. It’s a very long time.” Indeed it is. So how do people who thrive in these settings stay motivated?</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/89509/original/image-20150723-22816-i4g1p9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/89509/original/image-20150723-22816-i4g1p9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/89509/original/image-20150723-22816-i4g1p9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=448&fit=crop&dpr=1 600w, https://images.theconversation.com/files/89509/original/image-20150723-22816-i4g1p9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=448&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/89509/original/image-20150723-22816-i4g1p9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=448&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/89509/original/image-20150723-22816-i4g1p9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=563&fit=crop&dpr=1 754w, https://images.theconversation.com/files/89509/original/image-20150723-22816-i4g1p9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=563&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/89509/original/image-20150723-22816-i4g1p9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=563&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">We’ll be here waiting for you in the morning… for years on end.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/blakespot/5263917715">Blake Patterson</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>More than just patience</h2>
<p>Patience is, as they say, a virtue, and we admire Andy Cheng’s copious reserves of it, but we suspect there’s more to it than that. The pursuit of long-term goals poses challenges relevant to professionals in a variety of work settings, not just space scientists on a Pluto mission. Many lines of work involve balancing short-term demands with long-run hopes and strategies, and the tension between the two has a lengthy provenance in the study of management among both <a href="http://dx.doi.org/10.5465/AMR.1996.9702100316">academics</a> and <a href="http://www.amazon.com/Short-Term-America-Causes-Business-Myopia/dp/087584300X">practitioners</a>.</p>
<p>Much is known about the psychology of goals: <a href="http://dx.doi.org/10.1037/0003-066X.57.9.705">decades of research</a> have shed light on how and why goals motivate task performance in all sorts of settings. We know, for instance, that <a href="https://books.google.com/books/about/A_Theory_of_Goal_Setting_Task_Performanc.html?id=MHR9AAAAMAAJ">specific, challenging and attainable goals</a> motivate in the short run, and we know that <a href="http://dx.doi.org/10.1146/annurev.psych.47.1.593">short-term goals are more motivating</a> than long-term goals. Very little of this work, however, looks at goals and motivation beyond short time spans. </p>
<p>Until, that is, our <a href="http://dx.doi.org/10.1002/job.1778">research</a> on how people stay motivated when goals take not just years but decades to reach. We interviewed professionals (researchers as well as administrators) in various fields – biomedical science, nanotechnology, astronomy, biodiversity and others – whose work meets three criteria: goals with decades-long time horizons, very slow progress along the way and significant chance of failure.</p>
<h2>A complex stew of motivation</h2>
<p>We learned from our data that people mine several sources of motivation that sustain them for the long haul, some rooted in what is going on in the present, and some located in thoughts about the future.</p>
<p>In their present circumstances, people who persevere are deeply interested in their work, exploiting opportunities to apply their expertise, acquire knowledge, and make intermediate discoveries along the way. A learning <a href="http://mindsetonline.com/whatisit/about/index.html">mindset</a> is crucial, because orienting oneself solely toward accomplishing the task leads people to avoid or give up on difficult goals when performance payoffs don’t materialize quickly. Long-run motivation is also juiced by perceptions that the work alongside the waiting is challenging, risky, surprising and fun. Social and professional cachet matters as well: gaining recognition from peers, working with prestigious others, being first to the goal and ultimately having a chance to prove skeptics wrong.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/89515/original/image-20150723-22811-826d7h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/89515/original/image-20150723-22811-826d7h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/89515/original/image-20150723-22811-826d7h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=387&fit=crop&dpr=1 600w, https://images.theconversation.com/files/89515/original/image-20150723-22811-826d7h.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=387&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/89515/original/image-20150723-22811-826d7h.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=387&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/89515/original/image-20150723-22811-826d7h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=486&fit=crop&dpr=1 754w, https://images.theconversation.com/files/89515/original/image-20150723-22811-826d7h.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=486&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/89515/original/image-20150723-22811-826d7h.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=486&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Someday I’ll attain the goal….</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/taspicsvns/15516983503">Vern</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>In terms of the future, individuals pursuing very long-term goals sustain motivation by envisioning possible futures that result from the work they are doing. This can include not just contributions to their professional or scientific disciplines, but broader impacts on people, societies and future generations. </p>
<p>People find additional motivation by invoking symbols, metaphors and historical allegories to give life to these envisioned futures. The people in our study spoke of moon landings, the Wright Brothers, climbing Mount Everest and “doing it the same way Darwin did.”</p>
<p>They envision not only impacts on others, but a sense of how they themselves may be changed by pursuit of the goal. These “possible selves,” as we label them, are motivated by the prospect of finding new truths, having their beliefs confirmed, overcoming obstacles and becoming known for seizing rare opportunities.</p>
<p>Just as persistence isn’t everything, neither is money. Pecuniary rewards do motivate, of course, and the long-term goal pursuers we spoke with did mention dreams of a big payoff down the road. But the more common and emphatic observation we heard is the belief that they could make more money doing other things – a sense of sacrifice in the name of the goal. Psychological rewards are the important currency along the way, with a marked tolerance for uncertainty regarding more tangible payoffs down the road.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/89522/original/image-20150723-22821-1nfo6h6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/89522/original/image-20150723-22821-1nfo6h6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/89522/original/image-20150723-22821-1nfo6h6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/89522/original/image-20150723-22821-1nfo6h6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/89522/original/image-20150723-22821-1nfo6h6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/89522/original/image-20150723-22821-1nfo6h6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/89522/original/image-20150723-22821-1nfo6h6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/89522/original/image-20150723-22821-1nfo6h6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Old-you to young-you: stick with it.</span>
<span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-277962830/stock-photo-grandfather-and-grandson-eating-breakfast.html">People image via www.shutterstock.com.</a></span>
</figcaption>
</figure>
<h2>Regulate thyself</h2>
<p>Binding together these various forms of motivation is what psychologists call <a href="http://cnx.org/contents/cc1452b3-dbd8-45e7-ab9e-a141395322c4@26.1:13/The-Psychology-Of-Emotions,-Fe">self-regulation</a> – the processes through which we manage our own actions, thoughts and emotions. Research <a href="http://dx.doi.org/10.1016/B978-012109890-2/50034-2">highlights</a> several ways this happens: balancing multiple goals, avoiding distractions, keeping emotions in check, being receptive to feedback, coping with failure, rebounding from disappointments.</p>
<p>Being good at a job involving long time horizons is not just about being good at waiting; it’s about finding sources of motivation in the present you’re living as well as the future you’re envisioning, with advanced skills of self-awareness and self-regulation thrown into the mix.</p>
<p>The New Horizons mission is a compelling reminder that ambitious goals with extended time horizons are reachable when talented people find ways to stay motivated for the long haul. These are skills one can cultivate – and there’s a bit of irony in the fact that long-term pursuits do afford time to get better at it. </p>
<p>Masters of the long haul mark time not with superhuman patience, but with a variety of strategies that merge the journey with the destination. The long haul doesn’t feel so long when one is fully engaged. As one of the scientists we interviewed in our study observed, “Five years is the blink of an eye.”</p>
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<section class="inline-content">
<img src="https://images.theconversation.com/files/275743/original/file-20190521-23817-1fnbziu.png?w=128&h=128">
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<header></header>
<p><a href="http://aom.org/">Thomas Bateman is a member of the Academy of Management</a></p>
<footer>The academy is a funding partner of The Conversation US.</footer>
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</section>
</p><img src="https://counter.theconversation.com/content/44865/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Thomas Bateman is an Academy of Management scholar.</span></em></p><p class="fine-print"><em><span>Bruce Barry does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>New Year’s resolutions are one thing. But what does it take to devote your life to a work goal with such a long time horizon you might never reach it in your lifetime?Bruce Barry, Professor of Management and Sociology, Vanderbilt UniversityThomas S. Bateman, Emeritus professor, University of VirginiaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/450022015-07-23T05:24:09Z2015-07-23T05:24:09ZAfter Pluto there’s still plenty of the solar system left to explore<figure><img src="https://images.theconversation.com/files/89324/original/image-20150722-1460-12z4553.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/nasamarshall/5099713438/">NASA/JPL-Caltech</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span></figcaption></figure><p>The past couple of years have been very exciting for space exploration. We’ve watched as spacecraft made visits to <a href="https://theconversation.com/curiosity-catches-a-whiff-of-methane-on-mars-and-a-possibility-of-past-life-35595">Mars</a>, <a href="https://theconversation.com/explainer-what-philae-did-in-its-60-hours-on-comet-67p-34289">comet 67P</a> and, just last week, <a href="https://theconversation.com/new-horizons-finally-gets-up-close-with-pluto-for-15-minutes-44603">Pluto</a>, which for decades marked the edge of our solar system.</p>
<p>Given the fervour that surrounded last week’s New Horizons mission, it’s fair to wonder whether anything could be as exciting as flying past Pluto (with perhaps the exception of <a href="https://theconversation.com/if-we-are-to-find-life-beyond-earth-we-need-to-be-explorers-not-hunters-45001">discovering alien life</a>). We have a basic understanding of our solar system – such as how moons, rings and planets interact in planetary systems, and what their atmospheres are made of. We also have theories about how the solar system was formed and has evolved. But we’re far from finishing exploring our solar system and testing these theories. Several missions over the next decade and beyond will reveal new insights into our patch of the universe.</p>
<h2>What’s next?</h2>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/89323/original/image-20150722-1460-nozv2r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/89323/original/image-20150722-1460-nozv2r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/89323/original/image-20150722-1460-nozv2r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/89323/original/image-20150722-1460-nozv2r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/89323/original/image-20150722-1460-nozv2r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/89323/original/image-20150722-1460-nozv2r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/89323/original/image-20150722-1460-nozv2r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Brave new worlds.</span>
<span class="attribution"><span class="source">NASA, ESA, and G. Bacon</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>New Horizons will continue to produce new discoveries as it <a href="https://theconversation.com/new-horizons-is-an-old-spacecraft-but-it-will-transform-our-knowledge-of-pluto-44524">transmits its measurements over the next year</a>, but the <a href="https://theconversation.com/beyond-pluto-new-horizons-mission-is-not-over-yet-44520">next step</a> is a fly-by of another <a href="http://solarsystem.nasa.gov/planets/profile.cfm?Object=KBOs">Kuiper Belt</a> object beyond the orbit of Pluto. The preferred candidate is a body designated <a href="http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2014+MU69&orb=1">2014 MU69</a> that was discovered just <a href="http://hubblesite.org/newscenter/archive/releases/2014/35/image/a/">last year</a>. If approval is granted later this year, a possible fly-by in 2019 could allow us to discovering more about this mysterious object and help us understand what happens at the very edge of our solar system and how it was formed.</p>
<p>In July 2016, <a href="http://www.nasa.gov/mission_pages/juno/images/index.html">NASA’s Juno mission</a> will enter orbit around Jupiter, the first spacecraft to do so since the end of the Galileo mission in 2003. Juno will study the interior of Jupiter, looking at its composition for information that could teach us about the formation of the solar system. It will also study <a href="http://hubblesite.org/newscenter/archive/releases/2000/38/image/a/">Jupiter’s aurora</a> and how the planet connects with its <a href="http://solarsystem.nasa.gov/scitech/display.cfm?ST_ID=1589">enormous magnetosphere</a>, the largest physical structure in the solar system.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/89317/original/image-20150722-1426-1ugpmj0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/89317/original/image-20150722-1426-1ugpmj0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/89317/original/image-20150722-1426-1ugpmj0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/89317/original/image-20150722-1426-1ugpmj0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/89317/original/image-20150722-1426-1ugpmj0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/89317/original/image-20150722-1426-1ugpmj0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/89317/original/image-20150722-1426-1ugpmj0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Move over Curiosity, here comes ExoMars.</span>
<span class="attribution"><span class="source">ESA</span></span>
</figcaption>
</figure>
<p>Europe’s <a href="http://exploration.esa.int/mars/">ExoMars mission</a> aims to search for signatures of life on Mars using two spacecraft. The Trace Gas Orbiter, due to launch in 2016, will study the distribution of volatile gases such as water, methane and ozone in Mars’ atmosphere, all of which could provide evidence for life. It will also act as a telecommunications relay for <a href="http://exploration.esa.int/mars/51499-exomars-rover/">a rover</a> that will be launched in 2018, which will drill two metres under the surface of the planet in search of similar biosignatures.</p>
<p>There’s more. The joint European-Japanese <a href="http://sci.esa.int/bepicolombo/">BepiColombo mission</a> to Mercury will launch in 2017, with two spacecraft undertaking a detailed study of the planet’s interior, surface and magnetosphere. And in 2018, Japan’s <a href="http://global.jaxa.jp/projects/sat/hayabusa2/">Hayabusa 2</a> spacecraft will arrive at <a href="http://arxiv.org/abs/1302.1199">one of</a> the <a href="http://scienceworld.wolfram.com/astronomy/ApolloAsteroid.html">Apollo asteroids</a> that cross the Earth’s orbit and, after surveying it for a year, will return samples to Earth in 2020.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/89319/original/image-20150722-1432-1d4u20j.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/89319/original/image-20150722-1432-1d4u20j.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=393&fit=crop&dpr=1 600w, https://images.theconversation.com/files/89319/original/image-20150722-1432-1d4u20j.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=393&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/89319/original/image-20150722-1432-1d4u20j.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=393&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/89319/original/image-20150722-1432-1d4u20j.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=493&fit=crop&dpr=1 754w, https://images.theconversation.com/files/89319/original/image-20150722-1432-1d4u20j.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=493&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/89319/original/image-20150722-1432-1d4u20j.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=493&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A long way to go for ice.</span>
<span class="attribution"><span class="source">ESA/AOES</span></span>
</figcaption>
</figure>
<p>Further into the future, we have a big first to look forward to. In 2022, the European Space Agency (ESA) will send the <a href="http://sci.esa.int/juice/">Jupiter Icy Moon Explorer (JUICE)</a> mission on a 10-year journey <a href="http://solarsystem.nasa.gov/planets/profile.cfm?Object=Ganymede">to Ganymede</a>, the largest moon in the Solar System. This will be the first time we have put a <a href="https://www.youtube.com/watch?v=j8ZiNNIFzzQ&feature=youtu.be">spacecraft in orbit around the moon</a> of a giant planet. JUICE’s primary aim is to study whether the moons of giant planets can be viable locations for life. A NASA mission called <a href="http://solarsystem.nasa.gov/missions/profile.cfm?MCode=EuropaFlyby">Europa Clipper</a> will also explore another of Jupiter’s moons, Europa, in the late 2020s/early 2030s.</p>
<p>Even with all of these planned missions, there are plenty of other corners of the solar system worth visiting again. Many scientists are not satisfied with simply making measurements from afar but want to get samples back from our moon, Mars and its moon Phobos. These so-called sample return missions still require a huge amount of technology development that will push our capabilities much further. But they are also a stepping stone to <a href="http://www.esa.int/Our_Activities/Human_Spaceflight/Calling_new_partners_for_exploring_the_Moon_and_Mars">human exploration</a> as robotic exploration allows us to test technology and reconnoitre distant hostile environments before we send humans.</p>
<p>Comets also continue to be a focus of attention for space scientists because there is no typical comet. “<a href="http://www.scientificamerican.com/article/main-belt-comet-asteroid/">Main-belt comets</a>”, for example, are a recently discovered class of comet which reside in the asteroid belt and may hold the keys to understanding the source of Earth’s water. The recent <a href="http://news.nationalgeographic.com/2015/06/150623-venus-volcanoes-active-space/">discovery of volcanic activity on Venus</a> is also tempting atmospheric scientists and geologists to look again at Earth’s “evil twin”.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/89326/original/image-20150722-1473-kqouyi.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/89326/original/image-20150722-1473-kqouyi.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=377&fit=crop&dpr=1 600w, https://images.theconversation.com/files/89326/original/image-20150722-1473-kqouyi.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=377&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/89326/original/image-20150722-1473-kqouyi.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=377&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/89326/original/image-20150722-1473-kqouyi.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=474&fit=crop&dpr=1 754w, https://images.theconversation.com/files/89326/original/image-20150722-1473-kqouyi.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=474&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/89326/original/image-20150722-1473-kqouyi.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=474&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The outer reaches.</span>
