tag:theconversation.com,2011:/ca/topics/kuiper-belt-18849/articlesKuiper Belt – The Conversation2022-04-04T12:28:37Ztag:theconversation.com,2011:article/1788442022-04-04T12:28:37Z2022-04-04T12:28:37ZWhat is a dwarf planet?<figure><img src="https://images.theconversation.com/files/452922/original/file-20220317-13-1u6oyiu.jpg?ixlib=rb-1.1.0&rect=0%2C3%2C1039%2C713&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Pluto, the largest of the dwarf planets. This image was taken by NASA's New Horizons spacecraft.</span> <span class="attribution"><a class="source" href="https://solarsystem.nasa.gov/resources/699/pluto-dazzles-in-false-color/">NASA/JHUAPL/SwRI</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
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<p><strong>What is a dwarf planet? – Myranda, age 8, Knoxville, Tennessee</strong></p>
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<p>The word “planet” came from the ancient Greek words that mean “wandering star.” That makes sense, because for thousands of years, people have watched planets change position in the night sky – unlike stars, which appear fixed and unmoving to the naked eye. </p>
<p>That’s how the ancients discovered five of the planets: <a href="https://solarsystem.nasa.gov/planets/mercury/overview/">Mercury</a>, <a href="https://solarsystem.nasa.gov/planets/venus/overview/">Venus</a>, <a href="https://solarsystem.nasa.gov/news/1679/mars-resources/?">Mars</a>, <a href="https://solarsystem.nasa.gov/planets/jupiter/overview/">Jupiter</a> and <a href="https://solarsystem.nasa.gov/planets/saturn/overview/">Saturn</a>. Astronomers using telescopes found <a href="https://solarsystem.nasa.gov/planets/uranus/overview/">Uranus</a> in 1781, <a href="https://solarsystem.nasa.gov/planets/neptune/overview/">Neptune</a> in 1846, and <a href="https://solarsystem.nasa.gov/planets/dwarf-planets/pluto/overview/">Pluto</a> in 1930. </p>
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<img alt="Artist's impression of the dwarf planet Eris, a white and pale gray sphere." src="https://images.theconversation.com/files/454273/original/file-20220324-13-18yzsb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/454273/original/file-20220324-13-18yzsb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/454273/original/file-20220324-13-18yzsb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/454273/original/file-20220324-13-18yzsb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/454273/original/file-20220324-13-18yzsb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/454273/original/file-20220324-13-18yzsb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/454273/original/file-20220324-13-18yzsb.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 the dwarf planet Eris.</span>
<span class="attribution"><a class="source" href="https://www.eso.org/public/images/eso1142a/">ESO/L.Calçada and Nick Risinger</a></span>
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<h2>Solar system leftovers</h2>
<p><a href="https://dornsife.usc.edu/cf/faculty-and-staff/faculty.cfm?pid=1063926">I’m a space scientist</a> with a passion for astronomy and the exploration of the Solar System. I received my Ph.D. in physics in 1994, about the time astronomers began to find more and more objects beyond Neptune, in the <a href="https://spaceplace.nasa.gov/kuiper-belt/en/">Kuiper belt</a>. That’s a place in space that holds the “leftovers” of the solar system – particularly small icy bodies. </p>
<p>Three of those icy bodies – <a href="https://solarsystem.nasa.gov/planets/dwarf-planets/eris/in-depth/">Eris</a>, <a href="https://solarsystem.nasa.gov/planets/dwarf-planets/haumea/in-depth/">Haumea</a> and <a href="https://solarsystem.nasa.gov/planets/dwarf-planets/makemake/in-depth/">Makemake</a> – were discovered in the early to mid 2000s. They seemed large enough to be planets; all of them are roughly the same size as Pluto.</p>
<p>Astronomers then surmised that there were likely many more of these icy bodies in the Kuiper belt. They began to wonder: How many planets might we end up identifying in our solar system? Twenty? Thirty? A hundred? More?</p>
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<img alt="An artist's illustration of the dwarf planet Haumea, an oval shaped world surrounded by its ring." src="https://images.theconversation.com/files/454305/original/file-20220325-27-j10f5i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/454305/original/file-20220325-27-j10f5i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=480&fit=crop&dpr=1 600w, https://images.theconversation.com/files/454305/original/file-20220325-27-j10f5i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=480&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/454305/original/file-20220325-27-j10f5i.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=480&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/454305/original/file-20220325-27-j10f5i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=603&fit=crop&dpr=1 754w, https://images.theconversation.com/files/454305/original/file-20220325-27-j10f5i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=603&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/454305/original/file-20220325-27-j10f5i.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">
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<span class="caption">An artist’s illustration of the dwarf planet Haumea, surrounded by its ring.</span>
<span class="attribution"><a class="source" href="https://science.nasa.gov/haumea-outer-solar-system">Instituto de Asrofísica de Andalucía</a></span>
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<h2>Dwarf planet defined</h2>
<p>In 2006, and after much debate, the <a href="https://www.iau.org/">International Astronomical Union</a> came up with a new definition for a planet. And for the first time, the term “dwarf planet” was used.</p>
<p>Here’s what the IAU said: A planet has to orbit the Sun directly. It also must be large enough to have a round, or spherical, physical shape. </p>
<p>And the planet must “<a href="https://solarsystem.nasa.gov/planets/in-depth/">clear its neighborhood</a>.” That means, aside from any moons it might have, the planet can’t share its orbit with other objects of comparable size.</p>
<p>An object that satisfies only the first two criteria – but not the last – is now called a dwarf planet. </p>
<figure class="align-center ">
<img alt="Artist's illustration of Makemake, a dwarf planet in the Kuiper Belt. Nearby is its moon, MK 2. Off in the distance: the Sun." src="https://images.theconversation.com/files/454461/original/file-20220325-25-1th3ksp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/454461/original/file-20220325-25-1th3ksp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/454461/original/file-20220325-25-1th3ksp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/454461/original/file-20220325-25-1th3ksp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/454461/original/file-20220325-25-1th3ksp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/454461/original/file-20220325-25-1th3ksp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/454461/original/file-20220325-25-1th3ksp.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">
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<span class="caption">Artist’s illustration of Makemake, a dwarf planet in the Kuiper belt. Nearby is its moon, MK 2. Off in the distance: the Sun.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/sites/default/files/thumbnails/image/makemakemoon100mile.jpg">NASA/ESA/A. Parker/Southwest Research Institute</a></span>
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<h2>Pluto is demoted</h2>
<p>That’s why Pluto <a href="https://www.kidsnews.com.au/space/pluto-lost-its-spot-in-our-solar-system-but-still-holds-a-place-in-many-hearts/news-story/4b4f0862a47b089ea5850d9522f211ca">lost its status as a planet</a> and is now classified as a dwarf planet. It failed the final item on the checklist – other icy Kuiper belt bodies are within its orbital path. The decision, a controversial one to be sure, is <a href="https://www.sciencenewsforstudents.org/article/pluto-dwarf-planet-definition-iau-astronomy">debated by scientists to this very day</a>. </p>
<p>At the same time Pluto got demoted, another solar system object was promoted. <a href="https://solarsystem.nasa.gov/planets/dwarf-planets/ceres/overview/">Ceres</a>, once considered an asteroid, is now classified as a dwarf planet. It’s nowhere near the Kuiper belt; instead, Ceres is in <a href="https://solarsystem.nasa.gov/asteroids-comets-and-meteors/asteroids/overview/?">the main asteroid belt</a>, orbiting between Mars and Jupiter.</p>
<p>Add them up – Pluto, Ceres, Eris, Haumea and Makemake – and that brings the number of dwarf planets in our solar system to five. But that list is sure to grow. Already, hundreds of candidates, nearly all in the Kuiper belt, potentially satisfy the criteria to be a dwarf planet. </p>
<figure class="align-center ">
<img alt="A photo of the dwarf planet Ceres. To the human eye, it appears a sandy brown color and is pockmarked with craters." src="https://images.theconversation.com/files/454567/original/file-20220328-13-1wwgmnd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/454567/original/file-20220328-13-1wwgmnd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/454567/original/file-20220328-13-1wwgmnd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/454567/original/file-20220328-13-1wwgmnd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/454567/original/file-20220328-13-1wwgmnd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/454567/original/file-20220328-13-1wwgmnd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/454567/original/file-20220328-13-1wwgmnd.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">This photograph of Ceres, a dwarf planet in the main asteroid belt, was taken by NASA’s Dawn spacecraft.</span>
<span class="attribution"><a class="source" href="https://solarsystem.nasa.gov/resources/622/ceres-in-color/?category=planets/dwarf-planets_ceres">NASA/JPL-Caltech/UCLA/MPS/DLR/IDA</a></span>
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<h2>About the dwarf planets</h2>
<p>Dwarf planets are nothing like Earth. </p>
<p>As their name implies, they are much smaller. Pluto and Eris, the largest of the dwarfs, have less than one-fifth the diameter of the Earth. </p>
<p><a href="https://spaceplace.nasa.gov/planets-weight/en/#:%7E:text=Mass%20stays%20the%20same%20regardless,mass%20is%20the%20same%20everywhere!">They have less mass, too</a>. For example, Earth has <a href="https://theplanets.org/ceres/">about 6,400 times more mass</a> than Ceres. That’s like comparing two <a href="https://en.wikipedia.org/wiki/Orca">killer whales</a> to a <a href="https://en.wikipedia.org/wiki/Guinea_pig">guinea pig</a>.</p>
<p>And dwarf planets are cold. <a href="https://solarsystem.nasa.gov/planets/dwarf-planets/pluto/in-depth/#:%7E:text=On%20average%2C%20Pluto's%20temperature%20is,orbits%20in%20our%20solar%20system.">Pluto’s average temperature</a> is around minus 400 degrees Fahrenheit (minus 240 Celsius).</p>
<figure class="align-center ">
<img alt="A photograph of Pluto and one of its five moons, Charon." src="https://images.theconversation.com/files/454578/original/file-20220328-25-rfa5po.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/454578/original/file-20220328-25-rfa5po.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/454578/original/file-20220328-25-rfa5po.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/454578/original/file-20220328-25-rfa5po.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/454578/original/file-20220328-25-rfa5po.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/454578/original/file-20220328-25-rfa5po.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/454578/original/file-20220328-25-rfa5po.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">A photograph of Pluto and one of its five moons, Charon. Except for Ceres, all the dwarf planets have at least one moon. Charon is nearly half Pluto’s size.</span>
<span class="attribution"><a class="source" href="https://solarsystem.nasa.gov/resources/853/pluto-and-charon/?category=planets/dwarf-planets_pluto">NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute</a></span>
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<h2>Could life exist on a dwarf planet?</h2>
<p>Three things are needed for life: liquid water, an energy source and organic molecules – that is, molecules containing carbon. </p>
<p>More than 100 miles (161 kilometers) below Pluto’s surface, an enormous ocean of liquid water may exist; this might also be true for other Kuiper belt worlds. <a href="https://astronomy.com/news/2020/08/ceres-an-ocean-world-in-the-asteroid-belt">Ceres also has subsurface water</a>, remnants of what might have been an ancient global ocean. </p>
<p>Organic molecules, in abundance <a href="https://www.extremetech.com/extreme/271914-organic-molecules-on-ceres-are-more-abundant-than-previously-thought">everywhere in our solar system</a>, have been found on Ceres and Pluto. </p>
<p>But the one missing ingredient for all the dwarf planets is a source of energy. </p>
<p>Sunlight won’t work, particularly for the Kuiper belt dwarfs; they are simply too far away from the Sun. To reach the belt, the light must travel <a href="https://imagine.gsfc.nasa.gov/features/cosmic/solar_system_info.html">more than 2.7 billion miles</a> (4.4 billion km). By the time the sunshine arrives at these distant worlds, it’s <a href="https://solarsystem.nasa.gov/solar-system/kuiper-belt/in-depth/">too weak to significantly heat</a> any of them.</p>
