tag:theconversation.com,2011:/id/topics/saturn-5389/articlesSaturn – The Conversation2024-01-29T16:38:10Ztag:theconversation.com,2011:article/2221732024-01-29T16:38:10Z2024-01-29T16:38:10ZNasa’s Mars helicopter Ingenuity has ended its mission – its success paves the way for more flying vehicles on other planets and moons<figure><img src="https://images.theconversation.com/files/571847/original/file-20240129-15-v0glwl.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C2270%2C1360&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Ingenuity helicopter on Mars.</span> <span class="attribution"><a class="source" href="https://mars.nasa.gov/resources/27421/ingenuity-at-two-years-on-mars/">NASA/JPL-Caltech/ASU/MSSS</a></span></figcaption></figure><p>It is difficult to emphasise the significance of the milestone surpassed by Nasa’s Mars helicopter, Ingenuity. </p>
<p>The little (1.8kg) helicopter <a href="https://mars.nasa.gov/resources/25608/nasas-perseverance-rover-lands-successfully-on-mars/">touched down with the Perseverance rover in 2021</a>. On 25 January, Nasa announced that the flying vehicle <a href="https://www.nasa.gov/news-release/after-three-years-on-mars-nasas-ingenuity-helicopter-mission-ends/">had to perform an emergency landing</a> which damaged one of its rotors and ended its mission. </p>
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<p>This reminds us that space exploration is still difficult to do. But Ingenuity’s three years on Mars proved that powered, controlled flight on Mars was possible. </p>
<p>The little helicopter lasted for far longer than had been planned and flew higher and further than many had envisaged. Beyond this Martian experiment, the rotorcraft’s success paves the way for other missions using flying vehicles to explore planets and moons.</p>
<p>The first landings on the Moon were static. The year 1969 was probably the most important one for space exploration, when <a href="https://www.nasa.gov/mission/apollo-11/">Apollo 11</a> and <a href="https://www.nasa.gov/mission/apollo-12/">Apollo 12</a> brought astronauts to the lunar surface, but 1970 was the year for planetary exploration. </p>
<p>In 1970, we had the <a href="https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1970-060A">first soft landing on another planet</a>, Venus. The first robotic sample delivered to Earth from the Moon. And the first robot rover to drive around another body (also the Moon). </p>
<p>Since then, following over 50 years of planetary exploration and technology development, there have only been a small number of successful surface missions, and even fewer were able to move. Venus was visited by a dozen static landers between 1970 and 1985, and never again. </p>
<h2>From rovers to helicopters</h2>
<p>Mars was only successfully landed on three times between 1971 and 1976 before the <a href="https://mars.nasa.gov/mars-exploration/missions/pathfinder/">Pathfinder lander</a> and Sojourner rover arrived in 1997. The European Huygens spacecraft then landed on Titan, the moon of Saturn, in 2005. </p>
<p>These attempts at reaching the surface are rare, extremely difficult, and, historically, the landers were hardly ever mobile. Yet the Nasa <a href="https://mars.nasa.gov/mer/mission/overview/">Mars rovers Spirit, Opportunity</a>, <a href="https://mars.nasa.gov/msl/home/">Curiosity</a>, and <a href="https://mars.nasa.gov/mars2020/">Perseverance</a> have all exceeded their designs and travelled further and further.</p>
<p>And Ingenuity flew.</p>
<p>It wasn’t the first spacecraft to fly. Those would be the balloons deployed by the <a href="https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1984-128F">Soviet Vega 1 and 2 missions</a>, which floated over Venus in 1985. But Ingenuity had control, cameras, and connectivity. It took photos of its rover and of Mars from an entirely new perspective. It commanded the world’s attention and captured our hearts.</p>
<p>In Moscow, I had the chance to see models and replicas of the Vega balloons and the first lunar rover. They made a stronger impression on me than the Mars rover twins being used at Nasa’s Jet Propulsion Laboratory (JPL) in California. The Soviet missions were more audacious and different, and they were from generations ago, before my time and long before my career as a planetary scientist.</p>
<p>Ingenuity was audacious, original and completely new. The photos it took, of Perseverance, finding technology discarded from the descent module that carried it down to Mars and of the Martian vistas from a bird’s eye view, were breathtaking. Meanwhile, Perseverance also took videos of Ingenuity flying in the air. Nothing like it had ever seen before.</p>
<figure class="align-center ">
<img alt="CGI image of a silver drone with eight propellers over the Martian surface" src="https://images.theconversation.com/files/571881/original/file-20240129-23-b4r2m2.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/571881/original/file-20240129-23-b4r2m2.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=380&fit=crop&dpr=1 600w, https://images.theconversation.com/files/571881/original/file-20240129-23-b4r2m2.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=380&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/571881/original/file-20240129-23-b4r2m2.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=380&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/571881/original/file-20240129-23-b4r2m2.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=478&fit=crop&dpr=1 754w, https://images.theconversation.com/files/571881/original/file-20240129-23-b4r2m2.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=478&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/571881/original/file-20240129-23-b4r2m2.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=478&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">An artist’s impression of the Dragonfly spacecraft in flight.</span>
<span class="attribution"><a class="source" href="https://dragonfly.jhuapl.edu/Gallery/">NASA/Johns Hopkins APL/Steve Gribben</a></span>
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<h2>Future flights</h2>
<p>Ingenuity had a rough ride getting there, however. The entire Mars 2020 mission (of Perseverance, Ingenuity and their transport systems) was sudden. </p>
<p>Following Nasa’s withdrawal from the joint European Space Agency ExoMars programme, which included a Mars rover mission, the US space agency started developing one on its own. This rover, later named Perseverance, went from announcement to concept to development and launch in just seven-and-a-half years.</p>
<p>And Ingenuity wasn’t included onboard at first. As an idea, it was proposed late in the development phase of Mars 2020, and faced serious opposition. It added extra complexity, cost, risk and new failure modes. It was also driven by an engineering objective, with the possibility of a little outreach – the opportunity to communicate the mission’s science and engineering to the public – on the side.</p>
<p>Ingenuity wasn’t intended to last for very long. It was designed to prove helicopter flight in the thin Mars atmosphere. It targeted five short flights over a month. Possible outcomes included hard landings, toppling over, losing power if its solar panels were covered in dust, or losing communication when it was far from the rover (this happened several times). </p>
<figure class="align-center ">
<img alt="Large silver balloon being launched in the desert." src="https://images.theconversation.com/files/571874/original/file-20240129-25-1d0l8.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/571874/original/file-20240129-25-1d0l8.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/571874/original/file-20240129-25-1d0l8.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/571874/original/file-20240129-25-1d0l8.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/571874/original/file-20240129-25-1d0l8.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=425&fit=crop&dpr=1 754w, https://images.theconversation.com/files/571874/original/file-20240129-25-1d0l8.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=425&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/571874/original/file-20240129-25-1d0l8.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=425&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Aerial robotic balloons, or aerobots, like this Nasa prototype, could one day explore Venus.</span>
<span class="attribution"><a class="source" href="https://www.jpl.nasa.gov/news/jpls-venus-aerial-robotic-balloon-prototype-aces-test-flights">Nasa / JPL-Caltech</a></span>
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<p>But it went way beyond expectations, surviving three years on the Martian surface, even through a dusty season, and making 72 flights. Much of its success was aided by the communication network that now exists at Mars. </p>
<p>Ingenuity receives instructions and transmits data to Perseverance, which communicates with a fleet of satellites that include the European ExoMars Trace Gas Orbiter, Nasa’s Maven spacecraft, and the Mars Reconnaissance Orbiter. These, in turn, communicate with two deep space networks on Earth, systems of radio antennas around the world that command and track spacecraft. </p>
<p>It took 50 years of planetary exploration to get here, but already we can see the impact on future exploration that Ingenuity’s mission is having. The next interplanetary rotorcraft will be the <a href="https://dragonfly.jhuapl.edu/">Dragonfly mission to Saturn’s moon Titan</a>. </p>
<p>It will be a very different from Ingenuity. It will weigh about a ton and fly with eight rotors. It is a huge vehicle designed to fly in Titan’s thick atmosphere. </p>
<p>One of the next Red Planet missions will be Mars Sample Return, aiming to collect sample containers of Martian soil being prepared and cached by Perseverance. This has been planned to be carried out with use of a rover, but the success of Ingenuity has led to the idea – and now the development – of <a href="https://mars.nasa.gov/msr/spacecraft/sample-recovery-helicopters/">a helicopter</a> to do that. </p>
<p>The future that Ingenuity has opened up for us is exciting. We’ll see helicopters on Mars and Venus, more balloons on Venus, swimming vehicles under the icy moons of Jupiter and Saturn, and maybe even an aeroplane or two.</p><img src="https://counter.theconversation.com/content/222173/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Kevin Olsen in an employee of the University of Oxford and receives funding from the UK Space Agency in support of Mars science.</span></em></p>Among the missions being planned is a huge helicopter drone to explore Saturn’s moon Titan.Kevin Olsen, UKSA Mars Science Fellow, Department of Physics, University of OxfordLicensed 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>
