tag:theconversation.com,2011:/nz/topics/planets-146/articlesPlanets – The Conversation2024-03-22T14:32:05Ztag:theconversation.com,2011:article/2263612024-03-22T14:32:05Z2024-03-22T14:32:05ZStellar murder: when stars destroy and eat their own planets<figure><img src="https://images.theconversation.com/files/583649/original/file-20240322-22-txhykg.jpg?ixlib=rb-1.1.0&rect=3%2C0%2C1036%2C584&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/missions/chandra/nasas-chandra-planets-can-be-anti-aging-formula-for-stars/">NASA/CXC/M.Weiss</a></span></figcaption></figure><p>Our Sun is both our best friend and our worst enemy. On the one hand, we owe our very existence to our star. Earth and the other planets in the Solar System formed out of the same cloud of gas and dust as the Sun. </p>
<p>And without its light, there could be no life on this planet. On the other hand, there will come a day when the Sun ends all life on Earth and, eventually, destroys Earth itself.</p>
<p>The risks that stars can pose to their planets are highlighted by <a href="https://www.nature.com/articles/d41586-024-00847-6">a new study published in Nature</a>. The authors looked at stars similar to our Sun and found that at least one in 12 stars exhibits traces of metals in its atmosphere. These are thought to be the scars of planets and asteroids that have been ingested by the stars. </p>
<p>Planets should never feel too comfortable as they orbit their parent star, as there are at least two ways in which their star can betray their trust and bring about their violent demise. </p>
<h2>Tidal disruption</h2>
<p>The first is through a process called “tidal disruption”. As a planetary system forms, some planets will find themselves orbiting their star along paths that are either not quite circular or are slightly inclined relative to the plane of the star’s rotation. When that happens, the gravitational force exerted by the star on the planet will slowly correct the shape or the alignment of the wayward planet’s orbit. </p>
<p>In extreme cases, the gravitational force applied by the star will destabilise the planet’s orbit, slowly pulling it closer and closer. If the hapless planet strays too close, it will be torn apart by the star’s gravity. This happens because the side of the planet facing the star is slightly closer than the side facing away (the difference is the planet’s diameter). </p>
<p>The strength of the gravitational pull exerted by the star depends on the distance between it and the planet, so that the side of the planet facing the star feels a slightly stronger pull than the side facing away. </p>
<p>On Earth, this difference in the strength of the force of gravity creates the daily ebb and flow of the tides. In essence, the Sun is trying to deform Earth, but is far enough away that it only manages to pull on the waters of its oceans. But a planet dangerously close to its star will find its very crust and core being pulled apart by these tides. </p>
<p>If the planet is not too close to the star, its shape will merely be deformed into that of an egg. Just a little closer to the star, and the difference between the gravitational pull on its different sides will be enough to completely tear it apart, reducing it back to a cloud of gas and dust that spirals into the star and vaporises in its hellish fires.</p>
<p>The process of tidal disruption was first suggested some 50 years ago. For the last couple of decades, astronomers — including my group — have observed dozens of bright tidal disruption flares caused by <a href="https://science.nasa.gov/resource/tidal-disruption-event/">stars shredded by supermassive black holes</a> in the centres of galaxies. </p>
<figure class="align-center ">
<img alt="Planet and binary star." src="https://images.theconversation.com/files/583650/original/file-20240322-26-mpjqcm.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/583650/original/file-20240322-26-mpjqcm.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/583650/original/file-20240322-26-mpjqcm.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/583650/original/file-20240322-26-mpjqcm.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/583650/original/file-20240322-26-mpjqcm.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/583650/original/file-20240322-26-mpjqcm.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/583650/original/file-20240322-26-mpjqcm.jpeg?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">
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<span class="caption">The new study in Nature looked specifically at stars orbiting each other in binary systems.</span>
<span class="attribution"><a class="source" href="https://images.nasa.gov/details/PIA21470">NASA/JPL-Caltech</a></span>
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<p>Last year, for the first time, a group of astronomers reported observing a similar, dimmer flare that was consistent with <a href="https://www.nasa.gov/missions/neowise/caught-in-the-act-astronomers-detect-a-star-devouring-a-planet/">a planet being disrupted and consumed by its star</a>. </p>
<p>Tidal disruption of planets may be quite common, as shown by the new finding that at least 1 in 12 stars exhibits signs that <a href="https://www.nature.com/articles/d41586-024-00847-6">they have ingested planetary material</a>. </p>
<p>Other studies have found that between a quarter to half of all white dwarfs – the remnants of stars up to twice as massive as our Sun – sport similar scars. As their name implies, white dwarfs are white hot. With surface temperatures of tens of thousands of degrees, the hottest white dwarfs emit ultraviolet and X-ray light energetic enough to <a href="https://www.syfy.com/syfy-wire/a-dead-star-is-vaporizing-its-planets">vaporise their orbiting planets</a>.</p>
<h2>The end of Earth</h2>
<p>Rest assured; Earth won’t be destroyed via tidal disruption. Our planet’s end will come in about five billion years, when the Sun will transition into a red giant. </p>
<p>Stars are powered by <a href="https://www.energy.gov/science/doe-explainsnuclear-fusion-reactions#:%7E:text=Nuclear%20Fusion%20reactions%20power%20the,The%20leftover%20mass%20becomes%20energy.">the process known as fusion</a>, where two light elements are combined to make a heavier one. All stars start out their lives fusing the element hydrogen in their cores into the element helium. This fusion process both stabilises them against implosion, due to the incessant pull of gravity, and creates the light that makes them shine. Our Sun has been fusing hydrogen into helium for roughly 4.5 billion years. </p>
<p>But 4.5 billion years from now, the hydrogen in the Sun’s core will run out. All fusion in the core will stop, and gravity, unopposed, will force the star to contract. As the core contracts, it will heat up until the temperature is high enough for helium to fuse into carbon. </p>
<p>Fusion will once again stabilise the star. In the meantime, though, the outer envelopes of the star will expand and cool, giving the now giant star a redder hue. As the red giant Sun expands, it will <a href="https://www.scientificamerican.com/article/the-sun-will-eventually-engulf-earth-maybe/">engulf Mercury, Venus and Earth</a> – it may even reach all the way out to the orbit of Mars. </p>
<p>Earth may have another five billion years to go, but we will not be here to witness its extinction. As the Sun burns through its hydrogen stores, it steadily grows brighter: every billion years, its luminosity increases by about 10%. </p>
<p>A billion years from now, the Sun will be bright enough to <a href="https://theconversation.com/the-sun-wont-die-for-5-billion-years-so-why-do-humans-have-only-1-billion-years-left-on-earth-37379">boil away Earth’s oceans</a>. So, the next time you bask in the warm rays of the Sun, remember: it’s got it in for us.</p><img src="https://counter.theconversation.com/content/226361/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Or Graur receives funding from UKRI Science and Technology Facilities Council.. </span></em></p>There are several ways in which stars can destroy and swallow their own planets.Or Graur, Associate Professor of Astrophysics, University of PortsmouthLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2254842024-03-12T17:51:07Z2024-03-12T17:51:07ZOur survey of the sky is uncovering the secrets of how planets are born<figure><img src="https://images.theconversation.com/files/580926/original/file-20240311-22-5v1m89.jpeg?ixlib=rb-1.1.0&rect=22%2C44%2C2978%2C1165&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Discs giving birth to new planets, seen by the Very Large Telescope.</span> <span class="attribution"><span class="source">ESO/C. Ginski, A. Garufi, P.-G. Valegård et al.</span></span></figcaption></figure><p>When we look out to the stars, it is typically not a yearning for the distant depths of outer space that drives us. When we are looking out there, we are truly looking back at ourselves. We try to understand our place in the unimaginable vastness of the universe. </p>
<p>One of the most burning questions that drives us is how unique we are. Did life only emerge here on Earth or is our galaxy teaming with it? </p>
<p>The very first step in finding out is to understand how special the Earth really is – and, by extension, our entire Solar System. This requires knowledge about how solar systems actually form. And that’s exactly what <a href="https://www.eso.org/public/news/eso2405/">my colleagues and I have started to uncover</a> with a new series of studies of star-forming regions.</p>
<p>In the past decades, astronomers <a href="https://theconversation.com/explainer-how-do-you-find-exoplanets-24153">have spotted</a> more than 5,000 planets around distant stars – so called exoplanets. We now know that planets are so abundant that you can look up to almost any star in the night sky and be near certain that planets are circling around it. But what do these planets look like?</p>
<p>The first planet that was discovered around a star similar to the Sun came as a shock to us. It was a so-called <a href="https://exoplanets.nasa.gov/resources/1040/hot-jupiter/">hot Jupiter</a>, a massive gas giant that orbits its parent star on such a tight orbit that the length of a year is only four days. This is a truly alien world with no equal in our own solar system.</p>
<p>From this first groundbreaking discovery, astronomers have gone on and found tightly packed systems of super-Earths, rocky planets several times as massive as the Earth, as well as awesome gas giants in century-long orbits around their parent star. Of the many planetary systems that we have found, none equals our own solar system. In fact <a href="https://theconversation.com/more-than-1-000-new-exoplanets-discovered-but-still-no-earth-twin-59274">most of them are quite different.</a> </p>
<p>To understand how all of these different systems come to be, we have to turn to the very beginning. And that’s majestic discs of dust and gas that surround the youngest stars. These are the nurseries which will eventually bring forth new planetary systems. </p>
<p>These discs <a href="https://arxiv.org/abs/2002.00405">are enormous objects</a>, up to several hundred times as extended as the distance between the Earth and the Sun. Yet in the sky they appear tiny. This is because even the nearest ones, which are practically in our galactic backyard, are between 600 and 1,600 light years away.</p>
<p>That is a tiny distance when you consider that the Milky Way galaxy has a diameter of more than 100,000 light years, but it still means that light, the fastest thing in the universe, takes up to 1,600 years to reach us from there. </p>
<p>The typical size of one of these planetary nurseries, as seen from the Earth, would be an angle of 1 “arc-second” on sky, which is equivalent to a 3,600th part of a degree. To put it in perspective, it is like trying to observe a person standing on top of the Eiffel Tower from 500km away in the Dutch capital of Amsterdam. </p>
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<p>To observe these discs we need the most advanced and largest telescopes. And we need sophisticated instruments that can correct for atmospheric turbulence which blurs our images. This is no mean feat of engineering, with the latest generation of instruments only being available since about a decade. </p>
<h2>New findings</h2>
<p>Using the European Southern Observatory’s “<a href="https://www.eso.org/public/unitedkingdom/teles-instr/paranal-observatory/vlt/">Very Large Telescope</a>”, the VLT, and the <a href="https://www.eso.org/sci/facilities/paranal/instruments/sphere.html">Sphere extreme adaptive optics camera</a>, we have now started to survey nearby young stars.</p>
<p>Our team, consisting of scientists from more than ten countries was able to observe more than 80 of these young stars in amazing detail – with our findings published in a <a href="https://www.eso.org/public/news/eso2405/">series of papers</a> in the journal Astronomy and Astrophysics.</p>
<p>All the images were taken in near infrared light, invisible to the human eye. They show the light from the distant young stars as it is reflected from the tiny dust particles in the discs. This dust is much like sand on the beach and will eventually clump together to form new planets. </p>
<p>What we found was an astonishing diversity of shape and form of these planetary nurseries. Some of them have huge ring systems, others large spiral arms. Some of them are smooth and calm, and yet others are caught in the middle of a storm as dust and gas from the surrounding star-forming clouds rains down on them. </p>
<p>While we expected some of this diversity, our survey shows for the first time that this holds true even within the same star-forming regions. So even planetary systems that form within the same neighbourhood might look quite different from one another.</p>
<figure class="align-center ">
<img alt="Planet-forming discs within the gas-rich cloud of Chamaeleon I, roughly 600 light-years from Earth." src="https://images.theconversation.com/files/581242/original/file-20240312-22-tc1s5x.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/581242/original/file-20240312-22-tc1s5x.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=430&fit=crop&dpr=1 600w, https://images.theconversation.com/files/581242/original/file-20240312-22-tc1s5x.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=430&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/581242/original/file-20240312-22-tc1s5x.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=430&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/581242/original/file-20240312-22-tc1s5x.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=540&fit=crop&dpr=1 754w, https://images.theconversation.com/files/581242/original/file-20240312-22-tc1s5x.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=540&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/581242/original/file-20240312-22-tc1s5x.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=540&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Planet-forming discs within the gas-rich cloud of Chamaeleon I, roughly 600 light-years from Earth.</span>
<span class="attribution"><span class="source">Ginski et, al 2024</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Finding such wide range of discs suggests that the huge diversity in exoplanets discovered so far is a consequence of this broad spectrum of planetary nurseries. </p>
<p>Unlike the Sun, most stars in our galaxy have companions, with two or more stars orbiting a shared centre of mass. When looking at the constellation of Orion, we found that stars in groups of two or more were less likely to have large planet-forming discs than lone stars. This is a useful thing to know when hunting for exo-planets. </p>
<p>Another interesting finding was how uneven the discs in this region were, suggesting they may host massive planets that warp the discs. </p>
<p>The next step in our research will be to connect specific planets to their nurseries, to understand how the different systems might have formed in detail. We also want to zoom in even closer in the innermost regions of these discs in which terrestrial planets like our own Earth might already be forming.</p>
<p>For this, we will use the next generation of telescopes spearheaded by the “<a href="https://elt.eso.org/">Extremely Large Telescope</a>” of the European Southern Observatory that is right now under construction in the Chilean Atacama desert. </p>
<p>There are many questions to answer. But thanks to our survey we now know that the very first step on the long way for life to emerge is an utterly beautiful one.</p><img src="https://counter.theconversation.com/content/225484/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Christian Ginski works for the University of Galway and frequently works with ESO facilities. </span></em></p>Astronomers have spotted a surprisingly diverse set of planet-forming disks.Christian Ginski, Lecturer of astronomy, University of GalwayLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2232472024-02-12T19:33:22Z2024-02-12T19:33:22ZNewborn gas planets may be surprisingly flat – new research<p>A new planet starts its life in a rotating circle of gas and dust, a cradle known as a <a href="https://esahubble.org/wordbank/circumstellar-disc/">protostellar disc</a>. My colleagues and I have used computer simulations to show that newborn gas planets in these discs are likely to have surprisingly flattened shapes. This finding, <a href="https://www.aanda.org/articles/aa/full_html/2024/02/aa48753-23/aa48753-23.html">published in Astronomy and Astrophysics Letters</a>, could add to our picture of exactly how planets form.</p>
<p>Observing protoplanets that have just formed and are still within their protostellar discs is extremely difficult. Until now only three such young protoplanets have been observed, with two of them in the same system, PDS 70.</p>
<p>We need to find systems that are young, and close enough for our telescopes to be able to detect the dim light from the planet itself and distinguish it from that of the disc. The whole process of planetary formation lasts only a few million years which is nothing more than a blink of an eye in astrophysical scales. This means we need to have luck to catch them in the act of forming.</p>
<p>Our research group performed computer simulations to determine the properties of gaseous protoplanets under a variety of thermal conditions in the planets’ cradles. </p>
<p>The simulations have enough resolution to be able to follow the evolution of a protoplanet in the disc from an early stage, when it is just a mere condensation within the disc. Such simulations are computationally demanding and were run on <a href="https://dirac.ac.uk/">DiRAC, the UK’s astrophysics supercomputing facility</a>.</p>
<p>Typically, multiple planets form within a disc. The study found that protoplanets have a shape known as oblate spheroids, like Smarties or M&M’s, rather than being spherical. They grow by drawing gas predominantly through their poles rather than their equators. </p>
<p>Technically, the planets in our Solar System are also oblate spheroids but their flattening is small. <a href="https://spaceplace.nasa.gov/planets-round/en/#:%7E:text=Mercury%20and%20Venus%20are%20the,bit%20thicker%20in%20the%20middle.">Saturn has a flattening of 10%, Jupiter 6%, whereas Earth a mere 0.3%</a>.</p>
<p>In comparison, the typical flattening of protoplanets is 90%. Such a flattening will affect the observed properties of protoplanets, and it needs to be taken into account when interpreting observations.</p>
<h2>How planets start off</h2>
<p>The most widely accepted theory for planet formation <a href="https://faculty.ucr.edu/%7Ekrice/coreacc.html#:%7E:text=The%20most%20commonly%20accepted%20mechanism,to%20accrete%20a%20gaseous%20envelope.">is that of “core accretion”</a>. According to this model, tiny dust particles smaller than sand collide with each other, group together and progressively grow into larger and larger bodies. This is effectively what happens to the dust under your bed when it isn’t cleaned. </p>
<p>Once a core of dust with enough massive forms, it draws gas from the disc to form a gas giant planet. This bottom-to-top approach would take a few million years. </p>
<p>The opposite, top-to-bottom approach, is the <a href="https://blog.planethunters.org/tag/disk-instability/">theory of disc instability</a>. In this model, the protostellar discs that attend young stars are gravitationally unstable. In other words, they are too heavy to be maintained and so fragment into pieces, which evolve into planets. </p>
<p>The theory of core accretion has been around for a long time and it can explain many aspects of how our Solar System formed. However, disc instability can better explain some of the exoplanetary systems we have discovered in recent decades, such as those where a gas giant planet orbits very very far from its host star.</p>
<p>The appeal of this theory is that planet formation happens very fast, within a few thousand years, which is consistent with observations that suggest planets exist in very young discs.</p>
<p>Our study focused on gas giant planets formed via the model of disc instability. They are flattened because they form from the compression of an already flat structure, the protostellar disc, but also because of how they rotate. </p>
<h2>No flat Earths</h2>
<p>Although these protoplanets overall are very flattened, their cores, which will eventually evolve into gas giant planets as we know them, are less flattened – only by about 20%. This is just twice the flattening of Saturn. With time they are expected to become more spherical.</p>
<p>Rocky planets, like Earth and Mars, cannot form via disc instability. They are thought to form by slowly assembling dust particles to pebbles, rocks, kilometre-sized objects and eventually planets. They are too dense to be significantly flattened even when they are newly born. There is no possibility that Earth was flattened at such a high degree when it as young.</p>
<p>But our study does support a role for disc instability in the case of some worlds in some planetary systems.</p>
<p>We are now moving from the era of exoplanet discoveries to the era of exoplanet characterisation. Many new observatories are set to become operational. These will help discover more protoplanets embedded in their discs. Predictions from computer models are also becoming more sophisticated. </p>
<p>The comparison between these theoretical models and observations is bringing us closer and closer to understanding the origins of our Solar System.</p><img src="https://counter.theconversation.com/content/223247/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Dimitris Stamatellos receives funding from the Science and Technology Facilities Council (STFC).</span></em></p>The observation could fill in gaps in our knowledge about planet formation.Dimitris Stamatellos, Associate Professor in Astrophysics, University of Central LancashireLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2198922024-02-05T13:30:46Z2024-02-05T13:30:46ZUS Moon landing marks new active phase of lunar science, with commercial launches of landers that will study solar wind and peer into the universe’s dark ages<figure><img src="https://images.theconversation.com/files/567940/original/file-20240104-21-s3p58r.jpg?ixlib=rb-1.1.0&rect=4%2C17%2C2991%2C1868&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The dark, far side of the Moon is the perfect place to conduct radio astronomy. </span> <span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/LunarEclipse/704e3da2df90473486270e23aa73419d/photo?Query=moon&mediaType=photo&sortBy=&dateRange=Anytime&totalCount=399&digitizationType=Digitized&currentItemNo=12&vs=true&vs=true">AP Photo/Rick Bowmer</a></span></figcaption></figure><p>For the first time since 1972, NASA <a href="https://www.intuitivemachines.com/im-1">landed a craft on the surface of the Moon</a> in February 2024. But the agency didn’t do it alone – instead, it partnered with commercial companies. Thanks to new technologies and <a href="https://www.nasa.gov/commercial-lunar-payload-services/">public-private partnerships</a>, the scientific projects brought to the Moon on this craft and on future missions like it will open up new realms of scientific possibility. </p>
<p>As parts of several projects launching this year, teams of scientists, including myself, will conduct radio astronomy from the south pole and the far side of the Moon.</p>
<p>NASA’s <a href="https://www.nasa.gov/commercial-lunar-payload-services/">commercial lunar payload services program</a>, or CLPS, will use uncrewed landers to conduct NASA’s first science experiments from the Moon in over 50 years. The CLPS program differs from past space programs. Rather than NASA building the landers and operating the program, commercial companies will do so in a public-private partnership. NASA identified <a href="https://www.nasa.gov/commercial-lunar-payload-services/clps-providers/">about a dozen companies</a> to serve as vendors for landers that will go to the Moon. </p>
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<figcaption><span class="caption">CLPS will send science payloads to the Moon in conjunction with the Artemis program’s crewed missions.</span></figcaption>
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<p>NASA buys space on these landers for <a href="https://science.nasa.gov/lunar-science/clps-deliveries/">science payloads</a> to fly to the Moon, and the companies design, build and insure the landers, as well as contract with rocket companies for the launches. Unlike in the past, NASA is one of the customers and not the sole driver. </p>
<h2>Peregrine and Odysseus, the first CLPS landers</h2>
<p>The first two CLPS payloads are scheduled to launch during the first two months of 2024. There’s the <a href="https://science.nasa.gov/lunar-science/clps-deliveries/to2-astrobotic/">Astrobotics payload</a>, which launched Jan. 8 before its lander, named Peregrine, <a href="https://www.space.com/astrobotic-peregrine-moon-lander-headed-to-earth">experienced a fuel issue</a> that cut its journey to the Moon short. </p>
<p>Next, there’s the <a href="https://science.nasa.gov/lunar-science/clps-deliveries/op-to2-intuitive-machines/">Intuitive Machines payload</a>. Intuitive Machines’ lander, named Odysseus, <a href="https://www.intuitivemachines.com/im-1">landed near the south pole of the Moon</a> on Feb. 22, 2024. NASA has also planned a <a href="https://science.nasa.gov/lunar-science/clps-deliveries/">few additional landings</a> – about two or three per year – for each of the next few years.</p>
<p>I’m a <a href="https://www.colorado.edu/faculty/burns/">radio astronomer</a> and co-investigator on NASA’s <a href="https://www.colorado.edu/ness/projects/radiowave-observations-lunar-surface-photoelectron-sheath-rolses">ROLSES program</a>, otherwise known as Radiowave Observations at the Lunar Surface of the photoElectron Sheath. ROLSES was built by the NASA Goddard Space Flight Center and is led by <a href="https://science.gsfc.nasa.gov/sci/bio/natchimuthuk.gopalswamy-1">Natchimuthuk Gopalswamy</a>. </p>
<p>The ROLSES instrument landed on the Moon as <a href="https://www.intuitivemachines.com/_files/ugd/7c27f7_51f84ee63ea744a9b7312d17fefa9606.pdf">one of six NASA payloads</a> on the Intuitive Machines lander in February. Between ROLSES and another mission scheduled for the lunar far side in two years, LuSEE-Night, our teams will land NASA’s first two radio telescopes on the Moon by 2026. </p>
<h2>Radio telescopes on the Moon</h2>
<p>The Moon – particularly the far side of the Moon – is an ideal place to do radio astronomy and study signals from extraterrestrial objects such as the Sun and the Milky Way galaxy. On Earth, the ionosphere, which <a href="https://theconversation.com/earths-magnetic-field-protects-life-on-earth-from-radiation-but-it-can-move-and-the-magnetic-poles-can-even-flip-216231">contains Earth’s magnetic field</a>, distorts and absorbs radio signals below the <a href="https://www.fcc.gov/general/fm-radio">FM band</a>. These signals might get scrambled or may not even make it to the surface of the Earth.</p>
<p>On Earth, there are also TV signals, satellite broadcasts and defense radar systems <a href="https://theconversation.com/radio-interference-from-satellites-is-threatening-astronomy-a-proposed-zone-for-testing-new-technologies-could-head-off-the-problem-199353">making noise</a>. To do higher sensitivity observations, you have to go into space, away from Earth. </p>
<p>The Moon is what scientists call <a href="https://www.sciencefocus.com/space/what-is-tidal-locking">tidally locked</a>. One side of the Moon is always facing the Earth – the “<a href="https://www.rmg.co.uk/stories/topics/what-man-moon">man in the Moon</a>” side – and the other side, <a href="https://theconversation.com/whats-on-the-far-side-of-the-moon-111306">the far side</a>, always faces away from the Earth. The Moon has no ionosphere, and with about 2,000 miles of rock between the Earth and the far side of the Moon, there’s no interference. It’s radio quiet. </p>
<p>For our first mission with ROLSES, which launched in February 2024, we will collect data about environmental conditions on the Moon near its south pole. On the Moon’s surface, <a href="https://theconversation.com/solar-storms-can-destroy-satellites-with-ease-a-space-weather-expert-explains-the-science-177510">solar wind</a> directly strikes the lunar surface and creates a charged gas, called <a href="https://www.psfc.mit.edu/vision/what_is_plasma">a plasma</a>. Electrons lift off the negatively charged surface to form a highly ionized gas. </p>
<p>This doesn’t happen on Earth because <a href="https://theconversation.com/earths-magnetic-field-protects-life-on-earth-from-radiation-but-it-can-move-and-the-magnetic-poles-can-even-flip-216231">the magnetic field deflects</a> the solar wind. But there’s no global magnetic field on the Moon. With a low frequency radio telescope like ROLSES, we’ll be able to measure that plasma for the first time, which could help scientists figure out how to keep astronauts safe on the Moon. </p>
<p>When astronauts walk around on the surface of the Moon, they’ll pick up different charges. It’s like walking across the carpet with your socks on – when you reach for a doorknob, a spark can come out of your finger. The same kind of discharge happens on the Moon from the charged gas, but it’s potentially more harmful to astronauts. </p>
<h2>Solar and exoplanet radio emissions</h2>
<p>Our team is also going to use ROLSES to look at the Sun. The Sun’s surface releases shock waves that send out highly energetic particles and low radio frequency emissions. We’ll use the radio telescopes to measure these emissions and to see bursts of low-frequency radio waves from shock waves within the solar wind.</p>
<p>We’re also going to examine the Earth from the surface of the Moon and use that process as a template for <a href="https://theconversation.com/nasas-tess-spacecraft-is-finding-hundreds-of-exoplanets-and-is-poised-to-find-thousands-more-122104">looking at radio emissions from exoplanets</a> that may harbor life <a href="https://theconversation.com/are-there-any-planets-outside-of-our-solar-system-164062">in other star systems</a>. </p>
<p>Magnetic fields are important for life because they shield the planet’s surface from the <a href="https://theconversation.com/the-scorching-winds-on-the-surface-of-the-sun-and-how-were-forecasting-them-44098">solar/stellar wind</a>. </p>
<p>In the future, our team hopes to use specialized arrays of antennas on the far side of the Moon to observe nearby stellar systems that are known to have exoplanets. If we detect the same kind of radio emissions that come from Earth, this will tell us that the planet has a magnetic field. And we can measure the strength of the magnetic field to figure out whether it’s strong enough to shield life.</p>
<h2>Cosmology on the Moon</h2>