<p>And all the dwarf planets are too small to hold the inner heat that remains from the <a href="https://kids.britannica.com/kids/article/solar-system/353789#:%7E:text=The%20solar%20system%20was%20formed%20about%204.7%20billion%20years%20ago,that%20it%20got%20very%20hot.">solar system’s formation</a>. </p>
<p>Yet scientists have discovered life on Earth in the most hostile places imaginable – near the bottom of the ocean, miles deep in the soil and even inside an active volcano. When it comes to life in our solar system, never say never. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/nJiw2NxqoBU?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Take a tour of the dwarf planet Ceres.</span></figcaption>
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<p class="fine-print"><em><span>Vahe Peroomian has received funding in the past from the National Science Foundation and from the National Aeronautics and Space Administration.</span></em></p>The dwarf planets in our Solar System are cold, dark, far away and full of surprises.Vahe Peroomian, Professor of Physics and Astronomy, USC Dornsife College of Letters, Arts and SciencesLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1704272021-11-30T21:27:11Z2021-11-30T21:27:11ZSoon, 1 out of every 15 points of light in the sky will be a satellite<figure><img src="https://images.theconversation.com/files/434031/original/file-20211125-13-13t3ndk.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C3000%2C1998&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Starlink satellites are quite visible in the night sky.</span> <span class="attribution"><span class="source">(Shutterstock)</span></span></figcaption></figure><iframe style="width: 100%; height: 175px; border: none; position: relative; z-index: 1;" allowtransparency="" src="https://narrations.ad-auris.com/widget/the-conversation-canada/soon--1-out-of-every-15-points-of-light-in-the-sky-will-be-a-satellite" width="100%" height="400"></iframe>
<p>I’m outside at my rural Saskatchewan farm, chatting with my neighbours who I’ve invited over to appreciate the night sky through my telescope. After exclamations and open-mouthed wonder over Saturn’s rings, and light that has been travelling through space for more than two million years to reach our eyes from the Andromeda Galaxy, our conversation inevitably turns to the pandemic, our work-from-home arrangements and complaints about rural internet. My neighbour casually mentions they’ve just switched to using Starlink for their internet provider.</p>
<p>I glance up and notice a bright satellite moving across the sky, almost certainly a Starlink, since they now make up almost <a href="https://www.unoosa.org/oosa/osoindex/search-ng.jspx?lf_id=#?c=%7B%22filters%22:%5B%7B%22fieldName%22:%22en%23object.status.inOrbit_s1%22,%22value%22:%22Yes%22%7D%5D,%22sortings%22:%5B%7B%22fieldName%22:%22object.launch.dateOfLaunch_s1%22,%22dir%22:%22desc%22%7D%5D%7D">half of the nearly 4,000 operational satellites</a> and they’re extremely bright. I take a deep breath and carefully consider how to discuss the substantial cost that we’re all going to have to pay for Starlink internet.</p>
<p>I don’t blame my neighbours for switching. Here, as in many rural parts of North America, there aren’t <a href="https://www.npr.org/2021/02/16/968457180/how-a-project-to-get-humans-to-mars-could-solve-the-rural-internet-problem">great internet options</a>, and with many people working and taking classes from home during the pandemic, anything that makes life easier is immediately accepted.</p>
<p>But I know exactly how high this cost could be. My paper, forthcoming in <em>The Astronomical Journal</em>, has <a href="https://arxiv.org/pdf/2109.04328.pdf">predictions for what the night sky will look like if satellite companies follow through on their current plans</a>. I also know that because of the geometry of sunlight and the orbits that have been chosen, 50 degrees north, where I live, will be the most severely affected part of the world.</p>
<p>With no regulation, I know that in the near future, <a href="https://www.sciencenews.org/article/satellite-mega-constellations-night-sky-stars-simulations">one out of every 15 points</a> you can see in the sky will actually be relentlessly crawling satellites, not stars. This will be devastating to research astronomy, and will completely change the night sky worldwide.</p>
<h2>The future is too, too bright</h2>
<p>In order to find out how badly the night sky is going to be affected by sunlight reflected from planned satellite megaconstellations, we built an <a href="https://github.com/hannorein/megaconstellations">open-source computer model to predict satellite brightnesses</a> as seen from different places on Earth, at different times of night, in different seasons. We also built a simple <a href="http://megaconstellations.hanno-rein.de/">web app based on this simulation</a>.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/UieVD0nuKkY?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">A simulation of the brightness and number of satellites during a full night for 50 degrees north on the summer solstice.</span></figcaption>
</figure>
<p>Our model uses 65,000 satellites on the orbits filed by four megaconstellation companies: SpaceX Starlink and Amazon Kuiper (United States), OneWeb (United Kingdom) and StarNet/GW (China). We calibrated our simulation to match <a href="https://arxiv.org/pdf/2109.12494.pdf">telescope measurements of Starlink satellites</a>, since they are by far the most numerous.</p>
<p>Starlink has so far made some strides toward dimming their satellites since their first launch, but most are <a href="https://arxiv.org/pdf/2101.00374.pdf">still visible to the naked eye</a>.</p>
<p>Our simulations show that from everywhere in the world, in every season, there will be dozens to hundreds of satellites visible for at least an hour before sunrise and after sunset. Right now, it’s relatively easy to escape urban light pollution for dark skies while camping or visiting your cabin, but our simulations show that you can’t escape this new satellite light pollution anywhere on Earth, even at the North Pole.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/spacexs-starlink-satellites-are-about-to-ruin-stargazing-for-everyone-149516">SpaceX's Starlink satellites are about to ruin stargazing for everyone</a>
</strong>
</em>
</p>
<hr>
<p>The most severely affected locations on Earth will be 50 degrees north and south, near cities like London, Amsterdam, Berlin, Prague, Kiev, Vancouver, Calgary and my own home. On the summer solstice, from these latitudes, there will be close to 200 satellites visible to the naked eye all night long.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/434032/original/file-20211125-17-e7wdrr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A photo of the night sky showing telegraph wires, trees and streaks of light" src="https://images.theconversation.com/files/434032/original/file-20211125-17-e7wdrr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/434032/original/file-20211125-17-e7wdrr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/434032/original/file-20211125-17-e7wdrr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/434032/original/file-20211125-17-e7wdrr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/434032/original/file-20211125-17-e7wdrr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/434032/original/file-20211125-17-e7wdrr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/434032/original/file-20211125-17-e7wdrr.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">Megaconstellations of satellites will be a visible distraction at night.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/jabberwock/49863305786/">(Steve Elliott/flickr)</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>I study orbital dynamics of the Kuiper Belt, <a href="https://solarsystem.nasa.gov/news/792/10-things-to-know-about-the-kuiper-belt/">a belt of small bodies beyond Neptune</a>. My research relies on long time-exposure, wide-field imaging to <a href="https://theconversation.com/how-we-discovered-840-minor-planets-beyond-neptune-and-what-they-can-tell-us-96431">discover and track these small bodies</a> to learn about the history of our Solar System.</p>
<p>The telescope observations that are key to learning about our universe are about to get <a href="https://www.lsst.org/content/lsst-statement-regarding-increased-deployment-satellite-constellations">much, much harder</a> because of unregulated development of space. </p>
<p>Astronomers are creating some <a href="https://regmedia.co.uk/2021/11/04/satcon2_working_groups_reports.pdf">mitigation strategies</a>, but they will require time and effort that should be paid for by megaconstellation companies.</p>
<h2>Unknown environmental costs</h2>
<p>Starlink internet might appear cheaper than other rural options, but this is because <a href="https://doi.org/10.1038/s41598-021-89909-7">many costs are offloaded</a>. One immediate cost is <a href="https://www.theguardian.com/science/2021/jul/19/billionaires-space-tourism-environment-emissions">atmospheric pollution</a> from the hundreds of rocket launches required to build and maintain this system. </p>
<p>Every satellite deployment dumps spent rocket bodies and other debris into already-crowded low Earth orbit, increasing <a href="http://astriacss03.tacc.utexas.edu/ui/min.html">collision risks</a>. Some of this space junk will eventually fall back to Earth, and those parts of the globe with the highest overhead satellite densities will also be the <a href="https://www.smithsonianmag.com/smart-news/after-fiery-display-spacex-debris-landed-washington-farm-180977494/">most likely to be literally impacted</a>.</p>
<p>Starlink plans to replace each of the 42,000 satellites after five years of operation, which will require de-orbiting an average 25 satellites per day, about six tons of material. The mass of these satellites won’t go away — it will be <a href="https://www.space.com/starlink-satellite-reentry-ozone-depletion-atmosphere">deposited in the upper atmosphere</a>. Because satellites comprise mostly aluminium alloys, they may form alumina particles as they vaporize in the upper atmosphere, potentially destroying ozone and causing global temperature changes. </p>
<p>This has not yet been studied in-depth because low Earth orbit is not currently subject to any environmental regulations.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/434034/original/file-20211125-15-1xf2vkj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A rocket with a large white cloud trail against a bright blue sky" src="https://images.theconversation.com/files/434034/original/file-20211125-15-1xf2vkj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/434034/original/file-20211125-15-1xf2vkj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/434034/original/file-20211125-15-1xf2vkj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/434034/original/file-20211125-15-1xf2vkj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/434034/original/file-20211125-15-1xf2vkj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/434034/original/file-20211125-15-1xf2vkj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/434034/original/file-20211125-15-1xf2vkj.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">A SpaceX Falcon 9 rocket lifts off from Cape Canaveral, Fla., with satellites for SpaceX’s Starlink broadband network.</span>
<span class="attribution"><span class="source">(AP Photo/John Raoux)</span></span>
</figcaption>
</figure>
<h2>Regulating the sky</h2>
<p>Currently, low Earth orbit, where all of these satellites are planned to operate, is almost completely unregulated. There are no rules about light pollution, atmospheric pollution from launches, atmospheric pollution from re-entry, or collisions between satellites.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/its-not-too-late-to-save-the-night-sky-but-governments-need-to-get-serious-about-protecting-it-158394">It's not too late to save the night sky, but governments need to get serious about protecting it</a>
</strong>
</em>
</p>
<hr>
<p>These megaconstellations might not even be <a href="https://arxiv.org/pdf/2011.05168.pdf">financially viable over the long term</a>, and internet speeds may slow to a crawl when <a href="https://doi.org/10.1109/ACCESS.2021.3119634">many users connect at the same time</a> or when <a href="https://www.doi.org/10.1126/science.acx9299">it rains</a>.</p>
<p>But companies are launching satellites right now at a frenetic pace, and the damage they do to the night sky, the atmosphere and the safety of low Earth orbit will not be undone even if the operators go bankrupt.</p>
<p>There’s no doubt that rural and remote internet users in many places have been left behind by internet infrastructure development. But there are many other options for internet delivery that will not result in such extreme costs.</p>
<p>We can’t accept the <a href="https://www.vice.com/en/article/k78mnz/spacexs-satellite-megaconstellations-are-astrocolonialism-indigenous-advocates-say">global loss of access to the night sky</a>, which we’ve been able to see and connect with for as long as we’ve been human.</p>