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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>
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</em>
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<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>
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<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>
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<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/2077142023-06-14T23:03:46Z2023-06-14T23:03:46ZFor the first time, astronomers have found life-supporting molecules called phosphates on Enceladus<figure><img src="https://images.theconversation.com/files/531898/original/file-20230614-22-z3g0a3.png?ixlib=rb-1.1.0&rect=742%2C233%2C3155%2C1760&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">NASA/JPL/Space Science Institute</span></span></figcaption></figure><p>The search for habitable conditions beyond Earth has just become more interesting with the discovery of biologically available phosphorus from one of Saturn’s moons. Phosphorus is the most elusive of the six crucial elements needed for life.</p>
<p>In research <a href="https://doi.org/10.1038/s41586-023-05987-9">published today in Nature</a>, data from the Cassini spacecraft were used to find phosphorus compounds called phosphates in <a href="https://solarsystem.nasa.gov/news/13021/put-a-ring-on-it/">Saturn’s E ring</a> – one of the fainter outer rings of the planet.</p>
<p>These compounds likely came from the ice volcano (cryovolcano) plumes from the <a href="https://theconversation.com/waterworld-cassini-spots-the-motion-of-enceladuss-ocean-25069">sub-surface liquid water ocean</a> on Saturn’s moon Enceladus.</p>
<h2>A famous moon</h2>
<p>Enceladus seemed like a typical moon of Saturn until the Cassini spacecraft came to take a closer look. <a href="https://theconversation.com/a-look-back-at-cassinis-incredible-mission-to-saturn-before-its-final-plunge-into-the-planet-83226">Arriving at Saturn in 2005</a>, Cassini has been making <a href="https://solarsystem.nasa.gov/news/12892/cassini-10-years-at-saturn-top-10-discoveries/">discovery after discovery</a> that have catapulted Enceladus to one of the top places to look for life beyond Earth.</p>
<p>In particular, we learned Enceladus has a liquid water ocean beneath its icy surface, heated by gravitational tidal forcing – the kind of forcing that produces ocean tides on Earth.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/531895/original/file-20230614-19-jl252o.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/531895/original/file-20230614-19-jl252o.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/531895/original/file-20230614-19-jl252o.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=640&fit=crop&dpr=1 600w, https://images.theconversation.com/files/531895/original/file-20230614-19-jl252o.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=640&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/531895/original/file-20230614-19-jl252o.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=640&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/531895/original/file-20230614-19-jl252o.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=805&fit=crop&dpr=1 754w, https://images.theconversation.com/files/531895/original/file-20230614-19-jl252o.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=805&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/531895/original/file-20230614-19-jl252o.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=805&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 process of organic compounds making their way onto ice grains emitted in plumes from Saturn’s moon Enceladus, where they were detected by NASA’s Cassini spacecraft.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech</span></span>
</figcaption>
</figure>
<p>This environment is tantalisingly similar to the <a href="https://theconversation.com/origins-of-life-new-evidence-first-cells-could-have-formed-at-the-bottom-of-the-ocean-126228">hydrothermal vents thought by some</a> to be the place where life may have originated on Earth. Such vents certainly host life on Earth today.</p>
<p>Most life on Earth ultimately relies on photosynthesis – generating energy from sunlight. Meanwhile, the ultimate energy source for any life on Enceladus would be the gravity of Saturn producing tides far stronger than the Moon produces on Earth, allowing a liquid water ocean despite the very cold -200°C ice crust surface.</p>
<h2>Easy sampling</h2>
<p>The Enceladus plumes have been called a “gimme” for efforts to sample the oceans of alien worlds. One wouldn’t need to land to collect a sample, nor to then launch to return it for analysis.</p>
<p>An obvious approach to sampling an ice volcano is to simply fly through it. However, this is difficult because the speed at which a space probe would encounter the plume would likely kill most organics.</p>
<p>Instead, the easiest approach is to examine the accumulation of ejected material from Enceladus in Saturn’s E ring, which is what the team did in this latest study. </p>
<p>Using this approach, researchers have previously discovered <a href="https://academic.oup.com/mnras/article/489/4/5231/5573821">complex organic molecules</a> <a href="https://www.nature.com/articles/s41586-018-0246-4">coming from Enceladus</a>. These findings confirmed that the watery environment on Enceladus supports complex chemistry involving nitrogen and oxygen.</p>
<p>However, until now we didn’t know about the availability of phosphorus on Enceladus; in many environments this element is locked in rocks.</p>
<h2>A crucial element</h2>
<p>The discovery of phosphates in Saturn’s E ring suggests phosphates could be available within the oceans of Enceladus at a concentration 100 times higher than in Earth’s oceans.</p>
<p>Phosphorus is crucial for life as we know it, partly because it is a key building block of DNA and RNA, molecules essential to all life on Earth. Phosphate is also vital for a number of other metabolic processes in all life. </p>
<p>Many of the essential components necessary for the emergence of life as we know it have thus been discovered on Enceladus. This puts it at or near the top of lists of places to search for life beyond Earth in our Solar System. </p>
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Read more:
<a href="https://theconversation.com/humans-are-still-hunting-for-aliens-heres-how-astronomers-are-looking-for-life-beyond-earth-197621">Humans are still hunting for aliens. Here's how astronomers are looking for life beyond Earth</a>
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<p>Nevertheless, this discovery is only the start of the story. For phosphate to form bonds with carbon – this type of bond is found in the backbone of DNA – we need specialised chemistry that’s very dependent on the environment.</p>
<p>We’ll need further study of the chemistry in and under the crust of Enceladus. But a future detection of organic phosphate compounds would be particularly interesting for the potential for life in the moon’s oceans.</p>
<h2>No ‘smoking gun’</h2>
<p>This research is reminiscent of the reported detection of <a href="https://theconversation.com/the-detection-of-phosphine-in-venus-clouds-is-a-big-deal-heres-how-we-can-find-out-if-its-a-sign-of-life-146185">phosphine on Venus</a> in September 2020, which was <a href="https://www.universetoday.com/158983/sofia-fails-to-find-phosphine-in-the-atmosphere-of-venus-but-the-debate-continues/">cast into doubt by later evidence</a>.</p>
<p>However, the detection method is quite different. On Venus the presence of phosphine was proposed by observing the atmosphere from Earth. The phosphates in this study were detected using an instrument orbiting Saturn called a mass spectrometer, which measured the mass of individual compounds found in the ice of the E ring.</p>
<p>To verify the analysis, the authors created a water solution on Earth very similar to the predicted Enceladus ocean.</p>
<p>That said, both detection methods carry a risk of misidentification, where a different molecule that’s not phosphine is actually responsible for the result. </p>
<p>It would be great to have a “smoking gun” for life beyond Earth, but realistically it will instead be a trickle of evidence that grows as we discover more about these environments. </p>
<p>The study published today is one more piece of evidence supporting the fact that Enceladus may be a great location in our search for extraterrestrial life. </p>
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<p><em>Acknowledgements: We thank Prof Steve Benner from The Foundation For Applied Molecular Evolution for his insight and contributions to this article.</em></p><img src="https://counter.theconversation.com/content/207714/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>Phosphorus is the most elusive element crucial for life as we know it – and we now have the first evidence there’s some available in the oceans of Enceladus.Laura McKemmish, Lecturer, UNSW SydneyAlbert Fahrenbach, Senior Lecturer, UNSW SydneyMartin Van Kranendonk, Professor and Director of the Australian Centre for Astrobiology, UNSW SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2074562023-06-14T15:04:43Z2023-06-14T15:04:43ZAn element essential to life discovered on one of Saturn’s moons, raising hopes of finding alien microbes<figure><img src="https://images.theconversation.com/files/531159/original/file-20230609-25-9jhlr6.jpg?ixlib=rb-1.1.0&rect=17%2C19%2C974%2C358&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Ice particles, with just a trace of phosphates, venting from near Enceladus's south pole, as imaged by Cassini in 2010.</span> <span class="attribution"><a class="source" href="https://photojournal.jpl.nasa.gov/jpeg/PIA17184.jpg">NASA/JPL-Caltech/Space Science Institute</a></span></figcaption></figure><p>Enceladus is the tiny moon of Saturn that seems to have it all. Its icy surface is intricately carved by ongoing geological processes. Its icy shell overlies an internal, liquid ocean. There, chemically charged warm water seeps out of the rocky core onto the ocean floor – potentially providing nourishment for microbial life.</p>