<span class="attribution"><span class="source">NASA/JPL</span></span>
</figcaption>
</figure>
<p>The outer solar system beyond Saturn is still very poorly explored. Uranus and Neptune have only received single fly-bys, similar to New Horizons at Pluto, with visits in 1986 and 1989 respectively. These ice giant planets form a unique class of planet and are quite different to the gas giants, Jupiter and Saturn. Scientists have been arguing for a <a href="http://www.space.com/13248-nasa-uranus-missions-solar-system.html">return to the ice giants</a> for the last decade. Triton, the largest moon of Neptune is of particular interest because it is suspected to be a Kuiper Belt object that has been pulled into orbit in a similar way to the origins of Pluto. Without radically new technology, Triton is the only opportunity we have to encounter a Pluto-type object multiple times.</p>
<h2>What’s the point?</h2>
<p>It is part of the human condition to explore and ask questions about <a href="http://time.com/3957126/pluto-new-horizons-meaning/">where we came from</a>. Many of science’s big questions, such as: “how did our Solar System evolve?” and “is there life beyond Earth?” aren’t easy to answer without exploring the universe. One of Philae’s main science questions was to try to unravel <a href="https://theconversation.com/why-is-life-left-handed-the-answer-is-in-the-stars-44862">why certain biological molecules</a> are shaped the way they are.</p>
<p>These answers also come with a cost. New Horizons cost around US$700m (£450m), although this only works out at about US$2 (£1.30) for each US citizen. But this cash wasn’t just launched into space. The money for space exploration goes to the same industries that support other sectors we rely on, such as global communications, weather observations and navigation. The same scientists also educate the next generation of scientists and engineers who in turn will ask those same big questions and seek answers amongst the planets.</p><img src="https://counter.theconversation.com/content/45002/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Arridge receives funding from the the Royal Society and Science and Technology Facilities Council. He also chairs the Solar System Advisory Panel which provides advice to the Science and Technology Facilities Council on Solar System research carried out in the UK. He is involved in ESA's JUICE mission to Jupiter and NASA's Cassini mission to Saturn and is active in developing new missions to Uranus.</span></em></p>Space scientists have a busy decade ahead with plans to visit Jupiter, Mars, Mercury and other interplanetary bodies all on the cards.Chris Arridge, Research Fellow/Lecturer, Lancaster UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/448092015-07-21T10:18:51Z2015-07-21T10:18:51ZNew Horizons brought our last ‘first look’ at one of the original nine solar system planets<figure><img src="https://images.theconversation.com/files/89049/original/image-20150720-12527-w1dc8s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">We got you, Pluto!</span> <span class="attribution"><a class="source" href="http://pluto.jhuapl.edu/Multimedia/Images/Artist-Renderings.php">JHUAPL/SwRI</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>Carl Sagan <a href="http://www.cambridge.org/us/academic/subjects/astronomy/astronomy-general/carl-sagans-cosmic-connection-extraterrestrial-perspective">famously said</a> we were the luckiest generation, to be present during the first reconnaissance of the solar system. The New Horizons mission to Pluto completes this half-century project with its stunning images and data. Meanwhile, however, space science has helped change dramatically our notions of solar systems and planets, with Pluto’s status itself the subject of controversy while New Horizons was on its way.</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/88856/original/image-20150717-21052-17flsu8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/88856/original/image-20150717-21052-17flsu8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/88856/original/image-20150717-21052-17flsu8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=507&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88856/original/image-20150717-21052-17flsu8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=507&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88856/original/image-20150717-21052-17flsu8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=507&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88856/original/image-20150717-21052-17flsu8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=637&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88856/original/image-20150717-21052-17flsu8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=637&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88856/original/image-20150717-21052-17flsu8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=637&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">First image of the far side of the moon, courtesy of the USSR’s Luna 3 spacecraft.</span>
</figcaption>
</figure>
<p>I saw the first Soviet image of the far side of the moon in a grainy newspaper reproduction in 1959, and watched a <a href="http://www.jpl.nasa.gov/missions/ranger-7/">Ranger probe</a> hit the moon in 1964, from a black-and-white 10-inch television, picture by picture.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/89019/original/image-20150720-12543-1m62g2q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/89019/original/image-20150720-12543-1m62g2q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/89019/original/image-20150720-12543-1m62g2q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=636&fit=crop&dpr=1 600w, https://images.theconversation.com/files/89019/original/image-20150720-12543-1m62g2q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=636&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/89019/original/image-20150720-12543-1m62g2q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=636&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/89019/original/image-20150720-12543-1m62g2q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=800&fit=crop&dpr=1 754w, https://images.theconversation.com/files/89019/original/image-20150720-12543-1m62g2q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=800&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/89019/original/image-20150720-12543-1m62g2q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=800&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Saturn as seen by Voyager 2 upon approach.</span>
<span class="attribution"><a class="source" href="http://photojournal.jpl.nasa.gov/catalog/PIA03152">NASA/JPL</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>I followed the exploration of the inner solar system, and while in graduate school was an intern at NASA headquarters in 1981 when <a href="http://www.nasa.gov/mission_pages/voyager/overview">Voyager 2</a> encountered Saturn (the video projector failed, and a technician brought in a small, color set for an auditorium full of people).</p>
<p>By then, Pluto had long been axed from the Grand Tour that would have visited all the outer planets. While scientists, no less than the public, reveled in the episodic reports from the two Voyagers and others, the <a href="http://www.nytimes.com/2015/07/19/us/the-long-strange-trip-to-pluto-and-how-nasa-nearly-missed-it.html">friends of Pluto regrouped</a>. In the early 1980s, a wood model of a proposed Pluto explorer spacecraft adorned a hallway at NASA headquarters, its large radio dish oriented up like a giant bowl. A sign of those fiscal times, people started throwing spare change into the dish antenna.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/88863/original/image-20150717-21073-djnx81.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/88863/original/image-20150717-21073-djnx81.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88863/original/image-20150717-21073-djnx81.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=312&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88863/original/image-20150717-21073-djnx81.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=312&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88863/original/image-20150717-21073-djnx81.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=312&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88863/original/image-20150717-21073-djnx81.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=392&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88863/original/image-20150717-21073-djnx81.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=392&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88863/original/image-20150717-21073-djnx81.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=392&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">1994 Hubble Space Telescope image of Pluto and its moon, Charon.</span>
<span class="attribution"><a class="source" href="http://hubblesite.org/newscenter/archive/releases/1994/17/image/a/">Dr R Albrecht, ESA/ESO Space Telescope European Coordinating Facility; NASA</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>But, about that time, exciting astronomical observations and theory began to reveal the Pluto neighborhood. First, a companion moon, then more, and also discoveries of individual bodies in that remote part of our solar system. As it got more crowded, the almost underground murmurs among astronomers that had for decades suggested Pluto was not in fact the missing “Planet X” believed to have been found in 1930 grew louder.</p>
<p>At one astronomical meeting, I sat near Clyde Tombaugh, discoverer of Pluto, when its planetary status was challenged. Tombaugh, then in his 90’s, jumped to his feet to defend his charge with characteristic vigor. Ironically, it was in part that challenge to planetary status and the intellectual redefinition of the solar system within which it was embedded that may have shaken loose enough spare change to mount a Pluto mission. Incidentally, a small portion of Tombaugh’s cremains are on the New Horizons spacecraft.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/88877/original/image-20150717-21027-1rk5d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/88877/original/image-20150717-21027-1rk5d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88877/original/image-20150717-21027-1rk5d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=402&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88877/original/image-20150717-21027-1rk5d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=402&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88877/original/image-20150717-21027-1rk5d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=402&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88877/original/image-20150717-21027-1rk5d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=505&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88877/original/image-20150717-21027-1rk5d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=505&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88877/original/image-20150717-21027-1rk5d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=505&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Celebrating the success of the Apollo 11 lunar landing mission in the Mission Control Center.</span>
<span class="attribution"><a class="source" href="http://www.nasa.gov/multimedia/imagegallery/image_feature_1718.html">NASA</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>The boomers are the first generation to witness the <a href="http://www.nasa.gov/pdf/607087main_NASAsFirst50YearsHistoricalPerspectives-ebook.pdf#page=443">initial exploration of our solar system</a> and the last to be taught that standard phrase, “the nine planets.” During the last half-century, scientific research and Cold War politics brought to a head changes in scientific disciplines and organization that had been maturing for centuries.</p>
<p>Astronomers had done their work from afar using large telescopes, and geologists had done theirs up close with other tools. Astronomers saw the big picture and struggled to tease out the details. Geologists and other “earth scientists” crawled over the details and struggled to see the big picture. High-tech science and planetary voyages mixed up these tidy disciplinary lines, as much as they challenged the schemes that had organized our world too simplistically into galaxies, stars, planets and moons.</p>
<p>Cold War politics loosened funds and stimulated astronomy, which needed to get beyond our blurry and filtered atmosphere, and planetary science, which needed to get spacecraft and instruments directly to the planets. While astronomy enjoyed a true revolution in understanding the remote and energetic bodies of the universe, geosciences moved beyond just the earth and morphed into a truly comparative planetary science.</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/89028/original/image-20150720-12536-z9rr2l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/89028/original/image-20150720-12536-z9rr2l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/89028/original/image-20150720-12536-z9rr2l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=502&fit=crop&dpr=1 600w, https://images.theconversation.com/files/89028/original/image-20150720-12536-z9rr2l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=502&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/89028/original/image-20150720-12536-z9rr2l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=502&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/89028/original/image-20150720-12536-z9rr2l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=631&fit=crop&dpr=1 754w, https://images.theconversation.com/files/89028/original/image-20150720-12536-z9rr2l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=631&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/89028/original/image-20150720-12536-z9rr2l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=631&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">We’ve come a long way from Earth at the center of it all.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Cellarius_ptolemaic_system_c2.jpg">Johannes van Loon</a></span>
</figcaption>
</figure>
<p>Reporting his first telescopic observations in 1610, Galileo remarked that watching sunrise over the mountains of the moon from Venice must look much the same as watching sunrise over the mountains of Bohemia from the moon. The issue of Copernicanism at the time is often phrased as whether the Earth or the sun is the center.</p>
<p>The sleeper issue that would take another four centuries to mature, however, was really about worlds and planets. Galileo and his immediate successors realized that all the planets were worlds in themselves, kin to our previously unique world, and could all be studied in similar ways. While telescopes did get better and better over the next four centuries, only the very largest planets and moons could be observed.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/88876/original/image-20150717-21047-1df8np6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/88876/original/image-20150717-21047-1df8np6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88876/original/image-20150717-21047-1df8np6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=377&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88876/original/image-20150717-21047-1df8np6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=377&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88876/original/image-20150717-21047-1df8np6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=377&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88876/original/image-20150717-21047-1df8np6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=473&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88876/original/image-20150717-21047-1df8np6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=473&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88876/original/image-20150717-21047-1df8np6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=473&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The solar system as we’ve traditionally thought about it.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Solar_sys.jpg">NASA</a></span>
</figcaption>
</figure>
<p>Our simplistic diagram of nine planets in largely empty space circling a sun has yielded to a hugely complex and subtle collection of bodies of every size, interacting with one another, sometimes traveling widely, and kin to the one we call home. This is the completion of the Copernican revolution. It extends from gigantic and exotic worlds like Jupiter to the molecules and chemistry of the life that gives rise to our curiosity. To <a href="http://www.penguinrandomhouse.com/books/159730/cosmos-by-carl-sagan/">paraphrase Sagan</a> again, we are a part of the universe that has evolved to contemplate and study the rest.</p>
<figure>
<img src="http://www.nasa.gov/sites/default/files/thumbnails/image/pluto-observations-through-the-years.gif">
<figcaption><span class="caption">Animation of Pluto observations from 1930 to 2015.</span> <span class="source">Lowell Observatory and NASA</span></figcaption>
</figure>
<p>The entire New Horizons mission over 15 years cost about <a href="http://solarsystem.nasa.gov/missions/profile.cfm?MCode=PKB&Display=ReadMore">US$700 million</a>, or $47 million per year – less than Americans <a href="http://www.bea.gov/iTable/iTable.cfm?ReqID=21&step=2#reqid=21&step=9&isuri=1&2103=70">spend on soft drinks</a>. All of space exploration is but spare change, and this mission’s tariff almost invisible on <a href="http://www.lpi.usra.edu/exploration/multimedia/NASABudgetHistory.pdf">anybody’s ledger</a>.</p>
<p>Like the Romans, we demanded bread and circuses during the space program’s heyday in its first decade or so. This circus is already quite a bargain. Throw some spare change into the next model of an orphan mission of exploration. You will need to have patience, but you will be rewarded.</p><img src="https://counter.theconversation.com/content/44809/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Joseph N Tatarewicz has received funding from the NASA History Office and from the Smithsonian Institution for work on which some of this contribution is based.</span></em></p>In the long lead-up to our ultimate flyby of Pluto, space science has reconfigured our notions of what it means to be a solar system, a planet, a world.Joseph Tatarewicz, Associate Professor of History, University of Maryland, Baltimore CountyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/445082015-07-16T19:30:03Z2015-07-16T19:30:03ZFinding Pluto: the hunt for Planet X<figure><img src="https://images.theconversation.com/files/88608/original/image-20150716-26314-1kz0194.jpg?ixlib=rb-1.1.0&rect=739%2C178%2C2970%2C2314&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">What could be out there? That question eventually led to the discovery of Pluto</span> <span class="attribution"><span class="source">ESO/L. Calçada</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>Our solar system’s shadowy ninth (dwarf) planet was the subject of furious speculation and a frantic search for almost a century before it was finally discovered by <a href="http://www.britannica.com/biography/Clyde-W-Tombaugh">Clyde Tombaugh</a> in 1930. And remarkably, Pluto’s reality was deduced using a heady array of reasoning, observation and no small amount of imagination.</p>
<p>The 18th and 19th centuries were thick with astronomical discoveries; not least were the planets Uranus and Neptune. The latter, in particular, was predicted by comparing observed perturbations in the orbit of Uranus to what was expected. This suggested the gravitational influence of another nearby planet.</p>
<p><a href="http://www.britannica.com/biography/John-Couch-Adams">John Couch Adams</a> and <a href="http://www.britannica.com/biography/Urbain-Jean-Joseph-Le-Verrier">Urbain-Jean-Joseph Le Verrier</a> calculated the orbit of Neptune by comparing these perturbations in Uranus’ orbit to those of the other seven known planets. Neptune was hence discovered in the predicted location in 1846.</p>
<p>Soon after this, French physicist <a href="https://en.wikipedia.org/wiki/Jacques_Babinet">Jacques Babinet</a> proposed the existence of an even more distant planet, which he named Hyperion. Le Verrier wasn’t convinced, stating that there was “absolutely nothing by which one could determine the position of another planet, barring hypotheses in which imagination played too large a part”.</p>