<p>With co-operation instead of competition between satellite companies, we could have many fewer in orbit. By changing the design of satellites, they could be made much fainter, having less of an impact on the night sky. We shouldn’t have to make a choice between astronomy and the internet. </p>
<p>But without regulations requiring these changes, or strong pressure from consumers indicating the importance of the night sky, our view of the stars will soon be changed forever.</p><img src="https://counter.theconversation.com/content/170427/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Samantha Lawler receives funding from the Natural Sciences and Engineering Research Council of Canada.</span></em></p>Megaconstellations of satellites will visually clutter the night sky, disrupting astronomical research. And the environmental damage caused by these satellites is still unknown.Samantha Lawler, Assistant professor of astronomy, University of ReginaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1275982020-05-25T19:57:24Z2020-05-25T19:57:24ZWhy astronomers now doubt there is an undiscovered 9th planet in our solar system<figure><img src="https://images.theconversation.com/files/328170/original/file-20200415-153302-1fpfbot.jpg?ixlib=rb-1.1.0&rect=16%2C8%2C5574%2C3135&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An artist's concept of a hypothetical planet with a distant sun.</span> <span class="attribution"><span class="source">(Shutterstock)</span></span></figcaption></figure><p>Planet Nine is a <a href="https://doi.org/10.3847/0004-6256/151/2/22">theoretical, undiscovered</a> <a href="https://doi.org/10.1038/nature13156">giant planet</a> in the mysterious far reaches of our solar system.</p>
<p>The presence of Planet Nine has been hypothesized to explain everything from the <a href="https://doi.org/10.3847/0004-6256/152/5/126">tilt of the sun’s spin axis</a> to the <a href="https://doi.org/10.1016/B978-0-12-816490-7.00004-7">apparent clustering</a> in the orbits of small, icy asteroids beyond Neptune.</p>
<p>But does Planet Nine actually exist?</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/a-stolen-exoplanet-that-will-kill-us-all-heres-what-we-do-know-about-planet-nine-60407">A stolen exoplanet that will kill us all? Here's what we do know about 'Planet Nine'</a>
</strong>
</em>
</p>
<hr>
<h2>Discoveries at the edge of our solar system</h2>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/328164/original/file-20200415-153313-17oynol.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/328164/original/file-20200415-153313-17oynol.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/328164/original/file-20200415-153313-17oynol.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=745&fit=crop&dpr=1 600w, https://images.theconversation.com/files/328164/original/file-20200415-153313-17oynol.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=745&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/328164/original/file-20200415-153313-17oynol.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=745&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/328164/original/file-20200415-153313-17oynol.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=936&fit=crop&dpr=1 754w, https://images.theconversation.com/files/328164/original/file-20200415-153313-17oynol.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=936&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/328164/original/file-20200415-153313-17oynol.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=936&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">After Pluto, the second Kuiper Belt Object — 1992 QB1 — was discovered in 1992 by American astronomers David Jewitt and Jane Luu using the 2.2-m telescope at Mauna Kea in Hawaii.</span>
<span class="attribution"><a class="source" href="https://solarsystem.nasa.gov/resources/402/1992-qb1/">NASA</a></span>
</figcaption>
</figure>
<p>The Kuiper Belt is a collection of small, icy bodies that orbit the sun beyond Neptune, at distances larger than 30 AU (one astronomical unit or AU is the distance between the Earth and the sun). These Kuiper Belt objects (KBOs) range in size from large boulders to 2,000 km across. KBOs are leftover small bits of planetary material that were never incorporated into planets, similar to <a href="https://www.space.com/16105-asteroid-belt.html">the asteroid belt</a>. </p>
<p>The discoveries from the most successful Kuiper Belt survey to date, the <a href="http://www.ossos-survey.org/">Outer Solar System Origins Survey (OSSOS)</a>, suggest a sneakier explanation for the orbits we see. Many of these KBOs have been discovered to have very elliptical and tilted orbits, <a href="http://pluto.jhuapl.edu/Pluto/The-Pluto-System.php">like Pluto</a>.</p>
<p>Mathematical calculations and detailed computer simulations have shown that the orbits we see in the Kuiper Belt can only have been created if Neptune originally formed a few AU closer to the sun, and <a href="https://doi.org/10.1146/annurev-astro-081817-052028">migrated outward to its present orbit</a>. Neptune’s migration explains the pervasiveness of highly elliptical orbits in the Kuiper Belt, and can explain all the KBO orbits we’ve observed, except for a handful of KBOs on <a href="https://www.nature.com/articles/507435a">extreme orbits</a> that always stay at least 10 AU beyond Neptune.</p>
<h2>Proof of Planet Nine?</h2>
<p>These extreme orbits have provided the strongest evidence for Planet Nine. The first few that were discovered were all confined to one quadrant of the solar system. Astronomers expect to observe orbits at all different orientations, unless there is an outside force confining them. Finding several extreme KBOs on orbits pointed in the same direction was a hint that something was going on. Two <a href="https://doi.org/10.1038/nature13156">separate</a> <a href="https://doi.org/10.3847/0004-6256/151/2/22">groups</a> of researchers calculated that only a large, very distant planet could keep all the orbits confined to part of the solar system, and the theory of Planet Nine was born.</p>
<p>Planet Nine is <a href="https://doi.org/10.1016/j.physrep.2019.01.009">theorized</a> to be five to 10 times as massive as Earth, with an orbit ranging between 300-700 AU. There have been several <a href="https://iopscience.iop.org/article/10.3847/0004-6256/152/4/80">published predictions</a> for <a href="http://www.findplanetnine.com/p/blog-page.html">its location</a> in the solar system, but none of the search teams have yet discovered it. After more than four years of searching, there is still only <a href="https://astronomy.com/magazine/2020/01/in-pursuit-of-planet-nine">indirect evidence in favour of Planet Nine</a>.</p>
<h2>The search for KBOs</h2>
<p>Searching for KBOs requires careful planning, precise calculations and meticulous followup. I am part of the OSSOS, a collaboration of 40 astronomers from eight countries. We used the <a href="https://www.cfht.hawaii.edu/">Canada-France-Hawaii Telescope</a> over five years to discover and track more than <a href="https://doi.org/10.3847/1538-4365/aab77a">800 new KBOs</a>, nearly doubling the number of known KBOs with well-measured orbits. The KBOs discovered by OSSOS range in size from a few kilometres to over 100 km, and range in discovery distance from a few AU to over 100 AU, with the majority at 40-42 AU in the main Kuiper Belt. </p>
<p>KBOs do not emit their own light: these small, icy bodies only reflect light from the sun. Thus, the biases against detection at larger distances are extreme: if you move a KBO 10 times farther away, it will become 10,000 times fainter. And because of the laws of physics, KBOs on elliptical orbits will spend most of their time at the most distant parts of their orbits. So, while it is easy to find KBOs on elliptical orbits when they are close to the sun and bright, these KBOs spend most time being much fainter and harder to detect.</p>
<p>This means that the KBOs on elliptical orbits are particularly hard to discover, especially the extreme ones that always stay relatively far from the sun. Only a few of these have been found to date and, with current telescopes, we can only discover them when they are near pericentre — the closest point to the sun in their orbit. </p>
<p>This leads to another observation bias that has historically been ignored by many KBO surveys: KBOs in each part of the solar system can only be discovered at certain times of year. Ground-based telescopes are additionally limited by seasonal weather, with discoveries less likely to happen during when cloudy, rainy or windy conditions are more frequent. Discoveries of KBOs are also much less likely near the plane of the Milky Way galaxy, where countless stars make it difficult to find the faint, icy wanderers in telescopic images.</p>
<p>What makes OSSOS unique is that we are very public about these biases in discoveries. And because we understand our biases so well, <a href="https://doi.org/10.3389/fspas.2018.00014">we can use computer simulations</a> to reconstruct the true shape of the Kuiper Belt after removing these biases.</p>
<h2>Adjusting for biases</h2>
<p>OSSOS discovered a handful of new extreme KBOs, half of which are outside the confined region, and are <a href="https://doi.org/10.3847/1538-3881/aa7aed">statistically consistent</a> with a uniform distribution. A new study (currently in review) <a href="https://arxiv.org/abs/2003.08901">corroborates the non-clustered discoveries of OSSOS</a>. A team of astronomers using data from the Dark Energy Survey (DES) <a href="https://iopscience.iop.org/article/10.3847/1538-4365/ab6bd8">found over 300 new KBOs with no clustering of orbits</a>. So now two independent surveys — both of which carefully tracked and reported their observational biases in discovering independent sets of extreme KBOs — have found no evidence for clustered orbits.</p>
<p>All of the extreme KBOs that had been discovered prior to OSSOS and DES were from surveys that did not fully report their directional biases. So we do not know if all these KBOs were discovered in the same quadrant of the solar system because they are actually confined, or because no surveys searched deep enough in the other quadrants. We performed <a href="https://doi.org/10.1016/B978-0-12-816490-7.00003-5">additional simulations</a> that showed that if observations are made only in one season from one telescope, extreme KBOs will naturally only be discovered in one quadrant of the solar system.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/328956/original/file-20200419-152581-tlb1zz.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/328956/original/file-20200419-152581-tlb1zz.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/328956/original/file-20200419-152581-tlb1zz.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/328956/original/file-20200419-152581-tlb1zz.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/328956/original/file-20200419-152581-tlb1zz.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/328956/original/file-20200419-152581-tlb1zz.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/328956/original/file-20200419-152581-tlb1zz.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/328956/original/file-20200419-152581-tlb1zz.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"></a>
<figcaption>
<span class="caption">All known KBOs with orbits larger than 250 AU. The orbits of KBOs discovered by OSSOS and DES are in many directions; previous surveys with unknown biases discovered them in the same direction. This image was produced using public data from the Minor Planet Center Database.</span>
<span class="attribution"><span class="source">(Samantha Lawler)</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Further testing the Planet Nine theory, we looked in detail at the orbits of all known “extreme” KBOs and found that all but the two highest pericentre KBOs can be <a href="https://doi.org/10.1016/B978-0-12-816490-7.00003-5">explained by known physical effects</a>. These two KBOs are outliers, but our previous <a href="https://doi.org/10.3847/1538-3881/153/1/33">detailed computer simulations</a> of the Kuiper Belt, which included gravitational effects from Planet Nine, produced a set of “extreme” KBOs with pericentres smoothly ranging from 40 to over 100 AU. </p>
<p>These simulations predict that there should be many KBOs with pericentres as large as the two outliers, but also many KBOs with smaller pericentres, which should be much easier to detect. Why don’t the orbit discoveries match the predictions? The answer may be that the Planet Nine theory does not hold up to detailed observations. </p>
<p>Our observations with a careful survey have discovered KBOs that <a href="https://doi.org/10.3847/1538-3881/aa7aed">are not confined by Planet Nine</a>, and our simulations show that <a href="https://doi.org/10.3847/1538-3881/ab2383">the Kuiper Belt should contain different orbits than we observe if Planet Nine exists</a>. Other theories must be invoked to explain the high-pericentre extreme KBOs, but there is no lack of proposed theories in the scientific literature. </p>