<p>The Lunar Surface Electromagnetic Experiment at Night, or <a href="https://www.colorado.edu/ness/projects/lunar-surface-electromagnetics-experiment-night-lusee-night">LuSEE-Night</a>, will fly in early 2026 to the far side of the Moon. LuSEE-Night marks scientists’ first attempt to do cosmology on the Moon.</p>
<p>LuSEE-Night is a novel collaboration between NASA and the Department of Energy. Data will be sent back to Earth using a communications satellite in lunar orbit, <a href="https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/A_pathway_for_communicating_at_the_Moon">Lunar Pathfinder</a>, which is funded by the European Space Agency.</p>
<p>Since the far side of the Moon is <a href="https://cosmicdawn.astro.ucla.edu/lunar_telescopes.html">uniquely radio quiet</a>, it’s the best place to do cosmological observations. During the two weeks of lunar night that happen every 14 days, there’s no emission coming from the Sun, and there’s no ionosphere. </p>
<p>We hope to study an unexplored part of the early universe called the <a href="https://www.astronomy.com/science/the-beginning-to-the-end-of-the-universe-the-cosmic-dark-ages/">dark ages</a>. The dark ages refer to before and just after the formation of the very first stars and galaxies in the universe, which is beyond what the <a href="https://webb.nasa.gov/">James Webb Space Telescope</a> can study.</p>
<p>During the dark ages, the universe was less than 100 million years old – today the universe is 13.7 billion years old. The universe was full of hydrogen <a href="https://theconversation.com/after-our-universes-cosmic-dawn-what-happened-to-all-its-original-hydrogen-65527">during the dark ages</a>. That hydrogen radiates through the universe at low radio frequencies, and when new stars turn on, they ionize the hydrogen, producing a radio signature in the spectrum. Our team hopes to measure that signal and learn about how the earliest stars and galaxies in the universe formed.</p>
<p>There’s also a lot of potential new physics that we can study in this last unexplored cosmological epoch in the universe. We will investigate the nature of <a href="https://theconversation.com/dark-matter-the-mystery-substance-physics-still-cant-identify-that-makes-up-the-majority-of-our-universe-85808">dark matter</a> and early <a href="https://theconversation.com/explainer-the-mysterious-dark-energy-that-speeds-the-universes-rate-of-expansion-40224">dark energy</a> and test our fundamental models of physics and cosmology in an unexplored age.</p>
<p>That process is going to start in 2026 with the LuSEE-Night mission, which is both a fundamental physics experiment and a cosmology experiment.</p>
<p><em>This is an updated version of an article originally published on Feb. 5, 2024.</em></p><img src="https://counter.theconversation.com/content/219892/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jack Burns receives funding from NASA.</span></em></p>Projects under NASA’s CLPS program – including the Odysseus lander that made it to the lunar surface – will probe unexplored questions about the universe’s formation.Jack Burns, Professor of Astrophysical and Planetary Sciences, University of Colorado BoulderLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2190542024-02-02T13:17:20Z2024-02-02T13:17:20ZOrbital resonance − the striking gravitational dance done by planets with aligning orbits<figure><img src="https://images.theconversation.com/files/571696/original/file-20240126-29-xc09zr.jpg?ixlib=rb-1.1.0&rect=19%2C4%2C1578%2C792&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Planets can gravitationally affect each other when their orbits line up. </span> <span class="attribution"><a class="source" href="https://exoplanets.nasa.gov/trappist1/">NASA/JPL-Caltech</a></span></figcaption></figure><p>Planets orbit their parent stars while separated by enormous distances – in our solar system, planets are like <a href="https://science.nasa.gov/learning-resources/how-big-is-the-solar-system/">grains of sand</a> in a region the size of a football field. The time that planets take to orbit their suns have no specific relationship to each other. </p>
<p>But sometimes, their orbits display striking patterns. For example, astronomers studying <a href="https://exoplanets.nasa.gov/news/1771/discovery-alert-watch-the-synchronized-dance-of-a-6-planet-system/">six planets orbiting a star</a> 100 light years away have just found that they orbit their star with an almost rhythmic beat, in perfect synchrony. Each pair of planets completes their orbits in times that are the ratios of whole numbers, allowing the planets to align and exert a gravitational push and pull on the other during their orbit.</p>
<p>This type of gravitational alignment is called <a href="https://www.aanda.org/glossary/175-orbital-resonance">orbital resonance</a>, and it’s like a harmony between distant planets.</p>
<p>I’m an <a href="https://scholar.google.com/citations?user=OrRLRQ4AAAAJ&hl=en">astronomer</a> who studies and writes about <a href="https://wwnorton.com/books/9780393343861">cosmology</a>. Researchers have discovered <a href="https://exoplanets.nasa.gov/">over 5,600 exoplanets</a> in the past 30 years, and their extraordinary diversity continues to surprise astronomers.</p>
<h2>Harmony of the spheres</h2>
<p>Greek mathematician <a href="https://www.auroraorchestra.com/2019/05/pythagoras-the-music-of-the-spheres/">Pythagoras</a> discovered the principles of musical harmony 2,500 years ago by analyzing the sounds of blacksmiths’ hammers and plucked strings. </p>
<p>He believed mathematics was at the heart of the natural world and proposed that the Sun, Moon and planets each emit unique hums based on their orbital properties. He thought this “music of the spheres” would be imperceptible to the human ear.</p>
<p>Four hundred years ago, <a href="https://www.skyscript.co.uk/kepler.html">Johannes Kepler</a> picked up this idea. He proposed that musical intervals and harmonies described the motions of the six known planets at the time. </p>
<p>To Kepler, the solar system had two basses, Jupiter and Saturn; a tenor, Mars; two altos, Venus and Earth; and a soprano, Mercury. These roles reflected how long it took each planet to orbit the Sun, lower speeds for the outer planets and higher speeds for the inner planets. </p>
<p>He called the book he wrote on these mathematical relationships “<a href="https://archive.org/details/ioanniskepplerih00kepl">The Harmony of the World</a>.” While these ideas have some similarities to the concept of orbital resonance, planets don’t actually make sounds, since <a href="https://theconversation.com/why-isnt-there-any-sound-in-space-an-astronomer-explains-why-in-space-no-one-can-hear-you-scream-217885">sound can’t travel through the vacuum of space</a>.</p>
<h2>Orbital resonance</h2>
<p><a href="https://www.aanda.org/glossary/175-orbital-resonance">Resonance happens when</a> planets or moons have orbital periods that are <a href="https://www.youtube.com/watch?v=qDHKveVSc0Y">ratios of whole numbers</a>. The orbital period is the time taken for a planet to make one complete circuit of the star. So, for example, two planets orbiting a star would be in a 2:1 resonance when one planet takes twice as long as the other to orbit the star. Resonance is seen in only <a href="https://arxiv.org/abs/1703.03634">5% of planetary systems</a>.</p>
<figure class="align-center ">
<img alt="A simple animated diagram showing a planet, as a dot, with three smaller dots making circles around it, and occasionally flashing when two of the three line up." src="https://images.theconversation.com/files/571674/original/file-20240126-17-ofefj2.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/571674/original/file-20240126-17-ofefj2.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=403&fit=crop&dpr=1 600w, https://images.theconversation.com/files/571674/original/file-20240126-17-ofefj2.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=403&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/571674/original/file-20240126-17-ofefj2.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=403&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/571674/original/file-20240126-17-ofefj2.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=506&fit=crop&dpr=1 754w, https://images.theconversation.com/files/571674/original/file-20240126-17-ofefj2.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=506&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/571674/original/file-20240126-17-ofefj2.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=506&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Orbital resonance, as seen with Jupiter’s moons, happens when planetary bodies’ orbits line up – for example, Io orbits Jupiter four times in the time it takes Europa to orbit twice and Ganymede to orbit once.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/File:Galilean_moon_Laplace_resonance_animation_2.gif">WolfmanSF/Wikimedia Commons</a></span>
</figcaption>
</figure>
<p>In the solar system, Neptune and Pluto are in a 3:2 resonance. There’s also a <a href="https://www.planetary.org/space-images/orbital-resonances-of-galilean-moons">triple resonance</a>, 4:2:1, among Jupiter’s three moons: Ganymede, Europa and Io. In the time it takes Ganymede to orbit Jupiter, Europa orbits twice and Io orbits four times. Resonances occur naturally, when planets happen to have orbital periods that are the ratio of whole numbers. </p>
<p>Musical intervals describe the relationship between two musical notes. In the musical analogy, important <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/Music/mussca.html">musical intervals</a> based on ratios of frequencies are the fourth, 4:3, the fifth, 3:2, and the octave, 2:1. Anyone who plays the <a href="https://globalguitarnetwork.com/perfect-intervals/">guitar or the piano</a> might recognize these intervals.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/2V3bvZu2Xqo?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Musical intervals can be used to create scales and harmony.</span></figcaption>
</figure>
<p>Orbital resonances can change <a href="https://theconversation.com/earth-isnt-the-only-planet-with-seasons-but-they-can-look-wildly-different-on-other-worlds-216874">how gravity influences</a> two bodies, causing them to speed up, slow down, stabilize on their orbital path and sometimes have their orbits disrupted.</p>
<p>Think of pushing a <a href="https://astrobites.org/2018/07/05/small-black-hole-meets-big-black-hole/">child on a swing</a>. A planet and a swing both have a natural frequency. Give the child a push that matches the swing motion and they’ll get a boost. They’ll also get a boost if you push them every other time they’re in that position, or every third time. But push them at random times, sometimes with the motion of the swing and sometimes against, and they get no boost. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/qDHKveVSc0Y?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Orbital resonance can cause planets or asteroids to speed up or start to wobble.</span></figcaption>
</figure>
<p>For planets, the boost can keep them continuing on their orbital paths, but it’s much more likely to disrupt their orbits.</p>
<h2>Exoplanet resonance</h2>
<p>Exoplanets, or planets outside the solar system, show striking examples of resonance, not just between two objects but also between resonant “chains” involving three or more objects. </p>
<hr>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/567788/original/file-20240103-23-yg479z.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A square box with the words 'Art & Science Collide' and a drawing of a lightbulb with its wire filament in the shape of a brain, surrounded by a circle." src="https://images.theconversation.com/files/567788/original/file-20240103-23-yg479z.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/567788/original/file-20240103-23-yg479z.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/567788/original/file-20240103-23-yg479z.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/567788/original/file-20240103-23-yg479z.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/567788/original/file-20240103-23-yg479z.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/567788/original/file-20240103-23-yg479z.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/567788/original/file-20240103-23-yg479z.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Art & Science Collide series.</span>
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</figure>
<p><em><strong><a href="https://theconversation.com/us/topics/art-in-science-series-2024-149583">This article is part of Art & Science Collide</a></strong>, a series examining the intersections between art and science.</em></p>
<p><em>You may be interested in:</em></p>
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<p><a href="https://theconversation.com/i-wrote-a-play-for-children-about-integrating-the-arts-into-stem-fields-heres-what-i-learned-about-encouraging-creative-interdisciplinary-thinking-218001">I wrote a play for children about integrating the arts into STEM fields – here’s what I learned about interdisciplinary thinking</a> </p>
<p><a href="https://theconversation.com/pictures-have-been-teaching-doctors-medicine-for-centuries-a-medical-illustrator-explains-how-218998">Pictures have been teaching doctors medicine for centuries − a medical illustrator explains how</a></p>
<hr>
<p>The star <a href="http://oklo.org/2010/06/23/a-second-laplace-resonance/">Gliese 876</a> has three planets with orbit period ratios of 4:2:1, just like Jupiter’s three moons. <a href="https://skyandtelescope.org/astronomy-news/kepler-finds-planets-in-tight-dance/">Kepler 223</a> has four planets with ratios of 8:6:4:3. </p>
<p>The red dwarf <a href="https://arxiv.org/abs/2212.08695">Kepler 80</a> has five planets with ratios of 9:6:4:3:2, and <a href="https://www.esa.int/ESA_Multimedia/Images/2021/01/Infographic_of_the_TOI-178_planetary_system">TOI 178</a> has six planets, of which five are in a resonant chain with ratios of 18:9:6:4:3. </p>
<p><a href="https://www.sci.news/astronomy/trappist-1-planetary-harmonies-04851.html">TRAPPIST-1</a> is the record holder. It has seven Earth-like planets, two of which <a href="https://theconversation.com/ultracool-dwarf-star-hosts-three-potentially-habitable-earth-sized-planets-just-40-light-years-away-58695">might be habitable</a>, with orbit ratios of 24:15:9:6:4:3:2. </p>
<p>The newest example of a resonant chain is the <a href="https://www.digitaltrends.com/space/exoplanet-orbital-resonance-chain/">HD 110067</a> system. It’s about 100 light years away and has six sub-Neptune planets, a common type of exoplanet, with orbit ratios of 54:36:24:16:12:9. The discovery is interesting because most resonance chains are unstable and disappear over time. </p>
<p>Despite these examples, resonant chains are rare, and <a href="https://www.astronomy.com/science/astronomers-find-six-planets-orbiting-in-resonance/">only 1% of all planetary systems display them</a>. Astronomers think that planets form in resonance, but small gravitational nudges from passing stars and wandering planets erase the resonance over time. With HD 110067, the resonant chain has survived for billions of years, offering a rare and pristine view of the system as it was when it formed.</p>
<h2>Orbit sonification</h2>
<p>Astronomers use <a href="https://science.howstuffworks.com/sonification.htm">a technique called sonification</a> to translate complex visual data into sound. It gives people a different way to appreciate the beautiful images from the <a href="https://science.nasa.gov/mission/hubble/multimedia/sonifications/">Hubble Space Telescope</a>, and it has been applied to <a href="https://www.system-sounds.com/">X-ray data and gravitational waves</a>.</p>
<p>With exoplanets, sonification can convey the mathematical relationships of their orbits. Astronomers at the European Southern Observatory created what they call “<a href="https://www.youtube.com/watch?v=-WevvRG9ysY">music of the spheres</a>” for the TOI 178 system by associating a sound on a pentatonic scale to each of the five planets. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/-WevvRG9ysY?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Music from planetary orbits, created by astronomers at the European Southern Observatory.</span></figcaption>
</figure>
<p>A <a href="https://www.youtube.com/watch?v=WS5UxLHbUKc">similar musical translation</a> has been done for the TRAPPIST-1 system, with the orbital frequencies scaled up by a factor of 212 million to bring them into audible range. </p>
<p>Astronomers have also <a href="https://www.youtube.com/watch?v=2rrODAG7nmI&t=3s">created a sonification</a> for the HD 110067 system. People may not agree on whether these renditions sound like actual music, but it’s inspiring to see Pythagoras’ ideas realized after 2,500 years.</p><img src="https://counter.theconversation.com/content/219054/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Impey receives funding from the National Science Foundation. </span></em></p>Orbital resonance is kind of like musical harmony, but systems that display it are far more rare than songs with harmonic melodies.Chris Impey, University Distinguished Professor of Astronomy, University of ArizonaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2157652024-01-11T17:23:58Z2024-01-11T17:23:58ZHow much life has ever existed on Earth?<figure><img src="https://images.theconversation.com/files/567152/original/file-20231221-25-fybvl8.jpg?ixlib=rb-1.1.0&rect=0%2C5%2C3619%2C2197&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">In primary production, inorganic carbon is used to build the organic molecules life needs. </span> <span class="attribution"><span class="source">(Shutterstock)</span></span></figcaption></figure><iframe style="width: 100%; height: 100px; border: none; position: relative; z-index: 1;" allowtransparency="" allow="clipboard-read; clipboard-write" src="https://narrations.ad-auris.com/widget/the-conversation-canada/how-much-life-has-ever-existed-on-earth" width="100%" height="400"></iframe>
<p>All organisms are made of living cells. While it is difficult to pinpoint exactly when the first cells came to exist, geologists’ best estimates suggest at least as early as <a href="https://doi.org/10.1016/S0301-9268(00)00128-5">3.8 billion years ago</a>. But how much life has inhabited this planet since the first cell on Earth? And how much life will ever exist on Earth? </p>
<p>In our new study, published in <a href="https://doi.org/10.1016/j.cub.2023.09.040"><em>Current Biology</em></a>, my colleagues from the <a href="https://www.weizmann.ac.il/">Weizmann Institute of Science</a> and <a href="https://www.smith.edu/academics/geosciences">Smith College</a> and I took aim at these big questions.</p>
<h2>Carbon on Earth</h2>
<p>Every year, about 200 billion tons of carbon is taken up through what is known as primary production. During primary production, inorganic carbon — such as carbon dioxide in the atmosphere and bicarbonate in the ocean — is used for energy and to build the organic molecules life needs. </p>
<p>Today, the most notable contributor to this effort is <a href="https://doi.org/10.1038/nrm1525">oxygenic photosynthesis</a>, where sunlight and water are key ingredients. However, deciphering past rates of primary production has been a challenging task. In lieu of a time machine, scientists like myself rely on clues left in ancient sedimentary rocks to reconstruct past environments. </p>
<p>In the case of primary production, the isotopic composition of <a href="https://doi.org/10.1038/s41586-018-0349-y">oxygen</a> in the form of sulfate in ancient salt deposits allows for such estimates to be made. </p>
<p>In <a href="https://doi.org/10.1016/j.cub.2023.09.040">our study</a>, we compiled all previous estimates of ancient primary production derived through the method above, as well as many others. The outcome of this productivity census was that we were able to estimate that 100 quintillion (or 100 billion billion) tons of carbon has been through primary production since the origin of life. </p>
<p>Big numbers like this are difficult to picture; 100 quintillion tons of carbon is about 100 times the amount of carbon contained within the Earth, a pretty impressive feat for Earth’s primary producers. </p>
<h2>Primary production</h2>
<p>Today, primary production is mainly achieved by plants on land and marine micro-organisms such as algae and cyanobacteria. In the past, the proportion of these major contributors was very different; in the case of Earth’s earliest history, primary production was mainly conducted by an entirely different group of organisms that don’t rely on oxygenic photosynthesis to stay alive.</p>
<p>A combination of different techniques has been able to give a sense of when different primary producers were most active in Earth’s past. Examples of such techniques include identifying the <a href="https://doi.org/10.1016/j.cub.2021.07.038">oldest forests</a> or using molecular fossils called <a href="https://doi.org/10.1038/nature23457">biomarkers</a>. </p>
<p>In <a href="https://doi.org/10.1016/j.cub.2023.09.040">our study</a>, we used this information to explore what organisms have contributed the most to Earth’s historical primary production. We found that despite being late on the scene, land plants have likely contributed the most. However, it is also very plausible that cyanobacteria contributed the most.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/567163/original/file-20231221-21-1tcat1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="green hair-like strands of bacteria" src="https://images.theconversation.com/files/567163/original/file-20231221-21-1tcat1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/567163/original/file-20231221-21-1tcat1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/567163/original/file-20231221-21-1tcat1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/567163/original/file-20231221-21-1tcat1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/567163/original/file-20231221-21-1tcat1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=565&fit=crop&dpr=1 754w, https://images.theconversation.com/files/567163/original/file-20231221-21-1tcat1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=565&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/567163/original/file-20231221-21-1tcat1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=565&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Filamentous cyanobacteria from a tidal pond at Little Sippewissett salt marsh, Falmouth, Mass.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/argonne/26719316190">(Argonne National Laboratory)</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">CC BY-NC-SA</a></span>
</figcaption>
</figure>
<h2>Total life</h2>
<p>By determining how much primary production has ever occurred, and by identifying what organisms have been responsible for it, we were also able to estimate how much life has ever been on Earth. </p>
<p>Today, one may be able to approximate how many humans exist based on how much food is consumed. Similarly, we were able to calibrate a ratio of primary production to how many cells exist in the modern environment. </p>
<p>Despite the large variability in the number of cells per organism and the sizes of different cells, such complications become secondary since single-celled microbes dominate global cell populations. In the end, we were able to estimate that about 10<sup>30</sup> (10 noninillion) cells exist today, and that between 10<sup>39</sup> (a duodecillion) and 10<sup>40</sup> cells have ever existed on Earth. </p>
<h2>How much life will Earth ever have?</h2>
<p>Save for the ability to move Earth into the orbit of a younger star, the lifetime of Earth’s biosphere is limited. This morbid fact is a consequence of <a href="https://doi.org/10.1007/978-94-010-9633-1_4">our stars life cycle</a>. Since its birth, the sun has slowly been getting brighter over the past four and half billion years as hydrogen has been converted to helium in its core. </p>
<p>Far in the future, about two billion years from now, all of the biogeochemical fail-safes that keep Earth habitable will be pushed past their <a href="https://doi.org/10.1038/s41561-021-00693-5">limits</a>. First, land plants will die off, and then eventually the oceans will boil, and the Earth will return to a largely lifeless rocky planet as it was in its infancy. </p>
<p>But until then, how much life will Earth house over its entire habitable lifetime? Projecting our current levels of primary productivity forward, we estimated that about 10<sup>40</sup> cells will ever occupy the Earth. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/567209/original/file-20231222-15-cdexst.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="a blue planet in space" src="https://images.theconversation.com/files/567209/original/file-20231222-15-cdexst.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/567209/original/file-20231222-15-cdexst.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/567209/original/file-20231222-15-cdexst.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/567209/original/file-20231222-15-cdexst.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/567209/original/file-20231222-15-cdexst.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/567209/original/file-20231222-15-cdexst.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/567209/original/file-20231222-15-cdexst.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A planetary system 100 light-years away in the constellation Dorado is home to the first Earth-size habitable-zone planet, discovered by NASA’s Transiting Exoplanet Survey Satellite.</span>
<span class="attribution"><a class="source" href="https://images.nasa.gov/details/PIA23408">(NASA Goddard Space Flight Center)</a></span>
</figcaption>
</figure>
<h2>Earth as an exoplanet</h2>
<p>Only a few decades ago, exoplanets (planets orbiting other stars) were just a hypothesis. Now we are able to not only <a href="https://exoplanets.nasa.gov/">detect them</a>, but describe many aspects of thousands of far off worlds around distant stars. </p>
<p>But how does Earth compare to these bodies? In our new study, we have taken a birds eye view of life on Earth and have put forward Earth as a benchmark to compare other planets. </p>
<p>What I find truly interesting, however, is what could have happened in Earth’s past to produce a radically different trajectory and therefore a radically different amount of life that has been able to call Earth home. For example, what if oxygenic photosynthesis never took hold, or what if endosymbiosis never happened?</p>
<p>Answers to such questions are what will drive my laboratory at <a href="https://earthsci.carleton.ca/">Carleton University</a> over the coming years.</p><img src="https://counter.theconversation.com/content/215765/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Peter Crockford receives funding from the Canadian Natural Sciences and Engineering Research Council and Carleton University</span></em></p>Over two billion years from now, Earth will no longer be able to sustain life. A new study looks at how much life has ever existed and what this means for the discovery of new life-supporting planets.Peter Crockford, Assistant Professor, Earth Sciences, Carleton UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2168742024-01-10T13:28:57Z2024-01-10T13:28:57ZEarth isn’t the only planet with seasons, but they can look wildly different on other worlds<figure><img src="https://images.theconversation.com/files/561980/original/file-20231127-27-h9xkjy.jpg?ixlib=rb-1.1.0&rect=0%2C6%2C2055%2C1445&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Nearby planets can affect how one planet 'wobbles' on its spin axis, which contributes to seasons. </span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/orbits-of-planets-in-the-solar-system-royalty-free-illustration/1148112202?phrase=planets+orbit&adppopup=true">Mark Garlick/Science Photo Library via Getty Images</a></span></figcaption></figure><p>Spring, summer, fall and winter – the seasons on Earth change every few months, around the same time every year. It’s easy to take this cycle for granted here on Earth, but not every planet has a regular change in seasons. So why does Earth have regular seasons when other planets don’t? </p>
<p><a href="https://scholar.google.com/citations?user=vxyrNXoAAAAJ&hl=en">I’m an astrophysicist</a> who studies the movement of planets and the causes of seasons. Throughout my research, I’ve found that Earth’s regular pattern of seasons is unique. The <a href="https://theconversation.com/how-the-earths-tilt-creates-short-cold-january-days-173403">rotational axis that Earth spins on</a>, along the North and South poles, <a href="https://en.wikipedia.org/wiki/Axial_tilt">isn’t quite aligned</a> with the vertical axis perpendicular to Earth’s orbit around the Sun. </p>
<p>That slight tilt has big implications for everything from seasons to glacier cycles. The magnitude of that tilt can even determine whether a planet is habitable to life. </p>
<h2>Seasons on Earth</h2>
<p>When a planet has perfect alignment between the axis it orbits on and the rotational axis, the amount of sunlight it receives is fixed as it orbits around the Sun – assuming its orbital shape is a circle. Since seasons come from variations in how much sunlight reaches the planet’s surface, a planet that’s perfectly aligned wouldn’t have seasons. But Earth isn’t perfectly aligned on its axis.</p>
<p>This small misalignment, called an obliquity, is <a href="https://en.wikipedia.org/wiki/Axial_tilt">around 23 degrees</a> from vertical for Earth. So, the Northern Hemisphere experiences more intense sunlight during the summer, when the Sun is positioned more directly above the Northern Hemisphere.</p>
<p>Then, as the Earth continues to orbit around the Sun, the amount of sunlight the Northern Hemisphere receives gradually decreases as the Northern Hemisphere tilts away from the Sun. This causes winter. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/566402/original/file-20231218-21-biar6k.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing the Earth as a blue circle on the left and on the right, with a blue arrow tilted a few degrees towards the right cutting through it, and a green arrow tilted up cutting through it. The angle between the two arrows is red, labeled 'obliquity.' In the middle is a drawing of the Sun." src="https://images.theconversation.com/files/566402/original/file-20231218-21-biar6k.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/566402/original/file-20231218-21-biar6k.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/566402/original/file-20231218-21-biar6k.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/566402/original/file-20231218-21-biar6k.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/566402/original/file-20231218-21-biar6k.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/566402/original/file-20231218-21-biar6k.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/566402/original/file-20231218-21-biar6k.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The obliquity marks the difference between the Earth’s spin axis (blue) and the vertical from orbit (green). The Northern Hemisphere experiences summer when the tilt lines it up directly with light from the Sun.</span>
<span class="attribution"><span class="source">Gongjie Li</span></span>
</figcaption>
</figure>
<p>The planets spinning on their axes and orbiting around the Sun look kind of like spinning tops – they spin around and wobble because of gravitational pull from the Sun. As a top spins, you might notice that it doesn’t just stay perfectly upright and stationary. Instead, it may start to tilt or wobble slightly. This tilt is what astrophysicists call <a href="https://www.britannica.com/science/precession-of-the-equinoxes">spin precession</a>.</p>