<p>Despite that lack of evidence for perturbations in Neptune’s orbit, many predicted the existence of a ninth planet over the next 80 years. Frenchman <a href="http://www.jstor.org/stable/228182?seq=1#page_scan_tab_contents">Gabriel Dallet</a> called it “Planet X” in 1892 and 1901, and the famed American astronomer <a href="http://www.britannica.com/biography/William-Henry-Pickering">William Henry Pickering</a> proposed “Planet O” in 1908.</p>
<h2>Comets, the law of vegetable growth and a conspiracy</h2>
<p>In addition to the perturbations of known planets there were other hypotheses that foretold unknown bodies beyond Neptune.</p>
<p>In the 19th century, it was understood that many comets had highly elliptical orbits that swung past the outer planets at their farthest points from the sun. It was believed that these planets diverted the comets into their eccentric orbits.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/88605/original/image-20150716-26323-shvjhc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/88605/original/image-20150716-26323-shvjhc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/88605/original/image-20150716-26323-shvjhc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88605/original/image-20150716-26323-shvjhc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88605/original/image-20150716-26323-shvjhc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88605/original/image-20150716-26323-shvjhc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88605/original/image-20150716-26323-shvjhc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88605/original/image-20150716-26323-shvjhc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Pluto is not only distant, but it’s small. That makes it very difficult to see from Earth.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>In 1879 the French astronomer <a href="http://www.daviddarling.info/encyclopedia/F/Flammarion.html">Camille Flammarion</a> predicted a planet with an orbit 24 times that of Earth’s based on comet measurements. Using the same method, <a href="https://goo.gl/FqLO4n">George Forbes</a>, professor of astronomy at Glasgow University, confidently announced in 1880 that “two planets exist beyond the orbit of Neptune, one about 100 times, the other about 300 times the distance of the earth from the sun”. </p>
<p>Depending on how the calculations were done, the results predicted anything from one to four planets. </p>
<p>Other predictions were based on what can be described as numerical curiosities or speculations. One of these was the now-discredited <a href="http://www.britannica.com/science/Bodes-law">Bode’s law</a>, a sort of <a href="http://www.livescience.com/37470-fibonacci-sequence.html">Fibonacci sequence</a> for planets. The American mathematician <a href="http://www.britannica.com/biography/Benjamin-Peirce">Benjamin Pierce</a> was not a fan, claiming that “fractions which express the law of vegetable growth” were more accurate than Bode’s law. </p>
<p>As well as these earnest astronomers, the trans-Neptunian planet idea attracted cranks and visionaries. An interesting contribution came in 1875 from Count Oskar Reichenbach, who accused Le Verrier and Adams of conspiring to conceal the locations of two trans-Neptunian planets.</p>
<h2>The early photographic searches</h2>
<p>Theories and calculations were all well and good, but many hoped to actually see the hitherto invisible planet(s). From the late 1800s new powerful telescopes equipped with the latest dry-plate photographic technologies were employed to search for undiscovered planets.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/88604/original/image-20150716-26319-jtnan9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/88604/original/image-20150716-26319-jtnan9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88604/original/image-20150716-26319-jtnan9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=519&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88604/original/image-20150716-26319-jtnan9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=519&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88604/original/image-20150716-26319-jtnan9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=519&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88604/original/image-20150716-26319-jtnan9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=652&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88604/original/image-20150716-26319-jtnan9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=652&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88604/original/image-20150716-26319-jtnan9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=652&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Pluto isn’t easy to spot. This 10 minute exposure shows the apparent magnitude of Pluto compared to some nearby stars.</span>
<span class="attribution"><span class="source">Kevin Heider</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Amateur astronomers such <a href="http://www.britannica.com/biography/Isaac-Roberts">Isaac Roberts</a> and <a href="https://goo.gl/JC5ece">William Edwards Wilson</a> used the predictions of George Forbes to search the skies, taking many hundreds of photographic plates in the process. They found no lurking trans-Neptunian planets.</p>
<p>The professionals fared no better. <a href="http://www.britannica.com/biography/Edward-Charles-Pickering">Edward Charles Pickering</a>, director of the Harvard Observatory and William’s brother, spent around ten years from 1900 searching using his own data and those of earlier astronomers such as Dallet, all to no avail. </p>
<h2>Lowell’s approach</h2>
<p>In 1906 a new approach was introduced by the veteran astronomer <a href="http://www.space.com/19774-percival-lowell-biography.html">Percival Lowell</a>. Although best known to us for his (mistaken) observations of <a href="https://en.wikipedia.org/wiki/Martian_canal">canals on Mars</a>, Lowell bought a new rigour to analysing the orbit of Uranus based on observational data from 1750 to 1903. </p>
<p>With these improved calculations, hope for a visual fix on the elusive planet was renewed. With the aid of the brothers Vesto and Earl Slipher, Lowell spend the rest of his life scanning photographic plates with a hand magnifier and finally with a <a href="http://www.city-of-light.com/en/topics/topics-detailpage/?tx_ttnews%5Btt_news%5D=275&cHash=2e1a29de74aaa837a979293e8e926538">Zeiss blink comparator</a>.</p>
<p>In September 1919 William Pickering kicked off another search for “Planet O” based on deviations in Neptune’s orbit. <a href="https://en.wikipedia.org/wiki/Milton_L._Humason">Milton L Humason</a>, from the Mount Wilson Observatory in California, started a search based on these new predictions as well as Lowell’s and Pickering’s 1909 predictions. This search again failed to find any new planets. Pickering continued to publish articles on hypothetical planets but by 1928 he had become discouraged. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/88603/original/image-20150716-26314-1cwokdr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/88603/original/image-20150716-26314-1cwokdr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88603/original/image-20150716-26314-1cwokdr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=448&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88603/original/image-20150716-26314-1cwokdr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=448&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88603/original/image-20150716-26314-1cwokdr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=448&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88603/original/image-20150716-26314-1cwokdr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=563&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88603/original/image-20150716-26314-1cwokdr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=563&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88603/original/image-20150716-26314-1cwokdr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=563&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Zeiss Blink comparator at Lowell Observatory used in the discovery of Pluto by Clyde Tombaugh in 1930.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/Category:Clyde_Tombaugh#/media/File:Zeiss_Blink_comparator_at_Lowell_Observatory_used_in_the_discovery_of_Pluto_by_Clyde_Tombaugh_in_1930.jpg">nivium/Wikimedia</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>A planet among 160,000 stars</h2>
<p>As part of Lowell’s legacy, the Lowell Observatory built a <a href="http://lowell.edu/history/the-pluto-telescope/">special astrographic telescope</a>. It was completed in 1929, and under <a href="http://www.britannica.com/biography/Vesto-Slipher">Vesto Slipher’s</a> direction, a young assistant was assigned to take and examine the photographs of the farthest reaches of the solar system. His name was <a href="http://www.space.com/19824-clyde-tombaugh.html">Clyde Tombaugh</a>.</p>
<p>This was grim, unglamorous work. Each plate was exposed for an hour or more, with Tombaugh adjusting the telescope precisely to keep pace with the slowly turning sky. Today a computer would make the comparisons, but in 1929 they were made by eye, manually flicking between two images. Stars would remain motionless while other bodies would seem to jump between views. Some images would have 40,000 stars, others up to 1 million.</p>
<p>Nearly a year had elapsed when, on February 18, 1930, two images fifteen times fainter than Neptune were found among 160,000 stars on the photographic plates. The discovery was confirmed by examining earlier images. On February 20 the planet was observed to be yellowish, rather than bluish like Neptune. The new planet had revealed its true colours at last.</p>
<h2>Announcing a discovery</h2>
<p>Slipher waited until March 13 to announce the discovery. This was both Lowell’s birthday and the anniversary date of the discovery of Uranus. The announcement set off a worldwide rush to observe and photograph the new planet.</p>
<p>Now that astronomers, amateur and professional alike, knew what they were looking for, it turned out that Pluto had been hiding in plain view. Re-examination of Humanson’s plates showed four images of Pluto from his 1919 survey, and there were many others. </p>
<p>On March 14, an Oxford librarian read the news to his 11-year old granddaughter <a href="http://zoharesque.blogspot.com.au/2015/07/the-day-pluto-came-to-breakfast-venetia.html">Venetia Burney</a>, who suggested the name Pluto. It was also suggested independently in a letter by William Henry Pickering.</p>
<p>To complete the circle, some of Clyde Tombaugh’s remains are in a <a href="http://www.jhuapl.edu/newscenter/pressreleases/2006/060203_image1.asp">canister</a> attached to the New Horizons spacecraft. </p>
<p>Most people alive today would not remember a universe without Pluto. And from 2015, its patterned surface will enter our visual vocabulary of the planets. Once seen, it can never again be unseen. Planet X, welcome to our world.</p><img src="https://counter.theconversation.com/content/44508/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Kevin Orrman-Rossiter is affiliated with The Royal Society of Victoria.</span></em></p><p class="fine-print"><em><span>Alice Gorman is a member of the National Executive Council of the Space Industry Association of Australia.</span></em></p>The existence of a “Planet X” in the outer solar system was the subject of great speculation, and was finally settled with the discovery of Pluto in 1930.Kevin Orrman-Rossiter, Graduate Student, History & Philosophy of Science, The University of MelbourneAlice Gorman, Senior Lecturer in archaeology and space studies, Flinders UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/447582015-07-16T04:57:21Z2015-07-16T04:57:21ZWhat might Pluto sound like? Our musical love affair with the cosmos<figure><img src="https://images.theconversation.com/files/88598/original/image-20150716-26289-de09w9.jpg?ixlib=rb-1.1.0&rect=0%2C129%2C979%2C685&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Music and astronomy have been intimately linked since antiquity.</span> <span class="attribution"><span class="source">AAP Image/ NASA</span></span></figcaption></figure><p>Fans of astronomy who also have a musical bent may have experienced a “what if” moment this week. With NASA’s <a href="https://www.nasa.gov/mission_pages/newhorizons/main/index.html">New Horizons</a> currently thrilling the world with the <a href="https://theconversation.com/live-blog-new-horizons-flyby-of-pluto-44670">best ever images</a> of the dwarf planet, it would have been the perfect time to bust out a recording of <a href="http://www.gustavholst.info/biography/index.php?chapter=1">Gustav Holst</a>’s symphonic suite, The Planets, and propose a toast to Pluto.</p>
<p>Unfortunately, Holst didn’t write a movement for Pluto. Exactly 100 years ago, Holst was halfway through composing what would become his most famous work, but Pluto wasn’t <a href="http://news.sciencemag.org/space/2015/07/new-planet-beyond-neptune-year-we-discovered-pluto">discovered</a> until 1930, four years before the <a href="http://www.gustavholst.info/biography/index.php?chapter=6">composer’s death</a>.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/AHVsszW7Nds?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Gustav Holst’s seven-movement orchestral suite, The Planets (1914-16).</span></figcaption>
</figure>
<p>Holst was apparently <a href="http://www.gustavholst.info/compositions/listing.php?work=18">uninterested</a> in updating his planetary audio tour, slightly resenting the work’s popularity and the corresponding attention deficit afforded his other compositions.</p>
<p>Resentment may have given way to pride had he known just how influential and <a href="http://www.imdb.com/name/nm0392304/">ubiquitous</a> The Planets would become, especially in cinema.</p>
<p>The Imperial March from Star Wars, for example, was clearly based on Mars, The Bringer of War, the first movement in the video of The Planets above. Not so much as stealing, <a href="http://www.biography.com/people/john-williams-9532526">John Williams</a> was probably honouring <a href="http://www.imdb.com/name/nm0000184/">George Lucas</a>’s request to recreate the spirit of Holst – an acknowledgement of the grip Holst’s music has on the public’s imagining of outer space.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/8VwkyrTb6go?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">John Williams – Star Wars’ The Imperial March (1980).</span></figcaption>
</figure>
<p>The fact that Holst was actually composing music based on <em>astrologically</em> inspired themes rather than astronomical (hence no “Earth” movement) is curiously beside the point now – we are so used to hearing this music appropriated for the purpose of making imagined outer space audible.</p>
<p>Humans have always turned to music to help deal with the profoundly confronting enormity of the cosmos.</p>
<p>From humming Twinkle Twinkle Little Star to a child at bedtime while peering through the window at the night sky, to <a href="http://www.imdb.com/name/nm0000040/">Stanley Kubrick</a> <a href="http://www.newyorker.com/magazine/2013/09/23/space-is-the-place">exploiting</a> the raw power of <a href="http://www.johann-strauss.org.uk/strauss.php?id=121">Strauss</a> and the luminous intricacy of <a href="http://www.schott-music.com/shop/persons/featured/gyoergy-ligeti/">Ligeti</a> in <a href="http://www.imdb.com/title/tt0062622/">2001: A Space Odyssey</a>, somehow music and the cosmos go together.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/3XyS7uCtnq0?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Opening sequence for Stanley Kubrick’s 2001: A Space Odyssey (1968).</span></figcaption>
</figure>
<p>One of the most emotionally resonant items aboard NASA’s <a href="http://voyager.jpl.nasa.gov/where/">Voyager 1 spacecraft</a> on its interstellar journey is of course the <a href="http://voyager.jpl.nasa.gov/spacecraft/goldenrec.html">Golden Record</a>, with its extensive and diverse <a href="https://theconversation.com/beyond-the-morning-star-the-real-tale-of-voyagers-aboriginal-music-18288">musical selection</a>.</p>
<p>The 90-minute sampling of music from around the globe is hardly tokenistic and it implies that humanity regards music as a very good foot to put forward when sending messages to alien civilisations.</p>
<h2>The Music of the Spheres</h2>
<p>This is all nothing new – music and astronomy have been intimately linked since antiquity.</p>
<p>An inaudible expression of mathematics via harmony, the <a href="http://www.sensorystudies.org/picture-gallery/spheres_image/">Music of the Spheres</a> was thought to determine the celestial dance moves of the planets and moons.</p>
<p>It all stemmed from Greek mathematician <a href="http://www.britannica.com/biography/Pythagoras">Pythagoras</a>’s discovery that pitch is proportionally related to the length of the sounding body such as a string or air column, and that what humans perceive as “harmonious”-sounding intervals (two pitches sounding at the same time) corresponded with simple mathematical ratios.</p>
<p>Pythagoras’ 2,600-year-old <a href="https://en.wikipedia.org/wiki/Musica_universalis#History">suggestion</a> that planetary bodies emit a kind of orbital hum may have been off the mark in terms of function (believing the inaudible vibrations affected everyday life on Earth) but not in substance.</p>
<p>Translations of radio and electromagnetic waves from space into audible sound make for <a href="http://www-pw.physics.uiowa.edu/space-audio/">eerie listening</a>.</p>
<p>The pioneering American composer <a href="http://terryriley.net/">Terry Riley</a> <a href="http://www.npr.org/templates/story/story.php?storyId=930399">wrote</a> an evening-length composition based on sounds collected from across the solar system in collaboration with a scientist and the Kronos string quartet:</p>
<figure>
<iframe src="https://player.vimeo.com/video/9213829" width="500" height="281" frameborder="0" webkitallowfullscreen="" mozallowfullscreen="" allowfullscreen=""></iframe>
<figcaption><span class="caption">Kronos Quartet: Sun Rings (2002).</span></figcaption>
</figure>
<p>You can even listen to a <a href="http://www.radio-astronomy.net/index.htm">live performance</a> by space 24 hours a day, seven days a week if you so desire, or a <a href="http://lightyear.fm/">playback</a> of all radio waves that have travelled away from Earth since we began transmitting radio. </p>
<p>Despite this history of recruiting our aural imagination to help get our minds around space, I do wonder what kind of humanly constructed sound could actually do Pluto justice.</p>
<p>Rejected for a time by size-ist scientists, invited back on new terms, and for many ever-associated with a <a href="http://www.imdb.com/character/ch0027779/">cute dog cartoon</a> by <a href="http://www.disney.com.au/">Disney</a>, the sheer mysteriousness of Pluto is somewhat obscured by the jokes.</p>
<p>So many educational posters line the planets up like snooker balls, for eminently practical reasons, that our sense of Pluto’s vast distance from us is rarely accurate.</p>
<p>A <a href="http://www.vox.com/2015/7/13/8947339/new-horizons-pluto-mission-nasa#ooid=81NGQ0djoP4shu015hc2FomKCLo1sfxJ">recent video on Vox</a> explains that if Earth were the size of a basketball, then Pluto would be a golf ball. Maintaining that scale, the two objects would have to be more than 80 kilometres apart to accurately reflect how far away Pluto is.</p>
<p>Words like “cold” and “lonely” don’t seem to capture the devastating isolation Pluto endures, a vantage point from which the sun appears as not much more than a bright star.</p>
<p>The visionary German composer <a href="http://www.karlheinzstockhausen.org/">Karlheinz Stockhausen</a> wasn’t afraid to venture past Pluto, into deep musical space. His mid-1970s musical drama <a href="http://www.theguardian.com/music/2005/oct/13/classicalmusicandopera">Sirius</a> brings us some fantastically original and imaginative sounds courtesy of four emissaries from a planet orbiting Sirius. The extensive use of electronically generated sounds in addition to the live performers gives this music its unearthly quality.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/1G3b65VU3L4?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Karlheinz Stockhausen’s Sirius, Part 1 of 2 (1975-77).</span></figcaption>
</figure>
<h2>A lonely planet</h2>
<p>At least <a href="http://www.hyperion-records.co.uk/dc.asp?dc=D_CDH55350">one composer</a> has taken up the challenge to complete Holst’s Planets, but his version of Pluto was designed to work well in a complete performance of the original suite, more or less connected to the planets-as-astrology approach of Holst.</p>
<p>Are there undreamt-of sounds lurking in humanity’s various musical languages that could truly evoke Pluto-ness in all its mind-bending solitude? Will even deeper relationships between sound and space be discovered by scientists?</p>