<p>Many beautiful and surprising objects remain to be discovered in the <a href="http://pluto.jhuapl.edu/Arrokoth/Arrokoth.php">mysterious outer solar system</a>, but I don’t believe that Planet Nine is one of them.</p><img src="https://counter.theconversation.com/content/127598/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Samantha Lawler receives funding from the Natural Sciences and Engineering Research Council of Canada. </span></em></p>In the search for the hypothetical Planet Nine, scientists may have uncovered another explanation for the patterns in the orbits of Kuiper Belt objects.Samantha Lawler, Assistant professor of astronomy, University of ReginaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1337382020-04-19T12:23:08Z2020-04-19T12:23:08ZCurious Kids: Is Pluto a planet or not?<figure><img src="https://images.theconversation.com/files/328748/original/file-20200417-152558-j2y9c5.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C7964%2C7976&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A natural color image of Pluto taken by NASA's New Horizons spacecraft in 2015.</span> <span class="attribution"><span class="source">(NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Alex Parker)</span></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><em>Curious Kids is a series for children of all ages. Have a question you’d like an expert to answer? Send it to <a href="mailto:curiouskidscanada@theconversation.com">CuriousKidsCanada@theconversation.com</a>.</em></p>
<blockquote>
<p><strong>Why do some books say Pluto is a planet and other books say it is not? Also, if Pluto is not a planet, then what is it? — Carlos, 5, London, Ont.</strong> </p>
</blockquote>
<p>Pluto is one of hundreds of thousands of icy asteroids (<a href="https://solarsystem.nasa.gov/solar-system/kuiper-belt/overview/">called Kuiper Belt objects</a>) that orbit around the Sun farther away than Neptune. But for 76 years, Pluto was considered the ninth planet.</p>
<p>Pluto was discovered by <a href="https://starchild.gsfc.nasa.gov/docs/StarChild/whos_who_level2/tombaugh.html">Clyde Tombaugh</a> in 1930, when my grandma was a little girl. The <a href="https://astronomy.com/year-of-pluto/2015/06/1992-qb1-the-first-kuiper-belt-object-opened-a-realm-of-1000-plutos">second Kuiper Belt object</a> wasn’t discovered until 1992, when <em>I</em> was a little girl. So for most of my grandma’s lifetime, Pluto was the only object known beyond Neptune, and was naturally assumed to be a planet.</p>
<h2>Bigger telescopes</h2>
<p>As telescopes got bigger and better, and were able to take clearer pictures of distant bodies like Pluto, <a href="http://articles.adsabs.harvard.edu/pdf/1950PASP...62..133K">astronomers began to suspect</a> that Pluto was much, much smaller than the other planets. By the time the second Kuiper Belt object was discovered in 1992, astronomers knew that Pluto was even smaller than Earth’s moon, but it had been called a planet for so long that it retained its planetary status. </p>
<p>Astronomers had also known for decades that Pluto’s orbit actually crosses Neptune’s orbit. None of the other planets cross each other’s orbits, so why was Pluto’s orbit different?</p>
<p>Over the next few years, dozens and then hundreds <a href="https://minorplanetcenter.net/db_search/show_by_orbit_type?utf8=%E2%9C%93&orbit_type=10">more Kuiper Belt objects</a> were discovered by astronomers, until finally, in 2005, <a href="http://web.gps.caltech.edu/%7Embrown/planetlila/">astronomer Mike Brown discovered Eris</a>, which is even bigger than Pluto. </p>
<h2>Deciding on planets</h2>
<p>Now astronomers faced a decision: should Pluto and Eris both be planets? What about all the Kuiper Belt objects that were a little bit smaller than Pluto? Were they planets too? How many planet names should we expect people to remember?</p>
<p>In 2006, astronomers in the <a href="https://www.iau.org/news/pressreleases/detail/iau0603/">International Astronomical Union met</a> and took a vote to decide whether or not Pluto should continue to be called the ninth planet. Many astronomers were quite fond of Pluto, thinking of Pluto as a sort of baby brother in our solar system and were reluctant to kick Pluto out of the planet club. But many astronomers thought it was just a mistake that Pluto had ever been called a planet at all, and that it should have been called a Kuiper Belt object from the start. </p>
<p>So they reached a compromise. </p>
<p>Pluto was no longer <a href="https://www.iau.org/news/pressreleases/detail/iau0601/">one of the planets</a>, and was instead part of a brand new category called “<a href="https://www.iau.org/public/themes/pluto/">dwarf planets</a>.”</p>
<h2>Dwarf planets</h2>
<p>Dwarf planets are large enough that their own gravity pulls them into a round shape like a planet, so they’re not irregular or potato-shaped like many small asteroids. There may also be other similarly sized objects crossing the orbits of dwarf planets as opposed to planets, <a href="https://solarsystem.nasa.gov/planets/in-depth/">whose gravity has cleared large objects from near their orbits</a>.</p>
<p>There is one dwarf planet, <a href="https://solarsystem.nasa.gov/planets/dwarf-planets/ceres/overview/">Ceres</a>, in the asteroid belt, and there are several known dwarf planets in the Kuiper Belt, including Pluto; more will likely be discovered.</p>
<p>So, the reason that many books say that <a href="https://www.iau.org/public/themes/pluto/">Pluto is a planet</a>, is because for 76 years that was true. Everyone over age 30 knew Pluto as a planet for more than half their lifetimes. In 2015, the <a href="http://pluto.jhuapl.edu/">New Horizons space probe</a> flew past Pluto, taking the <a href="http://pluto.jhuapl.edu/Pluto/The-Pluto-System.php">highest resolution pictures</a> ever of the dwarf planet. These stunning images showed us that Pluto is a world with mountains, glaciers, craters and a thin atmosphere. It is not called a planet anymore, but it’s a very well-loved dwarf planet in the Kuiper Belt.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/326939/original/file-20200409-76432-1azil22.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/326939/original/file-20200409-76432-1azil22.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/326939/original/file-20200409-76432-1azil22.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/326939/original/file-20200409-76432-1azil22.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/326939/original/file-20200409-76432-1azil22.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/326939/original/file-20200409-76432-1azil22.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/326939/original/file-20200409-76432-1azil22.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/326939/original/file-20200409-76432-1azil22.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">Artist’s conception of the known dwarf planets.</span>
<span class="attribution"><span class="source">(Sylvia Lawler)</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidscanada@theconversation.com">CuriousKidsCanada@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
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<hr><img src="https://counter.theconversation.com/content/133738/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Samantha Lawler 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>A young reader asks: Is Pluto a planet?Samantha Lawler, Assistant professor of astronomy, University of ReginaLicensed as Creative Commons – attribution, no derivatives.tag: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>
<figure class="align-center ">
<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">
<figcaption>
<span class="caption">Arrokth image.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<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/1124362019-02-28T19:42:54Z2019-02-28T19:42:54ZThere are missing objects at the fringe of the solar system – new study puzzles astronomers<figure><img src="https://images.theconversation.com/files/261286/original/file-20190227-150698-64ge6x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Where are the smallest of the icy worlds we thought resided in the Kuiper belt?</span> <span class="attribution"><span class="source">ESO/Flickr</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>In the dimly lit spaces of our solar system beyond Neptune’s orbit lies the <a href="https://theconversation.com/after-pluto-theres-still-plenty-of-the-solar-system-left-to-explore-45002">Kuiper Belt</a>. This a region between about 35 and 50 times further from the sun than the Earth, populated by icy bodies so sparsely distributed that they never had the chance to collide and merge into planet sized objects. </p>
<p>Pluto is the largest that we know of, but only just. And over the past two decades, telescope surveys <a href="https://theconversation.com/how-we-discovered-840-minor-planets-beyond-neptune-and-what-they-can-tell-us-96431">have found</a> a couple of thousand more ranging down in size to only a few tens of kilometres across. The trouble is that most of the objects of that size or smaller are too faint to be spotted by telescopes. So it will be difficult to ever work out how many small but unseen bodies there actually are in the Kuiper belt. Now a new paper, <a href="http://science.sciencemag.org/cgi/doi/10.1126/science.aap8628">published in Science</a>, has used an ingenious method to help us find out.</p>
<p>This is important, because scientists believe Kuiper Belt objects are survivors from the solar system’s birth, developing from a primordial cloud of dust and gas. That means that their size distribution could have a lot to tell us about how the material from which the planets grew was initially assembled.</p>
<h2>Counting craters</h2>
<p>Instead of counting the small Kuiper belt objects directly, the researchers behind the new study counted the craters made by the random sample of objects that have impacted the surfaces of Pluto and its largest moon, <a href="https://theconversation.com/images-of-plutos-moon-charon-show-huge-fractures-and-hints-of-icy-lava-flows-48533">Charon</a>. There, craters 13km across would have been made by objects only 1km-2km in size. That is already way below the telescopic detection limit for Kuiper belt objects themselves, but images from <a href="https://theconversation.com/new-horizons-finally-gets-up-close-with-pluto-for-15-minutes-44603">the flyby of NASA’s New Horizons mission in 2015</a> allow craters as small as 1.4km to be mapped. Those must have been made by impacts of Kuiper Belt objects not much bigger than 100 metres in size.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/260674/original/file-20190225-26171-1u9e0w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/260674/original/file-20190225-26171-1u9e0w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=360&fit=crop&dpr=1 600w, https://images.theconversation.com/files/260674/original/file-20190225-26171-1u9e0w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=360&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/260674/original/file-20190225-26171-1u9e0w.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=360&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/260674/original/file-20190225-26171-1u9e0w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=453&fit=crop&dpr=1 754w, https://images.theconversation.com/files/260674/original/file-20190225-26171-1u9e0w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=453&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/260674/original/file-20190225-26171-1u9e0w.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=453&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Details of the ancient cratered surface of Charon’s Vulcan Planitia.</span>
<span class="attribution"><span class="source">: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/K. Singer</span></span>
</figcaption>
</figure>
<p>The researchers’ analysis shows that for craters of 13km or larger, on both Pluto and Charon, the frequency of impacts of various sizes seems to match with what would be expected from the known size distribution for Kuiper belt objects. However, for smaller craters the abundance falls off dramatically, and so by implication must the abundance of the Kuiper Belt objects capable of making those craters. The same does not happen for the well-documented asteroids that collide with the bodies in the region of Jupiter, Mars and Earth, nor is it consistent with theoretical models.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/260748/original/file-20190225-26177-o5p85w.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/260748/original/file-20190225-26177-o5p85w.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/260748/original/file-20190225-26177-o5p85w.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=363&fit=crop&dpr=1 600w, https://images.theconversation.com/files/260748/original/file-20190225-26177-o5p85w.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=363&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/260748/original/file-20190225-26177-o5p85w.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=363&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/260748/original/file-20190225-26177-o5p85w.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=457&fit=crop&dpr=1 754w, https://images.theconversation.com/files/260748/original/file-20190225-26177-o5p85w.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=457&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/260748/original/file-20190225-26177-o5p85w.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=457&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">800km wide view of part of Cthulhu Regio, extracted from the most detailed colour map of Pluto.</span>
<span class="attribution"><span class="source">NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute</span></span>