<p>Because of these wobbles, Earth’s obliquity isn’t perfectly fixed. These small variations in tilt can have <a href="https://www.jstor.org/stable/1746691">big effects on the Earth’s climate</a> when combined with small changes to Earth’s orbit shape. </p>
<p>The wobbling tilt and any natural variations to the shape of Earth’s orbit can change the amount and distribution of sunlight reaching Earth. These small changes contribute to the planet’s larger temperature shifts over thousands to hundreds of thousands of years. This can, in turn, <a href="https://climate.nasa.gov/news/2948/milankovitch-orbital-cycles-and-their-role-in-earths-climate/">drive ice ages and periods of warmth</a>.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/DD_8Jm5pTLk?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Earth’s seasons result from a variety of factors, including orbit and axial tilt.</span></figcaption>
</figure>
<h2>Translating obliquity into seasons</h2>
<p>So how do obliquity variations affect the seasons on a planet? Low obliquity, meaning the rotational spin axis is aligned with the planet’s orientation as it orbits around the Sun, <a href="https://climate.nasa.gov/news/2948/milankovitch-orbital-cycles-and-their-role-in-earths-climate/">leads to</a> stronger sunlight on the equator and low sunlight near the pole, like on Earth. </p>
<p>On the other hand, a high obliquity – meaning the planet’s rotational spin axis points toward or away from the Sun – <a href="https://climate.nasa.gov/news/2948/milankovitch-orbital-cycles-and-their-role-in-earths-climate/">leads to</a> extremely hot or cold poles. At the same time, the equator gets cold, as the Sun does not shine above the equator all year round. This leads to drastically varying seasons at high latitudes and low temperatures at the equator. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/566405/original/file-20231218-19-pudn6j.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A planet with a reversed zonation is represented by a blue circle next to a drawing of a sun, with a green oval representing the planet's orbit around the sun. A blue arrow pointing towards the sun represents the planet's spin axis, and a green arrow point up represents the planet's orbit direction." src="https://images.theconversation.com/files/566405/original/file-20231218-19-pudn6j.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/566405/original/file-20231218-19-pudn6j.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/566405/original/file-20231218-19-pudn6j.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/566405/original/file-20231218-19-pudn6j.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/566405/original/file-20231218-19-pudn6j.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/566405/original/file-20231218-19-pudn6j.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/566405/original/file-20231218-19-pudn6j.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">When a planet’s spin axis is tilted far from the vertical axis, it has a high obliquity. That means the equator barely gets any sunlight and the North Pole faces right at the Sun.</span>
<span class="attribution"><span class="source">Gongjie Li</span></span>
</figcaption>
</figure>
<p>When a planet has an obliquity of more than 54 degrees, that planet’s equator grows icy and <a href="https://doi.org/10.1016/0012-8252(93)90004-Q">the pole becomes warm</a>. This is called <a href="https://doi.org/10.1016/0012-8252(93)90004-Q">a reversed zonation</a>, and it’s the opposite of what Earth has. </p>
<p>Basically, if an obliquity has large and unpredictable variations, the seasonal variations on the planet become wild and hard to predict. A dramatic, large obliquity variation can turn the whole planet into a snowball, <a href="https://doi.org/10.1093/mnras/stab3179">where it’s all covered by ice</a>. </p>
<h2>Spin orbit resonances</h2>
<p>Most planets are not the only planets in their solar systems. Their planetary siblings can disturb each other’s orbit, which can lead to variations in the shape of their orbits and their orbital tilt. </p>
<p>So, planets in orbit look kind of like tops spinning on the roof of a car that’s bumping down the road, where the car represents the orbital plane. When the rate – or frequency, as scientists call it – at which the tops are precessing, or spinning, matches the frequency at which the car is bumping up and down, something called a <a href="https://doi.org/10.1038/361615a0">spin-orbit resonance</a> occurs.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/561691/original/file-20231126-23-xe830c.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing a planet, shown as a blue circle with an arrow through it representing a tilted, spinning axis, orbiting around the Sun, with another planet's orbit overlapping with it, causing the orbit to tilt up and down." src="https://images.theconversation.com/files/561691/original/file-20231126-23-xe830c.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/561691/original/file-20231126-23-xe830c.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/561691/original/file-20231126-23-xe830c.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/561691/original/file-20231126-23-xe830c.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/561691/original/file-20231126-23-xe830c.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/561691/original/file-20231126-23-xe830c.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/561691/original/file-20231126-23-xe830c.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The orbits of planets close by and the precession motion of a planet on its axis can affect seasonal patterns.</span>
<span class="attribution"><span class="source">Gongjie Li</span></span>
</figcaption>
</figure>
<p>Spin-orbit resonances can cause these obliquity variations, which is when a planet wobbles on its axis. Think about pushing a kid on a swing. When you push at just the right time – or at the resonant frequency – they’ll swing higher and higher.</p>
<p>Mars wobbles more on its axis than Earth does, even though the two are tilted about the same amount, and that actually has to do with the Moon orbiting around Earth. Earth and Mars have a <a href="https://doi.org/10.1038/361608a0">similar spin precession frequency</a>, which matches the orbital oscillation – the ingredients for a spin-orbit resonance. </p>
<p>But Earth has a massive Moon, which pulls on Earth’s spin axis and drives it to precess faster. This slightly faster precession prevents it from experiencing spin orbit resonances. So, the Moon stabilizes Earth’s obliquity, and Earth doesn’t wobble on its axis as much as Mars does. </p>
<h2>Exoplanet seasons</h2>
<p><a href="https://theconversation.com/are-there-any-planets-outside-of-our-solar-system-164062">Thousands of exoplanets</a>, or planets outside our solar system, have been discovered over the past few decades. My research group wanted to understand how habitable these planets are, and whether these exoplanets also have wild obliquities, or whether they have moons to stabilize them like Earth does. </p>
<p>To investigate this, my group has led the first investigation on <a href="https://doi.org/10.3847/1538-3881/aabfd1">the spin-axis variations of exoplanets</a>. </p>
<p>We investigated <a href="https://doi.org/10.3847/1538-3881/aabfd1">Kepler-186f</a>, which is the first discovered Earth-sized planet in a habitable zone. <a href="https://theconversation.com/an-earth-sized-planet-found-in-the-habitable-zone-of-a-nearby-star-129290">The habitable zone</a> is an area around a star where liquid water can exist on the surface of the planet and life may be able to emerge and thrive.</p>
<p>Unlike Earth, Kepler-186f is located far from the other planets in its solar system. As a result, these other planets have only a weak effect on its orbit and movement. So, Kepler-186f generally <a href="https://doi.org/10.3847/1538-3881/aabfd1">has a fixed obliquity</a>, similar to Earth. Even without a large moon, it doesn’t have wildly changing or unpredictable seasons like Mars.</p>
<p>Looking forward, more research into exoplanets will help scientists understand what seasons look like throughout the vast diversity of planets in the universe.</p><img src="https://counter.theconversation.com/content/216874/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Gongjie Li receives funding from NASA.</span></em></p>You might hate winter, but at least you know what to expect every year. Other planets have wobbly axes that lead to wild, unpredictable seasons.Gongjie Li, Assistant Professor of Physics, Georgia Institute of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2179272024-01-02T20:16:49Z2024-01-02T20:16:49ZMeteors, supermoons, a comet and more: your guide to the southern sky in 2024<figure><img src="https://images.theconversation.com/files/560591/original/file-20231121-15-ckqlc.jpg?ixlib=rb-1.1.0&rect=10%2C7%2C1715%2C1140&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Geoffrey Wyatt</span></span></figcaption></figure><p>What exciting events will we see in the southern sky in 2024? Meteor showers, Saturn covered by the Moon, close approaches of bright planets to each other, supermoons – and, if we’re lucky, a comet visible to the naked eye.</p>
<p>Even if you live in a city surrounded by light pollution, these are all worth looking out for. Here are some of the highlights.</p>
<h2>May – the Eta Aquarid meteors</h2>
<p>The first of the two main Southern Hemisphere meteor showers during the year is the <a href="https://science.nasa.gov/solar-system/meteors-meteorites/eta-aquarids/">Eta Aquariid or Eta Aquarid</a> shower. It’s named after a star in the constellation of Aquarius, the Water Carrier, as the meteors appear to originate from there. </p>
<p>Meteors are small particles hitting Earth’s atmosphere and creating a streak of light as they burn up. A meteor shower occurs when many particles hit, all coming from the same direction. </p>
<p>They are generally due to Earth passing through a stream of dust left behind by a comet. For the Eta Aquariids, the comet is the famous Halley’s Comet, which was first recorded more than 2,000 years ago.</p>
<p>In 2024, there will be a good opportunity to see them in the early mornings of Monday 6 and Tuesday 7 May, as the Moon will not be brightening the sky.</p>
<h2>December – the Geminid meteors</h2>
<p>The second of the two main meteor showers is the <a href="https://research.princeton.edu/news/researchers-demystify-unusual-origin-geminids-meteor-shower">Geminid shower</a>. This originates in the direction of the constellation of Gemini, the Twins. </p>
<p>Unusually, they are associated not with a comet but with a rocky asteroid named Phaeton. In 2024, they are likely to be best seen early on the morning of Saturday 14 December. </p>
<p>The peak time to view is during the short interval between the setting of the Moon and the start of dawn.</p>
<h2>March, June and August – the planets</h2>
<p>Celestial objects approaching one another in the sky can provide a nice view. On the evening of Friday 22 March, the brightest planet Venus is less than the width of the Moon away from the ringed planet Saturn. Look low down in the east. </p>
<p>For people in the eastern part of Australia, the Moon covers the planet Saturn low in the eastern sky on the night of Thursday 27 June. The event can be seen by eye, but binoculars or a small telescope would help. </p>
<p>It is safe to take images or video. From Sydney, Saturn disappears at the bright edge of the Moon at 10:55pm and reappears at its dark edge at 11:41pm. The times for Brisbane, Canberra and Melbourne are similar.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/560601/original/file-20231121-19-p42dv2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Diagram showing Saturn disappearing behind the Moon and later reappearing." src="https://images.theconversation.com/files/560601/original/file-20231121-19-p42dv2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/560601/original/file-20231121-19-p42dv2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/560601/original/file-20231121-19-p42dv2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/560601/original/file-20231121-19-p42dv2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/560601/original/file-20231121-19-p42dv2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/560601/original/file-20231121-19-p42dv2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/560601/original/file-20231121-19-p42dv2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The occultation or covering of Saturn on Thursday 27 June 2024.</span>
<span class="attribution"><span class="source">Nick Lomb / Stellarium</span></span>
</figcaption>
</figure>
<p>Another close approach is in the early morning of Thursday 15 August, when the red planet Mars is less than a Moon-width from the giant planet Jupiter.</p>
<h2>September and October – supermoons</h2>
<p>There will be two <a href="https://moon.nasa.gov/moon-in-motion/phases-eclipses-supermoons/supermoons/">supermoons</a> during 2024. The Moon has a path that sometimes takes it further from Earth and sometimes closer. </p>
<p>Recently, a time when the full Moon coincides with the Moon at its closest point to Earth has become known as a supermoon. At this time the Moon is slightly larger in the sky than usual. </p>
<p>It’s best to look at moonrise, as an illusion in our brains makes the Moon appear larger when it’s near the horizon. The supermoons in 2024 are on Wednesday 18 September and Thursday 17 October.</p>
<h2>October – Comet C/2023 A3 (Tsuchinshan-ATLAS)</h2>
<p>Comets visible to the naked eye are rare and exciting events. A comet with the impressive name of <a href="https://theconversation.com/astronomers-just-discovered-a-comet-that-could-be-brighter-than-most-stars-when-we-see-it-next-year-or-will-it-201377">Comet C/2023 A3 (Tsuchinshan-ATLAS)</a>, discovered in January 2023, is approaching the Sun and Earth, and may become bright enough to be easily seen. As yet, it is unknown whether this will happen – comets are notoriously fickle. </p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/astronomers-just-discovered-a-comet-that-could-be-brighter-than-most-stars-when-we-see-it-next-year-or-will-it-201377">Astronomers just discovered a comet that could be brighter than most stars when we see it next year. Or will it?</a>
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<p>At a distance of 71 million kilometres, the comet will be closest to Earth on Sunday 13 October. However, for the next six days a bright Moon will make sighting it unlikely. </p>
<p>By Saturday 19 October, the Moon will have moved out of the way. That evening and the following few evenings will give us the best chance to see it. Look low in the west.</p>
<h2>January and May – constellations</h2>
<p>Not only these highlighted events can be seen in the sky. There are star pictures or constellations that still stand out in the sky of bright cities. </p>
<p><a href="https://universe.nasa.gov/news/147/discovering-the-universe-through-the-constellation-orion/">Orion, the Hunter</a>, is a favourite Southern Hemisphere summer constellation, high in the northern sky on January evenings. It consists of four bright stars in a rectangle with a line of three stars, representing Orion’s belt, in the middle. </p>
<figure class="align-center ">
<img alt="A photo of the constellation Orion." src="https://images.theconversation.com/files/560603/original/file-20231121-23-z23tgd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/560603/original/file-20231121-23-z23tgd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=508&fit=crop&dpr=1 600w, https://images.theconversation.com/files/560603/original/file-20231121-23-z23tgd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=508&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/560603/original/file-20231121-23-z23tgd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=508&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/560603/original/file-20231121-23-z23tgd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=639&fit=crop&dpr=1 754w, https://images.theconversation.com/files/560603/original/file-20231121-23-z23tgd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=639&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/560603/original/file-20231121-23-z23tgd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=639&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The constellation Orion is named for a hunter from Greek myth.</span>
<span class="attribution"><span class="source">Nick Lomb</span></span>
</figcaption>
</figure>
<p>According to Greek legend, Orion was a great hunter who vowed to kill all animals. To stop him carrying out his threat, one of the gods sent a scorpion to kill him. This ancient story with <a href="https://chandra.harvard.edu/photo/constellations/scorpius.html">Scorpius, the Scorpion</a> chasing Orion takes place above our heads each night. </p>
<figure class="align-center ">
<img alt="A photo of the constellation Scorpius." src="https://images.theconversation.com/files/560604/original/file-20231121-4807-rtd2ia.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/560604/original/file-20231121-4807-rtd2ia.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=326&fit=crop&dpr=1 600w, https://images.theconversation.com/files/560604/original/file-20231121-4807-rtd2ia.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=326&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/560604/original/file-20231121-4807-rtd2ia.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=326&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/560604/original/file-20231121-4807-rtd2ia.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=409&fit=crop&dpr=1 754w, https://images.theconversation.com/files/560604/original/file-20231121-4807-rtd2ia.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=409&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/560604/original/file-20231121-4807-rtd2ia.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=409&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The constellation Scorpius is named for its resemblance to a scorpion.</span>
<span class="attribution"><span class="source">Nick Lomb</span></span>
</figcaption>
</figure>
<p>Scorpius is another spectacular constellation with a curved line of bright stars, with a red star forming the creature’s heart. In January, people who are up at around 3 am can see Scorpius rising in the east, while its quarry Orion is sinking in the west. Alternatively, if you don’t like early mornings you can see the same scene on May evenings after dusk.</p>
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<strong>
Read more:
<a href="https://theconversation.com/the-worlds-oldest-story-astronomers-say-global-myths-about-seven-sisters-stars-may-reach-back-100-000-years-151568">The world's oldest story? Astronomers say global myths about 'seven sisters' stars may reach back 100,000 years</a>
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<p><em>The information in this article is from the <a href="https://unsw.press/books/2024-australasian-sky-guide/">2024 Australasian Sky Guide</a>. The guide contains monthly star maps and has much more information to assist with viewing and enjoying the night sky from Australia and New Zealand.</em></p><img src="https://counter.theconversation.com/content/217927/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Nick Lomb received author fees from Powerhouse Publishing for writing the 2024 Australasian Sky Guide.</span></em></p>In 2024 we will see meteor showers, Saturn disappearing behind the Moon, and – if we’re lucky – a comet bright enough to see with the naked eye.Nick Lomb, Honorary Professor, Centre for Astrophysics, University of Southern QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2189212023-12-28T20:38:02Z2023-12-28T20:38:02ZWant to get into stargazing? A professional astronomer explains where to start<p>There are few things more peaceful and relaxing than a night under the stars. Through the holidays, many people head <a href="https://www.lightpollutionmap.info/#zoom=3.80&lat=-28.5041&lon=129.6954&state=eyJiYXNlbWFwIjoiTGF5ZXJCaW5nUm9hZCIsIm92ZXJsYXkiOiJ3YV8yMDE1Iiwib3ZlcmxheWNvbG9yIjpmYWxzZSwib3ZlcmxheW9wYWNpdHkiOjYwLCJmZWF0dXJlc29wYWNpdHkiOjg1fQ==">away from the bright city lights</a> to go camping. They revel in the dark skies, spangled with myriad stars.</p>
<p>As a child, I loved such trips, and they helped cement my passion for the night sky, and for all things space. </p>
<p>One of my great joys as an astronomer is sharing the night sky with people. There is something wondrous about helping people stare at the cosmos through a telescope, getting their first glimpses of the universe’s many wonders. But we can also share and enjoy the night sky just with our own eyes – pointing out the constellations and the planets, or discovering <a href="https://theconversation.com/the-geminids-the-years-best-meteor-shower-is-upon-us-and-this-one-will-be-a-true-spectacle-218923">the joys of watching meteor showers</a>.</p>
<p>It is easy to be bitten by the astronomy bug, and a common question I get asked is “how can I get more into stargazing?”. Here are ways to get started in this fascinating and timeless hobby that won’t break the bank.</p>
<h2>Learning the night sky</h2>
<p>A good place to start if you’re a budding astronomer is to learn your way around the night sky. When I was young, this involved getting hold of a planisphere (a star map, <a href="https://in-the-sky.org/planisphere/index.php">you can make your own here</a>), or a <a href="https://www.amazon.com.au/Turn-Left-Orion-Hundreds-Telescope-ebook/dp/B07H4KN8G2">good reference book</a>. </p>
<p>Today, there are <a href="https://www.space.com/best-stargazing-apps">countless good apps</a> to help you find your way around the night sky. </p>
<p>A great example of such an app is <a href="https://stellarium-web.org/">Stellarium</a> – a planetarium program allowing you to view the night sky from the comfort of your room or to plan an evening’s observing ahead of schedule.</p>
<p>To memorise the night sky, you can try star hopping. Pick out a bright, famous, easy to find constellation, and use it as a guide to help you identify the constellations around it. </p>
<p>Learn one constellation per week, and within a year, you’ll be familiar with most of <a href="https://www.iau.org/public/themes/constellations/">the constellations</a> visible from your location.</p>
<p>Let’s use Orion as an example. The slider below shows images from Stellarium, with Orion riding high in the sky on a summer’s evening. I’ve added arrows to show how you can use Orion (shown in the centre of the map below) to hop around the summer sky.</p>
<p><iframe id="tc-infographic-1007" class="tc-infographic" height="400px" src="https://cdn.theconversation.com/infographics/1007/811d84689c71ac5c004a402a84a7fb446f0ae803/site/index.html" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>To learn the constellations around Orion, your task is relatively straightforward. Head out on a clear, dark summer’s night, and find Orion high to the north. The three stars of Orion’s belt are a fantastic signpost to Orion’s neighbours. </p>
<p>If you follow the line of the belt upwards and to the right, you come to <a href="https://en.wikipedia.org/wiki/Sirius">Sirius</a> – the brightest star in the night sky, and the brightest star in <a href="https://en.wikipedia.org/wiki/Canis_Major">Canis Major</a>, the big hunting dog. Carry the line on and curve to the left as you go, and you’ll find <a href="https://en.wikipedia.org/wiki/Canopus">Canopus</a>, the second brightest star in the sky.</p>
<p>Now come back to Orion’s belt, and follow its line down and to the left. You’ll come to a V-shaped group of stars, including the bright red <a href="https://en.wikipedia.org/wiki/Aldebaran">Aldebaran</a>. This is the <a href="https://en.wikipedia.org/wiki/Hyades_(star_cluster)">Hyades star cluster</a> (with Aldebaran a foreground interloper), which makes up the head of <a href="https://en.wikipedia.org/wiki/Taurus_(constellation)">Taurus</a>, the bull.</p>
<p>Take the line further, and you come to <a href="https://www.space.com/pleiades.html">the Pleiades</a> – often known as the Seven Sisters – a beautiful star cluster easily visible to the naked eye.</p>
<p>Back to Orion again. This time, you’re going to draw a line from <a href="https://en.wikipedia.org/wiki/Rigel">Rigel</a> (the bright star at the top-left of Orion’s boxy body) through <a href="https://en.wikipedia.org/wiki/Betelgeuse">Betelgeuse</a> (the bright red star at the lower-right of the box) and continue it towards the horizon. This takes you to <a href="https://en.wikipedia.org/wiki/Gemini_(constellation)">Gemini</a> – the twins.</p>
<p>Just by using Orion as the signpost, you can find your way to a good number of constellations (the cyan line points to <a href="https://en.wikipedia.org/wiki/Lepus_(constellation)">Lepus</a>, the hare; the white line to <a href="https://en.wikipedia.org/wiki/Canis_Minor">Canis Minor</a>, the little hunting dog). </p>
<p>By star hopping, you’ll slowly but surely learn your way around the night sky until the constellations become familiar friends.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/kindred-skies-ancient-greeks-and-aboriginal-australians-saw-constellations-in-common-74850">Kindred skies: ancient Greeks and Aboriginal Australians saw constellations in common</a>
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<h2>Virtual observing</h2>
<p>Looking at the sky with the naked eye is a wonderful thing, but it’s also great to zoom in and see more detail.</p>
<p>What if you don’t have access to binoculars or a telescope of your own? Thankfully, software like Stellarium can give you a fantastic virtual observing experience.</p>
<p>Imagine you want to see Saturn’s rings – a spectacular sight through even a small telescope. You can easily do this with Stellarium. Find Saturn by using the search bar and click on it to bring up the planet’s info. </p>
<p>Click on the cross-hair symbol to “lock on”, then zoom in. The further you zoom in, the more you’ll see. You can even run the clock forwards or backwards to see the planet’s moons move in their orbits, or the tilt of Saturn’s rings <a href="https://theconversation.com/will-saturns-rings-really-disappear-by-2025-an-astronomer-explains-217370">changing from our viewpoint over time</a>.</p>
<p>A virtual observing session is as simple as that – just pan around the sky until you find something you want to see, and zoom in.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/564091/original/file-20231207-17-qvar43.gif?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A close up of rotating Saturn" src="https://images.theconversation.com/files/564091/original/file-20231207-17-qvar43.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/564091/original/file-20231207-17-qvar43.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=437&fit=crop&dpr=1 600w, https://images.theconversation.com/files/564091/original/file-20231207-17-qvar43.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=437&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/564091/original/file-20231207-17-qvar43.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=437&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/564091/original/file-20231207-17-qvar43.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=549&fit=crop&dpr=1 754w, https://images.theconversation.com/files/564091/original/file-20231207-17-qvar43.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=549&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/564091/original/file-20231207-17-qvar43.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=549&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Example of using the clock feature in Stellarium to see the movement of Saturn’s moons.</span>
<span class="attribution"><span class="source">Stellarium</span></span>
</figcaption>
</figure>
<h2>A hobby best shared</h2>
<p>Now, a virtual observing session is great, but it pales compared to the real thing. I’d recommend using planetarium programs like Stellarium to figure out what you want to see, then heading out to look at it with your own eyes.</p>
<p>Astronomy is a wonderful hobby, and one that is best shared. Most towns and cities have their own astronomy clubs, and they’re usually more than happy to welcome guests who want to gaze at the night sky. </p>
<p>I joined my local astronomy society, the <a href="https://www.wyas.org.uk/">West Yorkshire Astronomical Society</a> in the United Kingdom, when I was just eight years old. I owe them so much. The members were incredibly supportive of a young kid with so many questions, and I genuinely believe I would not be where I am today without their help. As a member, I saw firsthand just how fantastic the amateur astronomy community is. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/562685/original/file-20231130-29-ogkxpc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A telescope inside a dome during daytime, with a young teen and two older men standing next to it" src="https://images.theconversation.com/files/562685/original/file-20231130-29-ogkxpc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/562685/original/file-20231130-29-ogkxpc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=438&fit=crop&dpr=1 600w, https://images.theconversation.com/files/562685/original/file-20231130-29-ogkxpc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=438&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/562685/original/file-20231130-29-ogkxpc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=438&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/562685/original/file-20231130-29-ogkxpc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=550&fit=crop&dpr=1 754w, https://images.theconversation.com/files/562685/original/file-20231130-29-ogkxpc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=550&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/562685/original/file-20231130-29-ogkxpc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=550&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">The author Jonti Horner at age 16, showing then Astronomer Royal of the UK, Arnold Wolfendale (right), the WYAS 18-inch telescope, hand-made by members. Also seen is the society’s then president, Ken Willoughby.</span>
<span class="attribution"><span class="source">Alan Horner, author provided</span></span>
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<p>At the society, we had weekly talks on astronomy, given by the club members and visiting astronomers from local universities. We also had regular night sky viewing nights, using the society’s very own telescope – a behemoth the members had built themselves. </p>
<p>People who are passionate about their hobby love nothing more than sharing it with others. The members of astronomical societies are fantastic guides to the night sky, and they often have incredible equipment they’re more than happy to share with you.</p>
<p>Both astronomy clubs and universities often offer public night sky viewing nights, which are the perfect opportunity to peer at the sky through a telescope, with an experienced guide on hand to find the most impressive sights to share. </p>
<p>So, if you want to learn more about the night sky, reach out to your local astronomy society – it could be the start of something very special.</p>
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Read more:
<a href="https://theconversation.com/want-to-buy-a-home-telescope-tips-from-a-professional-astronomer-to-help-you-choose-218604">Want to buy a home telescope? Tips from a professional astronomer to help you choose</a>
</strong>
</em>
</p>