<p>I suspect the answers will be yes, and I can’t wait to hear what the music will be like.</p><img src="https://counter.theconversation.com/content/44758/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Liam Viney does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>From Twinkle Twinkle to Space Odyssey and beyond, humans have always turned to music to help deal with the profoundly confronting enormity of the cosmos. Is that a match made in the heavens?Liam Viney, Piano Performance Fellow , The University of QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/444512015-07-16T01:11:33Z2015-07-16T01:11:33ZIn focus: New Horizons’ crisp images shed new light on the origins of Pluto and its moons<figure><img src="https://images.theconversation.com/files/88562/original/image-20150715-26319-1n99yhf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Pluto's newly clear topography.</span> <span class="attribution"><a class="source" href="http://pluto.jhuapl.edu/Multimedia/Science-Photos/image.php?gallery_id=2&image_id=228">NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>Eighty-five years after Clyde Tombaugh discovered Pluto, we’re finally getting an up-close and personal look, thanks to <a href="https://www.nasa.gov/mission_pages/newhorizons/main/index.html">NASA’s New Horizons</a> mission. As a planetary astronomer who has investigated the formation of Pluto and other planets for nearly two decades, I’ve been waiting for New Horizons’ approach since it was launched in 2006. </p>
<p>We’re finally receiving the first detailed pictures of the icy dwarf planet. Data from the spacecraft should tell us more about the composition of the materials that originally spawned our solar system’s planets, and the nature of geological processes on icy planets.</p>
<p>Over the past month or so, as New Horizons approached the end of its three billion mile journey from Earth to Pluto, NASA has released <a href="http://www.nasa.gov/mission_pages/newhorizons/images/index.html">a stunning set of images</a> from the mission. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/88566/original/image-20150715-26325-15cmq1f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/88566/original/image-20150715-26325-15cmq1f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88566/original/image-20150715-26325-15cmq1f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88566/original/image-20150715-26325-15cmq1f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88566/original/image-20150715-26325-15cmq1f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88566/original/image-20150715-26325-15cmq1f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88566/original/image-20150715-26325-15cmq1f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88566/original/image-20150715-26325-15cmq1f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">New Horizons image taken July 13 2015 shows that Pluto has a ‘heart.’</span>
<span class="attribution"><a class="source" href="http://pluto.jhuapl.edu/Multimedia/Science-Photos/image.php?page=&gallery_id=2&image_id=225">NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>We now know that from a distance, Pluto has peach-colored surface features that resemble a heart, a whale and a doughnut. Pluto’s gray moon Charon has a dark polar cap (unofficially named Mordor) and several bright craters.</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/88573/original/image-20150715-26284-hrmq1e.gif?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/88573/original/image-20150715-26284-hrmq1e.gif?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/88573/original/image-20150715-26284-hrmq1e.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=661&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88573/original/image-20150715-26284-hrmq1e.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=661&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88573/original/image-20150715-26284-hrmq1e.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=661&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88573/original/image-20150715-26284-hrmq1e.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=830&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88573/original/image-20150715-26284-hrmq1e.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=830&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88573/original/image-20150715-26284-hrmq1e.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=830&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The four smaller moons.</span>
<span class="attribution"><a class="source" href="http://www.nasa.gov/image-feature/nasa-s-new-horizons-spots-pluto-s-faintest-known-moons">NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>We’ve seen four smaller (6–63 mile, or 10–100 km, diameter) moons orbiting the Pluto–Charon binary. <a href="http://dx.doi.org/10.1016/j.icarus.2014.03.015">Discovered by the Hubble Space Telescope,</a> moons Styx, Nix and Hydra are bright and probably icy, but Kerberos <a href="http://dx.doi.org/10.1038/nature.2015.17681">looks like a lump of coal</a>.</p>
<p>Despite the high quality of these images, what everyone was really waiting for was “closest approach,” when several instruments would finally be able to resolve kilometer-sized features on the surfaces of both planets. These instruments can spot cracks like those on Jupiter’s moon, Europa, and geysers like those on Saturn’s moon, Enceladus. On Tuesday, New Horizons successfully zoomed by Pluto. Here’s what the probe saw. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/88567/original/image-20150715-26280-l57no3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/88567/original/image-20150715-26280-l57no3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88567/original/image-20150715-26280-l57no3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=480&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88567/original/image-20150715-26280-l57no3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=480&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88567/original/image-20150715-26280-l57no3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=480&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88567/original/image-20150715-26280-l57no3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=603&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88567/original/image-20150715-26280-l57no3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=603&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88567/original/image-20150715-26280-l57no3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=603&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">An artist’s conception of New Horizons passing Pluto.</span>
<span class="attribution"><a class="source" href="http://www.nasa.gov/sites/default/files/thumbnails/image/nh-sc-pluto-illustration.jpg">NASA</a></span>
</figcaption>
</figure>
<h2>Logistics of the approach</h2>
<p>Traveling at about 31,000 mph (14 km/sec), New Horizons’ seven instruments <a href="http://pluto.jhuapl.edu/Mission/The-Path-to-Pluto/Mission-Timeline.php">had to work quickly during the fly-by</a>. Pluto is two-thirds the size of our moon; its binary companion, Charon, is only half the size of Pluto. Following a path that passes only 8,000 miles from Pluto (and 18,000 from Charon), on-board cameras snapped pictures of the surfaces of both worlds. Other instruments collected data on surface compositions, the extent of Pluto’s atmosphere, and the amount of dust orbiting them. After only 10 minutes, closest approach was over and New Horizons sped away from Pluto and the solar system, never to return.</p>
<p>Over the next 16 months, the on-board computer <a href="http://pluto.jhuapl.edu/Mission/Spacecraft/Data-Collection.php">will patiently transmit</a> all of the newly collected data back to Earth. With a <a href="http://pluto.jhuapl.edu/Mission/Spacecraft/Data-Collection.php">slow data rate of only 1 kb/sec</a>, it takes 42 minutes to transmit just one image.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/88568/original/image-20150715-26334-hf9abw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/88568/original/image-20150715-26334-hf9abw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/88568/original/image-20150715-26334-hf9abw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=449&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88568/original/image-20150715-26334-hf9abw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=449&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88568/original/image-20150715-26334-hf9abw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=449&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88568/original/image-20150715-26334-hf9abw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=564&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88568/original/image-20150715-26334-hf9abw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=564&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88568/original/image-20150715-26334-hf9abw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=564&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Pluto and Charon superimposed onto the Earth.</span>
<span class="attribution"><a class="source" href="http://www.nasa.gov/sites/default/files/styles/image_card_4x3_ratio/public/thumbnails/image/nh-pluto-charon-earth-size.jpg?itok=NHlBVaP5">NASA</a></span>
</figcaption>
</figure>
<p>The first set of images shows spectacular vistas on Pluto and Charon. Pluto has <a href="https://www.nasa.gov/press-release/from-mountains-to-moons-multiple-discoveries-from-nasa-s-new-horizons-pluto-mission">magnificent 11,000-foot mountains</a>! Relative to the size of Pluto, these mountains are comparable to a 65,000-foot mountain on Earth – more than twice the height of Mount Everest. </p>
<p>Aside from many craters, Charon has a large dark region, deep valleys, and prominent cliffs. One of the canyons is <a href="https://www.nasa.gov/press-release/from-mountains-to-moons-multiple-discoveries-from-nasa-s-new-horizons-pluto-mission">four to six miles deep</a>. Relative to Charon’s radius, this canyon corresponds to a 37 mile (60 km) deep canyon on the Earth – over 30 times deeper than the Grand Canyon!</p>
<h2>Learning more about the solar system’s start</h2>
<p>These data will help to complete a “fossil record” of the early history of the solar system. Nearly all stars like the sun form with a “<a href="https://en.wikipedia.org/wiki/Formation_and_evolution_of_the_Solar_System#Formation_of_the_planets">protosolar nebula,</a>” a disk-shaped collection of gas – mostly hydrogen and helium – and micron-sized dust grains. Over time, these tiny dust grains agglomerate into small pebbles. Pebbles grow into boulders, then mountains and finally planets.</p>
<p>The inner parts of this protosolar disk are warm, too warm for water to condense out of the gas. Agglomeration here leads to rocky planets like the Earth and Venus.</p>
<p>The outer parts of this disk are very cold. Ices of ammonia, methane and water condense out of the gas onto the grains and pebbles, leading to icy worlds like Pluto and Charon.</p>
<p>When icy worlds get large enough, they collect hydrogen and helium from the disk and grow into gas giants like Jupiter and Saturn. From the extreme pressure of the overlying gas, the iceball that became Jupiter has been crushed into a core of <a href="https://en.wikipedia.org/wiki/Metallic_hydrogen">metallic hydrogen</a>. Pluto can tell us what that iceball was like 4.5 billion years ago.</p>
<p>The canyons, mountains, and valleys on Pluto and Charon help us learn how rapidly Pluto and Charon formed. When planets form in a few million years, heat generated from collisions and the decay of radioactive nuclei melt the core (and sometimes, like the Earth, the entire planet). Within this liquid, heavy atoms like iron sink to the center; lighter atoms like oxygen rise to the surface. The planet becomes differentiated, where its various constituents separate into different layers based on their densities.</p>
<p>Differentiated planets have geysers and oceans. On Pluto and Charon, any surface water freezes quickly. But internal heat from radioactive decays and tides can maintain a subsurface ocean. This kind of <a href="http://www.nasa.gov/mission_pages/cassini/whycassini/cassini20120628.html">vast underground reservoir of water</a> keeps a planet round. Once New Horizons measures the “roundness” of Pluto and Charon, we will know whether either has a subsurface ocean. If they do, they probably formed rapidly.</p>
<p>Today’s images suggest Pluto and Charon are geologically active, differentiated worlds. Perhaps they have underground oceans. Once all the data are analyzed, we’ll know for sure.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/88564/original/image-20150715-26289-nwrlvi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/88564/original/image-20150715-26289-nwrlvi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88564/original/image-20150715-26289-nwrlvi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=454&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88564/original/image-20150715-26289-nwrlvi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=454&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88564/original/image-20150715-26289-nwrlvi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=454&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88564/original/image-20150715-26289-nwrlvi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=570&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88564/original/image-20150715-26289-nwrlvi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=570&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88564/original/image-20150715-26289-nwrlvi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=570&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Charon’s newly clear topography in a New Horizons image taken July 13 2015 from a distance of 289,000 miles.</span>
<span class="attribution"><a class="source" href="http://pluto.jhuapl.edu/Multimedia/Science-Photos/image.php?gallery_id=2&image_id=230">NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Hypothesis testing</h2>
<p>Personally, I’m looking forward to data that can test the <a href="http://dx.doi.org/10.1088/0004-6256/141/2/35">“Giant Impact” hypothesis</a> for the origin of the Pluto–Charon binary. The hypothesis states that Pluto and Charon formed in separate locations of the protosolar nebula. Much later, Charon skimmed the surface of Pluto and kicked up a lot of icy debris. Tides between Pluto and Charon stabilized their orbit, locking them into a structure where each has a “day” equal to their 6.4 Earth day orbit around a common center of mass. With this tidal-locking, one hemisphere of Pluto perpetually faces one hemisphere of Charon. The four small moons <a href="http://dx.doi.org/10.1088/0004-6256/147/1/8">formed out of the debris</a>.</p>
<p>For the next month or two, New Horizons will continue to collect images of the Pluto system. Once all these data are transmitted to Earth and analyzed in detail, we will know more about the shapes of Styx, Nix, Kerberos and Hydra. If these moons grew out of smaller particles in the debris from the Pluto–Charon collision, they should be round. If the moons are large fragments from the collision, they should have more jagged, irregular surfaces.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/88574/original/image-20150715-26319-10ah59.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/88574/original/image-20150715-26319-10ah59.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88574/original/image-20150715-26319-10ah59.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=402&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88574/original/image-20150715-26319-10ah59.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=402&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88574/original/image-20150715-26319-10ah59.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=402&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88574/original/image-20150715-26319-10ah59.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=506&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88574/original/image-20150715-26319-10ah59.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=506&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88574/original/image-20150715-26319-10ah59.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=506&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Hydra appears to be irregularly shaped.</span>
<span class="attribution"><a class="source" href="http://www.nasa.gov/image-feature/hydra-emerges-from-the-shadows">NASA-JHUAPL-SwRI</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>From the image released today, Hydra looks like an irregular fragment with bright and dark features on its surface. Once the New Horizons team processes all of the Hydra images, we will have a better idea of its true shape.</p>
<p>Now that New Horizons has done its job, scientists around the world will begin to analyze the data. It may take several years, but I am sure we will have some amazing surprises. In the meantime, we can rejoice that we live in an age where our tools can visit worlds throughout the solar system. And we can all enjoy the beautiful images of Pluto, Charon and their family of small moons.</p><img src="https://counter.theconversation.com/content/44451/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Scott Kenyon receives funding from NASA to study the formation and evolution of planetary systems.</span></em></p>Photos from the spacecraft’s close approach are dazzling. They and other data from the mission will fill in some of the blanks about Pluto and provide a snapshot of the infant solar system.Scott Kenyon, Senior Astrophysicist at the Smithsonian Astrophysical Observatory, Harvard-Smithsonian Center for AstrophysicsLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/447542015-07-15T21:07:20Z2015-07-15T21:07:20ZNew Horizons brings Pluto’s mysterious moons into play<figure><img src="https://images.theconversation.com/files/88548/original/image-20150715-26284-orxft4.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Pluto's enigmatic companion Charon.</span> <span class="attribution"><span class="source">NASA</span></span></figcaption></figure><p>Drifting along at what for decades was regarded as the outer boundary of our solar system, icy Pluto is far from alone. The dwarf planet has moons – <a href="http://www.space.com/16538-pluto-moons-explained-infographic.html">at least five of them</a> – which are all fascinating little worlds in their own right. Detailed views of these icy bodies, captured by the New Horizons spacecraft, have now begun to stream back to Earth as data and will reveal much about the chemistry and physics of the outer solar system.</p>
<p>Decades passed after Pluto’s discovery in 1930 before it was realised that the body had a companion. It was in 1978 that American astronomer James Christy noted that many photographic plates of Pluto <a href="http://www.astronomy.com/year-of-pluto/2015/06/an-interview-with-jim-christy-how-defective-images-revealed-the-first-double-planet">were marked as being defective</a>. A close look at these plates showed that despite background stars appearing perfectly sharp, images of Pluto almost always had a little bump on one side. Within a few hours of study, Christy came to realise that this bump was actually a moon, which he named Charon.</p>
<p>Compared to Pluto, which has a <a href="https://www.nasa.gov/feature/how-big-is-pluto-new-horizons-settles-decades-long-debate">diameter of 2,370km</a>, Charon is relatively large, measuring about <a href="http://www.space.com/29904-pluto-charon-different-new-horizons-photos.html">1,208 km across</a>. Indeed the size difference between the two is so small that they could be regarded as a <a href="http://www.spacetelescope.org/images/opo9014a/">double planet</a>. The large size of Charon has had a big effect on Pluto: both worlds are <a href="http://astro.unl.edu/classaction/questions/solarsystemdebris/ca_solarsystemdebris_tidallylocked.html">tidally locked</a>, meaning that the same hemispheres of the two worlds continually face each other. Charon is never visible from half of Pluto’s surface, and Pluto never rises above the horizon on half of Charon. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/88551/original/image-20150715-26314-qqt0fq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88551/original/image-20150715-26314-qqt0fq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=514&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88551/original/image-20150715-26314-qqt0fq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=514&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88551/original/image-20150715-26314-qqt0fq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=514&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88551/original/image-20150715-26314-qqt0fq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=646&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88551/original/image-20150715-26314-qqt0fq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=646&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88551/original/image-20150715-26314-qqt0fq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=646&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Pluto and its moons.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Pluto%27s_moons_2015-0603_115-111.jpg">NASA/ESA/A. Field (STScI)</a></span>