<p>Now, a new study, <a href="https://www.nature.com/articles/s41586-023-05987-9">published in Nature</a>, has uncovered more evidence. It presents the first proof that Enceladus’s ocean contains phosphorus, an element that is essential to life.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/531290/original/file-20230612-29-6bcdcp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Cross-cutting ridges and grooves on the surface of Enceladus" src="https://images.theconversation.com/files/531290/original/file-20230612-29-6bcdcp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/531290/original/file-20230612-29-6bcdcp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=431&fit=crop&dpr=1 600w, https://images.theconversation.com/files/531290/original/file-20230612-29-6bcdcp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=431&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/531290/original/file-20230612-29-6bcdcp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=431&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/531290/original/file-20230612-29-6bcdcp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=542&fit=crop&dpr=1 754w, https://images.theconversation.com/files/531290/original/file-20230612-29-6bcdcp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=542&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/531290/original/file-20230612-29-6bcdcp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=542&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">A complicated history of fracturing of the icy crust is apparent in this 80 km wide view of the Samarkand Sulci region of Enceladus.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech/Space Science Institute</span></span>
</figcaption>
</figure>
<p>The <a href="https://theconversation.com/bittersweet-feeling-as-cassini-mission-embarks-on-its-grand-finale-ahead-of-death-plunge-76670">Cassini spacecraft</a>, operated in orbit about Saturn 2004-17 by Nasa and the European Space Agency (Esa), found plumes of ice particles venting from cracks. These penetrate right through the icy shell so that the ocean water at the bottom of each crack is exposed to the vacuum of space, where the lack of confining pressure causes it to bubble and vaporise in the form of plumes. </p>
<p>These plumes provided samples of spray from Enceladus’s internal ocean that were scooped up for analysis by Cassini during several close fly-bys – a bonus that wasn’t anticipated when the mission was initially planned.</p>
<p>Particles analysed during these brief passages through the plumes demonstrated that the ice is contaminated by traces of <a href="https://theconversation.com/nasa-saturn-moon-enceladus-is-able-to-host-life-its-time-for-a-new-mission-76102">simple organic molecules as well as molecular hydrogen and tiny particles of silica</a>. Taken together, these indicate that chemical reactions between water and warm rock take place on the ocean floor, most probably at “<a href="https://oceanexplorer.noaa.gov/facts/mid-ocean-ridge.html">hydrothermal vents</a>” (a fissure releasing heated water) similar to those on Earth.</p>
<p>This is significant. It means Enceladus has all the ingredients for microbial life to sustain itself (in the absence of sunlight). It is in fact the setting considered most likely to have helped life on Earth begin. If it happened on Earth it could have happened inside Enceladus too.</p>
<h2>Missing link</h2>
<p>All life on Earth requires six essential elements: carbon, hydrogen, nitrogen, oxygen, phosphorus and sulphur – known collectively by the scarcely pronounceable acronym CHNOPS. Five of these six essential elements were detected in Enceladus plume samples several years ago, but phosphorus had never been found. </p>
<p>Phosphorus is a vital ingredient, because it is needed for the phosphate groups (phosphorus plus oxygen) that link the long chains of <a href="https://www.genome.gov/genetics-glossary/Nucleic-Acids">nucleic acids</a> such as DNA and RNA that store genetic information. It also allows cells to store energy by means of molecules such as <a href="https://www.ncbi.nlm.nih.gov/books/NBK553175/">adenoside triphosphate</a> (ATP for short).</p>
<p>Of course, we don’t know for sure that life inside Enceladus (if it exists) is obliged to use nucleic acids or ATP. However, because the presence of phosphorus is essential for life as we know it, it makes Enceladus a more likely prospect now that we are certain that there is enough phosphorus available there.</p>
<figure class="align-center ">
<img alt="Against black space, a diffuse arc which is invisibly small icy particles scattering sunlight. A bright dot within the arc in Enceladus." src="https://images.theconversation.com/files/531170/original/file-20230609-27-zq3ly3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/531170/original/file-20230609-27-zq3ly3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=397&fit=crop&dpr=1 600w, https://images.theconversation.com/files/531170/original/file-20230609-27-zq3ly3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=397&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/531170/original/file-20230609-27-zq3ly3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=397&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/531170/original/file-20230609-27-zq3ly3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=499&fit=crop&dpr=1 754w, https://images.theconversation.com/files/531170/original/file-20230609-27-zq3ly3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=499&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/531170/original/file-20230609-27-zq3ly3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=499&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Enceladus, a tiny dot embedded in Saturn’s, E-ring.</span>
<span class="attribution"><span class="source">NASA/JPL/Space Science Institute</span></span>
</figcaption>
</figure>
<h2>Canny collecting</h2>
<p>The team found Enceladus’s phosphorus by avoiding the cluttered data collected during the Cassini’s frantically quick zooms through the plumes. Instead, they scoured sparser data accumulated in a more leisurely fashion by Cassini’s Cosmic Dust Analyzer during 15 periods between 2004 and 2008 while Cassini was travelling within one of Saturn’s rings: the “<a href="https://solarsystem.nasa.gov/news/13021/put-a-ring-on-it/">E-ring</a>”. Enceladus travels along this hoop as it orbits.</p>
<p>The E-ring hoop is more than 2,000km thick. About 30% of the ice particles emitted in Enceladus’ plumes end up there, as demonstrated by a <a href="https://webbtelescope.org/contents/media/images/2023/112/01GYJ7H5VSDMPRWX0R0Z6R87EC">recent image from the James Webb Space Telescope</a>, which is the only proof we have that the plumes were still active five years after <a href="https://theconversation.com/cassini-crashes-its-time-for-a-new-mission-to-explore-the-possibility-of-life-on-saturns-moons-84016">the end of the Cassini mission</a>.</p>
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<span class="caption">Lower left: The plume from Enceladus, imaged at a range of more than a billion km by the James Webb (JWST) telescope, accompanied by an artist’s impression.</span>
<span class="attribution"><span class="source">NASA, ESA, CSA, STScI, Leah Hustak (STScI)</span></span>
</figcaption>
</figure>
<p>Sorting through analyses of nearly a thousand ice particles, which are believed to represent frozen spray from Enceladus, the researchers found nine of them that contained phosphates. This may sound like a slim haul, but it is enough to demonstrate that Enceladus has more than enough dissolved phosphorus in its ocean to permit the functioning of life there.</p>
<p>Indeed, follow-up laboratory experiments suggest that the concentration of dissolved phosphorus in Enceladus’s ocean water may even be hundreds of times greater than in Earth’s oceans.</p>
<p>The team argue that their findings and associated modelling make it likely that any icy moon that grew further from the Sun than the Solar System’s “carbon dioxide snowline” – a location where temperatures during planetary formation were low enough for carbon dioxide to become ice – is likely to contain abundant phosphorus. This condition is met for icy moons at Saturn and beyond, but not at Jupiter. </p>
<p>Jupiter’s distance from the Sun places it beyond the “water-ice snowline” (where water becomes ice), but it is too close to the Sun, and hence too warm, to be beyond the carbon dioxide snowline.</p>
<p>So where does this leave Jupiter’s moon <a href="https://theconversation.com/new-water-plumes-from-jupiters-moon-europa-raise-hopes-of-detecting-microbial-life-66019">Europa</a>, a target for <a href="https://theconversation.com/europa-there-may-be-life-on-jupiters-moon-and-two-new-missions-will-pave-the-way-for-finding-it-122551">missions</a> due to arrive about ten years from now? </p>
<p>This moon has been widely touted as potentially able to support a more flourishing biosphere than Enceladus because of its larger size and greater store of chemical energy in its rocky interior. The team behind the new study are reticent on this, but their modelling suggests a phosphate concentration in Europa’s internal ocean about a thousand times less than at Enceladus. </p>
<p>To me, that is not a gamechanger, and we should continue to expect Europa to be habitable. But it would be reassuring to find some proof of phosphorus there too.</p>
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Read more:
<a href="https://theconversation.com/the-chemistry-that-could-feed-life-within-saturns-moon-enceladus-study-gives-clue-ahead-of-flyby-49683">The chemistry that could feed life within Saturn's moon Enceladus: study gives clue ahead of flyby</a>