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<p><em>If you want to find a local astronomy group, check out <a href="https://astronomy.org.au/amateur/amateur-societies/australia/">this list</a>. If you’re a member of a group that isn’t listed, please reach out to get them to update the list using the ‘Contact Us’ link.</em></p><img src="https://counter.theconversation.com/content/218921/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jonti Horner 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>People have been looking up at the stars for thousands of years. Here’s where to start if you want to learn more about the night sky – from spotting easy-to-find constellations to using the best apps.Jonti Horner, Professor (Astrophysics), University of Southern QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2178852023-12-04T13:25:52Z2023-12-04T13:25:52ZWhy isn’t there any sound in space? An astronomer explains why in space no one can hear you scream<figure><img src="https://images.theconversation.com/files/560865/original/file-20231121-23-g49y80.png?ixlib=rb-1.1.0&rect=0%2C5%2C1957%2C1992&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Matter in deep space is very spread out, which makes it impossible for any sound waves to travel. </span> <span class="attribution"><a class="source" href="https://webbtelescope.org/contents/media/images/2022/038/01G7JGTH21B5GN9VCYAHBXKSD1?news=true">NASA, ESA, CSA, STScI</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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<blockquote>
<p><strong>How far can sound travel through space, since it’s so empty? Is there an echo in space? – Jasmine, age 14, Everson, Washington</strong></p>
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<p>In space, no one can hear you scream.</p>
<p>You may have heard this saying. It’s the tagline from the famous 1979 science fiction movie “<a href="https://screenrant.com/space-no-one-hear-scream-alien-movie-origin/">Alien</a>.” It’s a scary thought, but is it true? The simple answer is yes, no one can hear you scream in space because there is no sound or echo in space.</p>
<p>I’m a <a href="https://scholar.google.com/citations?user=OrRLRQ4AAAAJ&hl=en">professor of astronomy</a>, which means I study space and how it works. Space is silent – for the most part.</p>
<h2>How sound works</h2>
<p>To understand why there’s no sound in space, first consider how sound works. <a href="https://www.scienceworld.ca/resource/sound/">Sound is a wave</a> of energy that moves through a solid, a liquid or a gas. </p>
<p>Sound is <a href="https://www.britannica.com/science/longitudinal-wave">a compression wave</a>. The energy created when your vocal cords vibrate slightly compresses the air in your throat, and the compressed energy travels outward. </p>
<p>A good analogy for sound is a <a href="https://www.scienceworld.ca/resource/modelling-sound-wave/">Slinky toy</a>. If you stretch out a Slinky and push hard on one end, a <a href="https://www.youtube.com/watch?v=GKzpVUUrwM8">compression wave travels</a> down the Slinky.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/fMJrtheQfZw?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Slinky toys can demonstrate how sound waves, a type of compression wave, work.</span></figcaption>
</figure>
<p>When you talk, your vocal cords vibrate. They jostle air molecules in your throat above your vocal cords, which in turn jostle or bump into their neighbors, causing a sound to come out of your mouth. </p>
<p>Sound moves through air the same way it moves through your throat. Air molecules near your mouth bump into their neighbors, which in turn bump into their neighbors, and the sound moves through the air. The <a href="https://www.grc.nasa.gov/www/k-12/BGP/sound.html">sound wave travels quickly</a>, about 760 miles per hour (1,223 kilometers per hour), which is faster than a commercial jet.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/sQZtKAPv7lI?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Sound waves are created when matter vibrates.</span></figcaption>
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<h2>Space is a vacuum</h2>
<p>So what about in space?</p>
<p>Space is a vacuum, which means it contains almost no matter. The word vacuum <a href="https://www.etymonline.com/word/vacuum">comes from the Latin word for empty</a>.</p>
<p>Sound is carried by atoms and molecules. In space, with no atoms or molecules to carry a sound wave, there’s no sound. There’s nothing to get in sound’s way out in space, but there’s nothing to carry it, so it doesn’t travel at all. No sound also means no echo. <a href="https://theconversation.com/curious-kids-what-makes-an-echo-109141">An echo</a> happens when a sound wave hits a hard, flat surface and bounces back in the direction it came from.</p>
<p>By the way, if you were caught in space outside your spacecraft with no spacesuit, the fact that no one could hear your cry for help is the least of your problems. Any air you still had in your lungs would expand because it was at higher pressure than the vacuum outside. Your lungs would rupture. In a mere <a href="https://www.space.com/how-long-could-you-survive-in-space-without-spacesuit">10 to 15 seconds</a>, you’d be unconscious due to a lack of oxygen. </p>
<h2>Sound in the solar system</h2>
<p>Scientists have wondered how human voices would sound on our nearest neighboring planets, Venus and Mars. This experiment is hypothetical because <a href="https://www.space.com/16907-what-is-the-temperature-of-mars.html">Mars is usually below freezing</a>, and its atmosphere is <a href="https://science.nasa.gov/mars/facts/">thin, unbreathable carbon dioxide</a>. <a href="https://science.nasa.gov/venus/facts/">Venus is even worse</a> – its air is hot enough to melt lead, with a thick carbon dioxide atmosphere.</p>
<p>On Mars, your voice would sound tinny and hollow, like the <a href="https://www.youtube.com/watch?v=cE26bD_-hN4">sound of a piccolo</a>. <a href="https://www.nbcnews.com/science/cosmic-log/how-would-you-sound-mars-flna659387">On Venus</a>, the pitch of your voice would be much deeper, like the sound of a booming bass guitar. The reason is the thickness of the atmosphere. On Mars the thin air creates a high-pitched sound, and on Venus the thick air creates a low-pitched sound. The team that worked this out <a href="https://www.southampton.ac.uk/news/2012/04/the-sounds-of-mars-and-venus.page">simulated other solar system sounds</a>, like a waterfall on Saturn’s moon Titan.</p>
<h2>Deep space sounds</h2>
<p>While space is a good enough vacuum that normal sound can’t travel through it, it’s actually not a perfect vacuum, and it does have some particles floating through it.</p>
<p><a href="https://www.universetoday.com/34074/interplanetary-space/">Beyond the Earth</a> and its atmosphere, there are five particles in a typical cubic centimeter – the volume of a sugar cube – that are mostly hydrogen atoms. By contrast, the air you are breathing is 10 billion billion (10<sup>19)</sup> times more dense. The density goes down with distance from the Sun, and in <a href="https://www.space.com/interstellar-space-definition-explanation">the space between stars</a> there are 0.1 particles per cubic centimeter. In vast <a href="https://www.livescience.com/why-is-space-a-vacuum.html">voids between galaxies</a>, it is a million times lower still – fantastically empty.</p>
<p>The voids of space are kept very hot by radiation from stars. The very spread-out matter found there is in a physical state <a href="https://www.psfc.mit.edu/vision/what_is_plasma">called a plasma</a>. </p>
<p>A plasma is a gas in which electrons are separated from protons. In a plasma, the <a href="https://www.iflscience.com/is-there-really-no-sound-in-space-69612">physics of sound waves get complicated</a>. Waves travel much faster in this low-density medium, and their wavelength is much longer.</p>
<p>In 2022, NASA released a <a href="https://www.vice.com/en/article/y3p3dv/nasa-has-captured-actual-sound-in-space-and-its-honestly-terrifying">spectacular example of sound in space</a>. It used X-ray data to make an audible recording that represents the way a massive black hole stirs up plasma in the Perseus galaxy cluster, 250 million light years from Earth. The black hole itself emits no sound, but the diffuse plasma around it carries very long wavelength sound waves.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1561442514078314496"}"></div></p>
<p>The natural sound is far too low a frequency for the human ear to hear, 57 octaves below middle C, which is the middle note on a piano and in the middle of the range of sound people can hear. But after raising the frequency to the audible range, the result is chilling – it’s the sound of a black hole growling in deep space.</p>
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<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:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/217885/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Impey receives funding from the National Science Foundation. </span></em></p>Sound needs matter to propagate, so the vast vacuum of space is not just empty − it’s silent.Chris Impey, University Distinguished Professor of Astronomy, University of ArizonaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2178612023-11-30T19:06:13Z2023-11-30T19:06:13ZMassive planet too big for its own sun pushes astronomers to rethink exoplanet formation<figure><img src="https://images.theconversation.com/files/562186/original/file-20231128-23-oz4tck.jpg?ixlib=rb-1.1.0&rect=0%2C8%2C1997%2C1488&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">LHS 3154b, a newly discovered massive planet that should be too big to exist. </span> <span class="attribution"><span class="source">The Pennsylvania State University</span></span></figcaption></figure><p>Imagine you’re a farmer searching for eggs in the chicken coop – but instead of a chicken egg, you find an ostrich egg, much larger than anything a chicken could lay.</p>
<p>That’s a little how <a href="https://scholar.google.com/citations?user=cSnTlM4AAAAJ&hl=en">our team</a> <a href="https://scholar.google.com/citations?user=lN5yvjMAAAAJ&hl=en">of astronomers</a> <a href="https://science.psu.edu/astrp/people/mmd6393">felt when we</a> <a href="https://doi.org/10.1126/science.abo0233">discovered a massive planet</a>, more than 13 times heavier than Earth, around a cool, dim red star, nine times less massive than Earth’s Sun, in 2023. </p>
<p>The smaller star, called an M star, is not only smaller than the Sun in Earth’s solar system, but it’s 100 times less luminous. Such a star should not have the necessary amount of material in its planet-forming disk to birth such a massive planet.</p>
<h2>The Habitable Zone Planet Finder</h2>
<p>Over the past decade, our team designed and built a new instrument at Penn State capable of detecting the light from these dim, cool stars at wavelengths beyond the sensitivity of the human eye – in the near-infrared – where such cool stars <a href="https://www.e-education.psu.edu/astro801/book/export/html/1755">emit most of their light</a>. </p>
<p>Attached to the 10-meter Hobby-Eberly Telescope in West Texas, our instrument, dubbed the <a href="https://hpf.psu.edu/">Habitable Zone Planet Finder</a>, can measure the subtle change in a star’s velocity as a planet gravitationally tugs on it. This technique, called the Doppler radial velocity technique, is <a href="https://theconversation.com/rarity-of-jupiter-like-planets-means-planetary-systems-exactly-like-ours-may-be-scarce-52116">great for detecting exoplanets</a>. </p>
<p>“<a href="https://exoplanets.nasa.gov/">Exoplanet</a>” is a combination of the words extrasolar and planet, so the term applies to any planet-sized body in orbit around a star that isn’t Earth’s Sun.</p>
<p>Thirty years ago, Doppler radial velocity observations enabled the discovery of <a href="https://exoplanets.nasa.gov/exoplanet-catalog/7001/51-pegasi-b/">51 Pegasi b</a>, the first known exoplanet orbiting a Sunlike star. In the ensuing decades, astronomers like us have improved this technique. These <a href="https://noirlab.edu/public/projects/neid/">increasingly more precise</a> measurements have an important goal: to enable the discovery of rocky planets in <a href="https://exoplanets.nasa.gov/search-for-life/habitable-zone/">habitable zones</a>, the regions around stars where liquid water can be sustained on the planetary surface. </p>
<p>The Doppler technique doesn’t yet have the capabilities to discover habitable zone planets the mass of the Earth around stars the size of the Sun. But the cool and dim M stars show a larger Doppler signature for the same Earth-size planet. The lower mass of the star leads to it getting tugged more by the orbiting planet. And the lower luminosity leads to a <a href="https://exoplanets.nasa.gov/resources/2255/what-is-the-habitable-zone/">closer-in habitable zone</a> and a shorter orbit, which also makes the planet easier to detect. </p>
<p>Planets around these smaller stars were the planets our team designed the Habitable Zone Planet Finder to discover. Our new discovery, <a href="https://doi.org/10.1126/science.abo0233">published in the journal Science</a>, of a massive planet orbiting closely around the cool dim M star LHS 3154 – the ostrich egg in the chicken coop – came as a real surprise.</p>
<h2>LHS 3154b: The planet that should not exist</h2>
<p><a href="https://theconversation.com/astronomers-have-learned-lots-about-the-universe-but-how-do-they-study-astronomical-objects-too-distant-to-visit-214320">Planets form in disks</a> composed of gas and dust. These disks pull together dust grains that grow into pebbles and eventually combine to form a solid planetary core. Once the core is formed, the planet can gravitationally pull in the solid dust, as well as surrounding gas such as hydrogen and helium. But it needs a lot of mass and materials to do this successfully. This way to form planets is called <a href="https://earthhow.com/planet-formation/">core accretion</a>.</p>
<p>A star as low mass as LHS 3154, nine times less massive than the Sun, should have a correspondingly low-mass planet forming disk. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/eSdZR4zT_UM?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">An artist’s rendering of LHS 3154b. Video Credit: Abby Minnich.</span></figcaption>
</figure>
<p>A typical disk around such a low-mass star should simply not have enough solid materials or mass to be able to make a core heavy enough to create such a planet. From computer simulations our team conducted, we concluded that such a planet needs a disk at least 10 times more massive than typically assumed <a href="https://doi.org/10.48550/arXiv.1608.03621">from direct observations of planet-forming disks</a>.</p>
<p>A different planet formation theory, <a href="https://astrobites.org/2011/02/28/planet-formation-at-wide-orbits-through-gravitational-instability/">gravitational instability</a> – where gas and dust in the disk undergo a direct collapse to form a planet – also struggles to explain the formation of such a planet without a very massive disk.</p>
<iframe src="https://flo.uri.sh/visualisation/15761207/embed" title="Interactive or visual content" class="flourish-embed-iframe" frameborder="0" scrolling="no" style="width:100%;height:600px;" sandbox="allow-same-origin allow-forms allow-scripts allow-downloads allow-popups allow-popups-to-escape-sandbox allow-top-navigation-by-user-activation" width="100%" height="400"></iframe>
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<h2>Planets around the most common stars</h2>
<p>Cool, dim M stars are <a href="https://www.stsci.edu/contents/newsletters/2020-volume-37-issue-01/how-well-do-we-understand-m-dwarfs">the most common stars in our galaxy</a>. In DC comics lore, <a href="https://theconversation.com/how-astronomers-could-find-the-real-planet-krypton-56646">Superman’s home world</a>, <a href="https://www.theguardian.com/culture/us-news-blog/2012/nov/05/neil-degrasse-tyson-superman-planet">planet Krypton, orbited an M dwarf star</a>. </p>
<p>Astronomers know, from discoveries made with Habitable Zone Planet Finder and other instruments, that giant planets in close-in orbits around the most massive M stars are <a href="https://doi.org/10.48550/arXiv.2303.00659">at least 10 times rarer</a> than those around Sunlike stars. And we know of no such massive planets in close orbits around the least massive M stars – until the discovery of LHS 3154b. </p>
<p>Understanding how planets form around our coolest neighbors will help us understand both how planets form in general and how rocky worlds around the most numerous types of stars form and evolve. This line of research could also help astronomers understand whether M stars are capable of supporting life.</p><img src="https://counter.theconversation.com/content/217861/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Suvrath Mahadevan receives external funding from NSF, NASA, and the Heising-Simons Foundation, as well as research funding and support from Penn State.
</span></em></p><p class="fine-print"><em><span>Guðmundur Kári Stefánsson receives funding from NSF, NASA and the Heising-Simons Foundation.</span></em></p><p class="fine-print"><em><span>Megan Delamer receives funding from NSF, NASA, and Heising-Simons Foundation. </span></em></p>A newly discovered planet that should be too big to have formed around a tiny star is throwing into question what researchers know about planet formation.Suvrath Mahadevan, Verne M. Willaman Professor of Astronomy & Astrophysics, Penn StateGuðmundur Kári Stefánsson, NASA Hubble Fellow, Department of Astrophysical Sciences, Princeton UniversityMegan Delamer, Graduate Student, Department of Astronomy, Penn StateLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2162312023-11-27T13:40:39Z2023-11-27T13:40:39ZEarth’s magnetic field protects life on Earth from radiation, but it can move, and the magnetic poles can even flip<figure><img src="https://images.theconversation.com/files/559181/original/file-20231113-23-84pk4b.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C5167%2C3387&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Earth's magnetic field deflects particles emitted by the Sun.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/earths-magnetosphere-illustration-royalty-free-illustration/1316974949?phrase=earth+magnetosphere&adppopup=true">Mark Garlick/Science Photo Library via Getty Images</a></span></figcaption></figure><p>The Earth’s magnetic field plays a big role in protecting people from hazardous radiation and geomagnetic activity that could affect satellite communication and the operation of power grids. And it moves. </p>
<p>Scientists have studied and tracked the motion of the magnetic poles <a href="https://www.ncei.noaa.gov/products/wandering-geomagnetic-poles">for centuries</a>. The historical movement of these poles indicates a <a href="https://theconversation.com/old-stone-walls-record-the-changing-location-of-magnetic-north-112827">change in the global geometry</a> of the Earth’s magnetic field. It may even indicate the beginning of a field reversal – a “flip” between the north and south magnetic poles. </p>
<p><a href="https://www.uml.edu/research/locsst/about/faculty-staff/cohen-ofer.aspx">I’m a physicist</a> who studies the interaction between the planets and space. While the north magnetic pole moving a little bit isn’t a big deal, a reversal could have a big impact on Earth’s climate and our modern technology. But these reversals don’t happen instantaneously. Instead, they occur <a href="https://theconversation.com/does-an-anomaly-in-the-earths-magnetic-field-portend-a-coming-pole-reversal-47528">over thousands of years</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/557124/original/file-20231101-17-7nf5ns.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A map showing the north part of Canada, with yellow dots moving southwards." src="https://images.theconversation.com/files/557124/original/file-20231101-17-7nf5ns.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/557124/original/file-20231101-17-7nf5ns.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=316&fit=crop&dpr=1 600w, https://images.theconversation.com/files/557124/original/file-20231101-17-7nf5ns.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=316&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/557124/original/file-20231101-17-7nf5ns.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=316&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/557124/original/file-20231101-17-7nf5ns.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=397&fit=crop&dpr=1 754w, https://images.theconversation.com/files/557124/original/file-20231101-17-7nf5ns.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=397&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/557124/original/file-20231101-17-7nf5ns.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=397&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The north magnetic pole’s observed locations from 1831–2007 are yellow squares. Modeled pole locations from 1590–2025 are circles progressing from blue to yellow.</span>
<span class="attribution"><a class="source" href="https://www.ncei.noaa.gov/products/wandering-geomagnetic-poles">National Centers for Environmental Information</a></span>
</figcaption>
</figure>
<h2>Magnetic field generation</h2>
<p>So how are magnetic fields like the one around Earth generated?</p>
<p>Magnetic fields are generated by <a href="https://www.youtube.com/watch?v=PgM8zWJr8-U">moving electric charges</a>. A material that enables charges to easily move in it is <a href="https://en.wikipedia.org/wiki/Electrical_conductor">called a conductor</a>. Metal is one example of a conductor – people use it to transfer electric currents from one place to the other. The electric current itself is simply negative charges called electrons moving through the metal. This current <a href="https://www.youtube.com/watch?v=XoVW7CRR5JY">generates a magnetic field</a>. </p>
<p>Layers of conducting material can be found in the <a href="https://www.youtube.com/watch?v=4WILyDlmln8">Earth’s liquid iron core</a>. Currents of charges move throughout the core, and the liquid iron is also moving and circulating in the core. These movements generate the magnetic field. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/MtLC8evycaE?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Earth’s magnetic field is generated by what’s called a “dynamo effect.”</span></figcaption>
</figure>
<p>Earth isn’t the only planet with a magnetic field – gas giant planets like Jupiter have a <a href="https://doi.org/10.1038/s41586-018-0468-5">conducting metallic hydrogen layer</a> that generates their magnetic fields. </p>
<p>The <a href="https://iopscience.iop.org/article/10.1088/1361-6404/ab8780/pdf">movement of these conducting layers</a> inside planets results in two types of fields. Larger motions, such as large-scale rotations with the planet, lead to a symmetric magnetic field with a north and a south pole – similar to a toy magnet. </p>
<p>These conducting layers may have some local irregular motions due to <a href="https://www.youtube.com/watch?v=bw_WC-EVs_g">local turbulence</a> or smaller flows that do not follow the large-scale pattern. These irregularities will manifest in some small anomalies in the planet’s magnetic field or places where the field deviates from being a perfect dipole field. </p>
<p>These small-scale deviations in the magnetic field can actually <a href="https://www.youtube.com/watch?v=I3zFeV24or8">lead to changes</a> in the large-scale field over time and potentially even a complete reversal of the polarity of the dipole field, where the north becomes south and vice versa. The designations of “north” and “south” on the magnetic field refer to their opposite polarities – they’re not related to geographic north and south. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/559180/original/file-20231113-26-sdwidj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing the Earth, with two blocks on the inside, one pointing upward that says S and one pointing downward that says N, labeled South Magnetic pole and North magnetic pole, respectively. A slightly tilted line depicts the Earth's rotation axis." src="https://images.theconversation.com/files/559180/original/file-20231113-26-sdwidj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/559180/original/file-20231113-26-sdwidj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/559180/original/file-20231113-26-sdwidj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/559180/original/file-20231113-26-sdwidj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/559180/original/file-20231113-26-sdwidj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/559180/original/file-20231113-26-sdwidj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/559180/original/file-20231113-26-sdwidj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Earth’s magnetic field. The north and south magnetic poles mirror the geographic North and South poles.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/geomagnetic-field-planet-earth-royalty-free-illustration/470258936?phrase=earth+magnetosphere&adppopup=true">PeterHermesFurian/iStock via Getty Images Plus</a></span>
</figcaption>
</figure>
<h2>The Earth’s magnetosphere, a protective bubble</h2>
<p>The Earth’s magnetic field creates a magnetic “bubble” called the <a href="https://science.nasa.gov/heliophysics/focus-areas/magnetosphere-ionosphere">magnetosphere</a> above the uppermost part of the atmosphere, <a href="https://en.wikipedia.org/wiki/Ionosphere">the ionosphere layer</a>.</p>
<p>The magnetosphere plays a major role in protecting people. It shields and deflects damaging, high-energy, <a href="https://www.youtube.com/watch?v=KbZbfJjiil4">cosmic-ray radiation</a>, which is created in star explosions and moves constantly through the universe. The magnetosphere also interacts with <a href="https://en.wikipedia.org/wiki/Solar_wind">solar wind</a>, which is a flow of magnetized gas sent out from the Sun.</p>
<p>The magnetosphere and ionosphere’s interaction with magnetized solar wind creates what scientists call <a href="https://spaceplace.nasa.gov/spaceweather/en/">space weather</a>. Usually, the solar wind is mild and there’s little to no space weather. </p>
<p>However, there are times when the Sun sheds large magnetized clouds of gas called <a href="https://nso.edu/for-public/sun-science/coronal-mass-ejections-cme/">coronal mass ejections</a> into space. If these coronal mass ejections make it to Earth, their interaction with the magnetosphere can generate <a href="https://www.swpc.noaa.gov/phenomena/geomagnetic-storms">geomagnetic storms</a>. Geomagnetic storms <a href="https://www.swpc.noaa.gov/phenomena/aurora">can create auroras</a>, which happen when a stream of energized particles hits the atmosphere and lights up. </p>
<p>During space weather events, there’s <a href="https://theconversation.com/solar-storms-can-destroy-satellites-with-ease-a-space-weather-expert-explains-the-science-177510">more hazardous radiation</a> near the Earth. This radiation can <a href="https://www.youtube.com/watch?v=MEd2pvyRpfw">potentially harm satellites</a> and astronauts. Space weather can also damage large conducting systems, such as major pipelines and power grids, by overloading <a href="https://www.swpc.noaa.gov/impacts/electric-power-transmission">currents in these systems</a>. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/URN-XyZD2vQ?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Earth’s magnetosphere protects life on Earth from ejections from the Sun.</span></figcaption>
</figure>
<p>Space weather events can also disrupt satellite communication and <a href="https://www.swpc.noaa.gov/impacts/space-weather-and-gps-systems">GPS operation</a>, which many people rely on. </p>
<h2>Field flips</h2>
<p>Scientists map and track the overall <a href="https://www.ncei.noaa.gov">shape and orientation</a> of the Earth’s magnetic field using local measurements of the field’s orientation and magnitude and, <a href="http://doi.org/10.1098/rsta.2000.0569">more recently, models</a>. </p>
<p>The location of the north magnetic pole <a href="https://royalsocietypublishing.org/doi/10.1098/rsta.2000.0569">has moved</a> by about 600 miles (965 kilometers) since the first measurement was taken in 1831. The migration speed has increased from 10 miles per year to 34 miles per year (16 km to 54 km) in more recent years. This acceleration could indicate the beginning of a field reversal, but scientists really can’t tell with less than 200 years of data.</p>
<p>The Earth’s magnetic field reverses on time scales that vary between <a href="https://pubs.usgs.gov/of/2003/of03-187/of03-187.pdf">100,000 to 1,000,000 years</a>. Scientists can tell how often the magnetic field reverses by <a href="https://eos.org/research-spotlights/steadying-mid-ocean-ridge-spreading-rates">looking at volcanic rocks</a> in the ocean. </p>
<p>These rocks <a href="https://www.youtube.com/watch?v=4WILyDlmln8">capture the orientation and strength</a> of the Earth’s magnetic field when they are created, so dating these rocks provides a good picture of how the Earth’s field has <a href="https://eos.org/research-spotlights/steadying-mid-ocean-ridge-spreading-rates">evolved over time</a>.</p>
<p>Field reversals happen fast from a geologic standpoint, though slow from a human perspective. A reversal usually takes a few thousand years, but during this time the magnetosphere’s orientation may shift and <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2010JA016036">expose more of the Earth</a> to cosmic radiation. These events may <a href="https://doi.org/10.1126/science.abb8677">change the concentration of ozone</a> in the atmosphere. </p>
<p>Scientists can’t tell with confidence when the next field reversal will happen, but we can keep mapping and tracking the movement of Earth’s magnetic north.</p><img src="https://counter.theconversation.com/content/216231/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ofer Cohen works for the University of Massachusetts Lowell. The university benefits from any public article that is written by one of its faculty in terms of exposure and visibility. Ofer Cohen received NASA funding that is somehow related to the article. </span></em></p>Ever seen the northern lights? You have a magnetic layer in Earth’s atmosphere to thank for those beautiful displays. But the magnetosphere does a lot more than create auroras.Ofer Cohen, Associate Professor of Physics and Applied Physics, UMass LowellLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2175652023-11-20T14:37:39Z2023-11-20T14:37:39ZLibyan desert’s yellow glass: how we discovered the origin of these rare and mysterious shards<figure><img src="https://images.theconversation.com/files/559038/original/file-20231113-25-wg8y9j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The pieces of Libyan desert glass that formed the basis of the study.</span> <span class="attribution"><span class="license">Author provided</span></span></figcaption></figure><p>The <a href="https://www.lonelyplanet.com/egypt/western-desert/attractions/great-sand-sea/a/poi-sig/1500963/355269">Great Sand Sea Desert</a> stretches over an area of 72,000km² linking Egypt and Libya. If you find yourself in a particular part of the desert in south-east Libya and south-western parts of Egypt, you’ll spot pieces of yellow glass scattered across the sandy landscape. </p>
<p>It was first described in <a href="http://www.qattara.it/DESERTO%20EGIZIANO_FILES/silica.pdf">a scientific paper in 1933</a> and is known as <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/libyan-desert">Libyan desert glass</a>. Mineral collectors value it for its beauty, its relative rarity – and its mystery. A pendant found in Egyptian pharaoh Tutankhamun’s tomb <a href="https://egypt-museum.com/winged-scarab-pendant-of-tutankhamun/">contains a piece of the glass</a>. Natural glasses are found elsewhere in the world; examples include moldavites from the Ries crater in Europe and <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/tektite">tektites from the Ivory Coast</a>. But none are as rich in silica as Libyan desert glass, nor are they found in such large lumps and quantities.</p>