</figcaption>
</figure>
<p>The similarity in size between the worlds also has a big influence on the dwarf planet’s motion. An adult twirling a baby around stays in the same spot, but wobbles about a small circle when trying to do the same with a teenager. The same is true of Pluto: it actually <a href="http://www.solstation.com/stars/pluto.htm">moves in a circle every six days</a> as Charon orbits it, around a point in space well outside Pluto known as the barycentre, which is the pivot point for Pluto and Charon’s motion.</p>
<p>Two further moons – Nix and Hydra – <a href="http://www.nasa.gov/mission_pages/hubble/plutos_moons.html">were discovered in 2005</a>, using the Hubble Space Telescope, and the final two known moons, Kerberos and Styx, <a href="http://scitechdaily.com/kerberos-and-styx-accepted-by-iau-as-names-for-plutos-fourth-and-fifth-moon/">were found with the same telescope in 2011 and 2012</a>, respectively. Unlike Charon, these four small bodies measure only a few tens of kilometres across at most, but their orbital paths have <a href="http://www.nature.com/nature/journal/v522/n7554/full/nature14469.html">recently turned out to be fascinating</a>. The moons’ orbits have resonances, so their paths around Pluto follow a fixed pattern.</p>
<h2>Complex dance</h2>
<p>Guided by their mutual gravitational pull, the moons follow a dance: for every six orbits of Hydra about Pluto, Nix orbits nine times, and Styx 11 times. Rather than being tidally locked like Charon, these moons are almost certainly tumbling erratically due to the complex gravitational effects of the other moons.</p>
<p>Although the New Horizons images of these tiny moons will revolutionise our understanding of them, the amount of detail we will be able to see in the first images to be sent back will be limited. Each moon will occupy <a href="http://www.planetary.org/blogs/emily-lakdawalla/2015/06240556-what-to-expect-new-horizons-pluto.html">no more than two dozen pixels across</a> at best in each picture, surrounded by the blackness of space. We’ll however be able to tell their general shapes and we’ll see whether there are large impact craters, dark or bright patches present on their surfaces. First images of irregularly-shaped Hydra have revealed that it measures roughly 45km by 30km.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/88565/original/image-20150715-26309-q11uja.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88565/original/image-20150715-26309-q11uja.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=402&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88565/original/image-20150715-26309-q11uja.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=402&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88565/original/image-20150715-26309-q11uja.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=402&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88565/original/image-20150715-26309-q11uja.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=506&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88565/original/image-20150715-26309-q11uja.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=506&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88565/original/image-20150715-26309-q11uja.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=506&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Hydra photographed by New Horizons.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>As well as sharp images, New Horizons’s cameras will have caught colour views of the moons. Images of Charon already show it to be a colourful in places, likely influenced greatly by the presence of gases escaping from Pluto’s tenuous but extensive atmosphere. New Horizons has revealed already that Charon has a dark, reddish north pole, which may be formed of organic molecules that have escaped from Pluto and are trapped at the extra-frigid poles of the moon. Some areas of Charon are remarkably smooth with few craters, indicating regions that are relatively young, whilst other areas are cut by canyons up to 10 km deep.</p>
<p>Colour images of the smaller moons are also on their way. Will the moons also be colourful, exhibiting thin layers of ice captured from Pluto, or are they too small to keep hold of such material? All of Pluto’s moons may have been formed in a gargantuan collision in Pluto’s distant past; the moons’ colours will also help us test that scenario.</p>
<p>In the next few days, we’ll have big hints as to the nature of these fascinating worlds: more detailed views of Charon, measuring the same distance across as from London to Madrid, and four tiny new worlds. New Horizons is also searching for other moons, and may find some backlit by the Sun as it drifts into the cold depths of space beyond the fascinating Pluto system.</p><img src="https://counter.theconversation.com/content/44754/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Geraint Jones receives funding from the Science and Technology Facilities Council to carry out planetary and space science research.</span></em></p>What can the data from New Horizons tell us about the dwarf planet’s five moons?Geraint Jones, Reader in Planetary Science, UCLLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/446152015-07-15T20:41:06Z2015-07-15T20:41:06ZHistoric close-ups of Pluto and its moon Charon present puzzle for scientists<figure><img src="https://images.theconversation.com/files/88559/original/image-20150715-26319-1gitq6b.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">High resolution view of a 300 km wide region of Pluto. But where are the impact craters?</span> <span class="attribution"><a class="source" href="http://www.nasa.gov/image-feature/the-icy-mountains-of-pluto">NASA/JHUAPL/SWRI</a></span></figcaption></figure><p>After a decade-long journey by the New Horizons spacecraft through our solar system, we can finally add Pluto and its main moon Charon to the roster of large icy bodies whose landscapes we have seen. And it was worth the wait. The first detailed images are surprising, showing a remarkable lack of impact craters on both Pluto and Charon. </p>
<p>NASA’s probe passed within <a href="https://theconversation.com/new-horizons-finally-gets-up-close-with-pluto-for-15-minutes-44603">14,000 km of Pluto on July 14</a>, and – after a nervous 12-hour wait for its call home – has begun to send back its trove of data, which includes images revealing details as small as 100 metres across.</p>
<p>The most detailed image of part of Pluto (see lead image) is truly staggering. Not a single impact crater is to be seen in this region, so the surface must be very young – reshaped by some sort of geological activity such as faulting or icy volcanism. </p>
<p>It is rather early to speculate, but maybe Pluto captured Charon only a few hundred million years ago (rather than billions), and we are seeing the effect of the very <a href="http://www.open.edu/openlearn/science-maths-technology/science/physics-and-astronomy/icy-bodies-europa-and-elsewhere/content-section-1.4">strong tidal interactions</a> that would have ensued. Pluto could, in fact, even be geologically active today. I watched this image come in via a NASA press conference with a group of colleagues, and we were both amazed and mystified.</p>
<p>Pluto – which has a diameter of 2,370km – shares its orbital space with many comparable-sized bodies and crosses the orbit of the giant planet Neptune, which is why it <a href="https://theconversation.com/nasa-mission-brings-pluto-into-sharp-focus-but-its-still-not-a-planet-40495">does not qualify as a planet</a>. Nevertheless, it is a fascinating world, as indeed is Charon (1,208km diameter). </p>
<p>Both are bodies whose rocky interiors are deeply <a href="http://www.researchgate.net/profile/Tilman_Spohn/publication/225019299_Subsurface_Oceans_and_Deep_Interiors_of_Medium-Sized_Outer_Planet_Satellites_and_Large_Trans-Neptunian_Objects/links/55018a3a0cf24cee39f7b952.pdf">buried by ice of various kinds</a>. There is probably water-ice at depth on Pluto, but the surface ice is a mixture of frozen <a href="http://pluto.jhuapl.edu/News-Center/Science-Shorts.php?page=ScienceShorts_10_09_2014">methane, ethane, carbon monoxide and nitrogen</a>. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/88558/original/image-20150715-26334-45bev.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88558/original/image-20150715-26334-45bev.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=454&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88558/original/image-20150715-26334-45bev.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=454&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88558/original/image-20150715-26334-45bev.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=454&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88558/original/image-20150715-26334-45bev.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=570&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88558/original/image-20150715-26334-45bev.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=570&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88558/original/image-20150715-26334-45bev.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=570&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Latest image of Charon with its enigmatic dark polar cap, and a stupendous fracture system running near to its equator.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>Charon, with its weaker gravity, has lost the substances that can turn to vapour and escape more easily, and is mostly water-ice tainted by ammonia. That much we already knew. But New Horizons has been gathering data that will show us how these ices are arranged across each surface – and may find traces of other constituents.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/88517/original/image-20150715-26296-iacz74.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88517/original/image-20150715-26296-iacz74.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=314&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88517/original/image-20150715-26296-iacz74.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=314&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88517/original/image-20150715-26296-iacz74.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=314&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88517/original/image-20150715-26296-iacz74.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=394&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88517/original/image-20150715-26296-iacz74.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=394&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88517/original/image-20150715-26296-iacz74.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=394&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Pluto (left) and Charon (right) in slightly exaggerated colour.</span>
<span class="attribution"><span class="source">adapted from multiple datasets via http://www.nasa.gov/mission_pages/newhorizons/main/index.html</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Already the images are throwing up new questions. The composite image above, compiled from various images during New Horizons’ approach, shows slightly enhanced colour views of Pluto and Charon. Pluto is notable for patches of both bright and dark material in a belt straddling its equator. What are these? Is the bright, heart-shaped patch some kind of nitrogen frost or snow deposit? Is the dark stuff carbon or tar of some kind? (We know that solar ultraviolet <a href="https://en.wikipedia.org/wiki/Tholin">radiation turn methane into tar</a>). Charon, unique among known worlds, has a dark polar cap. Is that old, radiation-damaged methane, whereas the greyer equatorial region is cleaner water-ice?</p>
<p>The fact that Pluto has a red tint <a href="http://www.telegraph.co.uk/news/science/space/11737854/Pluto-flyby-the-first-pictures-of-dwarf-planet-from-New-Horizons-spacecraft-live.html">seems to have been surprising to some</a>, but it has actually been <a href="http://apod.nasa.gov/apod/ap010319.html">well-known for decades</a>.</p>
<p>An Open University PhD student has already made a preliminary <a href="http://dictionary.reference.com/browse/photogeology">photogeologic map</a> of the half of Pluto seen during approach (see below). It shows the “heart”, the dark patches and other units in different colours – representing different terrains. Several impact craters have also been marked in green, and a few wrinkles on the surface.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/88536/original/image-20150715-26323-1be8x6.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88536/original/image-20150715-26323-1be8x6.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=414&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88536/original/image-20150715-26323-1be8x6.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=414&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88536/original/image-20150715-26323-1be8x6.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=414&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88536/original/image-20150715-26323-1be8x6.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=520&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88536/original/image-20150715-26323-1be8x6.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=520&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88536/original/image-20150715-26323-1be8x6.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=520&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A preliminary map of terrain units on Pluto (right), based on the image on the left.</span>
<span class="attribution"><span class="source">Peter Fawden, Open University</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Then there are the <a href="http://www.lpi.usra.edu/education/explore/shaping_the_planets/tectonism.shtml">tectonic features</a>, the faulting or other deformation of the outer layer of a planet, to consider. These are better seen in black-and-white images. For example in the next image, just inside the eastern (right-hand) edge of the disk, the surface is cut by a fracture deep enough to cast shadows. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/88532/original/image-20150715-26277-yqakn0.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88532/original/image-20150715-26277-yqakn0.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=541&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88532/original/image-20150715-26277-yqakn0.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=541&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88532/original/image-20150715-26277-yqakn0.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=541&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88532/original/image-20150715-26277-yqakn0.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=680&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88532/original/image-20150715-26277-yqakn0.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=680&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88532/original/image-20150715-26277-yqakn0.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=680&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Pluto seen about a quarter of a rotation before the top image. The fractures at the lower right had rotated out of view by the time of closest approach. The ‘heart’ was just beginning to rotate into view on the left.</span>
<span class="attribution"><span class="source">NASA/JHUAPL/SWRI</span></span>
</figcaption>
</figure>
<p>Charon has similar fractures too. These are also known on several icy moons, such as Ariel and Titania at Uranus, and Tethys at Saturn, where they are described as chasmata (Latin for chasms). The image below shows
Charon and Uranus’s moon Titania at the correct relative scale. They both have fractures visible near their right-hand edges, which could be a remnant of a time when the surface became broken, <a href="http://www.open.edu/openlearn/science-maths-technology/science/physics-and-astronomy/icy-bodies-europa-and-elsewhere/content-section-1.4">perhaps by tidal forces</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/88538/original/image-20150715-26280-1aobzqe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/88538/original/image-20150715-26280-1aobzqe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88538/original/image-20150715-26280-1aobzqe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=310&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88538/original/image-20150715-26280-1aobzqe.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=310&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88538/original/image-20150715-26280-1aobzqe.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=310&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88538/original/image-20150715-26280-1aobzqe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=389&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88538/original/image-20150715-26280-1aobzqe.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=389&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88538/original/image-20150715-26280-1aobzqe.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=389&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Fractures can be seen both on Charon (left) and Titania (a moon of Uranus).</span>
<span class="attribution"><span class="source">NASA/JHUAPL/SWRI and NASA/JPL</span></span>
</figcaption>
</figure>
<p>Scientists are eagerly awaiting more data from New Horizons’ onboard memory, which is now nearly full, that will take a total of <a href="http://solarsystem.nasa.gov/news/display.cfm?News_ID=49503">16 months to transmit to Earth</a>. This is because at a range of more than 4.6 billion km from Earth the signal is so weak that it has to be transmitted at a slow rate of about 1 kilobit per second (you may be reading this via wi-fi operating at tens or hundreds of megabits per second). Although we may have to wait a while before we see the best of the pictures, what we already have already seen is enough to greatly intrigue planetary scientists such as myself.</p><img src="https://counter.theconversation.com/content/44615/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Rothery is author of Planets: A Very Short Introduction (Oxford University Press, 2010) and Moons: A Very Short Introduction (Oxford University Press, in press). He receives funding from the UK Space Agency and the Science & Technology Facilities Council for work related to Mercury and the European Space Agency's Mercury orbiter BepiColombo.</span></em></p>Lack of impact craters intrigues space experts who say it suggests the dwarf planet may be geologically active.David Rothery, Professor of Planetary Geosciences, The Open UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/446962015-07-15T18:39:40Z2015-07-15T18:39:40ZA team member’s view of all the work on Earth it took to get New Horizons to Pluto<figure><img src="https://images.theconversation.com/files/88545/original/image-20150715-26277-ujyla8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">It's all happening! New Horizons' science team members react to crisp shots of Pluto.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/nasahqphoto/19686046915">NASA/Bill Ingalls</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span></figcaption></figure><p>Science is hard and good science is harder – it takes persistence and tons of patience. When we began planning a mission to Pluto over 15 years ago, we knew it was going to be, as they say, a long haul. But we also knew it had a huge potential payoff. New Horizons would be the first closeup look at a world that we’d known about only distantly for 70 years. That kind of challenge is hard to pass by. And I didn’t.</p>
<h2>Earliest rumblings</h2>
<p>The first serious discussion of a mission to Pluto occurred in the late 1980s. That’s when telescope observations of distant stars going behind Pluto (known as <a href="http://occult.mit.edu/research/stellarOccultations.php">stellar occultations</a>) showed that it <a href="http://dx.doi.org/10.1006/icar.1997.5709">had a methane atmosphere</a>, probably rapidly evaporating to space. Considering Pluto’s small size, it was a surprise to see that its gravity was strong enough to hold on to an atmosphere at all.</p>