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<img src="https://counter.theconversation.com/content/207456/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Rothery is Professor of Planetary Geosciences at the Open University. He is co-leader of the European Space Agency's Mercury Surface and Composition Working Group, and a Co-Investigator on MIXS (Mercury Imaging X-ray Spectrometer) that is now on its way to Mercury on board the European Space Agency's Mercury orbiter BepiColombo. He has received funding from the UK Space Agency and the Science & Technology Facilities Council for work related to Mercury and BepiColombo, and from the European Commission under its Horizon 2020 programme for work on planetary geological mapping (776276 Planmap). He is author of Planet Mercury - from Pale Pink Dot to Dynamic World (Springer, 2015), Moons: A Very Short Introduction (Oxford University Press, 2015) and Planets: A Very Short Introduction (Oxford University Press, 2010). He is Educator on the Open University's free learning Badged Open Course (BOC) on Moons and its equivalent FutureLearn Moons MOOC, and chair of the Open University's level 2 course on Planetary Science and the Search for Life.</span></em></p>Five out of the six essential elements required for life on Earth were known to exist on Enceladus. Now the sixth and final one has been found too.David Rothery, Professor of Planetary Geosciences, The Open UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2005192023-05-23T12:26:55Z2023-05-23T12:26:55ZWhat Greek mythology teaches us about women’s resistance and rebellion<p>After some hard-fought victories, women’s rights are threatened again in many parts of the world. In the United States, the Supreme Court <a href="https://www.pbs.org/newshour/show/the-shifting-battle-over-abortion-rights-50-years-after-roe">overturned women’s right to abortion</a> in June 2022; women have also been <a href="https://penntoday.upenn.edu/news/how-have-women-workforce-fared-three-years-pandemic">leaving the workforce</a> since the COVID-19 pandemic, in many cases to care for children and elderly relatives. In other parts of the world, especially in developing countries, <a href="https://www.unwomen.org/en/news-stories/explainer/2022/02/explainer-how-gender-inequality-and-climate-change-are-interconnected#:%7E:text=The%20climate%20crisis%20is%20not,less%20access%20to%2C%20natural%20resources">women are disproportionately affected by climate change</a>.</p>
<p><a href="https://as.tufts.edu/classicalstudies/people/faculty/marie-claire-beaulieu">As a scholar of ancient mythology</a>, I’m aware of many female characters in Greek mythology who offer us models for today’s challenges. This may be a little surprising, because ancient Greece was under <a href="https://books.google.com/books/about/Women_in_Ancient_Greece.html?id=Xfx1VaSIOgQC">strict patriarchal rules</a>: Women were considered minors under the guardianship of their fathers or husbands for their whole lives and not allowed to vote. Yet women in these myths spoke truth to power and fiercely resisted injustice and oppression. </p>
<h2>Rebel goddesses</h2>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/520854/original/file-20230413-24-uceh0b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A painting showing a scary looking figure with long hair eating a child whose torso has blood trickling down." src="https://images.theconversation.com/files/520854/original/file-20230413-24-uceh0b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/520854/original/file-20230413-24-uceh0b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=1102&fit=crop&dpr=1 600w, https://images.theconversation.com/files/520854/original/file-20230413-24-uceh0b.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=1102&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/520854/original/file-20230413-24-uceh0b.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=1102&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/520854/original/file-20230413-24-uceh0b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1385&fit=crop&dpr=1 754w, https://images.theconversation.com/files/520854/original/file-20230413-24-uceh0b.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1385&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/520854/original/file-20230413-24-uceh0b.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1385&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 god Saturn devouring his child. A painting by Francisco José de Goya y Lucientes.</span>
<span class="attribution"><a class="source" href="https://www.museodelprado.es/en/the-collection/art-work/saturn/18110a75-b0e7-430c-bc73-2a4d55893bd6">Museo Nacional del Prado, Madrid</a></span>
</figcaption>
</figure>
<p>Female rebellion is at the heart of the Greek story <a href="http://www.perseus.tufts.edu/hopper/text?doc=urn:cts:greekLit:tlg0020.tlg001.perseus-eng1:104-138">about the creation of the world</a>. Gaia, the Earth goddess, rebels against her husband Ouranos, the Sky, who smothers her and refuses to let her children be free. She orders her son Kronos to castrate his father and take his throne. Once Kronos comes to power, however, he becomes afraid of being dethroned by his children, so <a href="http://www.perseus.tufts.edu/hopper/text?doc=urn:cts:greekLit:tlg0059.tlg001.perseus-eng1:6a">he swallows all the babies his wife Rhea gives birth to</a>. </p>
<p>Rhea rebels against this horrific act. She gives Kronos <a href="https://www.metmuseum.org/art/collection/search/247308?ft=06.1021.144&offset=0&rpp=40&pos=1">a stone wrapped in a blanket</a> to trick him into thinking that he is going to devour this baby as well. Rhea then hides her child, the god Zeus, who grows up and throws his father down into the depths of the Underworld. But history repeats itself, and the new leader of the gods again fears that his wife may plot to overthrow him. As the king of the gods, Zeus is forever afraid of his wife Hera, <a href="https://doi.org/10.1017/9781108888479">who exacts vengeance for all his transgressions</a>, especially his innumerable affairs. </p>
<p>Similarly, the story of Demeter and her daughter Persephone shows a powerful goddess holding her ground in the face of male deities. When Persephone is abducted by Hades, the king of the Underworld, Demeter, the goddess of agriculture, <a href="http://www.perseus.tufts.edu/hopper/text?doc=urn:cts:greekLit:tlg0013.tlg002.perseus-eng1:2">refuses to let the crops grow until Persephone is returned</a>. Despite Zeus’ pleading, Demeter does not relent. The entire world is barren of fruit, and humans starve. </p>
<p>Eventually Zeus is forced to negotiate, and Persephone <a href="https://www.metmuseum.org/art/collection/search/252973">rises from the Underworld</a> to be with her mother for a part of each year. During the months when Persephone is with Hades, Demeter holds back vegetation and it is winter on the Earth. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/520857/original/file-20230413-26-8ppfh5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A painting showing a man carrying a woman away in a chariot being driven by a white horse" src="https://images.theconversation.com/files/520857/original/file-20230413-26-8ppfh5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/520857/original/file-20230413-26-8ppfh5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=219&fit=crop&dpr=1 600w, https://images.theconversation.com/files/520857/original/file-20230413-26-8ppfh5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=219&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/520857/original/file-20230413-26-8ppfh5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=219&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/520857/original/file-20230413-26-8ppfh5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=275&fit=crop&dpr=1 754w, https://images.theconversation.com/files/520857/original/file-20230413-26-8ppfh5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=275&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/520857/original/file-20230413-26-8ppfh5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=275&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Mural with Hades abducting Persephone in a chariot.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Hades_abducting_Persephone.jpg">From Le Musée absolu, Phaidon, via Wikimedia Commons</a></span>
</figcaption>
</figure>
<h2>Mortal women</h2>
<p>Greek culture, however, was suspicious of strong-willed women and portrayed them as villains.</p>
<p>Classical scholar <a href="https://www.classics.cam.ac.uk/directory/mary-beard">Mary Beard</a> explains that women are characterized in this way by male writers to justify women’s exclusion from power. She argues that the Western definition of power applies intrinsically to males. Therefore, <a href="https://wwnorton.com/books/9781631494758">Beard explains</a>, “[Women] are, for the most part, portrayed as abusers rather than users of power. They take it illegitimately, in a way that leads to the fracture of the state, to death and destruction. … In fact, it is the unquestionable mess that women make of power that justifies their exclusion from it in real life.”</p>
<p>Beard uses the stories of Clytemnestra and Medea, among others, to illustrate her point. Clytemnestra punishes her husband, Agamemnon, for <a href="http://www.perseus.tufts.edu/hopper/text?doc=urn:cts:greekLit:tlg0006.tlg018.perseus-eng1:506-542">sacrificing their daughter Iphigenia</a> at the beginning of the Trojan War. She seizes power in his kingdom of Mycenae while Agamemnon is still at war, and when he returns, <a href="https://collections.louvre.fr/en/ark:/53355/cl010277267">she murders him in cold blood</a>. </p>
<p>Medea makes her husband, Jason, <a href="http://www.perseus.tufts.edu/hopper/text?doc=urn:cts:greekLit:tlg0006.tlg003.perseus-eng1">pay the ultimate price</a> for deserting her – <a href="https://collections.louvre.fr/en/ark:/53355/cl010274318">she kills their children</a>.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/520860/original/file-20230413-18-u8i33o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A black bowl from 400 B.C.E. with several figures painted on it." src="https://images.theconversation.com/files/520860/original/file-20230413-18-u8i33o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/520860/original/file-20230413-18-u8i33o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=644&fit=crop&dpr=1 600w, https://images.theconversation.com/files/520860/original/file-20230413-18-u8i33o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=644&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/520860/original/file-20230413-18-u8i33o.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=644&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/520860/original/file-20230413-18-u8i33o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=810&fit=crop&dpr=1 754w, https://images.theconversation.com/files/520860/original/file-20230413-18-u8i33o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=810&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/520860/original/file-20230413-18-u8i33o.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=810&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Painting on a bowl of Medea fleeing in a chariot pulled by dragons.</span>