<iframe title="" aria-label="Locator maps" id="datawrapper-chart-sLWYp" src="https://datawrapper.dwcdn.net/sLWYp/2/" scrolling="no" frameborder="0" style="width: 0; min-width: 100% !important; border: none;" height="600" data-external="1" width="100%"></iframe>
<p>The origin of the glass has been <a href="https://adsabs.harvard.edu/full/1998M%26PS...33..951G">the subject of debate</a> among scientists for almost a century. Some suggested it might be from <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/volcanic-glass">volcanoes on the moon</a>. Others propose it’s the product of lightning strikes (“<a href="https://museumsvictoria.com.au/media/5617/jmmv19592301.pdf#page=207">fulgurites</a>” – glass that forms from fusion of sand and soil where they are hit by lightning). Other theories suggest it’s the result of sedimentary or <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/hydrothermal-deposit#:%7E:text=From%20Hydrothermal%20Veins-,Hydrothermal%20deposits%20refer%20to%20the%20accumulation%20of%20minerals%20in%20fractures,can%20also%20heat%20circulating%20groundwater">hydrothermal processes</a>; caused by a massive explosion of a meteor in the air; or <a href="https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1945-5100.2001.tb01960.x">that it came from a nearby meteorite crater</a>.</p>
<p>Now, thanks to advanced microscopy technology, we believe we have the answer. Along with colleagues from universities and science centres in Germany, Egypt and Morocco, I <a href="https://www.degruyter.com/document/doi/10.2138/am-2022-8759/html">have identified</a> Libyan desert glass as originating from the impact of a meteorite on the Earth’s surface.</p>
<p>Space collisions are a primary process in the solar system, as planets and their natural satellites accreted via the asteroids and planet embryos (also called planetesimals) colliding with each other. These impacts helped our planet to assemble, too.</p>
<h2>Under the microscope</h2>
<p>In 1996 scientists determined that the glass was close to <a href="https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1945-5100.1996.tb02017.x">29 million years old</a>. A <a href="https://onlinelibrary.wiley.com/doi/full/10.1111/maps.12223">later study</a> suggested the source material was composed of quartz grains, coated with mixed clay minerals and iron and titanium oxides. </p>
<p>This latter finding raised more questions, since the proposed age is older than the matching source material in the relevant area of the Great Sand Sea desert. To put it simply: those source materials didn’t exist in that location 29 million years ago.</p>
<p>For our recent study, a co-author obtained two pieces of the glass from a local who had collected them in the Al Jaouf region in south-eastern Libya. </p>
<p>We studied the samples with a state-of-the-art transmission electron microscopy (TEM) technique, which allows us to see tiny particles of material – 20,000 times smaller than the thickness of a paper sheet. Using this super-high magnification technique, we found small minerals in this glass: different types of zirconium oxide (ZrO₂). </p>
<p>Minerals are composed of chemical elements, atoms of which form regular three-dimensional packaging. Imagine putting eggs or soda bottles on the shelf of a supermarket: layers on top of layers to ensure the most efficient storage. Similarly, atoms assemble into a crystal lattice that is unique for each mineral. Minerals that have the same chemical composition but different atomic structure (different ways of atom packaging into the crystal lattice) are called polymorphs. </p>
<p>One polymorph of ZrO₂ that we observed in Libyan desert glass is called cubic zirconia – the kind seen in some jewellery as a synthetic replacement for diamonds. This mineral can only form at a high temperature between 2,250°C and 2,700°C. </p>
<p>Another polymorph of ZrO₂ that we observed was a very rare one called ortho-II or OII. It forms at very high pressure – about 130,000 atmospheres, a unit of pressure. </p>
<p>Such pressure and temperature conditions provided us with the proof for the meteorite impact origin of the glass. That’s because such conditions can only be obtained in the Earth’s crust by a meteorite impact or the explosion of an atomic bomb.</p>
<h2>More mysteries to solve</h2>
<p>If our finding is correct (and we believe it is), the parental crater – where the meteorite hit the Earth’s surface – should be somewhere nearby. The nearest known meteorite craters, named GP and Oasis, are 2km and 18km in diameter respectively, and quite far away from where the glass we tested was found. They are too far and too small to be considered the parental craters for such massive amounts of impact glass, all concentrated in one spot.</p>
<figure class="align-center ">
<img alt="A landscape photograph of sand dunes that appear almost golden in colour, stretching far into the distance." src="https://images.theconversation.com/files/559039/original/file-20231113-25-mccnnq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/559039/original/file-20231113-25-mccnnq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/559039/original/file-20231113-25-mccnnq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/559039/original/file-20231113-25-mccnnq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/559039/original/file-20231113-25-mccnnq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/559039/original/file-20231113-25-mccnnq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/559039/original/file-20231113-25-mccnnq.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">The Great Sand Sea desert.</span>
<span class="attribution"><span class="source">Sylvester Adams</span></span>
</figcaption>
</figure>
<p>So, while we’ve solved part of the mystery, more questions remain. Where is the parental crater? How big is it – and where is it? Could it have been eroded, deformed or covered by sand? More investigations will be required, likely in the form of remote sensing studies coupled with geophysics.</p><img src="https://counter.theconversation.com/content/217565/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Elizaveta Kovaleva receives funding from the Alexander von Humboldt Foundation. </span></em></p>Libyan desert glass originated from the impact of a meteorite on the Earth’s surface.Elizaveta Kovaleva, Lecturer, University of the Western CapeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2173702023-11-10T00:44:23Z2023-11-10T00:44:23ZWill Saturn’s rings really ‘disappear’ by 2025? An astronomer explains<figure><img src="https://images.theconversation.com/files/558725/original/file-20231109-23-mux310.jpg?ixlib=rb-1.1.0&rect=359%2C215%2C3269%2C1562&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://images.nasa.gov/details/PIA17218">NASA/JPL-Caltech/Space Science Institute</a></span></figcaption></figure><p>If you can get your hands on a telescope, there are few sights more spectacular than the magnificent ringed planet – <a href="https://science.nasa.gov/saturn/">Saturn</a>.</p>
<p>Currently, Saturn is <a href="https://stellarium-web.org/">clearly visible in the evening sky</a>, at its highest just after sunset. It’s the ideal time to use a telescope or binoculars to get a good view of the Solar System’s sixth planet and its famous rings.</p>
<p>But in the past few days, a slew of articles have run like wildfire through social media. Saturn’s rings, those articles claim, <a href="https://www.earth.com/news/saturns-rings-will-vanish-from-sight-in-2025/">are rapidly disappearing</a> – and will be gone by 2025!</p>
<p>So what’s the story? Could the next couple of months, before Saturn drops out of view in the evening sky, really be our last chance to see its mighty rings? </p>
<p>The short answer is <strong>no</strong>. While it’s true the rings will become almost invisible from Earth in 2025, this is neither a surprise nor reason to panic. The rings will “reappear” soon thereafter. Here’s why.</p>
<h2>Tipping and tilting Earth</h2>
<p>To understand why our view of Saturn changes, let’s begin by considering Earth on its constant journey around the Sun. That journey takes us through the seasons – from winter to spring, summer and autumn, then back again. </p>
<p>What causes the seasons? Put simply, Earth is tilted towards one side, as seen from the Sun. Our equator is tilted by about 23.5 degrees from the plane of our orbit. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/558734/original/file-20231109-15-9f73cj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram of Earth showing its position during solstices and equinoxes" src="https://images.theconversation.com/files/558734/original/file-20231109-15-9f73cj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/558734/original/file-20231109-15-9f73cj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=440&fit=crop&dpr=1 600w, https://images.theconversation.com/files/558734/original/file-20231109-15-9f73cj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=440&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/558734/original/file-20231109-15-9f73cj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=440&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/558734/original/file-20231109-15-9f73cj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=553&fit=crop&dpr=1 754w, https://images.theconversation.com/files/558734/original/file-20231109-15-9f73cj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=553&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/558734/original/file-20231109-15-9f73cj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=553&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Earth has seasons because its axis is tilted. The axis always points in the same direction as our planet orbits the Sun.</span>
<span class="attribution"><a class="source" href="https://media.bom.gov.au/social/blog/1762/solstices-and-equinoxes-the-reasons-for-the-seasons/">Bureau of Meteorology</a></span>
</figcaption>
</figure>
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Read more:
<a href="https://theconversation.com/what-is-a-solstice-an-astronomer-explains-the-long-and-short-of-days-years-and-seasons-208178">What is a solstice? An astronomer explains the long and short of days, years and seasons</a>
</strong>
</em>
</p>
<hr>
<p>The result? As we move around the Sun, we alternately tip one hemisphere and then the other towards our star. When your home hemisphere is tilted more towards the Sun, you get longer days than nights and experience spring and summer. When you’re tilted away, you get shorter days and longer nights, and experience autumn and winter. </p>
<p>From the Sun’s viewpoint, Earth appears to “nod” up and down, alternately showing off its hemispheres as it moves around our star. Now, let’s move on to Saturn.</p>
<h2>Saturn, a giant tilted world</h2>
<p>Just like Earth, Saturn experiences seasons, but more than 29 times longer than ours. Where Earth’s equator is tilted by 23.5 degrees, Saturn’s equator has a 26.7 degree tilt. The result? As Saturn moves through its 29.4-year orbit around our star, it also appears to nod up and down as seen from both Earth and the Sun.</p>
<p>What about Saturn’s rings? The planet’s enormous ring system, comprised of bits of ice, dust and rocks, spreads out over a huge distance – <a href="https://science.nasa.gov/saturn/facts/">just over 280,000km from the planet</a>. But it’s very thin – in most places, just tens of metres thick. The rings orbit directly above Saturn’s equator and so they too are tilted to the plane of Saturn’s orbit. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/558739/original/file-20231109-17-qluj40.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Saturn and its rings, tilted at Saturnian midsummer" src="https://images.theconversation.com/files/558739/original/file-20231109-17-qluj40.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/558739/original/file-20231109-17-qluj40.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=469&fit=crop&dpr=1 600w, https://images.theconversation.com/files/558739/original/file-20231109-17-qluj40.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=469&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/558739/original/file-20231109-17-qluj40.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=469&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/558739/original/file-20231109-17-qluj40.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=589&fit=crop&dpr=1 754w, https://images.theconversation.com/files/558739/original/file-20231109-17-qluj40.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=589&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/558739/original/file-20231109-17-qluj40.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=589&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 mosaic of images from NASA’s Cassini mission taken in 2016, highlighting Saturn’s axial tilt during its northern hemisphere summer.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/lightsinthedark/49999550421">NASA/JPL-Caltech/SSI. Composite by Jason Major via Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">CC BY-NC-SA</a></span>
</figcaption>
</figure>
<h2>So why do Saturn’s rings ‘disappear’?</h2>
<p>The rings are so thin that, seen from a distance, they appear to vanish when edge on. You can visualise this easily by grabbing a sheet of paper, and rotating it until it is edge on – the paper almost vanishes from view.</p>
<p>As Saturn moves around the Sun, our viewpoint changes. For half of the orbit, its northern hemisphere is tilted towards us and the northern face of the planet’s rings is tipped our way. </p>
<p>When Saturn is on the other side of the Sun, its southern hemisphere is pointed our way. For the same reason, we see the southern face of the planet’s rings tilted our way.</p>
<p>The best way to illustrate this is to get your sheet of paper, and hold it horizontally – parallel to the ground – at eye level. Now, move the paper down towards the ground a few inches. What do you see? The upper side of the paper comes into view. Move the paper back up, through your eye line, to hold it above you and you can see the underside of the paper. But as it passes through eye level, the paper will all but disappear.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/558740/original/file-20231109-26-lli6wh.gif?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/558740/original/file-20231109-26-lli6wh.gif?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/558740/original/file-20231109-26-lli6wh.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=384&fit=crop&dpr=1 600w, https://images.theconversation.com/files/558740/original/file-20231109-26-lli6wh.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=384&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/558740/original/file-20231109-26-lli6wh.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=384&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/558740/original/file-20231109-26-lli6wh.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=483&fit=crop&dpr=1 754w, https://images.theconversation.com/files/558740/original/file-20231109-26-lli6wh.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=483&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/558740/original/file-20231109-26-lli6wh.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=483&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">This simulation demonstrates the 29.5-year orbital period of Saturn, as viewed from Earth. The ring system lies directly above Saturn’s equator, so both sides of its disk are visible from Earth during the course of one Saturnian year.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Saturnoppositions-animated.gif">Tdadamemd/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>That’s what we see with Saturn’s rings. As the seasons on Saturn progress, we go from having the southern side of the rings tilted our way to seeing the northern side. Then, the planet tips back, revealing the southern side once more.</p>
<p>Twice per Saturnian year, we see the rings edge on and they all but vanish from view.</p>
<p>That’s what’s happening in 2025 – the reason Saturn’s rings will seemingly “disappear” is because we will be looking at them edge on.</p>
<p>This happens regularly. The last time was in 2009 and the rings gradually became visible again, over the course of a few months. The rings will be edge on once again in March 2025. Then they’ll gradually come back into view as seen through large telescopes, before sliding out of view again in November 2025. </p>
<p>Thereafter, the rings will gradually get more and more obvious, reappearing first to the largest telescopes over the months that follow. Nothing to worry about.</p>
<p>If you want to clearly see Saturn’s rings, now is your best chance, at least until 2027 or 2028!</p><img src="https://counter.theconversation.com/content/217370/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jonti Horner 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>Viral headlines would have you think Saturn’s rings will vanish in just 18 months. Here’s what that really means and why you don’t need to worry.Jonti Horner, Professor (Astrophysics), University of Southern QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2172092023-11-09T17:25:57Z2023-11-09T17:25:57ZEarth has many objects in orbit but definitely only one Moon – despite what some people think<figure><img src="https://images.theconversation.com/files/558036/original/file-20231107-29-8yk81v.jpg?ixlib=rb-1.1.0&rect=6%2C0%2C4594%2C3062&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Wherever you view it from on Earth, it's the same Moon.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/super-full-moon-dark-background-madrid-1998077693">Fernando Astasio Avila / Shutterstock</a></span></figcaption></figure><p>Big Brother has always chosen its contestants for entertainment value rather than for intellectual debate. This was recently highlighted in a <a href="https://www.youtube.com/watch?v=hw4_axxhWwI">discussion started on the programme by dental therapist Chantelle</a>, who suggested there must be more than one moon in the sky because it changes size and can be seen around the world. </p>
<p>Chantelle had trouble believing that the Moon can be seen in the UK and Australia at the same time, when it takes almost a whole day and night to fly between the countries. Some of the other housemates tried to dissuade her of this view, while others decided not to get involved in the discussion.</p>
<p>In fact, Australia and the UK are not on opposite sides of the world. Additionally, the Moon lies at an average of 384,400km away from us. At this distance, both locations on Earth would have an unobstructed view of it – see the image below.</p>
<p>So, it is quite possible for people in both countries to be seeing the same Moon simultaneously - depending on the time of year and position of the Moon. It may well be rising in the UK as it is setting in Australia.</p>
<p>But the UK and Australia (along with other locations on Earth) will have different views of the Moon at different times of the year. Indeed, even from the same location, it can be seen at different positions in the sky on different days. This is because the Earth is tilted on its axis by about 23 degrees, so the planet’s rotational North Pole does not stick directly up.</p>
<p>This means that the Moon – and the Sun – move <a href="https://amazingsky.net/2017/07/12/arc-of-the-low-summer-moon/">across the sky in an arc</a> as the Earth rotates. The height of this arc depends on your location on Earth’s surface, and where the Earth is in its orbit. It also depends on the season: for example, during winter, the Moon has a lower height arc. </p>
<p>Our view of the Moon is further affected by the fact that its elliptical orbit around the Earth is itself tilted by <a href="https://manoa.hawaii.edu/exploringourfluidearth/physical/tides/tide-formation-tide-height">about five degrees</a> from the horizontal (the white hashed line in the illustration below). The top three depictions of the Sun, Earth and Moon are how you would see a full, new and half Moon respectively. </p>
<p>In the case of a full Moon, where the Moon is behind the Earth, the sunlight hits the Moon and is reflected off to be observed from Earth. </p>
<p>During a new Moon, where our only natural satellite is between the Sun and the Earth, the light hits the Moon and is reflected back towards the Sun. </p>
<p>In a half Moon, where the Moon is off to the side, we see a partial reflection of sunlight from the lunar surface. </p>
<h2>The Moon’s changing appearance</h2>
<p>Let’s look a bit further into the claims by Big Brother’s Chantelle. The average flight time between London and Sydney is roughly 21 hours, including stops. The average passenger plane travels at just under 1,000km per hour. The Moon, on the other hand, travels at an average of 3,600km per hour (1km per second, or 0.62 miles per second).</p>
<p>However, speed isn’t the issue here, as the Moon is so far away that it can be seen easily by people at quite different locations on the Earth’s surface – such as the UK and Australia.</p>
<p>Chantelle also mentioned how the different apparent size of the Moon in the sky suggests there is more than one object. As a percentage of the sky it takes up, the Moon could be very small and near to us (which is <a href="https://theconversation.com/you-dont-need-to-build-a-rocket-to-prove-the-earth-isnt-flat-heres-the-simple-science-88106">what some Flat Earth models assume</a>, or extremely large and very distant. </p>
<p>Changes in the apparent size can be explained by the orbit of the Moon around the Earth, which is not perfectly circular but elliptical (oval). This means that during certain points in its orbit the Moon will be closer to the Earth, and at other times slightly further away. </p>
<p>When you then combine the point at which our natural satellite is close to the Earth with a full Moon –- when the Sun is behind the Earth from our perspective and the Moon is in front – you get what’s known as a Supermoon. When this occurs, the Moon can appear to be about 14% larger than when it is at its furthest point from the Earth.</p>
<p>Accurately determining the size of the Moon only requires some basic orbital mechanics. You can work out the distance to the Moon by <a href="https://www.physicsclassroom.com/class/circles/Lesson-4/Mathematics-of-Satellite-Motion">measuring the time it takes to orbit Earth</a>. From the distance, we can calculate the Moon’s radius.</p>
<p>We see the same face of the Moon all the time because it orbits around the Earth in exactly the same amount of time it takes to rotate once on its axis.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/j91XTV_p9pc?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Why does one side of the Moon always face us?</span></figcaption>
</figure>
<h2>Mini-moons</h2>
<p>While there is only one Moon, there are of course millions of objects orbiting the Earth. These include anthropogenic material including rockets, satellites and space junk, as well as <a href="https://theconversation.com/earths-other-moon-and-its-crazy-orbit-could-reveal-mysteries-of-the-solar-system-38010">smaller pieces of rock</a>.</p>
<p>But very occasionally, the Earth’s gravity <a href="https://www.nytimes.com/2020/02/27/science/mini-moon-earth.html">temporarily captures small natural space rocks</a>. These are sometimes referred to as mini-moons. Unfortunately, while the term “planet” has a clear definition, there is no strict definition of a moon. We can either say that there is one moon around Earth, or more than <a href="https://www.esa.int/Space_Safety/Clean_Space/How_many_space_debris_objects_are_currently_i%20n_orbit">160 million moons</a>.</p>
<p>But an easy way to confirm that our Moon is the same moon (with the same face) is to take images or draw the lunar surface in the evenings. This has been performed throughout history, and you could compare any photos you take or sketches to a map of the Moon, identifying the dark “mare” patches to an image like the one below.</p>
<figure class="align-center ">
<img alt="A map of the Moon by the 18th-century German astronomer Tobias Mayer." src="https://images.theconversation.com/files/558416/original/file-20231108-19-wqbiqw.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/558416/original/file-20231108-19-wqbiqw.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=554&fit=crop&dpr=1 600w, https://images.theconversation.com/files/558416/original/file-20231108-19-wqbiqw.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=554&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/558416/original/file-20231108-19-wqbiqw.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=554&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/558416/original/file-20231108-19-wqbiqw.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=696&fit=crop&dpr=1 754w, https://images.theconversation.com/files/558416/original/file-20231108-19-wqbiqw.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=696&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/558416/original/file-20231108-19-wqbiqw.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=696&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A map of the Moon by the 18th Century German astronomer Tobias Mayer.</span>
<span class="attribution"><a class="source" href="https://www.researchgate.net/figure/Tobias-Mayers-moon-map-authors-archives_fig2_326136511">Public domain</a></span>
</figcaption>
</figure><img src="https://counter.theconversation.com/content/217209/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ian Whittaker 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>Despite the distances involved, people as far apart as the UK and Australia can see the Moon at the same time.Ian Whittaker, Senior Lecturer in Physics, Nottingham Trent UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2154842023-10-13T12:11:57Z2023-10-13T12:11:57ZOsiris-Rex: Nasa reveals evidence of water and carbon in sample delivered to Earth from an asteroid<figure><img src="https://images.theconversation.com/files/553639/original/file-20231013-21-8i85py.jpg?ixlib=rb-1.1.0&rect=8%2C0%2C2846%2C1517&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The "coal-like" material from Bennu.</span> <span class="attribution"><a class="source" href="https://images.nasa.gov/details/jsc2023e058642">Nasa / Erika Blumenfeld & Joseph Aebers</a></span></figcaption></figure><p>On September 24 this year, a Nasa capsule parachuted down to Earth carrying a precious cache of material grabbed from an asteroid. The space agency has now revealed images and a preliminary analysis of the space rocks it found after lifting the lid off that capsule.</p>
<p>The mission to the asteroid was called <a href="https://science.nasa.gov/mission/osiris-rex/">Osiris-Rex</a>, and in 2020, it collected a sample of material from the asteroid Bennu. Afterwards, it travelled back to Earth and released the capsule containing the rocks into our atmosphere three weeks ago. </p>
<p>The fine black dust and small coal-like rocks shimmering in the capsule are beautiful – and somewhat unassuming. But this handful of space rock has the potential to answer questions about not only how the Earth was created, but
also how water arrived here and how life got started.</p>
<p><a href="https://www.youtube.com/watch?v=oFvIuSpACQA">At the Nasa press conference</a> on October 11 held to <a href="https://www.nasa.gov/news-release/nasas-bennu-asteroid-sample-contains-carbon-water/">reveal details about the sample</a>, Dr Francis McCubbin hinted that, with careful storage and preparation, the material could be analysed and used in experiments for years to come. </p>
<p>“Scientists that aren’t even born yet, (will be able to) answer questions about the Universe using technology that has not even been invented,” said the <a href="https://curator.jsc.nasa.gov/curation.cfm">astromaterials curator</a> at Nasa’s Johnson Space Center, Houston, where the Bennu sample is being stored.</p>
<h2>Why collect asteroid samples?</h2>
<p>Sometimes material from space comes to Earth without our help, <a href="https://science.nasa.gov/solar-system/meteors-meteorites/">arriving as meteorites</a>. Nasa has hundreds of meteorite samples in its collection, which are believed to have come from asteroids. Useful analysis can be carried out on these samples.</p>
<p>However, it’s often not possible to track down which asteroids these meteorites came from. This limits the potential of the resulting science. Meteorites <a href="https://www.gla.ac.uk/news/headline_915275_en.html">are also contaminated</a> by their journey through the atmosphere and onto the Earth. The Osiris-Rex sample, in contrast, is “pristine”. We can be sure any discoveries made from this sample tell us about Bennu. </p>
<p>Some of the finer dust in the Bennu sample would never have been able to form a meteorite and fall to Earth. Going and retrieving it is the only way we would ever have seen this type of material.</p>
<figure class="align-center ">
<img alt="The Osiris-Rex sample return capsule shortly after touching down in the Utah desert." src="https://images.theconversation.com/files/553640/original/file-20231013-22-rk5i1m.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/553640/original/file-20231013-22-rk5i1m.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/553640/original/file-20231013-22-rk5i1m.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/553640/original/file-20231013-22-rk5i1m.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/553640/original/file-20231013-22-rk5i1m.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/553640/original/file-20231013-22-rk5i1m.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/553640/original/file-20231013-22-rk5i1m.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Osiris-Rex sample return capsule shortly after touching down in the Utah desert.</span>
<span class="attribution"><a class="source" href="https://images.nasa.gov/details/NHQ202309240003">NASA/Keegan Barber</a></span>
</figcaption>
</figure>
<p>This is not the first asteroid sample delivered to Earth. Two Japanese space agency (Jaxa) missions, <a href="https://www.isas.jaxa.jp/en/missions/spacecraft/past/hayabusa.html">Hayabusa 1</a> <a href="https://www.isas.jaxa.jp/en/missions/spacecraft/current/hayabusa2.html">and 2</a>, made deliveries of asteroid material in 2010 and 2020. However, this is the first US mission to do so. It also returned with significantly more material than the Hayabusa missions. </p>
<p>Osiris-Rex delivered an estimated 250g of space rock, compared to Hayabusa 2’s 5g. This means the sample can be distributed to scientists around the world and put on display in museums for the public to enjoy. It also means that some larger rock fragments were included, which gives a unique opportunity to examine how different minerals are arranged in bigger chunks of the asteroid. This unlocks even more scientific potential.</p>
<h2>What have they found?</h2>
<p><a href="https://science.nasa.gov/solar-system/asteroids/101955-bennu/">Bennu</a> is what is known as a “carbonaceous”, or C-Type, asteroid. These contain a large proportion of carbon and <a href="https://en.wikipedia.org/wiki/Volatile_(astrogeology)">“volatiles”</a> – compounds that can be readily vaporised, like water. These asteroids are believed to be relics from the formation of the Solar System, and so can help explain how the planets, including Earth, came to be. </p>
<p>Analysis of the main portion of the sample has taken longer than expected to get started, but it’s a nice problem to have. The sample collection technique was so successful that the sample was “spilling out” of the container within the return capsule. Because every grain is precious, all of this bonus material must be meticulously collected before the sample canister itself can be opened and preparation of the main body of the sample can begin.</p>
<figure class="align-center ">