</figcaption>
</figure>
<p>Interpretation of the most heavily cratered terrains led the researchers to rule out that the small craters have been erased by geological resurfacing such as cryovolcanic activity (eruptions of icy fluids) during the past four billion years. This reinforces the conclusion that smaller craters were never made in the expected numbers, so there must be a mysterious corresponding deficit of Kuiper belt objects less than about 1-2km in size.</p>
<h2>Blorping and flomping</h2>
<p>When the researchers, led by Kelsi Singer of the Southwest Research Institute (Boulder, Colorado), wrote their paper no one had yet seen a small Kuiper Belt object in detail. However, New Horizons recently flew past a 30km long object known as 2014 MU₆₉ <a href="https://gizmodo.com/new-horizons-scientists-double-down-on-ultima-thule-nic-1831439791">(more controversially nicknamed “Ultima Thule”</a>) on January 1, and has now transmitted probably the best images we are going to get. </p>
<p>Sometimes described as “snowman-shaped”, it is a two-lobed “contact binary”, almost certainly formed by a merger of two round objects that happened so slowly and gently that neither component was deformed in the process. But what happened before that? If you look at the larger of the two lobes, in particular, you can make out what looks like traces of component parts that merged vigorously enough to squish together into an approximate sphere, but with insufficient violence to smash each other apart.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/260705/original/file-20190225-26181-17snz3t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/260705/original/file-20190225-26181-17snz3t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/260705/original/file-20190225-26181-17snz3t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=490&fit=crop&dpr=1 600w, https://images.theconversation.com/files/260705/original/file-20190225-26181-17snz3t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=490&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/260705/original/file-20190225-26181-17snz3t.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=490&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/260705/original/file-20190225-26181-17snz3t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=616&fit=crop&dpr=1 754w, https://images.theconversation.com/files/260705/original/file-20190225-26181-17snz3t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=616&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/260705/original/file-20190225-26181-17snz3t.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=616&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Kuiper belt object 2014 MU₆₉. The two-lobed object is about 30km from end to end.</span>
<span class="attribution"><span class="source">NASA/Johns Hopkins Applied Physics Laboratory/Southwest Research Institute, National Optical Astronomy Observatory</span></span>
</figcaption>
</figure>
<p>These ideas have inspired <a href="https://www.hou.usra.edu/meetings/lpsc2019/pdf/1248.pdf">quirky new terms</a>. “Blorping” refers to the collisional merging of material to assemble each of the lobes, and “flomping” describes the coming together when two lobes meet without causing any deformation. More importantly, this could offer an insight into the processes that robbed the Kuiper belt of the smaller objects that would otherwise have impacted to make small craters on Pluto and Charon.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/260770/original/file-20190225-26174-1qfnbjm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/260770/original/file-20190225-26174-1qfnbjm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=549&fit=crop&dpr=1 600w, https://images.theconversation.com/files/260770/original/file-20190225-26174-1qfnbjm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=549&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/260770/original/file-20190225-26174-1qfnbjm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=549&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/260770/original/file-20190225-26174-1qfnbjm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=690&fit=crop&dpr=1 754w, https://images.theconversation.com/files/260770/original/file-20190225-26174-1qfnbjm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=690&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/260770/original/file-20190225-26174-1qfnbjm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=690&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Detail of Charon’s Vulcan Planitia, where small craters are deficient in numbers.</span>
<span class="attribution"><a class="source" href="http://pluto.jhuapl.edu/Galleries/Featured-Images/image.php?page=12&gallery_id=2&image_id=324">NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute</a></span>
</figcaption>
</figure>
<p>The relative lack of small Kuiper Belt objects may be because, instead of breaking each other apart in collisions, they tended to merge by blorping – eventually growing into objects like 2014 MU₆₉. If this is correct, then when we try to count them, we see a record of growth rather than collisional fragmentation. </p>
<p>Orbital speeds are slower the further you get from the sun, so we would expect collisions to be less violent in the Kuiper Belt than in the inner solar system. But even so, a “blorp” event to fuse two lumps together rather than break them apart probably requires the ices that make up the bulk of their substance to be a lot less brittle and more squishy than we might have expected. That is crucial information, as these lumps are made from the raw material that the solar system formed from, shedding important light on its evolution. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/images-of-plutos-moon-charon-show-huge-fractures-and-hints-of-icy-lava-flows-48533">Images of Pluto's moon Charon show huge fractures and hints of icy 'lava flows'</a>
</strong>
</em>
</p>
<hr>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/stunning-crystal-clear-images-of-pluto-but-what-do-they-mean-47517">Stunning, crystal-clear images of Pluto – but what do they mean?</a>
</strong>
</em>
</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/nasa-mission-brings-pluto-into-sharp-focus-but-its-still-not-a-planet-40495">NASA mission brings Pluto into sharp focus – but it's still not a planet</a>
</strong>
</em>
</p>
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<img src="https://counter.theconversation.com/content/112436/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>There’s a mysterious lack of small bodies beyond Neptune, but a ‘snowman-shaped’ object may help explain why.David Rothery, Professor of Planetary Geosciences, The Open UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/756562017-04-18T12:37:32Z2017-04-18T12:37:32ZOur discovery of a minor planet beyond Neptune shows there might not be a ‘Planet Nine’ after all<figure><img src="https://images.theconversation.com/files/165592/original/image-20170418-32700-1fxdsgo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Canada-France-Hawaii Telescope has spotted a new dwarf planet.</span> <span class="attribution"><span class="source">Michele Banister</span>, <span class="license">Author provided</span></span></figcaption></figure><p>Ever since <a href="https://theconversation.com/a-stolen-exoplanet-that-will-kill-us-all-heres-what-we-do-know-about-planet-nine-60407">enthusiasm started growing</a> over the possibility that there could be a ninth major planet orbiting the sun beyond Neptune, astronomers have been busy hunting it. One group is investigating <a href="http://www.independent.co.uk/news/science/planet-nine-9-found-new-astronomers-four-unknown-objects-citizen-neptune-pluto-a7668411.html">four new moving objects</a> found by members of the public to see if they are potential new solar system discoveries. As exciting as this is, researchers are also making discoveries that question the entire prospect of a ninth planet.</p>
<p>One such finding is <a href="https://arxiv.org/abs/1704.01952">our discovery of a minor planet</a> in the outer solar system: <a href="http://www.minorplanetcenter.net/mpec/K17/K17G55.html">2013 SY99</a>. This small, icy world has an orbit so distant that it takes 20,000 years for one long, looping passage. We found SY99 with the <a href="http://www.cfht.hawaii.edu/">Canada-France-Hawaii Telescope</a> as part of the <a href="http://www.ossos-survey.org/">Outer Solar System Origins Survey</a>. SY99’s great distance means it travels very slowly across the sky. Our measurements of its motion show that its orbit is a very stretched ellipse, with the closest approach to the sun at 50 times that between the Earth and the sun (a distance of 50 “astronomical units”). </p>
<p>The new minor planet loops even further out than previously discovered dwarf planets such as <a href="https://www.universetoday.com/37479/dwarf-planet-sedna/">Sedna</a> and 2013 VP113. The long axis of its orbital ellipse is 730 astronomical units. Our observations with other telescopes show that SY99 is a small, reddish world, some 250 kilometres in diameter, or about the size of Wales in the UK.</p>
<p>SY99 is one of only seven known small icy worlds that orbit beyond Neptune at remarkable distances. How these “extreme trans-Neptunian objects” were placed on their orbits is uncertain: their distant paths are isolated in space. Their closest approach to the sun is so far beyond Neptune that they are thought to be <a href="https://ui.adsabs.harvard.edu/#abs/2007Icar..189..213L/abstract">“detached”</a> from the strong gravitational influence of the giant planets in our solar system. But at their furthest points, they are still too close to be nudged around by the slow tides of the galaxy itself.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/108837/original/image-20160121-9766-aqpwmc.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/108837/original/image-20160121-9766-aqpwmc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/108837/original/image-20160121-9766-aqpwmc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/108837/original/image-20160121-9766-aqpwmc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/108837/original/image-20160121-9766-aqpwmc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/108837/original/image-20160121-9766-aqpwmc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=425&fit=crop&dpr=1 754w, https://images.theconversation.com/files/108837/original/image-20160121-9766-aqpwmc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=425&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/108837/original/image-20160121-9766-aqpwmc.png?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">Planet Nine could explain why the few known extreme trans-Neptunian objects seem to be clustered together in space. The diagram was created using WorldWide Telescope.</span>
<span class="attribution"><span class="source">Caltech/R. Hurt (IPAC)</span></span>
</figcaption>
</figure>
<p>It’s been suggested that the extreme trans-Neptunian objects could be clustered in space by the gravitational influence of a “Planet Nine” that orbits much further out than Neptune. This planet’s gravity could lift out and detach their orbits – constantly changing their tilt. But this planet is far from proven. </p>
<p>In fact, its existence is based on the orbits of only six objects, which are very faint and hard to discover even with large telescopes. They are therefore prone to odd biases. It’s a bit like looking down into the deep ocean at a school of fish. The fish swimming near the surface are clearly visible. But the ones even only a meter down are fainter and murky, and take quite a lot of peering to be certain. The great bulk of the school, in the depths, is completely invisible. But the fish at the surface and their behaviour betray the existence of a whole school.</p>
<p>The biases mean SY99’s discovery can’t prove or disprove the existence of a Planet Nine. However, <a href="https://ui.adsabs.harvard.edu/?#abs/2017AJ....153...63S">computer models</a> do show that a Planet Nine would be an unfriendly neighbour to tiny worlds like SY99: its gravitational influence would starkly change its orbit – throwing it from the solar system entirely, or poking it into an orbit so highly inclined and distant that we wouldn’t be able to see it. SY99 would have to be one of an utterly vast throng of small worlds, continuously being sucked in and cast out by the planet. </p>
<h2>The alternative explanation</h2>
<p>But it turns out that there are other explanations. Our study based on <a href="https://arxiv.org/abs/1704.01952">computer modelling</a>, accepted for publication in the Astronomical Journal, hint at the influence of an idea from everyday physics called <a href="http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/cells/cells3.shtml">diffusion</a>. This is a very common type of behaviour in the natural world. Diffusion typically explains the random movement of a substance from a region of higher concentration to one of lower concentration – such as the way perfume drifts across a room.</p>
<p>We showed that a related form of diffusion can cause the orbits of minor planets to change from an ellipse that is initially only 730 astronomical units on its long axis to one that is as big as 2,000 astronomical units or bigger – and change it back again. In this process, the size of each orbit would vary by a random amount.