<p>Several planetary scientists began working on Pluto in earnest around that time. Throughout the 1990s, it was pretty obvious who the enthusiastic contributors to Pluto science were, and we naturally congregated at scientific meetings to speculate about a mission to the ninth planet. Several <a href="http://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=PLUTOKE">attempts at a Pluto mission</a> were formulated by NASA, but for various reasons none came to fruition, usually because of insufficient funding. By the time NASA announced the opportunity for a Pluto mission in 2000, everyone was ready with some pretty clear plans for how to optimize the science that could be done via a flyby.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/88553/original/image-20150715-26334-l1f92w.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/88553/original/image-20150715-26334-l1f92w.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88553/original/image-20150715-26334-l1f92w.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88553/original/image-20150715-26334-l1f92w.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88553/original/image-20150715-26334-l1f92w.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88553/original/image-20150715-26334-l1f92w.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88553/original/image-20150715-26334-l1f92w.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88553/original/image-20150715-26334-l1f92w.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Checking New Horizons’ electronics, pre-launch.</span>
<span class="attribution"><a class="source" href="http://pluto.jhuapl.edu/Multimedia/Images/Spacecraft-Images.php">NASA/JHUAPL/SwRI</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Pluto’s mysterious atmosphere</h2>
<p>I became interested in Pluto as a graduate student at Caltech in 1984. So little was known about the atmosphere at the time that you could get a computer model to predict just about anything. But after those stellar occultations revealed its unexpected atmosphere, I was hooked on Pluto atmosphere research. I focused on the planet’s chemistry. When Alan Stern, the <a href="http://www.nasa.gov/mission_pages/newhorizons/main/index.html">New Horizons</a> principal investigator, started pulling together <a href="http://pluto.jhuapl.edu/Mission/The-Team.php">researchers to work on the mission</a>, he asked me to join the atmosphere science team. Other mission members are focused on surface geology, interior structure, and formation of the Pluto–Charon system of five moons, among other things.</p>
<p>My main interest is understanding the chemistry and stability of Pluto’s atmosphere. How could Pluto hold onto its extended layer of gases over the 4.5 billion year age of the solar system? It should have long ago escaped to space because of tiny Pluto’s low gravity. But apparently it hasn’t.</p>
<p>Also, I’m interested to see whether the methane in its atmosphere produced complex hydrocarbons that would condense onto aerosols, settle downward, and be deposited on Pluto’s surface. Over the age of the solar system, these molecules should accumulate so that now we’d expect to see tens of meters of the stuff on Pluto’s surface.</p>
<p>And in fact, New Horizons does see large very dark regions on Pluto that might be made up of these photochemical products, generated when the methane in Pluto’s atmosphere absorbs ultraviolet sunlight. Similar types of chemically processed hydrocarbons are seen elsewhere in the outer solar system. They are generally known as “tholins” – a generic term to describe this reddish material. We have further observations planned that will probe Pluto’s atmosphere and map the distributions of hydrocarbon gases such as ethane, acetylene and ethylene that condense to form the aerosols.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/88549/original/image-20150715-26284-19li3yf.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/88549/original/image-20150715-26284-19li3yf.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88549/original/image-20150715-26284-19li3yf.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88549/original/image-20150715-26284-19li3yf.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88549/original/image-20150715-26284-19li3yf.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88549/original/image-20150715-26284-19li3yf.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88549/original/image-20150715-26284-19li3yf.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88549/original/image-20150715-26284-19li3yf.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Pluto, in its full-color glory, taken by New Horizons from only 476,000 miles away.</span>
<span class="attribution"><a class="source" href="http://pluto.jhuapl.edu/Multimedia/Science-Photos/image.php?page=1&gallery_id=2&image_id=225">NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>The long haul behind a long-haul mission</h2>
<p>Of course we had to do tons of prep work – deciding what scientific questions we’d try to tackle, which instruments to include, how to effectively steer and communicate with the probe over decades. And our work didn’t end with the launch nine-and-a-half years ago – there was still plenty left for us to do here on Earth.</p>
<p>Maybe it’s surprising, but this project has been exciting all the way through. The science team meetings were always interesting and animated, and at every step our conversations were laced with wild speculation about Pluto. Even the zillions of teleconferences usually had doses of humor sprinkled throughout.</p>
<p>While New Horizons was plugging away on its journey, my work mostly consisted of trying to prepare computer models of Pluto’s atmosphere to help us understand our eventual observations. This was much more difficult that I had thought it would be. We’d never encountered a planetary atmosphere like Pluto’s: gases escaping at supersonic speeds from such a frigid planet are a completely new situation. And that challenge continues to complicate interpreting the observations that are rolling in right now. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/88546/original/image-20150715-26334-1a9hgu1.gif?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/88546/original/image-20150715-26334-1a9hgu1.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88546/original/image-20150715-26334-1a9hgu1.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=240&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88546/original/image-20150715-26334-1a9hgu1.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=240&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88546/original/image-20150715-26334-1a9hgu1.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=240&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88546/original/image-20150715-26334-1a9hgu1.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=302&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88546/original/image-20150715-26334-1a9hgu1.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=302&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88546/original/image-20150715-26334-1a9hgu1.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=302&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The four smaller known moons of Pluto in orbit.</span>
<span class="attribution"><a class="source" href="http://www.nasa.gov/image-feature/nasa-s-new-horizons-spots-pluto-s-faintest-known-moons">NASA</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Cracking Pluto’s mysteries</h2>
<p>Pluto’s intrigue seemed only to increase, even after we launched New Horizons, when <a href="http://www.planetsedu.com/moon/nix/">two more moons</a> were discovered in addition to its known large moon Charon. And later <a href="http://www.sci-news.com/space/science-kerberos-styx-pluto-moons-names-01192.html">two more were discovered</a>! People were drawn to Pluto’s mysteries and each new revelation seemed to captivate more of their interest. And the International Astronomical Union’s demotion of Pluto <a href="https://www.iau.org/public/themes/pluto/">from planet to dwarf planet status</a> in 2006 seemed to make it even more interesting to the public. The political wrangling over Pluto’s status, the bizarre discoveries and New Horizons’ continuing quest worked via synergy to increase public interest in and support for our mission, which in turn energized the team.</p>
<p>This was truly a once-in-a-lifetime opportunity to be involved in such a history-making event. It’s gratifying to know that for decades to come, the New Horizons mission will be known as the endeavor that gave us our biggest leap forward in understanding Pluto, and that I was a part of it.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/88547/original/image-20150715-26296-ymipcd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/88547/original/image-20150715-26296-ymipcd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88547/original/image-20150715-26296-ymipcd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=422&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88547/original/image-20150715-26296-ymipcd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=422&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88547/original/image-20150715-26296-ymipcd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=422&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88547/original/image-20150715-26296-ymipcd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=530&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88547/original/image-20150715-26296-ymipcd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=530&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88547/original/image-20150715-26296-ymipcd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=530&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Principal Investigator Alan Stern celebrates with New Horizons flight controllers after they received confirmation from the spacecraft that it had successfully completed the flyby of Pluto.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/nasahqphoto/19710637771">NASA/Bill Ingalls</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
</figure>
<p>As I write, this it’s the day after the encounter. We are getting back results that are astonishing! Discoveries left and right. We’ll be working on understanding the brand new data for years. And this is nowhere near the end for the New Horizons team. We’ll stay together to plan an Extended Mission for New Horizons to fly by another dwarf ice planet – either the cryptically named PT1 or PT3 – hopefully in mid-2018.</p><img src="https://counter.theconversation.com/content/44696/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Mike Summers receives research funding from NASA.</span></em></p>New Horizons mission members have worked on the project for even longer than it’s taken the spacecraft to get to Pluto. They’ve planned, built and researched – and now their efforts are paying off.Mike Summers, Professor of Planetary Science and Astronomy, George Mason UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/441582015-07-15T05:22:46Z2015-07-15T05:22:46ZFrom comets to planets near and far, space probes reveal the universe<figure><img src="https://images.theconversation.com/files/88370/original/image-20150714-21701-xe0wt3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="http://solarviews.com/cap/vss/VSS00041.htm">NASA/JHUAPL/SwRI</a></span></figcaption></figure><p>If space is humankind’s ultimate challenge, then the first step starts close to home – we have still to explore much of our solar system that spans across enormous distances, never mind those galaxies and stars more distant still. </p>
<p>To learn more we must get closer, dispatching spacecraft such as New Horizons – which has <a href="http://www.bbc.co.uk/news/science-environment-33524589">just returned our first ever close-up images of Pluto</a> after a nine year journey. Here are my top five missions that are chipping away at what we don’t know and building up a better sense of universe around us.</p>
<h2>1. New Horizons</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/88373/original/image-20150714-21719-1dnittw.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/88373/original/image-20150714-21719-1dnittw.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/88373/original/image-20150714-21719-1dnittw.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88373/original/image-20150714-21719-1dnittw.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88373/original/image-20150714-21719-1dnittw.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88373/original/image-20150714-21719-1dnittw.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88373/original/image-20150714-21719-1dnittw.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88373/original/image-20150714-21719-1dnittw.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Time for your close-up, Pluto.</span>
<span class="attribution"><a class="source" href="http://pluto.jhuapl.edu/Multimedia/Science-Photos/image.php?gallery_id=2&image_id=222">NASA/JHU APL/SwRI</a></span>
</figcaption>
</figure>
<p>Rocketing past at 14km/s, the New Horizons spacecraft has provided our first close view of Pluto which will enormously improve our understanding of this distant body. Our facts regarding this icy dwarf are sketchy at best. Just knowing what Pluto looks like makes it much more real.</p>
<p>The probe’s brief two-hour visit captured images of parts of Pluto and its largest moon Charon at high resolution, improving our understanding of planet formation. This is an amazing feat, considering the signals take more than 4.5 hours to reach Earth and that the sun is so weak at this extreme distance that solar power is not an option. </p>
<p>But the mission doesn’t end here: in 2019 New Horizons will visit a small object in the Kuiper belt, a region of space filled with small rocky planetoids, giving us a chance to examine the make-up of these remnants of the early solar system. And by 2026, it will reach the outer edges of the solar system. </p>
<h2>2. Rosetta</h2>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/87345/original/image-20150703-20478-13i4cyi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/87345/original/image-20150703-20478-13i4cyi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=534&fit=crop&dpr=1 600w, https://images.theconversation.com/files/87345/original/image-20150703-20478-13i4cyi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=534&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/87345/original/image-20150703-20478-13i4cyi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=534&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/87345/original/image-20150703-20478-13i4cyi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=671&fit=crop&dpr=1 754w, https://images.theconversation.com/files/87345/original/image-20150703-20478-13i4cyi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=671&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/87345/original/image-20150703-20478-13i4cyi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=671&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Comet 67P/Churyumov-Gerasimenko, as seen from Rosetta 20km above.</span>
<span class="attribution"><a class="source" href="http://www.esa.int/spaceinimages/Images/2014/12/Comet_on_10_December_2014_NavCam">ESA</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Conceived decades ago, Rosetta flew alone through space for years before it reached the tiny comet that was its target and swung into orbit around it. Given the comet’s highly irregular shape this is an outstanding feat by itself.</p>
<p>The lander Philae managed to touch down and collect surface data of the comet, and while it was forced to shut down from lack of sunlight falling on its solar panels, it has now awoken and is transmitting data again. The Rosetta orbiter mission has also been extended to 2016 when it will also attempt to land on the comet.</p>
<p>The missions have improved our understanding of comets which contain <a href="http://blogs.esa.int/rosetta/2015/06/24/exposed-water-ice-detected-on-comets-surface/">frozen, icy rocks</a>, and have measured the <a href="http://blogs.esa.int/rosetta/2015/06/02/ultraviolet-study-reveals-surprises-in-comet-coma">gas composition of jets streaming off the comet</a> before they are altered by solar radiation.</p>
<p>But more than just hard numbers, this mission has been capturing images that speak for themselves, showing an ambitious mission conceived by many nations working together. Images such as Rosetta’s pictures of Philae descending resonates with us more than just hard facts and figures.</p>
<h2>3. Dawn</h2>
<p>Dawn is another mission expanding our knowledge of dwarf planets, in this case Ceres. It is now orbiting this interesting object having spent 2011 conducting similar work around nearby Vesta. Both Vesta and Ceres in the asteroid belt are protoplanets but of quite different composition.</p>
<p>Dawn has illustrated how powerful imagery can be. The most intriguing image is a crater that contains a <a href="http://dawn.jpl.nasa.gov/news/news-detail.html?id=4633">handful of bright white spots</a> on a surface otherwise darker than coal – unexpected, unexplored, challenging terrain.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/87351/original/image-20150703-20462-1tdeqzs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/87351/original/image-20150703-20462-1tdeqzs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=328&fit=crop&dpr=1 600w, https://images.theconversation.com/files/87351/original/image-20150703-20462-1tdeqzs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=328&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/87351/original/image-20150703-20462-1tdeqzs.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=328&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/87351/original/image-20150703-20462-1tdeqzs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=412&fit=crop&dpr=1 754w, https://images.theconversation.com/files/87351/original/image-20150703-20462-1tdeqzs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=412&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/87351/original/image-20150703-20462-1tdeqzs.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=412&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">What is the bright spot on the surface of Ceres? Dawn will find out.</span>
<span class="attribution"><a class="source" href="http://dawn.jpl.nasa.gov/news/news-detail.html?id=4619">NASA</a></span>
</figcaption>
</figure>
<h2>4. Messenger</h2>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/88366/original/image-20150714-21701-nnpb7n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/88366/original/image-20150714-21701-nnpb7n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88366/original/image-20150714-21701-nnpb7n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88366/original/image-20150714-21701-nnpb7n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88366/original/image-20150714-21701-nnpb7n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88366/original/image-20150714-21701-nnpb7n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88366/original/image-20150714-21701-nnpb7n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Incredibly detailed images from Messenger’s visit to Mercury.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:PIA19419-Mercury-Messenger-MASCS-20150416.jpg">NASA/JHU APL/Carnegie Institution of Washington</a></span>
</figcaption>
</figure>
<p>Messenger is still in my list of impressive space probes even though the mission ended with its controlled crash on Mercury’s surface this April. Sent to explore a planet of which we had barely any imagery of its surface, in four years Messenger managed to not only give us high-resolution maps of the innermost planet, it <a href="http://www.space.com/29281-messenger-spacecraft-mercury-crash.html">discovered water in its dark polar craters</a>. On a planet baked by the sun this could only arrive from comets and water-rich asteroids – objects currently under investigation by Rosetta and New Horizons.</p>
<h2>5. Curiosity</h2>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/88368/original/image-20150714-21701-bgp637.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/88368/original/image-20150714-21701-bgp637.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88368/original/image-20150714-21701-bgp637.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88368/original/image-20150714-21701-bgp637.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88368/original/image-20150714-21701-bgp637.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88368/original/image-20150714-21701-bgp637.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88368/original/image-20150714-21701-bgp637.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Curiosity Rover’s famous off-world self-portrait from Mars.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:PIA16239_High-Resolution_Self-Portrait_by_Curiosity_Rover_Arm_Camera_square.jpg">NASA/JPL-Caltech/Malin Space Science Systems</a></span>