<span class="attribution"><a class="source" href="https://www.clevelandart.org/art/1991.1">Cleveland Museum of Art</a></span>
</figcaption>
</figure>
<p>Medea, as a foreign princess in the Greek city of Corinth, a powerful sorceress, and a Black individual, is marginalized in multiple ways. Yet she refuses to back down. Classical scholar and Black feminist intellectual <a href="https://www.hamilton.edu/academics/our-faculty/directory/faculty-detail/shelley-haley">Shelley Haley</a> stresses that Medea is proud, a characteristic that is viewed as typically masculine in Greek culture. </p>
<p>Haley sees Medea’s actions as a way to assert her individuality in the face of Greek societal expectations. Medea is not willing to give Jason the freedom to start a relationship with another woman, and she negotiates asylum on her own terms with the king of Athens. <a href="https://books.google.com/books?id=kjup9bBv168C&lpg=PA177&pg=PA177#v=onepage&q&f=true">According to Haley, Medea</a> “resists the cultural norms that inscribe child-bearing as the only raison d'être of female existence. Medea loves her children, but like a man, her pride comes first.”</p>
<h2>Comedy and tragedy</h2>
<p>In a more humorous way, in “Lysistrata,” the playwright Aristophanes imagines the women of Athens protesting the destructive <a href="http://www.perseus.tufts.edu/hopper/text?doc=urn:cts:greekLit:tlg0003.tlg001.perseus-eng3">Peloponnesian War</a> by going on a sex strike. Under such dire pressure, their husbands quickly give in and peace is negotiated with Sparta. </p>
<p>Lysistrata, the leader of the striking women, explains that <a href="http://www.perseus.tufts.edu/hopper/text?doc=urn:cts:greekLit:tlg0019.tlg007.perseus-eng1:551-597">women suffer doubly in war</a>, even though they have no say in the decision to enter warfare. They suffer first by bearing children and then by seeing them sent out as soldiers. They can be widowed and enslaved as well as a consequence of war.</p>
<p>Finally, in a famous tragedy by Sophocles, <a href="http://www.perseus.tufts.edu/hopper/text?doc=urn:cts:greekLit:tlg0011.tlg002.perseus-eng1">Antigone fights for human decency</a> in the face of autocracy. When Antigone’s brothers Eteocles and Polyneices fight for the throne of Thebes and ultimately kill one another, the new king, Creon, orders that only Eteocles, whom he considers to have been the rightful king, be buried with honor. Antigone revolts and says that she must uphold divine law <a href="https://www.youtube.com/watch?v=A9-W66xB-fM">rather than Creon’s tyrannical human law</a>. She sprinkles Polyneices’ body with a little dust, a symbolic gesture that allows the dead man to move on to the afterlife.</p>
<p>Antigone takes action knowing full well that Creon will kill her to enforce his edict. Yet she is prepared to offer the ultimate sacrifice for her beliefs. </p>
<h2>Women and moral justice</h2>
<p>Throughout these stories, female figures stand for moral justice and as an embodiment of the resistance of disempowered people. Perhaps for this reason the figure of Medusa, traditionally viewed as a terrifying female monster <a href="http://data.perseus.org/citations/urn:cts:greekLit:tlg0548.tlg001.perseus-eng1:2.4">defeated by the male hero Perseus</a>, has recently been reinterpreted as a symbol of strength and resilience.</p>
<p>Acknowledging that the <a href="http://www.perseus.tufts.edu/hopper/text?doc=urn:cts:latinLit:phi0959.phi006.perseus-eng1:4.706">mythological Medusa was turned into a monster</a> as a result of her rape by Poseidon, many survivors of sexual assault <a href="https://twitter.com/emberlilly_/status/1640423393806696469">have adopted the image of Medusa</a> as an image of resilience. </p>
<p>Sculptor <a href="https://www.lucianogarbati.com/">Luciano Garbati</a> turned the myth on its head. In a new take on the traditional image of the victorious <a href="https://en.wikipedia.org/wiki/Perseus_with_the_Head_of_Medusa#/media/File:Persee-florence.jpg">Perseus with the head of Medusa</a>, Garbati gave Medusa a powerful new stance with his statue “Medusa with the Head of Perseus.” Medusa’s thoughtful and determined demeanor became a symbol for the #MeToo movement <a href="https://www.nytimes.com/2020/10/13/arts/design/medusa-statue-manhattan.html">when the statue was set up outside the courtroom</a> where Harvey Weinstein and many others accused of sexual assault stood trial. </p>
<h2>What does this mean in today’s world?</h2>
<p>Echoes of all these stories resonate strongly <a href="https://www.boldtypebooks.com/titles/helen-morales/antigone-rising/9781568589343/">today in the words of fearless young female activists</a>. </p>
<p>Malala Yousafzai spoke up for girls’ education in Taliban-controlled Afghanistan although she knew the potential repercussions could be dire. In an interview for a podcast, <a href="https://podcasts.apple.com/gb/podcast/the-accomplishment-podcast-with-sir-michael-barber/id1605826027?i=1000601684803">she said</a>: “We knew that nothing would change if we remained quiet. Change comes when somebody is willing to step up and speak out.” </p>
<p>Greta Thunberg, <a href="https://www.npr.org/2019/09/23/763452863/transcript-greta-thunbergs-speech-at-the-u-n-climate-action-summit">addressing world leaders at the United Nations Climate Action Summit in 2019</a>, did not miss a beat: “You are failing us. But the young people are starting to understand your betrayal. The eyes of all future generations are upon you. And if you choose to fail us, I say: We will never forgive you. We will not let you get away with this. Right here, right now is where we draw the line.”</p>
<p>For the women who continue to fight against oppression, it can be both a comfort and a catalyst for action to know that they have been doing so for millennia.</p><img src="https://counter.theconversation.com/content/200519/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Marie-Claire Beaulieu does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Female characters in Greek mythology lived under strict patriarchal rules, but they spoke truth to power and resisted injustice.Marie-Claire Beaulieu, Associate Professor of Classical Studies, Tufts UniversityLicensed 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/2004542023-03-15T13:37:40Z2023-03-15T13:37:40ZCurious Kids: How are planets created?<figure><img src="https://images.theconversation.com/files/511620/original/file-20230222-16-c8nmnb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Eight planets, including Earth, revolve around our Sun.</span> <span class="attribution"><span class="source">Illustration by Tobias Roetsch/Future Publishing via Getty Images</span></span></figcaption></figure><p><em>Curious Kids is a <a href="https://theconversation.com/africa/topics/curious-kids-36782">series</a> for children in which we ask experts to answer questions from kids.</em></p>
<p><strong>How are planets created? - (Saba, 6, Kenya)</strong></p>
<p>Thanks for asking such an interesting question, Saba. When you talk about planets you’re probably thinking of the planets in our solar system – the ones orbiting (circling around) our sun. There are eight of these <a href="https://solarsystem.nasa.gov/planets/overview/#otp_planets_of_our_solar_system">planets</a>. One of them is where you and I live: Earth. The others are Mercury, Venus, Mars, Jupiter, Saturn, Uranus and Neptune.</p>
<p>There are many, many more planets way beyond our solar system and our galaxy, the Milky Way. Scientists like us, known as astronomers, have found <a href="https://www.planetary.org/worlds/exoplanets">over 5,000 planets</a> around other stars. We estimate that there may be trillions across the Universe.</p>
<p>How did they come into being? It all starts with a cloud of gas and dust.</p>
<h2>Gas and dust</h2>
<p>These clouds of gas and dust are called nebulae. They float around in space much like the clouds in our sky. There are some regions with more clouds and some with fewer and astronomers can see these using telescopes.</p>
<p>Nebulae contain gases like hydrogen, helium and carbon. When a nebula becomes dense enough its gravity pulls it together into a very dense core. This is a bit like the water in your bath swirling around the drain before getting sucked down. As the cloud gets dense it heats up. When it gets dense and hot enough the atoms – tiny building blocks for all the matter in the world – in the nebula start to fuse.</p>
<p>This process is called nuclear fusion and produces a lot of energy. And the cloud lights up like a firework. This is how a new star is born, just like our Sun was <a href="https://spaceplace.nasa.gov/sun-age/en/">4.5 billion years ago</a>.</p>
<p>A small amount of gas and dust remains around new stars in a spinning disc. Planets are formed from this disc of material.</p>
<h2>Protoplanets</h2>
<p>As the disc rotates, the material in it, small bits of rock and ice, lump together and get bigger and bigger. That forms what we call planetesimals, which collide with each other like bumper cars, creating even larger bodies known as protoplanets.</p>
<p>The protoplanets keep growing. While this is happening, they can attract gases from the surrounding disc, creating a thick atmosphere. This process is called accretion and it is how gas giant planets like Jupiter and Saturn are formed. If a protoplanet forms from heavier elements in the outer solar system it can create an ice giant. The planets Neptune and Uranus are ice giants.</p>
<p>Even after the planet is formed it can keep changing over time through processes such as volcanic activity, tectonic movement, and erosion. On Earth, mountains like Mount Kilimanjaro in Tanzania – the country next door to Kenya – formed from large volcanoes. And even larger mountains like the Himalayas have formed from tectonic plates colliding. Tectonic plates are big pieces of the Earth’s outer layer; sometimes they crash into each other and that creates things like mountains.</p>
<h2>Millions of years</h2>