<img alt="Tiny grain from Bennu sample." src="https://images.theconversation.com/files/553665/original/file-20231013-15-now15p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/553665/original/file-20231013-15-now15p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=377&fit=crop&dpr=1 600w, https://images.theconversation.com/files/553665/original/file-20231013-15-now15p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=377&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/553665/original/file-20231013-15-now15p.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=377&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/553665/original/file-20231013-15-now15p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=474&fit=crop&dpr=1 754w, https://images.theconversation.com/files/553665/original/file-20231013-15-now15p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=474&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/553665/original/file-20231013-15-now15p.jpg?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">Magnification of a tiny grain from the sample. The small bright specks in the image on the right (under UV light) reveal the presence of organic compounds.</span>
<span class="attribution"><a class="source" href="https://www.youtube.com/watch?v=oFvIuSpACQA">Nasa</a></span>
</figcaption>
</figure>
<p>Still, there have already been some exciting results from the initial analysis. Water has been found locked inside clay minerals from Bennu, which is an incredibly important discovery. One proposed mechanism for how water came to be on Earth and the other inner planets is that water was <a href="https://link.springer.com/article/10.1007/s11214-018-0474-9">trapped inside clay minerals</a> like these, which then formed rocks. These were eventually incorporated into planets during the birth of the solar system. </p>
<p>There’s abundant carbon in the sample – nearly 5% by weight – and sulphur. Both elements are essential for life. Carbon is the key ingredient in the organic compounds that make biology possible. Sulphur is an important component of amino acids, which form proteins.</p>
<p>Asteroids like Bennu are thought to have <a href="https://news.uchicago.edu/explainer/origin-life-earth-explained">“seeded” Earth with prebiotic compounds</a>: the building blocks of life. Magnetite (an iron oxide) found in the sample has been linked to chemical reactions crucial for the evolution of life. As Dr Daniel Glavin, Osiris-Rex sample analyst, <a href="https://www.nbcnews.com/science/space/nasa-unveils-asteroid-sample-reveal-details-life-earth-rcna119903">summarised</a>: “We picked the right asteroid. And not only that, we brought back the right sample.”</p>
<h2>What next?</h2>
<p>As well as helping answer the big questions of how we and our planet came to be here, finding water on asteroids is also destined to be a part of our future. Water can be broken down into hydrogen and oxygen, which can then be used as rocket fuel. While still some way off, spaceship <a href="https://en.wikipedia.org/wiki/Orbital_propellant_depot">refuelling stations</a> are moving out of the realms of science fiction and into reality.</p>
<p>There’s only so much fuel you can take with you on a rocket. Far better to take just what you need to get off the planet and then <a href="https://www.space.com/water-rich-asteroids-space-exploration-fuel.html">fuel up in space</a> for the rest of your journey.</p>
<p>Water can also be used for life support in future bases on the Moon and Mars. So it’s crucial to understand where we can access water in space, and how to extract it. The water on asteroids is one potential source.</p>
<p>Asteroids, once known best for their likely part in the demise of dinosaurs, are enjoying some positive time in the spotlight, showcasing their part in humanity’s past, present and future.</p><img src="https://counter.theconversation.com/content/215484/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Lucinda King 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>Studying the sample could help answer how water arrived on Earth and how life started.Lucinda King, Space Projects Manager & Mission Design Lead, University of PortsmouthLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2155472023-10-12T15:56:56Z2023-10-12T15:56:56ZNasa’s Psyche mission is set for launch – here’s how it could unveil the interior secrets of planets<figure><img src="https://images.theconversation.com/files/553482/original/file-20231012-25-cvqpz6.jpeg?ixlib=rb-1.1.0&rect=165%2C130%2C7716%2C4314&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Falcon Heavy rocket with Psyche.</span> <span class="attribution"><span class="source">Nasa</span></span></figcaption></figure><p>It’s unlikely to be a bad omen, but Nasa’s mission Psyche is currently due to launch on Friday 13 October. Lifting off at 10.19 EDT on a SpaceX Falcon Heavy rocket, it faces a perilous journey and isn’t scheduled for arrival at its namesake asteroid, <a href="https://science.nasa.gov/solar-system/asteroids/16-psyche/">16 Pscyhe</a>, until 2029. </p>
<p>Asteroid 16 Psyche (meaning “soul” in Greek) was discovered in 1852 and is named after an ancient Greek princess who married Eros (the namesake of another asteroid). It orbits the Sun in the main asteroid belt between Mars and Jupiter, at approximately three times the distance from the Sun as Earth. It is a massive M-type asteroid (M stands for “metal-rich”), over 230km across. </p>
<p>Astronomers have to be careful with the term metal though, as in stellar physics “metallicity” means anything heavier than helium. In this case though, we are talking about metals such as iron and cobalt. </p>
<p>To give an idea of scale, if the Sun was shrunk down to the size of an official NBA basketball, then the asteroid’s diameter would be about the same size as the thickness of three pieces of paper (0.3mm), and located at a distance of 161 metres away.</p>
<p>As you can see, a mission to an object so small is not straightforward, although smaller objects have been visited – for example the recent sample return of <a href="https://science.nasa.gov/mission/osiris-rex/">OSIRIS-REX from asteroid Bennu</a> or the <a href="https://science.nasa.gov/mission/hayabusa-2/">Hayabusa 2 mission to 162173 Ryugu</a>. </p>
<p>To accomplish this remarkable voyage, the Psyche spacecraft, once launched, will use solar-electric propulsion. This works by using an electrically charged gas that’s accelerated out of the rocket nozzle by a powerful electric field. This form of propulsion, unlike a chemical rocket, produces very modest thrust. But it can operate continuously over many months or even years, while using comparatively little fuel. </p>
<p>The technology is very useful for long-distance interplanetary missions, but it does require a decent amount of sunlight for the spacecraft’s solar panels to generate the necessary electrical power. <a href="https://science.nasa.gov/mission/lucy/">Lucy</a>, another recently launched Nasa mission to asteroids in the outer Solar System, uses the same propulsion.</p>
<h2>Mission goals</h2>
<p>So what makes this particular asteroid interesting? Planets are born in “<a href="https://aasnova.org/2016/12/19/selections-from-2016-gaps-in-hl-taus-protoplanetary-disk/">protoplanetary disks</a>” through a process called accretion. This involves small bits of material gradually acquiring more mass from gravitational attraction and collision with other nearby material. </p>
<p>Technically, this is an ongoing process as the Earth sweeps up some 100 tons of natural debris every day as it orbits the Sun. However, the bulk of a planet’s mass is acquired within the first few million years of its existence. </p>
<p>This is typically an extremely violent epoch in which catastrophic collisions between young worlds are common. Needless to say, not every <a href="https://www.science.org/doi/10.1126/science.aam6036">planet to be</a> survives to full planethood. And 16 Psyche may be an <a href="https://link.springer.com/article/10.1007/s11214-022-00880-9">example</a> of such as “stunted” planet. </p>
<p>If there’s enough internal radioactive decay and heat released by countless impacts during planetary formation, a young world will melt and undergo a process called “differentiation”, in which heavier material sinks to the core and lighter material floats to the surface. </p>
<p>There are several models of formation for 16 Psyche, but the simplest one consistent with present evidence is that 16 Psyche appears to have undergone differentiation, but subsequently <a href="https://link.springer.com/article/10.1007/s11214-022-00880-9#Sec22">suffered a catastrophic impact</a> with another young world – obliterating the outer layers, leaving a remnant dense metal-rich core exposed to space.</p>
<p>A key science objective of the Psyche mission will be to distinguish which of these models is most likely correct.</p>
<p>There are two main reasons for visiting Psyche. One is the scientific interest in visiting an object that could be similar to the iron core of a planet – including the Earth. The second is to found out whether it is possible to mine the metals – with <a href="https://www.forbes.com/sites/bridaineparnell/2017/05/26/nasa-psyche-mission-fast-tracked/#49cf598b4ae8">Forbes calling it a “quadrillion-dollar asteroid”</a>. </p>
<p>Venturing into the centre of a planet to directly study its core is <a href="https://www.sciencefocus.com/planet-earth/what-is-at-earths-core">impossible with our current technology</a>. However, visiting an exposed planetary core provides an excellent opportunity to test our current models of planetary formation. </p>
<p>The Psyche spacecraft carries a number of scientific instruments such as an imager for mapping the surface of the asteroid, a gravity experiment to help to determine the world’s interior structure, and a spectrometer for investigating the mineral content of the asteroid’s surface.</p>
<p>One of the instruments is a magnetometer which is designed to try and detect whether 16 Psyche has a magnetic field. This is useful because any remnant magnetic field could demonstrate that Psyche’s interior was once indeed molten and underwent differentiation.</p>
<p>As long as the spacecraft reaches the asteroid safely, there are great discoveries to look forward to. It will certainly provide a wealth of data for scientists to analyse back on Earth for years to come.</p><img src="https://counter.theconversation.com/content/215547/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The asteroid is interesting from a scientific perspective as well as a commercial one.Gareth Dorrian, Post Doctoral Research Fellow in Space Science, University of BirminghamIan Whittaker, Senior Lecturer in Physics, Nottingham Trent UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2143202023-10-12T12:29:48Z2023-10-12T12:29:48ZAstronomers have learned lots about the universe − but how do they study astronomical objects too distant to visit?<figure><img src="https://images.theconversation.com/files/551236/original/file-20230929-19-43qoyt.jpg?ixlib=rb-1.1.0&rect=11%2C8%2C1905%2C663&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Telescopes at the Cerro Tololo Inter-American Observatory near La Serena, Chile.</span> <span class="attribution"><a class="source" href="https://noirlab.edu/public/images/iotw2107a/">Guillaume Doyen/CTIO/NOIRLab/NSF/AURA</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>NASA’s <a href="https://science.nasa.gov/mission/osiris-rex">OSIRIS-REx spacecraft</a> flew by Earth on Sept. 24, 2023, dropping off its sample of dust and pebbles <a href="https://theconversation.com/7-years-billions-of-kilometres-a-handful-of-dust-nasa-just-brought-back-the-largest-ever-asteroid-sample-214151">gathered from the surface</a> of near-Earth asteroid Bennu.</p>
<p>Analysis of this sample will help scientists understand how the solar system formed and from what sorts of materials. Scientists will begin their analysis in the <a href="https://ares.jsc.nasa.gov">same facility</a> that analyzed rocks and dust from the Apollo lunar landings.</p>
<p><a href="https://scholar.google.com/citations?hl=en&user=BUAUD4YAAAAJ&view_op=list_works&sortby=pubdate">As an astronomer</a> studying how planets form around distant stars, I felt excited watching the broadcast of that Bennu sample descending to the Utah desert – and a little envious. Those of us who study distant young solar systems can’t send robotic spacecraft to get a closer look at them, let alone grab a sample for laboratory analysis. Instead, we rely on remote observations. </p>
<p>But what astronomers can measure using telescopes is not what we really want to know – instead, we calculate the properties we’re interested in studying by observing and interpreting apparent properties from afar.</p>
<h2>Astronomers’ tools</h2>
<p>Asteroids are like fossils – they’re composed of rocky material from the formation and early evolution of a solar system and they are preserved nearly unchanged. That’s how the pristine Bennu samples will help astronomers learn about our solar system’s formation.</p>
<p>Over the past several decades, astronomers have learned that <a href="https://www.planetary.org/articles/0416-the-birth-of-the-wanderers">disks of gas and dust</a> called protoplanetary disks orbit young stars. Observing these disks – located many light years outside our solar system – can help astronomers understand the early planet formation process, but they’re too distant to send a sample-return mission like OSIRIS-REx to directly measure what the <a href="https://public.nrao.edu/blogs/what-is-a-debris-disk/">dust and asteroids in these systems</a> are made of.</p>
<p>All that astronomers like me can do is observe those distant regions of the universe remotely, using telescopes here on Earth or in orbit near Earth. But even with limited tools and techniques, we’ve still managed to learn quite a bit about them.</p>
<h2>Distance and luminosity</h2>
<p>The <a href="https://www.eso.org/public/news/eso1611/">closest protoplanetary systems</a> are a few hundred light years from the Sun, but we can’t directly measure distances that large. Instead, we have to determine distance indirectly using precise <a href="https://www.space.com/30417-parallax.html">measurements of parallax</a> – small changes in the apparent position of the star caused by our changing perspective as Earth orbits the Sun.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/iwlMmJs1f5o?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Video illustration of determining distances to stars using measurements of parallax. Las Cumbres Observatory.</span></figcaption>
</figure>
<p>Once we know their distances from Earth, we can determine another essential physical property of protoplanetary disks: their luminosities and the luminosities of their stars.</p>
<p><a href="https://earthsky.org/astronomy-essentials/stellar-luminosity-the-true-brightness-of-stars/">Luminosity</a> is an object’s power output measured in watts. The luminosity of a star like our Sun is in <a href="https://www.space.com/57-stars-formation-classification-and-constellations.html">the hundreds of trillions of trillions of watts</a>. Just as sunlight influences weather and the chemistry of planetary atmospheres in our solar system, the luminosity of a young star directly affects the material in its protoplanetary disk. Luminosity can alter the size and composition of dust particles that will later form asteroids and planetary cores.</p>
<p>But brightness does not directly indicate luminosity. The measured brightness of a star or any luminous object decreases with the square of its distance from us. We measure the apparent brightness of a star, or how bright it looks in a digital image, and then <a href="https://earthsky.org/astronomy-essentials/stellar-luminosity-the-true-brightness-of-stars/">calculate its luminosity</a> from this observed brightness and the star’s distance.</p>
<h2>Color and temperature</h2>
<p>Luminosity also depends on temperature – warmer objects are usually more luminous – but we can’t directly measure the temperatures of distant systems. Astronomers <a href="https://www.atnf.csiro.au/outreach/education/senior/astrophysics/photometry_colour.html">determine temperature</a> using precise measurements of the apparent color of a star and of the gas and dust orbiting in its planet-forming disk. </p>
<p>The color images of celestial objects that you see from observatories like the Hubble or James Webb space telescopes are <a href="https://www.scientificamerican.com/article/are-the-james-webb-space-telescopes-pictures-real/">composites of multiple images</a> taken through a series of colored filters.</p>
<p>For astronomers, colors are numbers describing the brightness of an object at a particular wavelength compared with its brightness at another wavelength. Warmer objects emit more blue light relative to red light, so their color looks more blue and the corresponding number is smaller. Astronomers measure color in even more detail by passing starlight through a small prism installed in the telescope’s camera. This prism disperses the light into a spectrum.</p>
<p>The spectrum of light from a star and its surrounding material isn’t a smooth rainbow of color. Sharp bright and dark features in the spectra indicate the presence and relative abundances of atoms, molecules and even minerals. These chemical elements emit or absorb light in unique and recognizable <a href="https://www.astronomy.com/science/how-do-scientists-determine-the-chemical-compositions-of-the-planets-and-stars/">combinations of colors</a>.</p>
<h2>Measurement and interpretation</h2>
<p>Can you see a theme emerging? Astronomers can measure only a handful of apparent properties: brightness, color, position in the sky, shape, angular size and how each of these changes with time. These are the same properties each of us measures with our senses to navigate our surroundings in everyday life. They’re nothing exotic or special.</p>
<p>And yet everything astronomers know about distant solar systems and their formation we have derived from measurements of these familiar and unremarkable apparent properties. The rich and detailed descriptions that we’ve come to expect in astronomy and astrophysics come from applying our understanding of chemistry and physics to these measurements.</p>
<p>The arrival of the Bennu sample is exciting because it is “real.” In the coming months and years, scientists will examine this dust to inform our studies not only of asteroids and interplanetary dust, but also of interstellar dust in solar systems farther afield. I am eager to see what these new details will teach us about cosmic dust, some of the primary building blocks of planets everywhere.</p><img src="https://counter.theconversation.com/content/214320/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Luke Keller has received funding from the National Aeronautics and Space Administration. </span></em></p>Controlled experiments are impossible in astronomy, as are direct measurements of physical properties of objects outside our solar system. So how do astronomers know so much about them?Luke Keller, Professor of Physics and Astronomy, Ithaca CollegeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2154662023-10-11T15:14:41Z2023-10-11T15:14:41ZThe afterglow of an explosive collision between giant planets may have been detected in a far-off star system<figure><img src="https://images.theconversation.com/files/553243/original/file-20231011-25-y5wvfs.jpeg?ixlib=rb-1.1.0&rect=2%2C0%2C1914%2C1431&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A visualisation of the huge, glowing planetary body produced by a planetary collision.</span> <span class="attribution"><a class="source" href="https://www.eurekalert.org/multimedia/1001427">Mark Garlick</a>, <span class="license">Author provided</span></span></figcaption></figure><p>The afterglow of a massive collision between two giant planets may have been detected for the first time. The wreckage of the collision could eventually cool and form an entirely new planet. If the observation is confirmed, it provides an amazing opportunity to watch the birth of a new world in real time and open a window into how planets form.</p>
<p>In December 2021, astronomers watching an otherwise unremarkable sun-like star <a href="https://astronomerstelegram.org/?read=14879">saw it begin to flicker</a>. For a few months, the visible light (the light we can see with our eyes) from this star continued to change. At times it would almost disappear, before returning to its previous brightness. </p>
<p>The star, which sits roughly 1,800 light years from Earth, was given the identifier ASASSN-21qj, after the <a href="https://www.astronomy.ohio-state.edu/asassn/">ASASN-SN astronomy survey</a> that first observed the star’s dimming. </p>
<p>Seeing stars dim like this is not uncommon. It’s generally attributed to material passing between the star and Earth. ASASSN-21qj may just have been added to a growing list of similar observations had it not been for an amateur astronomer, <a href="https://science.nasa.gov/people/arttu-sainio/">Arttu Sainio</a>. Sainio pointed out on social media that some two and a half years before the star’s light was seen to fade, the emission of infrared light coming from its location rose by roughly 4%. </p>
<p>Infrared light is most strongly emitted by objects at relatively high temperatures of a few hundred degrees Celsius. This posed the questions: were these two observations related and, if so, what the heck was going on around ASASSN-21qj?</p>
<h2>Planetary cataclysm</h2>
<p>Publishing our findings <a href="https://www.nature.com/articles/s41586-023-06573-9">in Nature</a>, we propose that both sets of observations could be explained by a cataclysmic collision between two planets. Giant impacts, as such collisions are known, are thought to be common in the final stages of the formation of planets. They dictate the final sizes, compositions, and thermal states of planets and mould the orbits of objects in those planetary systems. </p>
<p>In our solar system, giant impacts are thought to be responsible for the <a href="https://science.nasa.gov/uranus/facts/">odd tilt of Uranus</a>, the <a href="https://science.nasa.gov/mercury/facts/">high density of Mercury</a> and the <a href="https://news.uchicago.edu/explainer/formation-earth-and-moon-explained#moonform">existence of Earth’s Moon</a>. However, until now, we had little direct evidence of giant impacts ongoing in the galaxy. </p>
<figure class="align-center ">
<img alt="Artist's impression of the WISE telescope." src="https://images.theconversation.com/files/553260/original/file-20231011-19-jdcjpm.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/553260/original/file-20231011-19-jdcjpm.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=337&fit=crop&dpr=1 600w, https://images.theconversation.com/files/553260/original/file-20231011-19-jdcjpm.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=337&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/553260/original/file-20231011-19-jdcjpm.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=337&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/553260/original/file-20231011-19-jdcjpm.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/553260/original/file-20231011-19-jdcjpm.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/553260/original/file-20231011-19-jdcjpm.jpeg?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">Nasa’s WISE telescope observed an increase in the infrared light coming from the star.</span>
<span class="attribution"><a class="source" href="https://photojournal.jpl.nasa.gov/catalog/PIA17254">NASA/JPL-Caltech</a></span>
</figcaption>
</figure>
<p>In order to explain the observations, a collision would have needed to release more energy in the first few hours after impact than would be emitted from the star. Material from the colliding bodies would have been superheated and melted, vaporised or both.</p>
<p>The impact would have formed a hot, glowing mass of material hundreds of times larger than the original planets. The infrared brightening of ASASSN-21qj was observed by <a href="https://www.jpl.nasa.gov/missions/wide-field-infrared-survey-explorer-wise">Nasa’s WISE space telescope</a>. WISE only looks at the star every 300 days or so, and probably missed the initial flash of light from the impact. </p>
<p>However, the expanded planetary body produced by the impact will take a long time, perhaps millions of years, to cool and shrink to something we might recognise as a new planet. Initially, when this “post-impact body” was at its greatest extent, the light emitted from it could still be as high as several percent of emission from the star. Such a body could have produced the infrared brightening that we saw.</p>
<p>The impact would also have ejected great plumes of debris into a range of different orbits around the star. A fraction of this debris would have been vaporised by the shock of the impact, later condensing to form clouds of tiny ice and rock crystals. Over time, some of this clumpy cloud of material passed between ASASSN-21qj and Earth, blocking out a fraction of the visible light from the star and producing the erratic dimming. </p>
<figure class="align-center ">
<img alt="Neptune." src="https://images.theconversation.com/files/553274/original/file-20231011-25-9485zg.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/553274/original/file-20231011-25-9485zg.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=599&fit=crop&dpr=1 600w, https://images.theconversation.com/files/553274/original/file-20231011-25-9485zg.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=599&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/553274/original/file-20231011-25-9485zg.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=599&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/553274/original/file-20231011-25-9485zg.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=753&fit=crop&dpr=1 754w, https://images.theconversation.com/files/553274/original/file-20231011-25-9485zg.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=753&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/553274/original/file-20231011-25-9485zg.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=753&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The planets may have been similar to Neptune in the solar system.</span>
<span class="attribution"><a class="source" href="https://photojournal.jpl.nasa.gov/catalog/PIA01492">NASA/JPL</a></span>
</figcaption>
</figure>
<p>If our interpretation of the events is correct, studying this star system could help us understand a key mechanism of planet formation. Even from the limited set of observations we have so far, we have learned some very interesting things. </p>
<p>Firstly, to emit the amount of energy observed, the post-impact body must have been many hundreds of times the size of Earth. To create a body that large, the planets that collided must each have been several times the mass of Earth – possibly as large as the <a href="https://www.lpi.usra.edu/opag/outer_planets.pdf">“ice giant”</a> planets Uranus and Neptune. </p>
<p>Secondly, we estimate the temperature of the post-impact body to be around 700°C. For the temperature to be that low, the colliding bodies could not have been entirely made of rock and metal. </p>
<h2>Ice giants</h2>
<p>The outer regions of at least one of the planets must have contained elements with low boiling temperatures, such as in water. We therefore think that we have seen a collision between two Neptune-like worlds that are rich in ice. </p>
<p>The delay that was seen between the emission of infrared light and the observation of debris crossing the star suggests that the collision took place quite far away from the star – further away than the Earth is from the Sun. Such a system, in which there are ice giants far from the star, is more similar to our solar system than to many of the tightly-packed planetary systems astronomers often observe around other stars.</p>
<p>The most exciting aspect of this is that we can continue to watch the system evolve for many decades and test our conclusions. Future observations, using telescopes such as <a href="https://webbtelescope.org/home">Nasa’s JWST</a>, will determine the sizes and compositions of particles in the debris cloud, identify the chemistry of the upper layers of the post-impact body and track how this hot mass of debris cools down. We may even see new moons emerge. </p>
<p>These observations can inform our theories, helping us understand how giant impacts shape planetary systems. So far the only examples we’ve had are the echoes of impacts in our own solar system. We will now be able to watch the birth of a new planet in real time.</p><img src="https://counter.theconversation.com/content/215466/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Simon Lock receives funding from the UK Natural Environment Research Council (grant NE/V014129/1).</span></em></p><p class="fine-print"><em><span>Zoe Leinhardt receives funding from UK Science and Technology Facilities Council (grant number ST/V000454/1). </span></em></p><p class="fine-print"><em><span>Matthew Kenworthy 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>The discovery provides a way to study the birth of an entirely new planet in real time.Simon Lock, NERC Research Fellow, School of Earth Sciences, University of BristolMatthew Kenworthy, Associate professor in Astronomy, Leiden UniversityZoe Leinhardt, Associate Professor, School of Physics, University of BristolLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2133422023-10-11T12:30:02Z2023-10-11T12:30:02ZComets 101 − everything you need to know about the snow cones of space<figure><img src="https://images.theconversation.com/files/551230/original/file-20230929-15-mbvm9p.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C1200%2C1200&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Comet Hale-Bopp was visible from Earth in 1997.</span> <span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Comet_Hale-Bopp_1995O1.jpg">E. Kolmhofer, H. Raab; Johannes-Kepler-Observatory, Linz, Austria</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span></figcaption></figure><p>When you hear the word comet, you might imagine a bright streak moving across the sky. You may have a family member who saw a comet before you were born, or you may have seen one yourself when <a href="https://www.livescience.com/space/comets/green-comet-nishimura-survives-its-superheated-slingshot-around-the-sun-will-we-get-another-chance-to-see-it">comet Nishimura passed by Earth</a> in September 2023. But what are these special celestial objects made of? Where do they come from, and why do they have such long tails?</p>
<p>As a <a href="https://msutoday.msu.edu/for-media/experts/details?u=shannon.schmoll">planetarium director</a>, I spend most of my time getting people excited about and interested in space. Nothing piques people’s interest in Earth’s place in the universe quite like comets. They’re unpredictable, and they often go undetected until they get close to the Sun. I still get excited when one comes into view.</p>
<h2>What exactly is a comet?</h2>
<p>Comets are leftover material from the formation of the solar system. As the solar system formed about <a href="https://science.nasa.gov/solar-system/facts/">4.5 billion years ago</a>, most gas, dust, rock and metal ended up in the Sun or the planets. What did not get captured was <a href="https://solarsystem.nasa.gov/solar-system/our-solar-system/in-depth/">left over as comets and asteroids</a>. </p>