When SY99 comes to its closest approach every 20,000 years, Neptune will often be in a different part of its orbit on the opposite side of the solar system. But at encounters where both SY99 and Neptune are close, Neptune’s gravity will subtly nudge SY99, minutely changing its velocity. As SY99 travels out away from the sun, the shape of its next orbit will be different. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/164426/original/image-20170407-29365-1illepf.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/164426/original/image-20170407-29365-1illepf.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/164426/original/image-20170407-29365-1illepf.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/164426/original/image-20170407-29365-1illepf.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/164426/original/image-20170407-29365-1illepf.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/164426/original/image-20170407-29365-1illepf.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/164426/original/image-20170407-29365-1illepf.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">
<figcaption>
<span class="caption">New discovery 2013 SY99 (red) and the orbits of the other known trans-Neptunian minor planets with orbits larger than 250 astronomical units (grey). All their orbits are far outside the outermost known planet, Neptune (blue), even at their closest approach to the sun.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The long axis of SY99’s ellipse will alter, becoming either larger or smaller, in what physicists call a “random walk”. The orbit change takes place on truly astronomical time scales. It diffuses over the space of tens of millions of years. The long axis of SY99’s ellipse would change by hundreds of astronomical units over the 4.5 billion-year history of the solar system.</p>
<p>Several other extreme trans-Neptunian objects with smaller orbits also show diffusion, on a smaller scale. Where one goes, more can follow. It’s <a href="https://arxiv.org/abs/1704.01952">entirely plausible</a> that the gradual effects of diffusion act on the tens of millions of tiny worlds orbiting in the near fringe of the <a href="https://solarsystem.nasa.gov/planets/oort">Oort cloud</a> (a shell of icy objects at the edge of the solar system). This gentle influence would slowly lead some of them to randomly shift their orbits closer to us, where we see them as extreme trans-Neptunian objects. </p>
<p>However, diffusion won’t explain the distant orbit of Sedna, which has its closest point too far out from Neptune for it to change its orbit’s shape. Perhaps Sedna gained its orbit from a passing star, aeons ago. But diffusion could certainly be bringing in extreme trans-Neptunian objects from the inner Oort cloud – without the need for a Planet Nine. To find out for sure, we’ll need to make more discoveries in this most distant region using our largest telescopes.</p><img src="https://counter.theconversation.com/content/75656/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Michele Bannister receives funding from the STFC, and has previously been funded by Canada's NRC and NSERC. </span></em></p>It turns out that a common physical process called diffusion can explain the orbits of faraway minor planets – no need for a Planet Nine.Michele Bannister, Research Fellow, planetary astronomy, Queen's University BelfastLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/535052016-02-03T19:04:29Z2016-02-03T19:04:29ZThe long hunt for new objects in our expanding solar system<figure><img src="https://images.theconversation.com/files/109933/original/image-20160202-32231-1jjqrhe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Artist's impression: Looking back 12.9-billion km towards the sun and the inner solar system from Sedna, one of the recently discovered minor planets in the Kuiper belt.</span> <span class="attribution"><a class="source" href="http://hubblesite.org/newscenter/archive/releases/2004/14/image/e/">NASA, ESA and Adolf Schaller</a></span></figcaption></figure><p>Recognise these planet names: Vulcan, Neptune, Pluto, Nemesis, Tyche and Planet X? They all have one thing in common: their existence was predicted to account for unexplained phenomena in our solar system.</p>
<p>While the predictions of Neptune and Pluto proved correct, Nemesis and Tyche probably don’t exist. Now we have another contender, <a href="https://theconversation.com/somewhere-out-there-could-be-a-giant-new-planet-in-our-solar-system-so-where-is-it-53501">Planet Nine</a> – the existence of which astronomers predicted last month – but we may need to wait ten or more years for it to be confirmed.</p>
<p>Compare this to Vulcan. While many claimed to have observed the predicted planet, it took 75 years and Einstein’s <a href="https://theconversation.com/from-newton-to-einstein-the-origins-of-general-relativity-50013">general theory of relativity</a> to consign it to the dustbin of history. </p>
<h2>Somewhere out there</h2>
<p>Astronomers are finding new <a href="https://theconversation.com/au/topics/exoplanets">exoplanets</a> in other parts of the galaxy all the time. So why is it so hard to pin down exactly what is orbiting our own sun?</p>
<p>One reason is that very different methods are used to identify planets in other solar systems. Most involve observing periodic changes in the star’s light as the planet swings around it, as intercepted by telescopes such as <a href="http://kepler.nasa.gov/">Kepler</a>.</p>
<p>Inside our own solar system, we can’t see these effects when we’re looking out into the darkness rather than towards the sun. Instead, planet-hunters use indirect means. Slight wobbles and perturbations in the orbits of planets, comets and other objects may reveal the gravitational presence of ghostly neighbours we didn’t know we had.</p>
<p>This method has been used often over the past two centuries to predict new planets.</p>
<h2>The planet that arrived late</h2>
<p>In 1843, French mathematician <a href="http://www.britannica.com/biography/Urbain-Jean-Joseph-Le-Verrier">Urbain Le Verrier</a> published his provisional theory on the planet Mercury’s orbital motion.</p>
<p>Three years in the writing, it would be tested during a transit of Mercury across the face of the sun in 1845. But predictions from Le Verrier’s theory failed to match the observations. Mercury was late by 16 seconds! </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/110097/original/image-20160203-5857-10xqk0x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/110097/original/image-20160203-5857-10xqk0x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/110097/original/image-20160203-5857-10xqk0x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=456&fit=crop&dpr=1 600w, https://images.theconversation.com/files/110097/original/image-20160203-5857-10xqk0x.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=456&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/110097/original/image-20160203-5857-10xqk0x.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=456&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/110097/original/image-20160203-5857-10xqk0x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=573&fit=crop&dpr=1 754w, https://images.theconversation.com/files/110097/original/image-20160203-5857-10xqk0x.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=573&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/110097/original/image-20160203-5857-10xqk0x.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=573&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 photomosaic of images collected by Mariner 10 as it flew past Mercury. But was there another planet nearby?</span>
<span class="attribution"><a class="source" href="http://solarsystem.nasa.gov/galleries/mariner-10s-mercury">NASA</a></span>
</figcaption>
</figure>
<p>Le Verrier was not deterred. Further study showed that Mercury’s <a href="http://astronomy.swin.edu.au/cosmos/P/Perihelion">perihelion</a> – the point when it’s closest to the sun – advances by a small amount each orbit, technically called perihelion precession.</p>
<p>But the amount predicted by classical mechanics differed from the observed value by a minuscule 43 <a href="http://mathworld.wolfram.com/ArcSecond.html">arcseconds</a> per century. </p>
<p>Initially, Le Verrier proposed that the excess precession could be explained by the presence of an asteroid belt inside the orbit of Mercury. Further calculations led him to prefer a small planet, which he named Vulcan after the Roman god of fire.</p>
<h2>The search for Vulcan</h2>
<p>It was a credible claim, as in 1845 Le Verrier had also successfully predicted the position of Neptune from perturbations of Uranus’s orbit. Now astronomers just had to find Vulcan.</p>
<p>As planet fever hit the popular press, professional and amateur astronomers reviewed solar photographs to see whether Vulcan transits had been mistaken as mere sunspots.</p>
<p>The first possible sighting came immediately. In 1859 Edmond Lescarbault, a country doctor and gentleman astronomer in France, claimed to have seen Vulcan transit across the sun.</p>
<p>Further sightings continued, and by the mid-1860s <a href="http://adsabs.harvard.edu/full/1990JBAA..100...62J">The Astronomical Register</a> listed Vulcan as the innermost planet. </p>
<p>Vulcan’s moment in the sun came to a head in 1869. Observations of solar transits in March and April and a solar eclipse in August failed to see the elusive planet. </p>
<p>Not everyone was ready to give up, though. At the Sydney Observatory, astronomer <a href="http://adb.anu.edu.au/biography/russell-henry-chamberlain-4525">Henry Chamberlain Russell</a> watched the sun for three days in March 1877, according to a report in <a href="http://trove.nla.gov.au/ndp/del/article/108201398">Sydney’s Evening News</a>, on Friday March 23, which said:</p>
<blockquote>
<p>No sign of Vulcan appeared all through the 20th and 21st. But in watching for this planet several interesting observations were made of the sun’s spots.</p>
</blockquote>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/110095/original/image-20160203-28534-l1hc3i.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/110095/original/image-20160203-28534-l1hc3i.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/110095/original/image-20160203-28534-l1hc3i.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=307&fit=crop&dpr=1 600w, https://images.theconversation.com/files/110095/original/image-20160203-28534-l1hc3i.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=307&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/110095/original/image-20160203-28534-l1hc3i.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=307&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/110095/original/image-20160203-28534-l1hc3i.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=385&fit=crop&dpr=1 754w, https://images.theconversation.com/files/110095/original/image-20160203-28534-l1hc3i.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=385&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/110095/original/image-20160203-28534-l1hc3i.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=385&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Newspaper report on the search Vulcan by Sydney astronomer H C Russell.</span>
<span class="attribution"><a class="source" href="http://trove.nla.gov.au/ndp/del/article/108201398">National Library of Australia/Evening News</a></span>
</figcaption>
</figure>
<p>The explanation for the missing seconds came from a completely different direction. After Einstein published his general theory of relativity in 1915, it was revealed that the discrepancy was caused by the sun’s distortion of spacetime. </p>
<h2>Beyond Planet X</h2>
<p>In 1905, the American astronomer <a href="http://www.space.com/19774-percival-lowell-biography.html">Percival Lowell</a> <a href="https://theconversation.com/finding-pluto-the-hunt-for-planet-x-44508">started hunting</a> for a Planet X. He predicted it would lie beyond Neptune, just as Neptune lies beyond Uranus. His calculations led astronomers at Lowell’s <a href="https://lowell.edu/history/the-pluto-telescope/">namesake observatory</a> to find Pluto in 1930.</p>