</figcaption>
</figure>
<p>The last is the Curiosity rover. For me it sums up the efforts to explore our neighbour, Mars. These missions went in search of life and traces of water, carrying a complex laboratory, drills, laser and high resolution cameras.</p>
<p>Curiosity particularly illustrates the challenges we are capable of mastering to land a probe on Mars – described by NASA themselves as “seven minutes of terror”.</p>
<p>These rovers have achieved an outstanding feat, where now those exploring beyond Earth are not astronomers but geologists, the rovers’ equipment replacing the hammer and microscope used during fieldwork. The missions have added Mars to the “territory” that humans have access to. It’s even on <a href="http://www.google.co.uk/mars/">Google Maps</a> – imagery so good that we can see its surface as if we were there and can <a href="http://www.huffingtonpost.com/2014/09/02/11-rocks-on-mars-illusions_n_5697695.html">look at rocks in such detail</a> as if we were picking up pebbles at the beach.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/Ki_Af_o9Q9s?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
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<h2>It’s out there waiting for us</h2>
<p>Probes have witnessed solar eclipses and comet fly-bys that provide an entirely different view than is possible from Earth – something that adds a feel of awe and wonder, like looking back on Earth from the moon.</p>
<p>The sort of incredible images provided by these probes connects us with the solar system, bringing it closer to home. Famous images of Earth from space, such as the <a href="http://visibleearth.nasa.gov/view_cat.php?categoryID=1484">Blue Marble</a> and the <a href="https://www.youtube.com/watch?v=p86BPM1GV8M">Pale Blue Dot</a> catalysed our ecological conscience, reminding us of the fragility of our world in comparison to the vast, cold emptiness of outer space. </p>
<p>Such images lead us on to explore the universe and ourselves, and the findings of these remarkable spacecraft that have travelled millions, sometimes billions of miles through space over many years remind us that it’s out there to be discovered. The challenge and rewards await, as J F Kennedy said: we choose to go to space not because it is easy, but because it is hard.</p><img src="https://counter.theconversation.com/content/44158/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Daniel Brown does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Everything in space is so far away, but probes bring us closer.Daniel Brown, Lecturer in Astronomy, Nottingham Trent UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/445202015-07-15T05:14:37Z2015-07-15T05:14:37ZBeyond Pluto: New Horizons’ mission is not over yet<figure><img src="https://images.theconversation.com/files/88444/original/image-20150715-21711-1yzwq6u.jpg?ixlib=rb-1.1.0&rect=139%2C273%2C1694%2C1343&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">One of the most detailed images of Pluto captured by New Horizons just before it's closest approach to the dwarf planet.</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/image-feature/pluto-image-sent-to-earth-on-july-14-2015">NASA/APL/SwRI</a></span></figcaption></figure><p>When <a href="https://www.nasa.gov/mission_pages/newhorizons/main/index.html">New Horizons</a> phoned home this morning (Australian time) after its close encounter with <a href="http://pluto.jhuapl.edu/Mission/Where-is-New-Horizons/index.php">Pluto</a>, there was jubilation and excitement.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"621120974667259904"}"></div></p>
<p>Now, as Pluto retreats into the distance, the slow trickle of data can begin. Sent to us at a rate of just one kilobit a second, it will take months to receive it all, and astronomers around the world are waiting on tenterhooks to get their hands on the data. </p>
<h2>Pluto: Once shattered, twice shy</h2>
<p>Like our own Earth, Pluto has an oversized satellite, Charon. It was <a href="http://pluto.jhuapl.edu/Participate/learn/What-We-Know.php?link=Discovery-of-Charon">discovered back in 1978</a> and is more than half the diameter of its parent. </p>
<p>Over the past few years, intense observation of Pluto in preparation for New Horizons’ arrival has revealed four more smaller satellites, <a href="http://www.nasa.gov/mission_pages/hubble/plutos_moons_prt.htm">Hydra and Nix</a>, and tiny <a href="http://www.nasa.gov/mission_pages/hubble/science/pluto-moon.html">Kerberos</a> and <a href="http://www.nasa.gov/mission_pages/hubble/science/new-pluto-moon.html">Styx</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/88310/original/image-20150714-21719-1vw4vp2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/88310/original/image-20150714-21719-1vw4vp2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88310/original/image-20150714-21719-1vw4vp2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=613&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88310/original/image-20150714-21719-1vw4vp2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=613&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88310/original/image-20150714-21719-1vw4vp2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=613&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88310/original/image-20150714-21719-1vw4vp2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=770&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88310/original/image-20150714-21719-1vw4vp2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=770&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88310/original/image-20150714-21719-1vw4vp2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=770&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Prior to New Horizons, our best view of the Pluto system came from the Hubble Space Telescope.</span>
<span class="attribution"><a class="source" href="http://hubblesite.org/newscenter/archive/releases/2012/32/image/c/">NASA, ESA, and L Frattare (STScI)</a></span>
</figcaption>
</figure>
<p>But how did this satellite system come to be? And why the striking similarity to our double-planet?</p>
<p>If we look at the great majority of satellites in our solar system we find that they can be split into two groups. First, we have those that we think formed around their host planet like miniature planetary systems, mimicking the process of planet formation itself. </p>
<p>These regular satellites most likely <a href="http://www.sciencedirect.com/science/article/pii/S0019103503000769">accreted from disks of material</a> around the giant planets as those planets gobbled up material from the proto-planetary disk from which they formed. This explains the orbits of those satellites – perfectly aligned with the equator of their hosts and moving on circular orbits.</p>
<p>Then we have the irregular satellites. These are (with a couple of noteworthy exceptions) <a href="http://www2.ess.ucla.edu/%7Ejewitt/papers/2006/JSK06.pdf">tiny objects</a> and move on a wide variety of orbits, which are typically great distances from their host planets.</p>
<p>These, too, are easily explained – thought to be captured from the debris moving around the solar system late in its formation, relics of the swarm of minor bodies from which the planets formed.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/88311/original/image-20150714-21721-xyyx50.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/88311/original/image-20150714-21721-xyyx50.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88311/original/image-20150714-21721-xyyx50.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88311/original/image-20150714-21721-xyyx50.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88311/original/image-20150714-21721-xyyx50.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88311/original/image-20150714-21721-xyyx50.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88311/original/image-20150714-21721-xyyx50.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88311/original/image-20150714-21721-xyyx50.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">NASA graphic using New Horizons’ early pictures of Pluto and Charon to compare their sizes to that of the Earth.</span>
<span class="attribution"><a class="source" href="http://www.nasa.gov/image-feature/recent-measurements-of-pluto-and-charon-obtained-by-new-horizons">NASA</a></span>
</figcaption>
</figure>
<p>By contrast, our moon and Pluto’s Charon are far harder to explain. Their huge size, relative to their host, argues against their forming like the regular satellites. Likewise, their orbits are tilted both to the plane of the equator and to the plane of the host body’s orbit around the sun. It also seems very unlikely they were captured – that just doesn’t fit with our observations.</p>
<p><a href="https://theconversation.com/giant-impacts-planet-formation-and-the-search-for-life-elsewhere-33478">The answer</a> to this conundrum, in both cases, is violent.</p>
<p>Like our moon, Charon and, by extension, Pluto’s other satellites are thought to have been born in a giant collision, so vast that it tore their host asunder. This model does a remarkable job of explaining the makeup of our own moon and fits what we know (so far) about Pluto and its satellites.</p>
<p>Pluto and its moons will therefore be the second shattered satellite system we’ve seen up close. The results from New Horizons will be key to interpreting their formation. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/88312/original/image-20150714-21734-1ax0fmg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/88312/original/image-20150714-21734-1ax0fmg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88312/original/image-20150714-21734-1ax0fmg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=395&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88312/original/image-20150714-21734-1ax0fmg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=395&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88312/original/image-20150714-21734-1ax0fmg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=395&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88312/original/image-20150714-21734-1ax0fmg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=497&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88312/original/image-20150714-21734-1ax0fmg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=497&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88312/original/image-20150714-21734-1ax0fmg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=497&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Schematic describing our best theory for the formation of Pluto’s satellite system.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Creation_of_the_moons_of_Pluto.jpg">Wikimedia/Acom</a></span>
</figcaption>
</figure>
<p>Studying the similarities and differences between Pluto and Charon will teach us a huge amount about that ancient cataclysmic collision. We already know that Pluto and Charon are different colours, but the differences likely run deeper. </p>
<p>If Pluto was differentiated at the time of impact (in other words, if it had a core, mantle and crust, like the Earth) then Charon should be mostly comprised of material from the crust and mantle (like our moon). So it will be less dense and chemically different to Pluto. The same goes for Pluto’s other moons: Nix, Hydra, Styx and Kerberos.</p>
<h2>Pluto, the unknown</h2>
<p>The most exciting discoveries from New Horizons will likely be those we can’t predict. Every time we visit somewhere new, the unexpected discoveries are often the most scientifically valuable. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/88313/original/image-20150714-21721-198tdn5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/88313/original/image-20150714-21721-198tdn5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88313/original/image-20150714-21721-198tdn5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88313/original/image-20150714-21721-198tdn5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88313/original/image-20150714-21721-198tdn5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88313/original/image-20150714-21721-198tdn5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88313/original/image-20150714-21721-198tdn5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88313/original/image-20150714-21721-198tdn5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1005&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Jupiter and its volcanic moon Io, taken by New Horizons as it tore past the giant planet en route to Pluto.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/multimedia/imagegallery/image_feature_956.html">NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Goddard Space Flight Center</a></span>
</figcaption>
</figure>
<p>When we first visited Jupiter, 36 years ago, we found that its moon Io was a <a href="http://voyager.jpl.nasa.gov/science/jupiter.html">volcanic hell-scape</a>. We also found that Europa hosts a salty ocean, buried beneath a thick ice cap. Both of these findings were utterly unexpected. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/88319/original/image-20150714-21725-1lbqcdd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/88319/original/image-20150714-21725-1lbqcdd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88319/original/image-20150714-21725-1lbqcdd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=289&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88319/original/image-20150714-21725-1lbqcdd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=289&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88319/original/image-20150714-21725-1lbqcdd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=289&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88319/original/image-20150714-21725-1lbqcdd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=363&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88319/original/image-20150714-21725-1lbqcdd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=363&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88319/original/image-20150714-21725-1lbqcdd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=363&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Death Star terrorised peaceful planets before Voyager sent back images of Mimas.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/cosmobc/4484688366/">Flickr/Paul T</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>At Saturn, we found the satellite Mimas looked like the Death Star and another, Iapetus, <a href="http://www.planetary.org/blogs/emily-lakdawalla/2012/3389.html">like a two-tone cricket ball</a>, complete with a seam. Uranus had a satellite, Miranda, that looked like it had been <a href="https://www.youtube.com/watch?v=O-KE30osVGw">shattered and reassembled many times over</a>, while Neptune’s moon Triton turned out to be <a href="http://www.space.com/26907-neptune-moon-triton-map-voyager-2.html">dotted with cryo-volcanoes</a> that spew ice instead of lava. </p>
<p>The story continues for the solar system’s smaller bodies. The asteroid Ida, visited by Galileo on its way to Jupiter, <a href="http://www.jpl.nasa.gov/spaceimages/details.php?id=PIA00333">has a tiny moon, Dactyl</a>. Ceres, the dwarf planet in the asteroid belt, has astonishingly <a href="https://www.nasa.gov/jpl/dawn/ceres-bright-spots-come-back-into-view/">reflective bright spots</a> upon its surface.</p>
<p>Pluto, too, will have many surprises in store. There have already been a few, including the <a href="https://www.nasa.gov/image-feature/pluto-s-bright-mysterious-heart-is-rotating-into-view">heart</a> visible in the latest images (see top) – possibly the most eye catching feature to date. The best is doubtless still to come.</p>
<h2>To infinity, and beyond!</h2>
<p>Despite the difficulties posed by being more than <a href="https://theconversation.com/new-horizons-close-encounter-with-pluto-will-reveal-its-icy-secrets-44361">4.5 billion kilometres from home</a>, New Horizons is certain to revolutionise our understanding of the Pluto system. </p>
<p>The data it obtains will shed new light on the puzzle of our solar system’s <a href="https://theconversation.com/pluto-and-its-collision-course-place-in-our-solar-system-43404">formation and evolution</a>, and provide our first detailed <a href="https://www.nasa.gov/mission_pages/newhorizons/images/index.html">images of one of the system’s most enigmatic objects</a>.</p>
<p>But the story doesn’t end there. Once Pluto recedes into the distance, New Horizons will continue to do exciting research. The craft has a limited amount of fuel remaining, nowhere near enough to turn drastically, but enough to nudge it towards another one or two conveniently placed targets. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/87759/original/image-20150708-31601-1wb8j4g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/87759/original/image-20150708-31601-1wb8j4g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/87759/original/image-20150708-31601-1wb8j4g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=448&fit=crop&dpr=1 600w, https://images.theconversation.com/files/87759/original/image-20150708-31601-1wb8j4g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=448&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/87759/original/image-20150708-31601-1wb8j4g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=448&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/87759/original/image-20150708-31601-1wb8j4g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=562&fit=crop&dpr=1 754w, https://images.theconversation.com/files/87759/original/image-20150708-31601-1wb8j4g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=562&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/87759/original/image-20150708-31601-1wb8j4g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=562&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">New Horizons’ will continue its mission after flying past Pluto, studying objects in the Edgeworth-Kuiper belt.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>Since the launch of New Horizons, astronomers have been searching for suitable targets for it to visit as it hurtles outward through the <a href="http://www.britannica.com/topic/Kuiper-belt">Edgeworth-Kuiper belt</a>, en route to the stars.</p>
<p>In October 2014, as a result of that search, three potential targets were identified. Follow-up observations of those objects narrowed the list of <a href="http://plutopostcards.tumblr.com/post/114890975293/picture-from-the-colorado-dmv-im-super-excited">possible destinations</a> to two, known as 2014 MU69 (the favoured target) and 2014 PN70.</p>
<p>The final decision on which target to aim for will be taken after New Horizons has left Pluto far behind, but we can expect to keep hearing about the spacecraft for years to come.</p><img src="https://counter.theconversation.com/content/44520/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Now the flypast of Pluto is over the space probe New Horizons will begin sending the data back to Earth. It will take many months but what will it reveal about the dwarf planet?Jonti Horner, Vice Chancellor's Senior Research Fellow, University of Southern QueenslandJonathan P. Marshall, Vice Chancellor's Post-doctoral Research Fellow, UNSW SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/446222015-07-14T14:44:10Z2015-07-14T14:44:10ZFly-by missions: what is the point when we have the technology to go into orbit?<figure><img src="https://images.theconversation.com/files/88333/original/image-20150714-21721-1altasy.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Preparation of Mariner 4 before its fly-by of Mars, exactly 50 years ago.</span> <span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Mariner_4_Launch_Preparations.jpeg">NASA/JPL</a></span></figcaption></figure><p>New Horizons’ <a href="http://pluto.jhuapl.edu/">fly-by of Pluto</a> and its moons is the latest in a historic string of missions to objects in the solar system. But given that a fly-by lasts for just a short time, how much can we really get out of it? There’s no doubt that the mission will yield a great deal of interesting data, but surely more would be gained if the spacecraft could go into orbit for a number of days or actually land on the surface and take physical samples.</p>
<p>New Horizons is hugely important because it is giving us a first glimpse into the unseen world of a third class of objects in the <a href="http://www2.ess.ucla.edu/%7Ejewitt/kb.html">Kuiper belt</a> – the building blocks of the outer solar system, located beyond the terrestrial and gas-giant planets. Fly-bys such as this are very exciting as they provide just one chance for unique measurements at the target. </p>