<p>The way I’ve described this makes it sound as though planets are formed quickly. But the process which begins with those clouds of gas and dust takes millions of years to transform into the beautiful and diverse worlds we see in our Solar System and beyond.</p><img src="https://counter.theconversation.com/content/200454/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Daniel Cunnama receives funding from the National Research Foundation and the South African Astronomical Observatory. </span></em></p>It all starts with a cloud of gas and dust.Daniel Cunnama, Science Engagement Astronomer, South African Astronomical Observatory, South African Astronomical ObservatoryLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1895042022-08-30T17:50:24Z2022-08-30T17:50:24ZWho is Artemis? NASA’s latest mission to the Moon is named after an ancient lunar goddess turned feminist icon<figure><img src="https://images.theconversation.com/files/481419/original/file-20220828-49487-qajm6m.jpeg?ixlib=rb-1.1.0&rect=0%2C23%2C2592%2C1901&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Diana by Augustus Saint Gaudens, 1928, Metropolitan Museum of Art, New York.</span> <span class="attribution"><a class="source" href="https://upload.wikimedia.org/wikipedia/commons/c/c5/Diana_by_Augustus_Saint-Gaudens_02.jpg">Postdlf via Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>NASA <a href="https://qz.com/artemis-1-moon-launch-1849788717">launched the Artemis I moon rocket</a> on the morning of Nov. 16, 2022, after several delays earlier this year. This first flight is without a crew and expected to last four to six weeks. The program aims to increase women’s participation in space exploration – <a href="https://www.unr.edu/nevada-today/blogs/2021/the-artemis-program-women-going-to-the-moon">30% of its engineers are women</a>. In addition, the Artemis I mission is carrying two mannequins designed to study the effects <a href="https://www.nasa.gov/feature/orion-passengers-on-artemis-i-to-test-radiation-vest-for-deep-space-missions">of radiation on women’s bodies</a> so that NASA can learn how to protect female astronauts better.</p>
<p>Female astronauts are currently less likely to be selected for missions than men because their bodies tend to hit NASA’s <a href="https://www.nature.com/articles/d41586-022-02293-8">maximum acceptable threshold of radiation</a> earlier. NASA expects to bring the first woman and person of color to the Moon on <a href="https://www.nasa.gov/specials/artemis/">Artemis III</a> sometime after 2024.</p>
<p>As a <a href="https://as.tufts.edu/classicalstudies/people/faculty/marie-claire-beaulieu">scholar of Greek mythology</a>, I find the name of the mission quite evocative: The Greeks and Romans associated Artemis <a href="http://www.perseus.tufts.edu/hopper/text?doc=urn:cts:latinLit:phi0472.phi001.perseus-eng2:34">with the Moon</a>, and she has also become a modern-day feminist icon.</p>
<figure class="align-left ">
<img alt="Greek goddess Artemis with a mass of curls along her face that flow down her neck." src="https://images.theconversation.com/files/481421/original/file-20220828-10694-hfrglg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/481421/original/file-20220828-10694-hfrglg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=706&fit=crop&dpr=1 600w, https://images.theconversation.com/files/481421/original/file-20220828-10694-hfrglg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=706&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/481421/original/file-20220828-10694-hfrglg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=706&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/481421/original/file-20220828-10694-hfrglg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=888&fit=crop&dpr=1 754w, https://images.theconversation.com/files/481421/original/file-20220828-10694-hfrglg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=888&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/481421/original/file-20220828-10694-hfrglg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=888&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Bust of Artemis with crescent moon headband.</span>
<span class="attribution"><a class="source" href="https://collections.mfa.org/objects/180369/oval-gem-with-bust-of-artemis?ctx=51a2d53b-11bc-4547-891c-21b0c8389732&idx=0">Museum of Fine Arts, Boston </a></span>
</figcaption>
</figure>
<p>Artemis was a major deity in ancient Greece, worshiped at least as early as the <a href="https://press.uchicago.edu/ucp/books/book/distributed/F/bo14317059.html">beginning of the first millennium B.C., or even earlier</a>. She was a daughter of Zeus, the chief god of the Olympians, who ruled the world from the summit of Mount Olympus. She was also the twin sister of Apollo, god of the Sun and oracles.</p>
<p>Artemis was a virgin goddess of the wilderness and hunting. Her independence and strength have long inspired women in a wide range of activities. For example, in a poem titled “<a href="https://www.jstor.org/stable/44978722">Artemis</a>,” author <a href="https://www.ohioswallow.com/author/Allison+Eir+Jenks">Allison Eir Jenks</a> writes: “I’m no longer your god-mother … your chef, your bus-stop, your therapist, your junk-drawer,” emphasizing women’s freedom and autonomy.</p>
<p>As the goddess of animals and the wilderness, Artemis has also inspired <a href="https://artemis.nwf.org/">environmental conservancy programs</a>, in which the goddess is viewed as an example of a woman exercising her power by caring for the planet.</p>
<p>However, while the Greek Artemis was strong and courageous, she wasn’t always kind and caring, even toward women. Her rashness was used to explain a <a href="http://data.perseus.org/citations/urn:cts:greekLit:tlg0012.tlg002.perseus-eng1:11.138-11.179">woman’s sudden death</a>, especially while giving birth. This aspect of the goddess has faded away with time. With the rise of feminism, Artemis has become an icon of feminine power and self-reliance.</p>
<figure class="align-right ">
<img alt="A black vase from 470 B.C. showing two figures, one turning toward a hunter to shoot him with her bow." src="https://images.theconversation.com/files/481626/original/file-20220829-6503-phq2k6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/481626/original/file-20220829-6503-phq2k6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=485&fit=crop&dpr=1 600w, https://images.theconversation.com/files/481626/original/file-20220829-6503-phq2k6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=485&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/481626/original/file-20220829-6503-phq2k6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=485&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/481626/original/file-20220829-6503-phq2k6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=609&fit=crop&dpr=1 754w, https://images.theconversation.com/files/481626/original/file-20220829-6503-phq2k6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=609&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/481626/original/file-20220829-6503-phq2k6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=609&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Mixing bowl showing Artemis killing the hunter Actaeon.</span>
<span class="attribution"><a class="source" href="https://collections.mfa.org/objects/153654/mixing-bowl-bell-krater-with-the-death-of-aktaion-and-a-pu?ctx=3953ce93-11da-4ac3-957b-4242cc63cb7c&idx=9">Museum of Fine Arts, Boston. Bradford Huntington James Fund and Museum purchase with funds donated by contribution</a></span>
</figcaption>
</figure>
<p><a href="https://history.nasa.gov/SP-4402.pdf">NASA has a long history</a> of naming its missions after mythological figures. Starting in the 1950s, many rockets and launch systems were named after Greek sky deities, like <a href="https://science.nasa.gov/missions/atlas">Atlas</a> and <a href="https://spacecenter.org/exhibits-and-experiences/nasa-tram-tour/saturn-v-at-rocket-park/">Saturn</a>, whose Greek name is Cronos.</p>
<p>Atlas and Saturn weren’t just gods, they were Titans. In Greek mythology, Titans represent the untamed, primordial forces of nature, and so they evoke the prodigious vastness of space exploration. Although the Titans were known for their immense strength and power, they were also rebellious and dangerous and were eventually defeated by the Olympians, who represent civilization in Greek mythology.</p>
<p>Following the advent of human space flight, NASA began naming missions after children of Zeus who are associated with the sky. The <a href="https://www.nasa.gov/mission_pages/mercury/missions/program-toc.html">Mercury program</a>, active from 1958 to 1963, was named after Hermes’ Roman counterpart, the messenger god who flies between Olympus, Earth and the underworld with his winged sandals. </p>
<p>Starting in 1963, the three-year-long <a href="https://www.nasa.gov/specials/gemini_gallery/">Gemini program</a> featured a capsule designed for two astronauts and was named after the twin sons of Zeus – Castor and Pollux, known as the Dioscuri in Greek – who were cast in the stars as the <a href="https://topostext.org/work/207">constellation of Gemini</a>. They were regularly represented with a star above their heads in Greek and Roman art.</p>
<p>The <a href="https://www.nasa.gov/mission_pages/shuttle/flyout/index.html">space shuttle program</a>, which lasted from 1981 to 2011, diverted from mythological monikers, and the names Columbia, Challenger, Discovery, Atlantis and Endeavour were meant to evoke a spirit of innovation. </p>
<p>With Artemis, NASA is nodding back to the <a href="https://www.nasa.gov/mission_pages/apollo/missions/index.html">Apollo program</a>, which lasted from 1963 to 1972 and put the first men on the Moon in 1969. Over 50 years later, Artemis picks up where her twin brother left off, ushering in a more diverse era of human space flight.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/481424/original/file-20220828-30736-t3iovl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A bronze coin showing two engraved faces." src="https://images.theconversation.com/files/481424/original/file-20220828-30736-t3iovl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/481424/original/file-20220828-30736-t3iovl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=612&fit=crop&dpr=1 600w, https://images.theconversation.com/files/481424/original/file-20220828-30736-t3iovl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=612&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/481424/original/file-20220828-30736-t3iovl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=612&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/481424/original/file-20220828-30736-t3iovl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=769&fit=crop&dpr=1 754w, https://images.theconversation.com/files/481424/original/file-20220828-30736-t3iovl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=769&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/481424/original/file-20220828-30736-t3iovl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=769&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 coin showing the Dioscuri, also known as the Gemini in Latin (Castor and Pollux) with a star above their heads.</span>