<p>Speculation about unsighted planets never entirely died down in the astronomical community, but decades passed without any major breakthroughs.</p>
<p>In the 1950s, though, the solar system potentially expanded to a distance 100,000 times further that Earth’s orbit. The Dutch astronomer <a href="http://www.britannica.com/biography/Jan-Hendrik-Oort">Jan Hendrik Oort</a> hypothesised the existence of a spherical distribution of icy bodies. The <a href="http://astronomy.swin.edu.au/cosmos/o/oort+cloud">Oort Cloud</a> is thought to be the source of long period comets, which have eccentric orbits and periods from 200 to many thousands of years. </p>
<p>In 1951 the Dutch-American astronomer <a href="http://www.britannica.com/biography/Gerard-Peter-Kuiper">Gerard Kuiper</a> proposed that a similar belt of icy objects beyond Neptune’s orbit could account for short-period and short-lived comets. In 1992 astronomers <a href="http://www.astro.ucla.edu/personnel/david-jewitt">David Jewitt</a> and Jane Luu discovered the first of these Kuiper Belt Objects (<a href="http://solarsystem.nasa.gov/planets/kbos/indepth">KBO</a>) – originally called “Smiley”, it is now catalogued more prosaically as 1992 QB1.</p>
<p>The most well-known KBOs are <a href="http://solarsystem.nasa.gov/planets/eris">Eris</a>, <a href="http://www.nasa.gov/vision/universe/solarsystem/planet_like_body.html">Sedna</a> and the dwarf planet <a href="http://solarsystem.nasa.gov/planets/pluto">Pluto</a>. After flying by Pluto on July 15, 2015, the <a href="http://pluto.jhuapl.edu/">New Horizons</a> spacecraft is due to encounter KBO-2014 MU69 on January 1, 2019.</p>
<h2>Speculation and measurement</h2>
<p>Other predictions for new solar system objects came from looking at the terrestrial fossil record, rather than the skies. </p>
<p>On the basis of statistical analysis of mass extinctions, the America palaeontologists David Raup and Jack Sepkoski <a href="http://www.pnas.org/content/81/3/801">proposed in 1984</a> that they coincided with large-impact events. Independently, two teams of astronomers suggested that a dwarf star, later named <a href="http://www.space.com/22538-nemesis-star.html">Nemesis</a>, passes through the solar system every 26 million years, flinging comets on a path to impact Earth.</p>
<p>Comets provide key evidence in these studies. Analysis of perturbations in comet orbits led astronomers to propose that a brown dwarf (bigger than a planet but smaller than a star) exists in the outer solar system. It is named <a href="http://www.space.com/10952-nasa-giant-planet-tyche-faq-wise.html">Tyche</a>, the good sister of Nemesis.</p>
<p>A search of the Wide-Field Infrared Survey Explorer (<a href="https://www.nasa.gov/mission_pages/WISE/main/">WISE</a>) satellite data in 2014 <a href="http://www.jpl.nasa.gov/news/news.php?release=2014-075">ruled out the existence</a> of both Nemesis and Tyche. </p>
<p>In 2003, the “<a href="http://web.gps.caltech.edu/%7Embrown/howikilled.html">Pluto killer</a>” Michael Brown was part of a team that discovered what <a href="http://web.gps.caltech.edu/%7Embrown/sedna/">he called</a> “the coldest most distant place known in the solar system”, which came to be known as <a href="http://www.mikebrownsplanets.com/2010/10/there-is-something-out-there.html">Sedna</a>. The discovery of this Kuiper belt object prompted further searches and much speculation as to its origin – particularly its <a href="http://www.mikebrownsplanets.com/2010/11/theres-something-out-there-part-3.html">strange orbit</a>.</p>
<p>As more and more objects were identified in the Kuiper Belt, it was possible to observe orbital anomalies more precisely. The simplest way to explain them was another planet.</p>
<p>The 2016 orbital calculations by <a href="http://web.gps.caltech.edu/%7Ekbatygin/Home.html">Konstantin Batygin</a> and <a href="http://web.gps.caltech.edu/%7Embrown/">Mike Brown</a> strengthen the concept of an unseen planet, which they call <a href="https://www.caltech.edu/news/caltech-researchers-find-evidence-real-ninth-planet-49523">Planet Nine</a>. </p>
<h2>Planet Nine from Outer Space</h2>
<p>What difference does it make if there is another planet lurking out there? We’re not likely to see it any time soon.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/110080/original/image-20160203-28559-pejpx0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/110080/original/image-20160203-28559-pejpx0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/110080/original/image-20160203-28559-pejpx0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=357&fit=crop&dpr=1 600w, https://images.theconversation.com/files/110080/original/image-20160203-28559-pejpx0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=357&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/110080/original/image-20160203-28559-pejpx0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=357&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/110080/original/image-20160203-28559-pejpx0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=449&fit=crop&dpr=1 754w, https://images.theconversation.com/files/110080/original/image-20160203-28559-pejpx0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=449&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/110080/original/image-20160203-28559-pejpx0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=449&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Artist’s impression: The distant view from Planet Nine back towards the sun.</span>
<span class="attribution"><span class="source">Caltech/R. Hurt (IPAC)</span></span>
</figcaption>
</figure>
<p>At its closest approach to Earth, the predicted Planet Nine will still be 200 astronomical units (<a href="http://astronomy.swin.edu.au/cosmos/A/Astronomical+Unit">au</a>) away (about 30 billion kilometres). Compare this to Pluto’s orbit, which is an average of 39 au from the sun (5.8 billion kilometres). We don’t even know where Planet Nine is right now, if it exists at all. </p>
<p>But everything we learn about the dark outer regions contributes to the story of how our solar system evolved, and, more importantly, how it will change in the future. </p>
<p>In 1957, journalist John Barbour <a href="https://news.google.com/newspapers?nid=1928&dat=19571108&id=_0MpAAAAIBAJ&sjid=yWYFAAAAIBAJ&pg=953,792962&hl=en">quipped</a>:</p>
<blockquote>
<p>What with Russia’s Sputniks, and the gaudy possibilities of interplanetary travel to come, our solar system seems to be shrinking somewhat like the Earth did when aeroplanes came into use.</p>
</blockquote>
<p>Now, it seems, the opposite is true: the mysterious trans-Neptunian region of the solar system has still much to surprise us.</p><img src="https://counter.theconversation.com/content/53505/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 Executive Council of the Space Industry Association of Australia.</span></em></p>The search for new objects, including new planets, in our solar system has turned up some interesting finds. There have been a few failures over the years too.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/535732016-01-22T13:53:38Z2016-01-22T13:53:38ZClaims about new planets that turned out to be wrong – and why ‘Planet Nine’ may be different<figure><img src="https://images.theconversation.com/files/108985/original/image-20160122-425-m7zfyi.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/11304375@N07/2818891443">Image Editor/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>There’s a real buzz among planetary scientists after <a href="http://iopscience.iop.org/article/10.3847/0004-6256/151/2/22;jsessionid=B5568D507489BB2DCDD6751E7F29C6D8.c1.iopscience.cld.iop.org">a new study</a> suggested that an unseen planet, dubbed “Planet Nine”, of about ten times the Earth’s mass could be lurking in the Kuiper belt, a band of icy objects beyond Neptune. The latest theory was put forward after scientists noticed that six objects in the belt were behaving strangely, something that they said could be explained by the existence of a new planet.</p>
<p>It’s not the first time such a case has been made for a new planet. So how does this new theory compare to similar claims made in the past?</p>
<h2>Kuiper belt and Planet Nine</h2>
<p>The Kuiper belt, which we started discovering in the early 1990s, is a region of the solar system beyond the major eight planets that we are are only just starting to explore in more detail with space probes like NASA’s <a href="http://pluto.jhuapl.edu/Mission/The-Path-to-Pluto/Mission-Timeline.php">New Horizons mission</a>. The Kuiper belt is home to many comets formed in the Uranus-Neptune region <a href="http://astron-soc.in/outreach/2015/07/new-horizon-keeps-its-date-with-pluto/">4.6 billion years ago</a> – Rosetta’s comet 67P comes from here. Even more comets populate the spherical, but as yet unseen “<a href="http://www.universetoday.com/32522/oort-cloud/">Oort cloud</a>”, another belt of rocks far beyond the Kuiper belt, where most comets spend most of their time. The Oort cloud is 10,000 astronomical units (AU) away from us (one AU is roughly equal to the distance between the Earth and the sun, or 149.6m kilometres).</p>
<p>The basis of the new theoretical evidence for the new planet is the strange alignment of the six Kuiper belt objects, and the deflection out of the ecliptic plane of others – this would seem to indicate that the objects are being disturbed by the gravitational pull of a huge planet far beyond Neptune and Pluto, and which has been calculated to have an orbit around the sun of 15,000 years. So how do we know it is a planet and not just a large object in the Kuiper belt? The implied mass of the object that could disturb these orbits is simply too high for it to be a very large Kuiper belt object like a dwarf planet or an asteroid. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/jy6JcViPkWg?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>Theoretically, it is possible to explain how an additional outer planet core could have formed further away and alongside Jupiter, Saturn, Uranus and Neptune using models of the birth of our solar system 4.6 billion years ago. And observations of exoplanets show that, elsewhere, large objects can <a href="http://phys.org/news/2013-06-exoplanet-formation.html">form at relatively large distances</a> from their parent star. However, another possibility that could explain the odd behaviour of the Kuiper objects may be that “Planet Nine”, if it exists, could be a large object in the inner Oort cloud rather than a planet. </p>
<p>It may seem hard to believe that we could suddenly discover a new planet. Since ancient times, humans have been able to observe all of the planets out to Saturn and in the 1600s realised they were in orbit around the sun. William Herschel then <a href="http://www.space.com/17432-william-herschel.html">discovered Uranus in 1781</a>, and observations of its orbit led to the <a href="http://www.universetoday.com/21621/who-discovered-neptune/">discovery of Neptune in 1846</a>. Pluto was added in 1930, following a search for a larger “Planet X”, but was <a href="https://theconversation.com/nasa-mission-brings-pluto-into-sharp-focus-but-its-still-not-a-planet-40495">demoted to an ice dwarf planet</a> in 2006. Many Kuiper belt objects have also been observed, with at least one of them, <a href="http://www.universetoday.com/37285/dwarf-planet-eris/">Eris</a>, more massive than Pluto (which eventually forced the demotion of Pluto).</p>
<h2>The search for Planet X</h2>
<p>In the past there have been claims for an extra “Planet X” (now planet IX, or the more familiar Planet Nine, due to Pluto’s demotion). But none of them have fully held up so far. </p>
<ol>
<li><p>When further irregularities in the orbit of Uranus were <a href="http://adsabs.harvard.edu/abs/1946ASPL....5...73T">first noticed in 1906</a> it sparked a search for a Planet X that was thought to be massive. Eventually, however, the less-massive Pluto was found instead by Clyde Tombaugh in 1930.</p></li>
<li><p>In the 1980s, a Planet X <a href="http://adsabs.harvard.edu/full/1988AJ.....96.1476H">was proposed</a> by <a href="http://yowusa.com/planetx/2008/planetx-2008-05b/1.shtml">Robert S Harrington</a> based on the irregular orbits of Neptune and Uranus. This was <a href="http://www.americaspace.com/?p=90864">later disproved by Myles Standish</a>, who was able to explain the irregularities by revising the mass for Neptune using data from the Voyager flyby.</p></li>