<p>Because <a href="https://www.universetoday.com/40692/what-are-comets-made-of/">comets are</a> clumps of rock, dust, ice and the frozen forms of various gases and molecules, <a href="https://adsabs.harvard.edu/full/1989ESASP.302...39K">they’re often called</a> “dirty snowballs” or “icy dirtballs” by astronomers. Theses clumps of ice and dirt make up what’s called the comet nucleus.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/549442/original/file-20230920-29-htg22i.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing comet nuclei, which look like gray rocks, of progressively larger sizes." src="https://images.theconversation.com/files/549442/original/file-20230920-29-htg22i.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/549442/original/file-20230920-29-htg22i.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=296&fit=crop&dpr=1 600w, https://images.theconversation.com/files/549442/original/file-20230920-29-htg22i.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=296&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/549442/original/file-20230920-29-htg22i.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=296&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/549442/original/file-20230920-29-htg22i.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=373&fit=crop&dpr=1 754w, https://images.theconversation.com/files/549442/original/file-20230920-29-htg22i.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=373&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/549442/original/file-20230920-29-htg22i.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=373&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Size comparison of various comet nuclei.</span>
<span class="attribution"><a class="source" href="https://hubblesite.org/contents/media/images/2022/020/01FZGSSNBGK1ZSFW2DCS2GYFZC?news=true">NASA, ESA, Zena Levy (STScI)</a></span>
</figcaption>
</figure>
<p>Outside the nucleus is a porous, almost fluffy layer of ice, kind of like a snow cone. This layer is surrounded by a <a href="https://www.jpl.nasa.gov/news/why-comets-are-like-deep-fried-ice-cream">dense crystalline crust</a>, which forms when the comet passes near the Sun and its outer layers heat up. With a crispy outside and a fluffy inside, astronomers have compared comets to <a href="https://www.nasa.gov/jpl/rosetta/why-comets-are-like-deep-fried-ice-cream">deep-fried ice cream</a>.</p>
<p>Most comets are <a href="https://www.vanderbilt.edu/AnS/physics/astrocourses/AST101/readings/comets.html">a few miles wide</a>, and the largest known is <a href="https://www.nasa.gov/feature/goddard/2022/hubble-confirms-largest-comet-nucleus-ever-seen">about 85 miles</a> wide. Because they are relatively small and dark compared with other objects in the solar system, people can’t see them unless the comet gets close to the Sun.</p>
<h2>Pin the tail on the comet</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/551217/original/file-20230929-25-us7tnz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Starry sky with a comet in the mid left portion of the image and a tree in the foreground" src="https://images.theconversation.com/files/551217/original/file-20230929-25-us7tnz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/551217/original/file-20230929-25-us7tnz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=783&fit=crop&dpr=1 600w, https://images.theconversation.com/files/551217/original/file-20230929-25-us7tnz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=783&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/551217/original/file-20230929-25-us7tnz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=783&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/551217/original/file-20230929-25-us7tnz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=983&fit=crop&dpr=1 754w, https://images.theconversation.com/files/551217/original/file-20230929-25-us7tnz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=983&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/551217/original/file-20230929-25-us7tnz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=983&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Comet Hale-Bopp as seen from Earth in 1997. The blue ion tail is visible to the top left of the comet.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Comet-Hale-Bopp-29-03-1997_hires.jpg">Philipp Salzgeber</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>As a comet moves close to the Sun, it heats up. The various frozen gases and molecules making up the comet change directly from solid ice to gas in a <a href="https://www.britannica.com/science/sublimation-phase-change">process called sublimation</a>. This sublimation process releases dust particles trapped under the comet’s surface. </p>
<p>The dust and released gas form a cloud around the comet called a coma. This gas and dust interact with the Sun to form <a href="https://skyandtelescope.org/astronomy-resources/why-do-comets-have-tails/">two different tails</a>. </p>
<p>The first tail, made up of gas, is called <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/comet-tails">the ion tail</a>. The Sun’s radiation strips electrons from the gases in the coma, leaving them with a positive charge. These charged gases are called ions. Wind from the Sun then pushes these charged gas particles directly away from the Sun, forming a tail that appears blue in color. The blue color comes from large numbers of <a href="https://astronomy.swin.edu.au/cosmos/c/Cometary+Gas+Tail">carbon monoxide</a> ions in the tail.</p>
<p>The dust tail forms from the dust particles released during sublimation. These are pushed away from the Sun by <a href="https://science.nasa.gov/structured-tails-comet-neowise">pressure caused by the Sun’s light</a>. The tail reflects the sunlight and swoops behind the comet as it moves, giving <a href="https://spaceplace.nasa.gov/comets/en/">the comet’s tail a curve</a>. </p>
<p>The closer a comet gets to the Sun, the longer and brighter its tail will grow. The tail can grow significantly longer than the nucleus and clock in around <a href="https://coolcosmos.ipac.caltech.edu/ask/182-What-is-the-size-of-a-comet-">half a million miles long</a>. </p>
<h2>Where do comets come from?</h2>
<p>All comets have <a href="https://www.st-andrews.ac.uk/%7Ebds2/ltsn/ljm/JAVA/COMETORB/COMET.HTM">highly eccentric orbits</a>. Their paths are elongated ovals with extreme trajectories that take them both very close to and very far from the Sun. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/Ia1k4Jec1Dc?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Comets’ orbits can be very long, meaning they may spend most of their time in far-off reaches of the solar system.</span></figcaption>
</figure>
<p>An object will <a href="https://solarsystem.nasa.gov/resources/310/orbits-and-keplers-laws/">orbit faster the closer it is</a> to the Sun, as <a href="https://www.britannica.com/science/Keplers-second-law-of-planetary-motion">angular momentum is conserved</a>. Think about how an <a href="https://news.unl.edu/newsrooms/today/article/physics-of-olympian-feats-spinning-figure-skater/">ice skater spins faster</a> when they bring their arms in closer to their body – similarly, comets speed up when they get close to the Sun. Otherwise, comets spend most of their time moving relatively slowly through the outer reaches of the solar system.</p>
<p>A lot of comets likely originate in a far-out region of our solar system called <a href="https://solarsystem.nasa.gov/solar-system/oort-cloud/overview/">the Oort cloud</a>. </p>
<p>The Oort cloud is predicted to be a round shell of <a href="https://science.nasa.gov/planetary-science/focus-areas/small-bodies-solar-system/">small solar system bodies</a> that surround the Earth’s solar system with an innermost boundary about 2,000 times farther from the Sun than Earth. For reference, Pluto is only about <a href="https://solarsystem.nasa.gov/planets/dwarf-planets/pluto/in-depth/">40 times farther</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/551201/original/file-20230929-27-56dxz8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Sphere of small particles with a disk like structure in the middle. A tiny rectangle in the center points to a zoomed in image of the Sun and planet orbits" src="https://images.theconversation.com/files/551201/original/file-20230929-27-56dxz8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/551201/original/file-20230929-27-56dxz8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=515&fit=crop&dpr=1 600w, https://images.theconversation.com/files/551201/original/file-20230929-27-56dxz8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=515&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/551201/original/file-20230929-27-56dxz8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=515&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/551201/original/file-20230929-27-56dxz8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=647&fit=crop&dpr=1 754w, https://images.theconversation.com/files/551201/original/file-20230929-27-56dxz8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=647&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/551201/original/file-20230929-27-56dxz8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=647&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 NASA diagram of the Oort cloud’s structure. The term KBO refers to Kuiper Belt objects near where Pluto lies.</span>
<span class="attribution"><a class="source" href="https://solarsystem.nasa.gov/resources/491/oort-cloud/">NASA</a></span>
</figcaption>
</figure>
<p>Comets from the Oort cloud take over 200 years to complete their orbits, a metric called the orbital period. Because of their long periods, they’re called <a href="https://astronomy.swin.edu.au/cosmos/l/Long-period+Comets">long-period comets</a>. Astronomers often don’t know much about these comets until they get close to the inner solar system. </p>
<p><a href="https://starchild.gsfc.nasa.gov/docs/StarChild/questions/question40.html">Short-period comets</a>, on the other hand, have orbital periods of less than 200 years. Halley’s comet is a famous comet that comes close to the Sun every 75 years. </p>
<p>While that’s a long time for a human, that’s a short period for a comet. Short-period comets generally come from the <a href="https://solarsystem.nasa.gov/solar-system/kuiper-belt/overview/">Kuiper Belt</a>, an asteroid belt out beyond Neptune and, most famously, the home of Pluto. </p>
<p>There’s a subset of short-period comets that get only to about Jupiter’s orbit at their farthest point from the Sun. These have orbital periods of less than 20 years and are called <a href="https://astronomy.swin.edu.au/cosmos/J/Jupiter-family+comets">Jupiter-family comets</a>.</p>
<p>Comets’ time in the inner solar system is relatively short, generally on the order of <a href="https://eyes.nasa.gov/apps/asteroids/#/home">weeks to months</a>. As they approach the Sun, their tails grow and they brighten before fading on their way back to the outer solar system. </p>
<p>But even the short-period comets don’t come around often, and their porous interior means they can sometimes fall apart. All of this makes their behavior <a href="https://www.space.com/20347-comet-brightness-predictions-difficult.html">difficult to predict</a>. Astronomers can track comets when they are coming toward the inner solar system and make predictions based on observations. But they never quite know if a comet will get bright enough to be seen with the naked eye as it passes Earth, or if it will fall apart and fizzle out as it enters the inner solar system. </p>
<p>Either way, comets will keep people looking up at the skies for years to come.</p><img src="https://counter.theconversation.com/content/213342/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Shannon Schmoll receives funding from National Science Foundation, president-elect of the International Planetarium Society, and treasurer of the Great Lakes Planetarium Association.</span></em></p>There’s a flurry of excitement every time a comet comes into view from Earth. But what are these celestial objects, and where do they come from?Shannon Schmoll, Director of the Abrams Planetarium, Michigan State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2058092023-10-02T12:29:02Z2023-10-02T12:29:02ZHow do astronomers know the age of the planets and stars?<figure><img src="https://images.theconversation.com/files/529821/original/file-20230602-6875-7ttf8v.jpg?ixlib=rb-1.1.0&rect=1%2C16%2C1005%2C671&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Astronomers can estimate ages for stars outside the Solar System, but not planets.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/the-constellation-sagittarius-taken-from-the-u-s-naval-news-photo/615295876?adppopup=true">Corbis Historical via Getty Images</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>
<hr>
<blockquote>
<p><strong>How do we know the age of the planets and stars? – Swara D., age 13, Thane, India</strong></p>
</blockquote>
<hr>
<p>Measuring the ages of planets and stars helps scientists understand when they formed and how they change – and, in the case of planets, if <a href="https://theconversation.com/ancestor-of-all-life-on-earth-evolved-earlier-than-we-thought-according-to-our-new-timescale-101752">life has had time to have evolved on them</a>.</p>
<p>Unfortunately, age is hard to measure for objects in space.</p>
<p>Stars like the Sun maintain the same <a href="https://en.wikipedia.org/wiki/Stellar_evolution">brightness, temperature and size for billions of years</a>. Planet properties <a href="https://en.wikipedia.org/wiki/Planetary_equilibrium_temperature">like temperature</a> are often set by the star they orbit rather than their own age and evolution.</p>
<p>Determining the age of a star or planet can be as hard as guessing the age of a person who looks exactly the same from childhood to retirement. </p>
<h2>Sussing out a star’s age</h2>
<p>Fortunately, <a href="http://astronomy.nmsu.edu/jasonj/565/docs/11_07.pdf">stars change subtly</a> in brightness and color over time. With very accurate measurements, astronomers can compare these measurements of a star to <a href="https://doi.org/10.3847/0067-0049/222/1/8">mathematical models</a> that predict what happens to stars as they get older and estimate an age from there. </p>
<p>Stars don’t just glow, they also spin. Over time, <a href="https://doi.org/10.1086/151310">their spinning slows down</a>, similar to how a spinning wheel slows down when it encounters friction. By comparing the spin speeds of stars of different ages, astronomers have been able to <a href="https://doi.org/10.1086/367639">create mathematical relationships for the ages of stars</a>, a method known as <a href="https://en.wikipedia.org/wiki/Gyrochronology">gyrochronology</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/530378/original/file-20230606-25-mkkjms.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A close up image of the Sun in outer space" src="https://images.theconversation.com/files/530378/original/file-20230606-25-mkkjms.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/530378/original/file-20230606-25-mkkjms.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=567&fit=crop&dpr=1 600w, https://images.theconversation.com/files/530378/original/file-20230606-25-mkkjms.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=567&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/530378/original/file-20230606-25-mkkjms.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=567&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/530378/original/file-20230606-25-mkkjms.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=713&fit=crop&dpr=1 754w, https://images.theconversation.com/files/530378/original/file-20230606-25-mkkjms.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=713&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/530378/original/file-20230606-25-mkkjms.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=713&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Researchers estimate the Sun is 4.58 billion years old.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/in-this-handout-photo-provided-by-nasa-a-solar-and-news-photo/2740385?adppopup=true">NASA via GettyImages</a></span>
</figcaption>
</figure>
<p>A star’s spin also generates a strong magnetic field and produces magnetic activity, such as <a href="https://en.wikipedia.org/wiki/Solar_flare">stellar flares</a> – powerful bursts of energy and light that occur on stars’ surfaces. A steady decline in magnetic activity from a star can also help estimate its age.</p>
<p>A more advanced method for determining the ages of stars is called <a href="https://en.wikipedia.org/wiki/Asteroseismology">asteroseismology</a>, or star shaking. Astronomers study vibrations on the surfaces of stars caused by waves that travel through their interiors. Young stars have different vibrational patterns than old stars. By using this method, <a href="https://doi.org/10.1051/0004-6361/201526419">astronomers have estimated</a> the Sun to be 4.58 billion years old.</p>
<h2>Piecing together a planet’s age</h2>
<p>In the solar system, <a href="https://en.wikipedia.org/wiki/Radionuclide">radionuclides</a> are the key to dating planets. These are special atoms that slowly release energy over a long period of time. As natural clocks, radionuclides help scientists determine the ages of all kinds of things, from <a href="https://www.nps.gov/subjects/geology/radiometric-age-dating.htm">rocks</a> to <a href="https://theconversation.com/radiocarbon-dating-only-works-half-the-time-we-may-have-found-the-solution-189493">bones</a> and <a href="https://physicsworld.com/a/archaeological-dating-by-re-firing-ancient-pots/">pottery</a>.</p>
<p>Using this method, scientists have determined that the oldest known meteorite is <a href="https://doi.org/10.1073/pnas.2026129118">4.57 billion years old</a>, almost identical to the Sun’s asteroseismology measurement of 4.58 billion years. The oldest known rocks on Earth have slightly younger ages of <a href="https://doi.org/10.1038/35051550">4.40 billion years</a>.
Similarly, soil brought back from the Moon during the Apollo missions had <a href="https://doi.org/10.1016/0012-821X(70)90093-2">radionuclide ages of up to 4.6 billion years</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/535816/original/file-20230705-7861-tqlx1p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A close up image of craters on the surface of the moon." src="https://images.theconversation.com/files/535816/original/file-20230705-7861-tqlx1p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/535816/original/file-20230705-7861-tqlx1p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/535816/original/file-20230705-7861-tqlx1p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/535816/original/file-20230705-7861-tqlx1p.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/535816/original/file-20230705-7861-tqlx1p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/535816/original/file-20230705-7861-tqlx1p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/535816/original/file-20230705-7861-tqlx1p.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">Craters on the moon’s surface.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/mondoberfl%C3%A4che-royalty-free-image/1174421451?phrase=crater+moon&adppopup=true">Tomekbudujedomek/Moment via Getty Images</a></span>
</figcaption>
</figure>
<p>Although studying radionuclides is a powerful method for measuring the ages of planets, it usually requires having a rock in hand. Typically, astronomers only have a picture of a planet to go by. Astronomers often determine the ages of rocky space objects like Mars or the Moon by <a href="https://en.wikipedia.org/wiki/Crater_counting#:%7E:text=Crater%20counting%20is%20a%20method,rate%20that%20is%20assumed%20known.">counting their craters</a>. Older surfaces have more craters than younger surfaces. However, erosion from water, wind, <a href="https://phys.org/news/2021-09-cosmic-rays-erode-largest-interstellar.html">cosmic rays</a> and lava flow from volcanoes can wipe away evidence of earlier impacts.</p>
<p>Aging techniques don’t work for giant planets like Jupiter that have deeply buried surfaces. However, astronomers can estimate their ages by <a href="https://doi.org/10.1016/j.icarus.2020.114184">counting craters on their moons</a> or studying the <a href="https://doi.org/10.1073/pnas.1704461114">distribution of certain classes of meteorites</a> scattered by them, which are consistent with radionuclide and cratering methods for rocky planets.</p>
<p>We cannot yet directly measure the ages of planets outside our solar system with current technology.</p>
<h2>How accurate are these estimates?</h2>
<p>Our own solar system provides the best check for accuracy, since astronomers can compare the radionuclide ages of rocks on the Earth, Moon, or asteroids to the asteroseismology age of the Sun, and these match very well. </p>
<p>Stars in clusters like the <a href="https://en.wikipedia.org/wiki/Pleiades">Pleiades</a> or <a href="https://en.wikipedia.org/wiki/Omega_Centauri">Omega Centauri</a> are believed to have all formed at roughly the same time, so age estimates for individual stars in these clusters should be the same. In some stars, <a href="https://ui.adsabs.harvard.edu/abs/2023ApJ...948..122S/abstract">astronomers can detect</a> radionuclides like uranium – a heavy metal found in rocks and soil – in their atmospheres, which have been used to check the ages from other methods. </p>
<p>Astronomers believe planets are roughly the same age as their host stars, so improving methods to determine a star’s age helps determine a planet’s age as well. By studying subtle clues, it’s possible to make an educated guess of the age of an otherwise steadfast star.</p>
<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:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/205809/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Adam Burgasser receives funding from NASA and the National Science Foundation.</span></em></p>Measuring the ages of planets and stars is tricky. An observational astrophysicist describes the subtle clues that provide good estimates for how old different space objects are.Adam Burgasser, Professor of Astronomy & Astrophysics, University of California, San DiegoLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2133942023-09-13T13:57:15Z2023-09-13T13:57:15ZPossible hints of life found on distant planet – how excited should we be?<figure><img src="https://images.theconversation.com/files/547762/original/file-20230912-19-lzosd4.jpeg?ixlib=rb-1.1.0&rect=5%2C0%2C3811%2C2160&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The exoplanet K2-18b might host a water ocean.</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/goddard/2023/webb-discovers-methane-carbon-dioxide-in-atmosphere-of-k2-18b">Credits: Illustration: NASA, CSA, ESA, J. Olmsted (STScI), Science: N. Madhusudhan (Cambridge University)</a></span></figcaption></figure><p>Data from the <a href="https://webb.nasa.gov/">James Webb Space Telescope</a> (JWST) has shown that an exoplanet around a star in the constellation Leo has some of the chemical markers that, on Earth, are associated with living organisms. But these are vague indications. So how likely is it that this exoplanet harbours alien life?</p>
<p>Exoplanets are worlds that orbit stars other than the Sun. The planet in question is named <a href="http://www.exoplanetkyoto.org/exohtml/K2-18.html">K2-18b</a>. It’s so named because it was the first planet found to orbit the red dwarf star K2-18. There is a K2-18c as well – the second planet to be discovered. The star itself is dimmer and cooler than the Sun, meaning that, to get the same level of light as we do on Earth, the planet would need to be much closer to its star than we are. </p>
<p>The system is roughly 124 light years away, which is close in astronomical terms. So what are conditions like on this exoplanet? This is a difficult question to answer. We have telescopes and techniques powerful enough to tell us what the star is like, and how far away the exoplanet is, but we can’t capture direct images of the planet. We can work out a few basics, however. </p>
<p>Working out how much light hits K2-18b is important for assessing the planet’s potential for life. K2-18b orbits closer to its star than Earth does: it’s at roughly 16% of the distance from Earth to the Sun. Another measurement we need is the star’s power output: the total amount of energy it radiates per second. K2-18’s power output is 2.3% that of the Sun. </p>
<p>Using geometry, we can work out that K2-18b receives about 1.22 kilowatts (kW) in solar power per square metre. <a href="https://www.sws.bom.gov.au/Educational/2/1/12">This is similar</a> to the 1.36 kW of incoming light we receive on Earth. Although there’s less energy coming from K2-18, it evens out because the planet is closer. So far, so good. However, the incoming light calculation doesn’t take into account clouds or how reflective the planet’s surface is.</p>
<figure class="align-center ">
<img alt="JWST" src="https://images.theconversation.com/files/548036/original/file-20230913-19-odwob3.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/548036/original/file-20230913-19-odwob3.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/548036/original/file-20230913-19-odwob3.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/548036/original/file-20230913-19-odwob3.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/548036/original/file-20230913-19-odwob3.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/548036/original/file-20230913-19-odwob3.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/548036/original/file-20230913-19-odwob3.jpeg?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">Artist’s impression of the James Webb Space Telescope (JWST).</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/feature/ames/webb">NASA</a></span>
</figcaption>
</figure>
<p>When we consider life on other planets, a popular term to use is the <a href="https://exoplanets.nasa.gov/search-for-life/habitable-zone/">habitable zone</a>, which means that at an average surface temperature, water will be in a liquid state – as this condition is considered essential for life. In 2019, the Hubble Space Telescope determined that K2-18b showed signs of <a href="https://www.nature.com/articles/s41550-019-0878-9#change-history">water vapour</a>, suggesting that liquid water would be present on the surface. It is currently thought that there are large oceans on the planet.</p>
<p>This caused a ripple of excitement at the time, but without further evidence it was just an interesting result. Now we have reports that JWST has identified carbon dioxide, methane and – possibly – the compound dimethyl sulfide (DMS) <a href="https://www.nasa.gov/goddard/2023/webb-discovers-methane-carbon-dioxide-in-atmosphere-of-k2-18b">in the atmosphere</a>. The tentative detection of DMS is significant because it is only produced on Earth by <a href="https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/dimethyl-sulfide">algae</a>. We currently know of no way it can be naturally produced without a life-form.</p>
<h2>Is there life on K2-18b?</h2>
<p>All these indications seem to suggest that K2-18b might be the place to go to find alien life. It is not quite as simple as that, though, as we have no idea how accurate the results are. The method used to determine what is in the atmosphere of an exoplanet involves light from a different source (usually a star or galaxy) passing through the edge of the atmosphere that is then observed by us. Any chemical compounds will <a href="https://webbtelescope.org/contents/media/images/01FEE26XVSM851DHPVCE1KB4S2">absorb light in specific wavelengths</a> which can then be identified. </p>
<p>Imagine it as looking at a light bulb through a glass tumbler. You can see through it perfectly when empty. If you fill it with water, you can still see through pretty well, but there are some optical effects and colouration, which are the equivalent of hydrogen and dust clouds in space. Now imagine you poured in red food dye – this might be the equivalent of the main chemical constituent in a planet’s atmosphere. </p>
<p>But most atmospheres are made up of many chemicals. The equivalent of looking for any one of them would be like pouring 50 – likely many more – coloured food dyes, in different amounts, into your tumbler and trying to identify how much of one particular colour is present. It is an incredibly difficult task with plenty of room for subjective assessment and errors. In addition, the light going through the atmosphere contains a signal of the star’s chemical constituents – further complicating the analysis.</p>
<figure class="align-center ">
<img alt="Atmospheric composition of K2-18 b." src="https://images.theconversation.com/files/547763/original/file-20230912-17-ds12z4.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/547763/original/file-20230912-17-ds12z4.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/547763/original/file-20230912-17-ds12z4.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/547763/original/file-20230912-17-ds12z4.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/547763/original/file-20230912-17-ds12z4.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/547763/original/file-20230912-17-ds12z4.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/547763/original/file-20230912-17-ds12z4.png?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">The chemical composition of K2-18b’s atmosphere.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/goddard/2023/webb-discovers-methane-carbon-dioxide-in-atmosphere-of-k2-18b">Credits: Illustration: NASA, CSA, ESA, R. Crawford (STScI), J. Olmsted (STScI), Science: N. Madhusudhan (Cambridge University)</a></span>
</figcaption>
</figure>
<p>Only a few years ago there was a surge of interest in <a href="https://www.nytimes.com/2020/09/14/science/venus-life-clouds.html">whether life existed on Venus</a>, as observations had indicated the presence of phosphine gas, which can be produced by microbes. </p>
<p>However, this finding was later successfully refuted by <a href="https://arxiv.org/pdf/2010.09761.pdf">several studies</a>. If there can be confusion about what is in the atmosphere of a planet that’s just next door, in astronomical terms, it’s easy to see why analysing a planet that’s many times further away is a difficult task.</p>
<h2>What can we take from this?</h2>
<p>The chances of life on exoplanet K2-18b are low but not impossible. These results will likely not change anybody’s opinions or beliefs about extraterrestrial life. Instead, they do demonstrate the advancing ability to look into worlds that are not our own and find more information. </p>
<figure class="align-center ">
<img alt="Rho Ophiuchi" src="https://images.theconversation.com/files/548021/original/file-20230913-21-su4cro.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/548021/original/file-20230913-21-su4cro.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=562&fit=crop&dpr=1 600w, https://images.theconversation.com/files/548021/original/file-20230913-21-su4cro.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=562&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/548021/original/file-20230913-21-su4cro.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=562&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/548021/original/file-20230913-21-su4cro.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=706&fit=crop&dpr=1 754w, https://images.theconversation.com/files/548021/original/file-20230913-21-su4cro.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=706&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/548021/original/file-20230913-21-su4cro.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=706&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">JWST image of Rho Ophiuchi, the closest star-forming region to Earth.</span>
<span class="attribution"><a class="source" href="https://webbtelescope.org/contents/media/images/2023/128/01H449193V5Q4Q6GFBKXAZ3S03?news=true">NASA, ESA, CSA, STScI, Klaus Pontoppidan (STScI)</a></span>
</figcaption>
</figure>
<p>The power of JWST is not only in producing incredible pictures, but in providing <a href="https://webbtelescope.org/contents/news-releases/2023/news-2023-103.html">more detailed</a> and accurate data on celestial objects themselves. Knowing which exoplanets host water and which do not could provide information on how the Earth formed. </p>