<span class="attribution"><a class="source" href="http://numismatics.org/collection/1944.100.8104">American Numismatic Society, Bequest of E.T. Newell</a></span>
</figcaption>
</figure>
<p><em>This piece has been updated to include the date of the launch.</em></p><img src="https://counter.theconversation.com/content/189504/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Marie-Claire Beaulieu does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>A scholar of Greek mythology explains the naming of NASA’s missions after mythological figures and why the name Artemis is indicative of a more diverse era of space exploration.Marie-Claire Beaulieu, Associate Professor of Classical Studies, Tufts UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1759182022-02-21T05:00:45Z2022-02-21T05:00:45ZJupiter, Saturn, Uranus, Neptune: why our next visit to the giant planets will be so important (and just as difficult)<figure><img src="https://images.theconversation.com/files/446075/original/file-20220213-17-1s3hlo0.jpg?ixlib=rb-1.1.0&rect=15%2C3%2C2580%2C1191&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.youtube.com/watch?v=sOpMrVnjYeY&t=2225s&ab_channel=SpaceX">SpaceX</a></span></figcaption></figure><p>The giant planets – Jupiter, Saturn, Uranus and Neptune - are some of the most awe-inspiring in our Solar System, and have great importance for space research and our comprehension of the greater universe.</p>
<p>Yet they remain the least explored – especially the “ice giants” Uranus and Neptune – due to their distance from Earth, and the extreme conditions spacecraft must survive to enter their atmospheres. As such, they’re also the least understood planets in the Solar System.</p>
<p>Our <a href="https://arc.aiaa.org/doi/10.2514/1.A34282">ongoing</a> <a href="https://doi.org/10.2514/1.J060560">research</a> looks at how to overcome the harsh entry conditions experienced during giant planet missions. As we look forward to potential future missions, here’s what we might expect.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/446070/original/file-20220213-13-wp9do.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/446070/original/file-20220213-13-wp9do.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/446070/original/file-20220213-13-wp9do.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=227&fit=crop&dpr=1 600w, https://images.theconversation.com/files/446070/original/file-20220213-13-wp9do.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=227&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/446070/original/file-20220213-13-wp9do.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=227&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/446070/original/file-20220213-13-wp9do.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=286&fit=crop&dpr=1 754w, https://images.theconversation.com/files/446070/original/file-20220213-13-wp9do.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=286&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/446070/original/file-20220213-13-wp9do.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=286&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Jupiter is about ten times as large as Earth – with a 69,911km radius (compared to Earth’s 6,371km radius).</span>
<span class="attribution"><span class="source">Beinahegut</span></span>
</figcaption>
</figure>
<h2>But first, what are giant planets?</h2>
<p>Unlike rocky planets, giant planets don’t have a surface to land on. Even in their lower atmospheres they remain gaseous, reaching extremely high pressures that would crush any spacecraft well before it could land on anything solid.</p>
<p>There are two types of giant planets: gas giants and ice giants. </p>
<p>The larger Jupiter and Saturn are gas giants. These are mainly made of hydrogen and helium, with an outer gaseous layer and a partially liquid “metallic” layer below that. They’re also believed to have a small rocky core. </p>
<p>Uranus and Neptune have similar outer atmospheres and rocky cores, but their inner layer is made up of about 65% water and other so-called “ices” (although these technically remain liquid) such as <a href="https://www.lpi.usra.edu/icegiants/mission_study/Exec-Summary.pdf">methane and ammonia</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/446068/original/file-20220213-17-gke7kv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/446068/original/file-20220213-17-gke7kv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/446068/original/file-20220213-17-gke7kv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/446068/original/file-20220213-17-gke7kv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/446068/original/file-20220213-17-gke7kv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/446068/original/file-20220213-17-gke7kv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/446068/original/file-20220213-17-gke7kv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/446068/original/file-20220213-17-gke7kv.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">Relative size and composition of the giant planets in our solar system (with Earth also shown for comparison).</span>
<span class="attribution"><span class="source">JPL/Caltech (based on material from the Lunar and Planetary Institute)</span></span>
</figcaption>
</figure>
<h2>Slingshots to the edge of the Solar System</h2>
<p>Any giant planet mission is extremely difficult. Still, there have been some past missions sent to the gas giants.</p>
<p>NASA’s 1989 Galileo mission had to slingshot around Venus and Earth to give it enough momentum to <a href="https://www.nasa.gov/feature/30-years-ago-galileo-off-to-orbit-jupiter">get to Jupiter</a>, which it orbited for eight years. The 2011 <a href="https://spaceflight101.com/juno/juno-mission-trajectory-design/">Juno mission</a> spent five years in transit, using a flyby around Earth to reach Jupiter (which it still orbits).</p>
<p>Similarly, the Cassini-Huygens mission run by NASA and the European Space Agency (ESA) <a href="https://sci.esa.int/web/cassini-huygens/-/31240-getting-to-saturn">took seven years</a> to reach Saturn. The spacecraft spent 13 years exploring the planet and its surrounds, and launched a probe to explore Saturn’s moon, <a href="https://solarsystem.nasa.gov/missions/cassini/science/titan/">Titan</a>.</p>
<p>Flight times get even longer for the two ice giants, which are much further from the Sun. Neither has had a dedicated mission so far. </p>
<h2>A complex journey</h2>
<p>The last and only spacecraft to visit the ice giants was <a href="https://solarsystem.nasa.gov/missions/voyager-2/in-depth/">Voyager 2</a>, which flew by Uranus in 1986 and Neptune in 1989. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/446498/original/file-20220215-17-rqmzoy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/446498/original/file-20220215-17-rqmzoy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/446498/original/file-20220215-17-rqmzoy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/446498/original/file-20220215-17-rqmzoy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/446498/original/file-20220215-17-rqmzoy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/446498/original/file-20220215-17-rqmzoy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/446498/original/file-20220215-17-rqmzoy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Voyager 2, the only spacecraft ever to have visited Neptune, took a photo of the planet in 1989.</span>
<span class="attribution"><span class="source">NASA/JPL</span></span>
</figcaption>
</figure>
<p>While momentum is building for a return, it won’t be simple. If we launch during the next convenient <a href="https://www.lpi.usra.edu/icegiants/mission_study/Exec-Summary.pdf">launch windows</a> of 2030–34 for Uranus and 2029–30 for Neptune, flight times would vary from 11 to 15 years.</p>
<p>A major issue is power. The Juno spacecraft is the most distant object from the Sun to have <a href="https://www.jpl.nasa.gov/news/nasas-juno-spacecraft-breaks-solar-power-distance-record">used solar panels</a>. It orbits Jupiter, which is <a href="https://solarsystem.nasa.gov/planets/jupiter/in-depth/">five times further away</a> from the Sun than Earth is. Yet, where Juno’s solar cells would generate 14 kilowatts of continuous power on Earth, they only <a href="https://www.jpl.nasa.gov/news/nasas-juno-spacecraft-breaks-solar-power-distance-record">generate 0.5kW at Jupiter</a>. </p>
<p>Meanwhile, Uranus and Neptune are <a href="https://solarsystem.nasa.gov/planets/uranus/in-depth/">20</a> and <a href="https://solarsystem.nasa.gov/planets/neptune/in-depth/">30</a> times further away, respectively, from the Sun than Earth is. Power for these missions would have to be generated from the radioactive <a href="https://solarsystem.nasa.gov/missions/galileo/in-depth/#otp_spacecraft_and_instruments">decay of plutonium</a> (the power source for both the Galileo and Cassini missions). </p>
<p>This radioactive decay can damage and interfere with instruments. It is therefore reserved for spacecraft which really need it, such as missions operating far away from the Sun. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/so-a-helicopter-flew-on-mars-for-the-first-time-a-space-physicist-explains-why-thats-such-a-big-deal-159334">So a helicopter flew on Mars for the first time. A space physicist explains why that's such a big deal</a>
</strong>
</em>
</p>
<hr>
<h2>Fighting the heat</h2>
<p>The massive scale of giant planets means orbit speeds for incoming spacecraft are incredibly fast. And these speeds greatly heat up the spacecraft. </p>
<p>The Galileo probe entered Jupiter’s atmosphere at <a href="https://solarsystem.nasa.gov/missions/galileo-probe/in-depth/">47.5 kilometres per second</a>, surviving the harshest entry conditions ever experienced by an entry probe. The shock layer which formed at the front of the spacecraft during entry reached a temperature of 16,000°C – around three times the temperature of the Sun’s surface.</p>
<p>Even so, the distribution of the <a href="https://arc.aiaa.org/doi/10.2514/2.3293">heat shield’s</a> mass was found to be inefficient – showing we still have a lot to learn about entering giant planets.</p>
<p>Proposed future probe missions to Uranus and Neptune would occur at slower entry speeds of <a href="https://link.springer.com/article/10.1007/s11214-020-0638-2">22km/s and 26km/s</a>, respectively. </p>