<li><p>In the 1990s, a large planet near the Oort cloud, dubbed Tyche, <a href="http://www.independent.co.uk/news/science/up-telescope-search-begins-for-giant-new-planet-2213119.html">was proposed</a> to explain the orbits of certain comets. This was ruled out for Saturn-sized objects or larger by NASA’s Wide-field Infrared Survey Explorer satellite although smaller as yet undetected objects may be possible.</p></li>
<li><p>Sedna, <a href="http://www.space.com/25695-sedna-dwarf-planet.html">discovered in 2003</a>, is a dwarf planet in our solar system with an elliptical 11,400-year orbit between 76AU and 937AU (which is 2.5 to 31 times the distance from the sun to Neptune). Its discovery led to suggestions that it was an inner Oort-cloud object, deflected either by a passing star or by a large, unseen planet. If such a planet existed, the orbits of other nearby objects would also be disturbed, and this received <a href="http://www.theguardian.com/science/2014/mar/26/dwarf-planet-super-earth-solar-system-2012-vp113">some support from observations</a> of another object, dubbed 2012 VP113. But orbital calculations indicated that this may be smaller and orbiting at a distance of 1,000AU or more. </p></li>
<li><p>In December 2015, there was a <a href="http://arstechnica.co.uk/science/2015/12/astronomers-question-claim-of-super-planet-found-at-solar-systems-edge/">hint of a large object</a> 300AU away – about six times further than Pluto – in data from the Atacama Large Millimeter/submillimeter Array. However, the chance of catching such an object with a telescope is small, and many scientists think this is more likely a Kuiper belt object.</p></li>
</ol>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/108992/original/image-20160122-441-153obkw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/108992/original/image-20160122-441-153obkw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/108992/original/image-20160122-441-153obkw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=383&fit=crop&dpr=1 600w, https://images.theconversation.com/files/108992/original/image-20160122-441-153obkw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=383&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/108992/original/image-20160122-441-153obkw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=383&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/108992/original/image-20160122-441-153obkw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=481&fit=crop&dpr=1 754w, https://images.theconversation.com/files/108992/original/image-20160122-441-153obkw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=481&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/108992/original/image-20160122-441-153obkw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=481&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">ALMA Prototype Antennas at the ALMA Test Facility.</span>
<span class="attribution"><span class="source">(ESO/NAOJ/NRAO)</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Compared to all of these examples, “Planet Nine” has arguably the best supporting evidence. This is partly because effects have been seen in the orbits of the six Kuiper belt objects rather than just one or two, which makes the theory seem potentially plausible. The dynamics of the outer solar system is delivering more surprises as our detection technology gets better, and we may expect much more knowledge of the Kuiper belt, or perhaps the Oort cloud in the coming years.</p>
<p>In the meantime, we will clearly have to wait for direct evidence from ground or space-based telescopes to see if Planet Nine, or indeed other large objects, actually exist. Only armed with direct proof should we start worrying about a name.</p><img src="https://counter.theconversation.com/content/53573/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Andrew Coates receives funding from STFC and UKSA. </span></em></p>A new planet in our solar system? Let’s get direct proof before we start naming it.Andrew Coates, Professor of Physics, Deputy Director (Solar System) at the Mullard Space Science Laboratory, UCLLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/521052015-12-09T18:08:10Z2015-12-09T18:08:10ZCeres reveals its salty secrets – and blurs the line between comets and asteroids<figure><img src="https://images.theconversation.com/files/105065/original/image-20151209-15556-1c6g1dn.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Ceres: a bright spot in planetary exploration.</span> <span class="attribution"><span class="source">NASA/JPL-Caltech/UCLA/MPS/DLR/IDA</span></span></figcaption></figure><p>When <a href="http://dawn.jpl.nasa.gov/DawnCommunity/flashbacks/fb_04.asp">Guiseppe Piazzi</a> reported his observations of a minor planet in 1801, he originally thought it might be a comet. But follow-up observations by fellow astronomers suggested that Ceres was actually an asteroid. So it’s somewhat ironic that the latest results from <a href="http://dawn.jpl.nasa.gov/">NASA’s Dawn mission</a> suggest this asteroid is confusingly similar to a comet.</p>
<p>Dawn has found a number of mysterious features on Ceres so far, including <a href="https://theconversation.com/dawn-breaks-over-distant-ceres-and-perhaps-reveals-signs-of-habitability-38967">bright white spots</a> on its surface. Its latest results suggest that these are salts left behind as ice vaporised from the surface by sublimation – a process often seen in comets. They also suggest Ceres may have formed far away from its current location in orbit between Mars and Jupiter. This would be surprising as many astronomers believe that a key <a href="http://www.universetoday.com/33006/what-is-the-difference-between-asteroids-and-comets/">difference between comets and asteroids</a> is that asteroids form closer to the sun.</p>
<h2>Mysterious spots</h2>
<p>Ceres is the largest asteroid we know of – it is also classified as a <a href="https://theconversation.com/nasa-missions-may-re-elevate-pluto-and-ceres-from-dwarf-planets-to-full-on-planet-status-36081">dwarf planet</a>. Its bright spots were first discovered when Dawn started orbiting Ceres in 2014, the largest at a latitude of around 25°N. There was intense speculation about what these features were, as they had the characteristics of ice. The Herschel Space Observatory later found that <a href="http://www.bbc.co.uk/news/science-environment-25849871">water vapour</a> was being produced at specific locations on Ceres. </p>
<p>It therefore seemed that Ceres was acting like a comet, with ice-rich regions releasing dust and vapour during daylight hours. If that were the case, then ice might be a major component of the asteroid, buried below a surface of dust and rubble. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/YNjktBvsGA0?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>But the two new studies (see <a href="http://nature.com/articles/doi:10.1038/nature15754">here</a> and <a href="http://nature.com/articles/doi:10.1038/nature16172">here</a>), using information from different instruments on the Dawn spacecraft, did not record any ice on the surface. However, one article speculates that ice may still be buried just below the surface while the other suggests that water bound in minerals is abundant.</p>
<p>The researchers also investigated the bright feature at the bottom of <a href="https://www.nasa.gov/jpl/dawn/pia19617/occator-crater-enhanced-view">Occator Crater</a>, the brightest of the white spots, and concluded that they may be hydrated magnesium salts. The salts are deposits left behind from recent sublimation of water ice that have not yet been covered by soil. Other bright spots, although not as prominent, may also be salt deposits, but that material is likely to be older.</p>
<h2>A Kuiper Belt Object?</h2>
<p>The researchers also identified a mixture of minerals on the surface of Ceres, which they think are ammonia-bearing clay minerals and <a href="http://pubchem.ncbi.nlm.nih.gov/compound/magnesium_carbonate">magnesium carbonate</a>. The clay minerals could have been produced by <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/geophys/silicate.html">silicates</a> reacting with ammonia ice. However, if Ceres had formed where it is now, it would not have been able to pick up any ammonia ice to enable such a reaction, because the ice would not be stable.</p>
<p>This means that Ceres may have originally formed in the <a href="http://solarsystem.nasa.gov/planets/kbos">Kuiper Belt</a> on the outskirts of the solar system and then scattered inwards as the giant planets migrated outwards. Alternatively, Ceres could have formed more or less where it is, and incorporated nitrogen-containing organic molecules, which, like the water ice, were transported inwards from beyond Neptune.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/105064/original/image-20151209-15567-14qwjcc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/105064/original/image-20151209-15567-14qwjcc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/105064/original/image-20151209-15567-14qwjcc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=404&fit=crop&dpr=1 600w, https://images.theconversation.com/files/105064/original/image-20151209-15567-14qwjcc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=404&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/105064/original/image-20151209-15567-14qwjcc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=404&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/105064/original/image-20151209-15567-14qwjcc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=507&fit=crop&dpr=1 754w, https://images.theconversation.com/files/105064/original/image-20151209-15567-14qwjcc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=507&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/105064/original/image-20151209-15567-14qwjcc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=507&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Did Ceres form in the main belt and incorporate ammonia from the outer solar system or did Ceres itself form there?</span>
<span class="attribution"><span class="source">L.Giacomini</span></span>
</figcaption>
</figure>
<p>While this might not sound all that significant, it does have quite profound ramifications for our understanding of how material has been mixed to form planets, minor planets, comets and Kuiper Belt Objects. </p>
<p>This year has been an amazing one for small icy bodies. <a href="https://theconversation.com/stunning-crystal-clear-images-of-pluto-but-what-do-they-mean-47517">Images from the New Horizons mission</a> to Pluto have shown us the variety of landscapes that can be sculpted on an icy surface. Similarly, pictures of the surface of <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> taken by Rosetta have revealed canyons and pits probably caused by fracturing and ice sublimation. </p>
<p>Now we can add a third small body where a combination of ice, water and salts have left behind an environment in which there is the potential for an active, sub-surface chemistry that might, eventually, result in formation of complex molecules. It is also becoming more clear than ever that strict division between comets and asteroids is no longer realistic, and that they represent a spectrum of objects of varying activity and orbit.</p>
<p>Just one last word about the surface of Ceres. I might not be much of a farmer – but I’m fairly certain that magnesium salts and nitrogen-bearing clays are important ingredients in a good, rich soil for raising crops. So naming Ceres after a <a href="http://www.ceresva.org/Goddess/Ceres.htm">harvest deity</a> was more appropriate than Piazzi could have imagined!</p><img src="https://counter.theconversation.com/content/52105/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>Is it a dwarf planet, an asteroid or a comet? All of the above? Well, with the latest results about Ceres, researchers aren’t entirely sure anymore.Monica Grady, Professor of Planetary and Space Sciences, The Open UniversityLicensed 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.