<p>While we are only at the very first stage of exploring Pluto and its moons, the fly-by will provide the foundations for future missions. Indeed, a fly-by is the first in the classical four <a href="http://rsta.royalsocietypublishing.org/content/357/1763/3299">stages of solar-system exploration</a> and is followed – in this order – by an orbiter, a lander and the return of a sample from a body (marked 1-4 in the table below).</p>
<h2>Lessons from the past</h2>
<p>The first fly-by was of our Moon, made in 1959 by the Russian <a href="http://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=1959-012A">Luna-1 spacecraft</a>. And 50 years ago, nearly to the day (July 15), the US <a href="http://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=1964-077A">Mariner 4</a> made the first fly-by of Mars.</p>
<p>My generation was captivated by the historic fly-bys of the outer planets and some of their moons, and I’ve been lucky enough in my own career to have been involved in instrument teams for several historic fly-bys. These were the <a href="http://sci.esa.int/giotto/">Giotto mission to comets Halley (1986)</a> and <a href="http://sci.esa.int/giotto/31880-grigg-skjellerup/">Grigg-Skjellerup (1992)</a>, as well as several close “fly-by firsts” in the Saturn system with the <a href="https://www.nasa.gov/mission_pages/cassini/main/index.html">Cassini mission</a> (such as moons Titan, Enceladus, Rhea, Dione, Hyperion).</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/88272/original/image-20150713-11804-p7yxrn.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88272/original/image-20150713-11804-p7yxrn.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=382&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88272/original/image-20150713-11804-p7yxrn.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=382&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88272/original/image-20150713-11804-p7yxrn.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=382&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88272/original/image-20150713-11804-p7yxrn.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=480&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88272/original/image-20150713-11804-p7yxrn.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=480&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88272/original/image-20150713-11804-p7yxrn.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=480&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Flyby firsts.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The Giotto fly-by of comet Halley only lasted a few days, but our knowledge of comets was revolutionised by this encounter. One of several probes to explore Halley in the mid-1980s, Giotto had the widest and most capable set of instruments and passed closer to its target than any of its companions. </p>
<p>It found <a href="http://www.nature.com/nature/journal/v321/n6067s/abs/321357a0.html">cometary jet activity</a>, a surprisingly dark surface, hydrocarbons in a crust and a complex bow shock and tail formation mechanism. <a href="http://astrosociety.org/edu/publications/tnl/06/06.html">These discoveries</a> are now being followed up by the Rosetta mission and Philae lander at comet 67P.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/88345/original/image-20150714-21728-17g0zj4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88345/original/image-20150714-21728-17g0zj4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88345/original/image-20150714-21728-17g0zj4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88345/original/image-20150714-21728-17g0zj4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88345/original/image-20150714-21728-17g0zj4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88345/original/image-20150714-21728-17g0zj4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88345/original/image-20150714-21728-17g0zj4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Artist’s impression of Giotto approaching a comet.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Giotto_%28spacecraft%29#/media/File:Giotto_spacecraft.jpg">Mirecki/wikimedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>But the fact that fly-bys happen so quickly can also make them very stressful and difficult to manage. When we were monitoring the Giotto spacecraft, flying past Halley at 68.4 km/s, it suddenly started spinning off its axis after encountering a dust particle near its closest approach. Fortunately it was possible to stop the wobble.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/88344/original/image-20150714-21728-1q4n7qn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88344/original/image-20150714-21728-1q4n7qn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88344/original/image-20150714-21728-1q4n7qn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88344/original/image-20150714-21728-1q4n7qn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88344/original/image-20150714-21728-1q4n7qn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88344/original/image-20150714-21728-1q4n7qn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88344/original/image-20150714-21728-1q4n7qn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Comet Wild 2 as seen from Stardust on January 2, 2004.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Stardust_%28spacecraft%29#/media/File:Wild2_3.jpg">NASA/wikimedia</a></span>
</figcaption>
</figure>
<p>There are many other examples where data have been rescued – including with New Horizons during its <a href="http://www.space.com/29854-new-horizons-glitch-pluto-flyby.html">worrying glitch</a> (now fixed) on July 4.</p>
<h2>New Horizons and beyond</h2>
<p>After <a href="http://www.nasa.gov/mission_pages/newhorizons/launch/launch-index.html">launch on an Atlas V in 2006</a>, the <a href="http://app.plutosafari.com/articles/guide/trivia.html">478kg</a> spacecraft passed Jupiter only 13 months later, which was an express route. The main reason for the hurry was to reach Pluto before its tenuous atmosphere collapses by freezing as the planet moves further away from the Sun. The mission design of New Horizons gives a very fast fly-by at over 14 km/s (50,000 km/hour), with only a few hours and days for the highest resolution measurements. </p>
<p>Measured in “<a href="https://theconversation.com/explainer-light-years-and-units-for-the-stars-16995">astronomical units</a>” (one AU is about 149.6m kilometres), Pluto’s orbit takes it from its closest point to the Sun (29.7 AU, 1989), inside Neptune’s orbit (30.1 AU), through its current distance (nearly 33 AU) out to its furthest distance from the Sun (48.9 AU, 2113). Receding from the Sun, the surface temperature reduces from its current 40 Kelvin, leading to freezing of the atmosphere.</p>
<p>But why fly past, rather than going into orbit? The most simple answer is that a lot of energy, meaning a lot of fuel, would be needed to slow New Horizons enough to capture it into orbit. Instead, NASA opted to get to the Pluto-Charon system quickly with a relatively capable 30 kg payload, rather than taking a large amount of extra fuel using a different fly-by scheme, to get there before the atmosphere collapses.</p>
<p>New Horizons is already expanding the thin textbooks on the Pluto-Charon system with early images, and the data to be returned over the next 16 months from visible, infrared and ultraviolet spectrometers as well as plasma, dust and radio science instruments will broaden and rewrite them again. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/88347/original/image-20150714-21707-1q4agqt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88347/original/image-20150714-21707-1q4agqt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=314&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88347/original/image-20150714-21707-1q4agqt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=314&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88347/original/image-20150714-21707-1q4agqt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=314&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88347/original/image-20150714-21707-1q4agqt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=394&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88347/original/image-20150714-21707-1q4agqt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=394&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88347/original/image-20150714-21707-1q4agqt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=394&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Image of Pluto and Charon, taken with New Horizons.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/image-feature/a-portrait-from-the-final-approach-to-pluto-and-charon">NASA</a></span>
</figcaption>
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<p>But new questions will almost certainly arise, which can only be answered by a more detailed orbiter mission, following the usual exploration sequence. When that would happen is hard to say. The relative priority will need to be compared with missions to other objects, particularly those where the exploration stage is low, before possible implementation. </p>
<p>In the future, we can look forward to more detailed fly-by missions of objects where our knowledge is limited and later-stage missions such as Rosetta. Also we will visit new dimensions, such as <a href="http://exploration.esa.int/mars/46048-programme-overview/">ExoMars drilling</a> underneath the Mars surface by up to 2 metres for the first time. The <a href="http://science.nasa.gov/missions/juice/">JUICE fly-bys</a> of Jupiter’s moons Europa, Ganymede, and Callisto, before entering Ganymede orbit, will allow comparison of subsurface oceans, and <a href="http://www.jpl.nasa.gov/missions/europa-mission/">Europa Clipper</a> will fly past Europa 45 times to complete a detailed reconnaissance there.</p>
<p>These missions, and their follow-ons, will help us discover more about the humankind’s place in the universe – and whether we are alone. But it is clear that, while we have achieved a lot in solar-system exploration so far, there is still a large amount left to do.</p><img src="https://counter.theconversation.com/content/44622/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Andrew Coates receives funding from the Science and Technology Facilities Council (STFC, UK) and the UK Space Agency.</span></em></p>Exactly half a century ago the US Mariner 4 made the first flyby of Mars. But why are we still doing flybys today?Andrew Coates, Professor of Physics, Head of Planetary Science at the Mullard Space Science Laboratory, UCLLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/446032015-07-14T12:08:03Z2015-07-14T12:08:03ZNew Horizons finally gets up close with Pluto – for 15 minutes<figure><img src="https://images.theconversation.com/files/88364/original/image-20150714-21696-1akm2s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Latest and most detailed image of Pluto, just before the fly-by.</span> <span class="attribution"><span class="source">NASA</span></span></figcaption></figure><p>As I began typing this column, <a href="https://www.nasa.gov/mission_pages/newhorizons/main/index.html">NASA’s New Horizon</a> mission was on its final approach to its primary target, Pluto. By the time I finished composing my deathless prose, the main mission was over. And I’m not a slow writer. </p>
<p><a href="http://www.nasa.gov/mission_pages/newhorizons/launch/index.html">Launched in January 2006</a>, the spacecraft has travelled for nine and a half years for a flyby <a href="http://pluto.jhuapl.edu/Mission/The-Flyby.php">lasting only about 15 minutes</a>. It doesn’t sound much of a reward for all the effort of designing and building the spacecraft – but for planetary scientists, the data coming back from the mission is pure gold. </p>
<p>For now all we can do is wait. Early in the morning on July 15, New Horizons is expected to phone home and confirm that the fly-by went well. Later that day the first high-resolution images should start trickle back to Earth – revealing what Pluto and its moon Charon actually look like up close. However, it will take nearly a year for all the data from the instruments aboard the spacecraft to come back.</p>
<p>But what is so exciting about Pluto? It <a href="https://theconversation.com/nasa-missions-may-re-elevate-pluto-and-ceres-from-dwarf-planets-to-full-on-planet-status-36081">isn’t even a planet</a> anymore! When the New Horizons mission was conceived, Pluto stood (or rather, orbited) proudly as the ninth, and newest, planet in the Solar System. But eight months after New Horizons left Earth on its journey to Pluto, the International Astronomical Union <a href="https://www.iau.org/public/themes/pluto/">downgraded Pluto</a> from “planet” to “minor planet”. </p>
<p>Pluto’s change in status has, however, definitely not diminished the importance of the mission. Indeed, it has probably enhanced the scientific significance of the findings. Back when we thought Pluto was a planet, it was merely the last member of a series which represented a progression from the inner rocky and metallic bodies such as Mercury, through the gas and ice giants like Jupiter and Neptune, to Pluto – a small body of ice and rock. </p>
<p>But we now know that Pluto is not an isolated entity – it is the largest body in a huge family of primitive objects, many of which have their own moons. According to current models of how the solar system formed, there were once several hundred thousands of objects beyond Neptune, but Jupiter’s motion <a href="http://www.geotimes.org/june05/WebExtra060705.html">scattered most of them</a> much further out from the Sun. </p>
<p>There are, however, still likely to be more such remaining bodies, known as <a href="http://www.sciencedaily.com/releases/2015/01/150115083036.htm">Trans-Neptunian Objects</a>, than the asteroids in the main belt between Mars and Jupiter. These objects are probably even more primitive in nature than some comets, which have been modified as they approach the Sun.</p>
<p>We already know that methane and ammonia ices are present on Pluto – but are there any higher hydrocarbons, or biologically interesting compounds such as amino acids? It will be interesting to see how analysis of the surface ices compare with results from the Rosetta mission or from the Dawn mission at Ceres. Can we draw any comparisons with the <a href="http://www.ncbi.nlm.nih.gov/pubmed/11541963">photo-chemistry</a> on Saturn’s giant moon, Titan? Will Pluto demonstrate that trans-Neptunian objects are the most unchanged and unprocessed objects in the Solar System?</p>
<h2>First look</h2>
<p>Previous images of Pluto have been poorly resolved – the best view by the Hubble Space Telescope is of a fuzzy grey blob (see image below). But over the past few weeks, we have been able to enjoy increasingly more detailed images taken by the New Horizons spacecraft on its approach to Pluto. For example, we’ve learned that <a href="http://www.nasa.gov/feature/how-big-is-pluto-new-horizons-settles-decades-long-debate">the planet is slightly bigger than we thought</a>. We have also seen features on the surface, including what are probably <a href="http://news.discovery.com/space/nasa-probe-spies-possible-polar-ice-cap-on-pluto-150429.htm">ice-caps</a>. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/88224/original/image-20150713-11825-195zcs7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88224/original/image-20150713-11825-195zcs7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=335&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88224/original/image-20150713-11825-195zcs7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=335&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88224/original/image-20150713-11825-195zcs7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=335&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88224/original/image-20150713-11825-195zcs7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=422&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88224/original/image-20150713-11825-195zcs7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=422&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88224/original/image-20150713-11825-195zcs7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=422&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Images of Pluto generated with the Hubble Space Telescope and advanced computers.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Pluto-map-hs-2010-06-a-faces.jpg">NASA, ESA, and Marc W. Buie/wikimedia</a></span>
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<p>Although the closest approach to Pluto will be over in a matter of minutes, the amount of data captured will be immense. It could help us answer a number of questions about Pluto – such as the distribution of <a href="http://www.nature.com/news/pluto-may-have-icy-cap-1.17454">different ices</a> (water, ammonia, methane), the relationship between rock and ice and the <a href="http://pluto.jhuapl.edu/News-Center/Science-Shorts.php?page=ScienceShorts_02_24_2015">presence of a thin atmosphere</a>. The fly-by could also shed light on whether there are indeed craters on the body and whether there is any evidence of resurfacing. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/88217/original/image-20150713-11831-9xtn8p.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88217/original/image-20150713-11831-9xtn8p.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88217/original/image-20150713-11831-9xtn8p.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88217/original/image-20150713-11831-9xtn8p.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88217/original/image-20150713-11831-9xtn8p.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88217/original/image-20150713-11831-9xtn8p.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88217/original/image-20150713-11831-9xtn8p.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Image of Pluto and its moon Charon, taken with New Horizons.</span>
<span class="attribution"><a class="source" href="http://www.nasa.gov/image-feature/pluto-and-charon-new-horizons-dynamic-duo">NASA</a></span>
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<p>There is no expectation that <a href="http://astrogeology.usgs.gov/geology/titan-cryovolcanism">cryovolcanism</a> or ice geysers will be observed on Pluto, it doesn’t have the same gravitational heat source derived from a giant companion such as the case for Jupiter’s moon Europa. But it is in a binary system with its almost equally-sized moon, Charon – so it may surprise us yet.</p>
<p>For me, one of the highlights of the coming months will be synthesis of three sets of data - from New Horizons on Pluto, <a href="https://theconversation.com/dawn-breaks-over-distant-ceres-and-perhaps-reveals-signs-of-habitability-38967">Dawn on Ceres</a> and <a href="https://theconversation.com/explainer-why-rosetta-comet-mission-is-such-a-big-deal-34037">Rosetta-Philae on comet 67P/Churyumov-Gerasimenko.</a> This will give us real insight to comet-asteroid interrelationships, and the primitive material from which the Solar System was built.</p>
<p>Whatever comes from the fly-by, we already have enough fresh information about our far-distant neighbour to ensure it is no longer seen as an underworld, the underdog of our planetary system. It is not the last planet to be visited but it is the first trans-Neptunian object to be seen – and so becomes a member of a very exclusive club.</p>
<p><strong>15 July: Success confirmed</strong></p>
<p>Following a long day of waiting, mission scientists got their reward just before 01:00 (UT), when the signal transmitted from the New Horizons spacecraft about four hours earlier was received at mission control. Cheers were heard from the team as Alice Bowman, the Mission Control Manager announced “we have telemetry lock”. This translates as “the spacecraft has called up, we have answered the phone, and we can hear what New Horizons is saying”. More cheers as each sub-system reported in: “thermal systems nominal”; “propulsion systems nominal”.</p>
<p>During the wait, we were tantalised with a fresh image of Pluto and its largest moon, Charon. New images will be released soon. For now, the waiting continues as New Horizons moves away from Pluto and its moons, and looks for its next target, a second TNO, which will be encountered in around 4 years time…</p><img src="https://counter.theconversation.com/content/44603/count.gif" alt="The Conversation" width="1" height="1" />
<h4 class="border">Disclosure</h4><p class="fine-print"><em><span>Monica Grady receives funding from the STFC and is a Trustee of Lunar Mission One.</span></em></p>After a decade in space, New Horizons has finally completed its fly-by of Pluto. And the fact that it is no longer a planet makes it all the more interesting.Monica Grady, Professor of Planetary and Space Sciences, The Open UniversityLicensed as Creative Commons – attribution, no derivatives.