<p>Studying the atmospheres of gas giant exoplanets can inform the study of similar worlds in the Solar System, such as Jupiter and Saturn. And identifying levels of CO2 indicates how an extreme greenhouse effect might affect a planet. This is the real power of studying the composition of planetary atmospheres.</p><img src="https://counter.theconversation.com/content/213394/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ian Whittaker 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>The results are intriguing, but analysing the atmospheres of exoplanets is no easy task.Ian Whittaker, Senior Lecturer in Physics, Nottingham Trent UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2058662023-06-04T07:47:14Z2023-06-04T07:47:14ZWhat are meteorites? I visit and study the craters they’ve left across our planet<figure><img src="https://images.theconversation.com/files/528816/original/file-20230529-17-32pv8c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Impact cratering, caused by meteorites colliding with planetary surfaces, is one of the most fundamental cosmic processes.</span> <span class="attribution"><span class="source">Eshma/Shutterstock</span></span></figcaption></figure><p>Tens of thousands of <a href="https://spaceplace.nasa.gov/asteroid/en/">asteroids</a> – that we know of – are roaming our solar system. These are building blocks made up of metal, silicates, and ice left over from the beginning of time when the <a href="https://theconversation.com/curious-kids-how-are-planets-created-200454">planets</a> (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune) and their moons were assembling. </p>
<p>For the most part, the asteroids quietly orbit the Sun – but sometimes they collide with each other or the planets and their moons. An asteroid hitting a planetary surface is called a meteorite. When a meteorite moves at a hyper-speed, between 10km and 70km per second, the collision releases an enormous wave of energy and leaves something in its place on the planetary surface.</p>
<p>These meteorite or impact craters appear as scars. Some planets are more pockmarked with craters than others: <a href="https://www.google.com/maps/space/moon/@-17.1912213,44.6295626,11521099m/data=!3m1!1e3?entry=ttu">the Moon is covered</a> with thousands but the Earth has <a href="https://www.sciencedirect.com/science/article/pii/S0012825222001969">only 200 confirmed meteorite craters</a>. There are several reasons for this. First, meteorites slow down or even burn out in our atmosphere before they can reach the surface. Second, 70% of Earth is covered with water – we can only see craters on land. Earth also has <a href="https://theconversation.com/plate-tectonics-new-findings-fill-out-the-50-year-old-theory-that-explains-earths-landmasses-55424">tectonic plates</a>, which shift and constantly renew the surface.</p>
<p>I am a geoscientist who studies impact craters. I have visited 10 of Earth’s confirmed crater sites, in places as diverse as the Amazon jungle, the Arctic polar circle, central Europe, and South Africa. I’ve even studied lunar samples collected by the Apollo missions.</p>
<p>Impact cratering is one of the most fundamental cosmic processes. It is responsible for the growth of planetary bodies through accretion (the accumulation of mass). For example, the Moon was created as a result of a collision between the young Earth and a smaller planet, Theia. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/p5E_esHiA5Q?wmode=transparent&start=24" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The moon started with a literal ‘bang’</span></figcaption>
</figure>
<p>It has been proven that the <a href="https://theconversation.com/how-the-dinosaurs-went-extinct-asteroid-collision-triggered-potentially-deadly-volcanic-eruptions-112134">extinction of dinosaurs</a> was caused by a massive impact event. Thus, studying impact craters can broaden our understanding of the Earth’s evolution and life, as well its possible future.</p>
<h2>Studying impactites</h2>
<p>I moved to the Free State province in South Africa after defending my doctoral thesis at Austria’s University of Vienna. The closest, most interesting geological site was the Vredefort impact crater. It is <a href="https://earthobservatory.nasa.gov/images/92689/vredefort-crater">the world’s oldest and largest known impact structure</a>, dating back some 2 billion years and spanning between 180km and 300km in diameter.</p>
<p>With fellow researchers, I visited Vredefort several times a year to collect a variety of data. <a href="https://scholar.google.com/citations?hl=ru&user=KIoAMa0AAAAJ&view_op=list_works&sortby=pubdate">Impact cratering research</a> helps me to combine two of my big passions - metamorphic petrology (how rocks can be transformed from one type into another) and the deformation of minerals (how they change their shape and structure under stress). </p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/what-a-moroccan-crater-reveals-about-a-rare-double-whammy-from-the-skies-61406">What a Moroccan crater reveals about a rare double whammy from the skies</a>
</strong>
</em>
</p>
<hr>
<p>So, what happens when an impact crater is formed? A combination of intense heat (reaching thousands of degrees Celsius) and pressure (millions of <a href="https://education.nationalgeographic.org/resource/atmospheric-pressure/">atmospheres</a>) at the moment the meteorite hits the planetary surface. The meteorite is destroyed and part of the target evaporates. </p>
<p>That spot of collision is what’s known as an impact crater; the ground around and below it is full of rocks called <a href="https://www.lpi.usra.edu/publications/books/CB-954/chapter5.pdf">impactites</a>. These cannot be found anywhere else: impactites are not formed by any natural processes, only by meteorite impacts. Unique deformation features form in the minerals that were already on the planet’s surface. </p>
<figure class="align-center ">
<img alt="An aerial view of a rugged, rocky landscape interspersed with patches of green" src="https://images.theconversation.com/files/528822/original/file-20230529-9150-asis0o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/528822/original/file-20230529-9150-asis0o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=424&fit=crop&dpr=1 600w, https://images.theconversation.com/files/528822/original/file-20230529-9150-asis0o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=424&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/528822/original/file-20230529-9150-asis0o.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=424&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/528822/original/file-20230529-9150-asis0o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=533&fit=crop&dpr=1 754w, https://images.theconversation.com/files/528822/original/file-20230529-9150-asis0o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=533&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/528822/original/file-20230529-9150-asis0o.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=533&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A satellite image of the Vredefort impact crater in South Africa’s Free State province.</span>
<span class="attribution"><span class="source">Planet Observer/Universal Images Group via Getty Images</span></span>
</figcaption>
</figure>
<p>Sometimes, new minerals are found – examples include <a href="https://link.springer.com/referenceworkentry/10.1007/0-387-30720-6_25">coesite and stishovite</a>, which are high-pressure modifications of quartz, and <a href="https://pubchem.ncbi.nlm.nih.gov/compound/Reidite">reidite</a> - a high-pressure modification of zircon. Another one is impact diamond, called <a href="https://www.nature.com/articles/ncomms6447">lonsdaleite</a>.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/glass-beads-in-lunar-soil-reveal-ancient-asteroid-bombardments-on-the-moon-and-earth-191342">Glass beads in lunar soil reveal ancient asteroid bombardments on the Moon and Earth</a>
</strong>
</em>
</p>
<hr>
<h2>Cutting-edge technology</h2>
<p>Studying impactites isn’t, of course, as easy as looking at them with the naked eye or even putting them under a conventional microscope. A technology called <a href="https://www.sciencedirect.com/topics/physics-and-astronomy/transmission-electron-microscopy">transmission electron microscopy</a> (TEM) is driving the latest research in this field. It has been used for a few decades but, in recent years, there have been big improvements in its quality and precision.</p>
<p>TEM is a way to observe the micro- and nano-structures of impactites at an unbelievably high resolution. Using thin, specially prepared samples, features as small as a few nanometers in size – that’s about 1/10,000th of the diameter of a human hair – can be characterised in terms of their composition, shape, crystalline structure and relationship with the surroundings. Individual molecules and their patterns in crystals can be recognised and imaged. We can even identify what mineral we are looking at by analysing the arrangement of molecules.</p>
<p>This technology is opening the door to an entirely new world of impactite study. Our small-scale analyses will reveal ever more of the Universe’s huge secrets.</p><img src="https://counter.theconversation.com/content/205866/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Elizaveta Kovaleva receives funding from the National Research Foundation of South Africa, the Alexander Von Humboldt Foundation of Germany, and in the past received funding from the Russian Science Foundation. </span></em></p>Studying impact craters can broaden our understanding of the Earth’s evolution and life, as well as its possible future.Elizaveta Kovaleva, Lecturer, University of the Western CapeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2056712023-05-16T10:16:15Z2023-05-16T10:16:15ZSaturn: we may finally know when the magnificent rings were formed<figure><img src="https://images.theconversation.com/files/526289/original/file-20230515-24420-u00yee.jpg?ixlib=rb-1.1.0&rect=8%2C4%2C2737%2C1337&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A colour-exaggerated view of Saturn backlit by the sun.</span> <span class="attribution"><a class="source" href="https://solarsystem.nasa.gov/resources/13315/in-saturns-shadow-color-exaggerated-view/">NASA/JPL/Space Science Institute</a></span></figcaption></figure><p>Saturn’s rings are one of the jewels of the solar system, but it seems that their time is short and their existence fleeting.</p>
<p><a href="https://www.science.org/doi/10.1126/sciadv.adf8537">A new study</a> suggests the rings are between 400 million and 100 million years old – a fraction of the age of the solar system. This means we are just lucky to be living in an age when the giant planet has its magnificent rings. Research also reveals that they could be gone in another 100 million years.</p>
<p>The rings were first observed in 1610 by the astronomer Galileo Galilei who, owing to the resolution limits of his telescope, initially described them as two smaller planets on each side of Saturn’s main orb, apparently in physical contact with it. </p>
<p>In 1659, the Dutch astronomer Christiaan Huygens published <a href="https://www.loc.gov/item/2021666744">Systema Saturnium</a>, in which he became the first to describe them as a thin, flat ring system that was not touching the planet.</p>
<p>He also showed how their appearance, as viewed from Earth, changes as the two planets orbit the Sun and why they seemingly disappear at certain times. This is due to their viewing geometry being such that we on Earth periodically see them edge-on.</p>
<p>The rings are visible to anyone with a decent pair of binoculars or a modest back garden telescope. Cast white against the pale yellow orb of Saturn, the rings are composed almost entirely of billions of particles of water ice, which shine by scattering sunlight. </p>
<figure class="align-center ">
<img alt="Page from Systema Saturnium showing the changing view of Saturn's rings as Earth and Saturn orbit the sun" src="https://images.theconversation.com/files/526275/original/file-20230515-27-k825du.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/526275/original/file-20230515-27-k825du.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=826&fit=crop&dpr=1 600w, https://images.theconversation.com/files/526275/original/file-20230515-27-k825du.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=826&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/526275/original/file-20230515-27-k825du.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=826&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/526275/original/file-20230515-27-k825du.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1038&fit=crop&dpr=1 754w, https://images.theconversation.com/files/526275/original/file-20230515-27-k825du.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1038&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/526275/original/file-20230515-27-k825du.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1038&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A page from the System Saturnium published in 1659.</span>
<span class="attribution"><a class="source" href="https://www.loc.gov/resource/gdcwdl.wdl_04302/?sp=75">US Library of Congress</a></span>
</figcaption>
</figure>
<p>Amid this icy material are deposits of darker, dusty stuff. In space science, “dust” usually refers to <a href="https://www.britannica.com/science/micrometeoroid">tiny grains</a> of rocky, metallic, or carbon-rich material that is noticeably darker than ice. It is also collectively referred to as micrometeoroids. These grains permeate the solar system. </p>
<p>Occasionally, you can see them entering the Earth’s atmosphere at night as shooting stars. The gravitational fields of the planets have the effect of magnifying or focusing this dusty, planetary “in-fall”. </p>
<p>Over time, this in-fall adds mass to a planet and alters its chemical composition. Saturn is a massive gas giant planet with a radius of some 60,000km, about 9.5 times that of Earth, and a mass of about 95 times that of Earth. This means it has a very large “gravity well” (the gravitational field surrounding a body in space) that is very effective at funnelling the dusty grains towards Saturn. </p>
<figure class="align-center ">
<img alt="Saturn" src="https://images.theconversation.com/files/526288/original/file-20230515-22664-8oxknm.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/526288/original/file-20230515-22664-8oxknm.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=305&fit=crop&dpr=1 600w, https://images.theconversation.com/files/526288/original/file-20230515-22664-8oxknm.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=305&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/526288/original/file-20230515-22664-8oxknm.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=305&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/526288/original/file-20230515-22664-8oxknm.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=384&fit=crop&dpr=1 754w, https://images.theconversation.com/files/526288/original/file-20230515-22664-8oxknm.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=384&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/526288/original/file-20230515-22664-8oxknm.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=384&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A view of Saturn’s northern hemisphere in 2016.</span>
<span class="attribution"><a class="source" href="https://photojournal.jpl.nasa.gov/catalog/PIA21046">NASA/JPL-Caltech/Space Science Institute</a></span>
</figcaption>
</figure>
<h2>Collision course</h2>
<p>The rings extend from some 2,000km above Saturn’s cloud tops to about 80,000km away, occupying a large area of space. When in-falling dust passes through, it can collide with icy particles in the rings. Over time, the dust gradually darkens the rings and adds to their mass.</p>
<p>Cassini-Huygens was a robotic spacecraft launched in 1997. It reached Saturn in 2004 and entered orbit around the planet, where it stayed until the end of the mission in 2017. One of the instruments aboard was the <a href="https://link.springer.com/article/10.1007/s11214-004-1435-z">Cosmic Dust Analyzer (CDA)</a>. </p>
<p>Using data from the CDA, the authors in the new paper compared the current dust counts in space around Saturn with the estimated mass of dark dusty material in the rings. They found that the rings are no older than 400 million years and may be as young as 100 million years. These may seem like lengthy time scales, but they are less than one-tenth of the 4.5 billion-year age of the solar system.</p>
<p>This also means that the rings did not form at the same time as Saturn or the other planets. They are, cosmologically speaking, a recent addition to the solar system. For over 90% of Saturn’s existence, they were not present.</p>
<h2>Death Star</h2>
<p>This leads to another mystery: how did the rings first form, given that all of the solar system’s major planets and moons formed much earlier? The total mass of the rings is estimated to be about half as much as one of Saturn’s smaller icy moons, many of which exhibit enormous impact features on their surfaces. </p>
<p>One in particular, the little moon <a href="https://solarsystem.nasa.gov/moons/saturn-moons/mimas/in-depth/">Mimas</a>, which is nicknamed the Death Star, has a 130km-wide impact crater called Herschel on its surface. </p>
<figure class="align-center ">
<img alt="Mimas" src="https://images.theconversation.com/files/526286/original/file-20230515-25-xl63fg.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/526286/original/file-20230515-25-xl63fg.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/526286/original/file-20230515-25-xl63fg.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/526286/original/file-20230515-25-xl63fg.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/526286/original/file-20230515-25-xl63fg.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/526286/original/file-20230515-25-xl63fg.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/526286/original/file-20230515-25-xl63fg.jpeg?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">Saturn’s moon Mimas, showing Herschel crater.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/mission_pages/cassini/multimedia/pia12570.html">NASA/JPL/SSI</a></span>
</figcaption>
</figure>
<p>This is by no means the largest crater in the solar system. However, Mimas is only about 400km across, so this impact would not have needed much more energy to obliterate the moon. Mimas is made of water-ice, just like the rings, so it’s possible that the rings were formed from just such a cataclysmic impact. </p>
<h2>Ring rain</h2>
<p>However they formed, the future of Saturn’s rings is in little doubt. The impact of the dust grains against the icy particles happens at very high velocities, leading to tiny fragments of ice and dust getting chipped away from their parent particles. </p>
<p>Ultra-violet light from the Sun causes these fragments to become electrically charged via the <a href="https://www.britannica.com/science/photoelectric-effect">photo-electric effect</a>. Like the Earth, Saturn has a magnetic field, and once charged, these tiny icy fragments are released from the ring system and trapped by the planet’s magnetic field. </p>
<p>In concert with the gravity of the giant planet, they are then funnelled down into Saturn’s atmosphere. This “ring rain” was first observed from afar by the Voyager 1 and Voyager 2 spacecraft during their brief Saturn flybys in the early 1980s. </p>
<p>In a more recent <a href="https://www.science.org/doi/10.1126/science.aat3185">paper from 2018</a> scientists used dust counts, again from the CDA, as Cassini flew between the rings and Saturn’s cloud tops, to work out how much ice and dust is lost from the rings over time. This study demonstrated that about one Olympic-sized swimming pool of mass from the rings is lost into Saturn’s atmosphere every half-hour. </p>
<p>This flow rate was used to estimate that, given their current mass, the rings will probably be gone in as little as 100 million years. These beautiful rings have a turbulent history, and unless they are somehow replenished, they will be gobbled up by Saturn.</p><img src="https://counter.theconversation.com/content/205671/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Gareth Dorrian 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>New research suggests Saturn’s rings may be surprisingly young.Gareth Dorrian, Post Doctoral Research Fellow in Space Science, University of BirminghamLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2052652023-05-10T12:28:10Z2023-05-10T12:28:10ZAstronomers just saw a star eat a planet – an astrophysicist on the team explains the first-of-its-kind discovery<figure><img src="https://images.theconversation.com/files/525217/original/file-20230509-17-8m0pr7.jpg?ixlib=rb-1.1.0&rect=0%2C137%2C3460%2C2017&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">New research shows that the destructive merging of a star and a planet expels huge amounts of gas, as shown in this artist's impression.</span> <span class="attribution"><a class="source" href="https://www.nature.com/articles/d41586-023-01385-3">K. Miller/R. Hurt (Caltech/IPAC)</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>For the first time, astronomers have captured images that show a star consuming one of its planets. The star, named ZTF SLRN-2020, is located in the Milky Way galaxy, in the constellation Aquila. As the star swallowed its planet, the star brightened to 100 times its normal level, allowing the 26-person team of astronomers I worked with to <a href="https://doi.org/10.1038/s41586-023-05842-x">detect this event as it happened</a>.</p>
<p><a href="https://itc.cfa.harvard.edu/people/morgan-macleod">I am a theoretical astrophysicist</a>, and I developed the computer models that our team uses to interpret the data we collect from telescopes. Although we only see the effects on the star, not the planet directly, our team is confident that the event we witnessed was a star swallowing its planet. Witnessing such an event for the first time has confirmed the long-standing assumption that stars swallow their planets and has illuminated how this fascinating process plays out.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/524944/original/file-20230508-247807-drmefx.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A white domed building at sunset." src="https://images.theconversation.com/files/524944/original/file-20230508-247807-drmefx.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/524944/original/file-20230508-247807-drmefx.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/524944/original/file-20230508-247807-drmefx.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/524944/original/file-20230508-247807-drmefx.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/524944/original/file-20230508-247807-drmefx.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/524944/original/file-20230508-247807-drmefx.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/524944/original/file-20230508-247807-drmefx.jpeg?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">The Zwicky Transient Facility in Southern California is one of the observatories that captured the flash of light caused by the star consuming its planet.</span>
<span class="attribution"><a class="source" href="https://www.ztf.caltech.edu/multimedia.html#">Caltech/Palomar</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
</figure>
<h2>Finding a flash in the dynamic night sky</h2>
<p>The team I work with searches for the bursts of light and gas that occur when two stars merge into a bigger, single star. To do this, we have been using data from the <a href="https://www.ztf.caltech.edu/">Zwicky Transient Facility</a>, a telescope located on Palomar Mountain in Southern California. It takes nightly images of broad swaths of the sky, and astronomers can then compare these images to find stars that change in brightness over time, or what are called astronomical transients.</p>
<p>Finding stars that change in brightness isn’t the challenge – it’s sorting out the cause behind any specific change to a star. As my colleague <a href="https://space.mit.edu/people/de-kishalay/">Kishalay De</a> likes to say, “There are plenty of things in the sky that go boom.” The trick to identifying stellar mergers is to combine visible light – like the data collected at Palomar – with infrared data from <a href="https://www.nasa.gov/mission_pages/WISE/main/index.html">NASA’s WISE space telescope</a>, which has been surveying the entire sky for the past decade.</p>
<p>In 2020, the star ZTF SLRN-2020 suddenly became 100 times brighter in visible light over just 10 days. It then slowly started to fade back toward its normal brightness. About nine months before, the same object started to emit a lot of infrared light, too. This is exactly what it looks like when two stars merge together, with one critical difference – everything was scaled down. The brightness and total energy of this event were about a thousand times lower than any of the merging stellar pairs astronomers had found to date. </p>
<h2>When a star swallows its planets</h2>
<p>The idea that stars could engulf some of their planets has been a long-standing assumption in astronomy. Astronomers have long known that when stars <a href="https://www.teachastronomy.com/textbook/Star-Birth-and-Death/Nuclear-Reactions-in-Main-Sequence-Stars/">run out of hydrogen in their cores</a>, they get brighter and begin to <a href="https://www.teachastronomy.com/textbook/Star-Birth-and-Death/Red-Giants/">increase in size</a>.</p>
<p>Many planets have orbits that are <a href="https://doi.org/10.5281/zenodo.6368226">smaller than the eventual size of their parent stars</a>. So, when a star runs out of fuel and starts to expand, the planets nearby are inevitably consumed.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/525243/original/file-20230509-43918-15gi7w.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A graph showing two lines increasing to a peak near the same time with one increasing over a much shorter period of time." src="https://images.theconversation.com/files/525243/original/file-20230509-43918-15gi7w.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/525243/original/file-20230509-43918-15gi7w.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=305&fit=crop&dpr=1 600w, https://images.theconversation.com/files/525243/original/file-20230509-43918-15gi7w.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=305&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/525243/original/file-20230509-43918-15gi7w.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=305&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/525243/original/file-20230509-43918-15gi7w.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=383&fit=crop&dpr=1 754w, https://images.theconversation.com/files/525243/original/file-20230509-43918-15gi7w.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=383&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/525243/original/file-20230509-43918-15gi7w.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=383&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The star ZTF SLRN-2020 increased in brightness in both visible and infrared wavelengths of light, with the peak occurring on May 24, 2020.</span>
<span class="attribution"><span class="source">M. MacLeod</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Interpreting a stellar flash</h2>
<p>In the ZTF SLRN-2020 outburst, our team never saw the planet itself, only the brightening from when the star absorbed the planet. This is where combining theoretical models with the observational data allowed us to understand what the telescopes captured.</p>
<p>The merging of two stars into a single, bigger star is a <a href="https://doi.org/10.3847/1538-4357/835/2/282">dramatic event</a> that throws matter out into the stars’ surroundings. A large part of my career has focused on <a href="https://doi.org/10.3847/1538-4357/aacf08">modeling the way stellar gas moves</a> and crashes into itself and is expelled in these moments of intense interaction. </p>
<p>My work has shown that the total mass of matter ejected in a merging event is proportional to the <a href="https://doi.org/10.3847/1538-4357/ab89b6">size of the objects involved in the merger</a>. Merge two equally large stars and you see a huge disturbance. Merge one star with a much smaller companion and the event might throw out a tiny fraction of the total mass of the stars.</p>
<p>The energy released during ZTF SLRN-2020’s outburst was a thousand times lower than typical for a two-star merger. This implies that the object that merged with the star weighed a thousand times less than a normal star. This clue pointed our team toward a gas giant planet – like Jupiter in our own solar system, which weighs roughly a thousand times less than the Sun.</p>
<p>Compared to Jupiter, however, this planet must have <a href="https://doi.org/10.48550/arXiv.2210.15848">orbited much closer to the star</a>, with one revolution around the star only taking a few days. <a href="https://doi.org/10.1146/annurev-astro-082214-122246">About 1% of stars</a> share this configuration of a large planet orbiting incredibly close to its parent star. </p>
<p>Further, I think that this configuration of a big planet close to its star is important in generating the event our team saw. My past research suggests that smaller planets – or ones in more-distant orbits that only get consumed once a star has grown massively in size – might be <a href="https://doi.org/10.3847/2041-8213/aaa5fa">swallowed without a detectable flash</a>.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/nDi0JIRDXI0?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The planet around ZTF SLRN-2020 skimmed the stellar surface before eventually falling into the star.</span></figcaption>
</figure>
<h2>Learning from the real thing</h2>
<p>From our data and modeling for ZTF SLRN-2020, our team has been able to paint a much clearer picture of how stars and planets merge. First, the planet skims across the surface of the star for many years, slowly heating up and expelling material <a href="https://doi.org/10.1038/d41586-023-01385-3">from the star’s atmosphere</a>. As this gas expands and cools, some of it forms molecules and dust. This cloud of dust gives the star a progressively redder color and emits increasing amounts of infrared radiation.</p>
<p>In the case of ZTF SLRN-2020, the orbit of the planet shrank slowly at first, then faster and faster as the planet smashed through the denser layers of the star’s atmosphere. Eventually, in just a few final days, the planet plunged below the surface of the star and was torn apart by the heat and force of the collision. This rapid injection of energy supplied heat to power ZTF SLRN-2020’s 10-day, hundredfold increase in brightness. Following this climactic moment, the star began to fade, telling our team that the planet-swallowing process was over and that the star was beginning to go back to business as usual. </p>
<p>While the destructive event has passed, there is still much to be learned. Next week our team will start analyzing data from the <a href="https://webb.nasa.gov/">James Webb Space Telescope</a> in the hopes of learning about the chemistry of the gas that now surrounds ZTF SLRN-2020.</p><img src="https://counter.theconversation.com/content/205265/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Morgan MacLeod is grateful for support from the Clay Postdoctoral Fellowship at the Smithsonian Astrophysical Observatory and from the National Science Foundation. </span></em></p>Stars begin to expand when they run out of fuel and can become thousands of times larger, consuming any planets in the way. For the first time, astronomers have witnessed one such event.Morgan MacLeod, Postdoctoral Fellow in Theoretical Astrophysics, Harvard UniversityLicensed as Creative Commons – attribution, no derivatives.