<p>For this, NASA have developed a tough but relatively lightweight material woven from carbon fibre, called <a href="https://www.nasa.gov/ames/heeet">HEEET</a> (Heatshield for Extreme Entry Environment Technology), designed specifically for surviving giant planet and Venusian entry. </p>
<p>While the material has been tested with a <a href="https://www.nasa.gov/centers/ames/entry-systems-vehicle-development/tps-materials.html">full-scale prototype</a>, it has yet to fly on a mission.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/446526/original/file-20220215-8037-1brq7ct.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/446526/original/file-20220215-8037-1brq7ct.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/446526/original/file-20220215-8037-1brq7ct.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/446526/original/file-20220215-8037-1brq7ct.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/446526/original/file-20220215-8037-1brq7ct.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/446526/original/file-20220215-8037-1brq7ct.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/446526/original/file-20220215-8037-1brq7ct.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">It’s planned NASA’s HEEET material will be used for future ice giant entry missions.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<h2>The next steps</h2>
<p>In 2024, NASA’s Europa Clipper mission <a href="https://europa.nasa.gov/">will launch</a> to investigate Jupiter’s moon Europa, which is believed to house an <a href="https://europa.nasa.gov/why-europa/overview/">ocean of liquid water</a> below its icy surface, where signs of life may be found. The <a href="https://www.nasa.gov/press-release/nasas-dragonfly-will-fly-around-titan-looking-for-origins-signs-of-life/">Dragonfly</a> mission, planned to launch in 2026, will similarly aim to search for signs of life on Saturn’s moon Titan.</p>
<p>There are plans for a joint <a href="https://www.sciencedirect.com/science/article/pii/S0032063318303507">NASA-ESA mission</a> to visit one of the ice giants within the upcoming launch window. But while there has been <a href="https://www.lpi.usra.edu/icegiants/documents_presentations/">extensive</a> <a href="https://sci.esa.int/web/future-missions-department/-/61307-cdf-study-report-ice-giants">preparation</a>, it’s undecided which ice giant will be visited. </p>
<p>A single mission to both planets is being considered. An entry probe is planned, too. But if the mission visits both planets, it’s undecided which planet’s <a href="https://www.sciencedirect.com/science/article/pii/S003206331830350">atmosphere the probe would explore</a>.</p>
<p>If we want to meet the upcoming launch window, it’s expected mission concepts will need to be finalised <a href="https://www.sciencedirect.com/science/article/pii/S0032063320300040">by 2025</a>, at the latest. In other words, crunch time is coming. </p>
<p>Should a mission go forward, the two most important <a href="https://www.lpi.usra.edu/icegiants/mission_study/Full-Report.pdf">goals</a> for NASA’s scientists will be to determine the interior makeup of ice giants (exactly what they are made of) and their composition (how they are formed).</p>
<p>Other objectives will include studying their magnetic fields, which are <a href="https://www.lpi.usra.edu/icegiants/mission_study/Full-Report.pdf">very different</a> to gas giants and all other types of planets. </p>
<p>They’ll also want to study the heat released by both Uranus and Neptune, which both have average temperatures of around -200°C. All giant planets are meant to be very slowly cooling down, as they release energy gained during their formation. </p>
<p>This heat release can be detected for Jupiter, Saturn and Neptune. Uranus, however, doesn’t seem to release heat – and scientists don’t know why.</p><img src="https://counter.theconversation.com/content/175918/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris James receives funding from the University of Queensland, the Australian Research Council, and the U.S. Office of Naval Research. </span></em></p><p class="fine-print"><em><span>Yu Liu 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>There has never been a dedicated mission sent to the “ice giants”, Uranus and Neptune. But there may be one on the horizon.Chris James, ARC DECRA Fellow, Centre for Hypersonics, School of Mechanical and Mining Engineering, The University of QueenslandYu Liu, Honorary Fellow, The University of QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1719912021-11-23T11:46:20Z2021-11-23T11:46:20ZCurious Kids: what are the rings around planets made of?<figure><img src="https://images.theconversation.com/files/433144/original/file-20211122-13-bf557y.jpg?ixlib=rb-1.1.0&rect=12%2C12%2C4077%2C2139&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The planet Saturn. </span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/saturn-3d-rings-moons-solar-system-1677454126">viktorov.pro/Shutterstock</a></span></figcaption></figure><p><strong>What are the rings around planets made of? – Vihan, aged five, Chennai, India</strong></p>
<p>Lots of us are familiar with pictures of the planet Saturn and its unmistakable ring. In fact, Saturn doesn’t have just one ring – if you look through a telescope, you will see that Saturn actually has <a href="https://openaccess.inaf.it/handle/20.500.12386/28625">at least eight rings</a>. This is called a ring system. </p>
<p>Saturn is not the only planet with rings. Jupiter, Neptune and Uranus all have ring systems too, but their rings are smaller, dimmer and more difficult to see.</p>
<hr>
<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><em><a href="https://theconversation.com/au/topics/curious-kids-36782">Curious Kids</a> is a series by <a href="https://theconversation.com/uk">The Conversation</a> that gives children the chance to have their questions about the world answered by experts. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskids@theconversation.com">curiouskids@theconversation.com</a>. We won’t be able to answer every question, but we’ll do our very best.</em></p>
<hr>
<p>These rings are formed of billions of small particles orbiting close to their planet. However, what these particles are made of can vary from planet to planet. Even rings in the same ring system can be made of <a href="https://royalsocietypublishing.org/doi/pdf/10.1098/rsta.2019.0482">different things</a>. </p>
<h2>Radio waves</h2>
<p>We can start to get an idea of what these particles are made of by working out how big they are and how heavy they are. One way of doing this is with a technique called <a href="https://www.sciencedirect.com/science/article/pii/0032063373900597">radio occultation</a>. </p>
<p>Objects in space with changing magnetic fields – such as planets or even space satellites – produce radio waves. As they pass through the rings around planets, these radio signals are affected in different ways by the particles in the ring, depending on the size of the particles and how heavy they are. If the radio signals show that the particles are heavy, they might be made of a material such as iron. Less heavy particles might be made of a less dense material, such as aluminium. </p>
<p>We can also measure how reflective the particles are to help work out what they are made of and what state they are in – such as whether they are liquid or solid. Water can come in different states: it can be liquid, but it can also be solid as ice or snow. Ice is more reflective than water, and snow is extremely reflective – more so than ice or water. Thanks to measurements like this, we know that <a href="http://lasp.colorado.edu/%7Eespoclass/ASTR_5835_Fall-2017-Review%20Chapters-Saturn/15-Ring%20Particle%20Composition%20and%20Size%20Distribution.pdf">Saturn’s ring particles</a> are mostly made up of water ice. </p>
<figure class="align-center ">
<img alt="Black and white photograph of planet with rings" src="https://images.theconversation.com/files/433147/original/file-20211122-21-185yjqg.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/433147/original/file-20211122-21-185yjqg.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/433147/original/file-20211122-21-185yjqg.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/433147/original/file-20211122-21-185yjqg.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/433147/original/file-20211122-21-185yjqg.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/433147/original/file-20211122-21-185yjqg.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/433147/original/file-20211122-21-185yjqg.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">An image of Saturn and its rings taken by the Cassini spacecraft in 2014.</span>
<span class="attribution"><a class="source" href="https://images.nasa.gov/details-PIA18295">NASA/JPL-Caltech/Space Science Institute</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p><a href="https://www.sciencedirect.com/science/article/pii/S0019103506002417?via%3Dihub">Jupiter’s ring system</a> is made up of fine dust particles, but these are not water ice particles like Saturn. Instead the particles are likely to be rocky, made up of similar materials as asteroids and rocky moons.</p>
<p>Although what <a href="https://arxiv.org/pdf/1805.08963.pdf">Uranus’ rings</a> are made of is still unknown, they are dark and not very reflective. This suggests that they are not made of water ice. Instead, they may be dust particles made from carbon or containing carbon like charcoal.</p>
<p><a href="https://arxiv.org/pdf/1805.08963.pdf">Neptune’s rings</a> are even darker than those of Uranus, and the density suggests that they are made of even finer dust. This is likely to be some kind of carbon or a source of carbon such as methane ice.</p>
<h2>Measuring light</h2>
<p>In order to get more detailed information about what rings are made of, scientists examine the light that the particles emit. We do this by splitting the light up into a rainbow, just like how rain droplets split sunlight up into a rainbow. This rainbow is called the <a href="https://imagine.gsfc.nasa.gov/science/toolbox/spectra1.html">spectra</a>, and it can tell us detailed information about the colour of the particles and what they are made of. At the moment, Saturn is the only planet for which we have high resolution spectra that can tell us about its rings. </p>
<p>Measuring the spectra of <a href="http://lasp.colorado.edu/%7Eespoclass/ASTR_5835_Fall-2017-Review%20Chapters-Saturn/15-Ring%20Particle%20Composition%20and%20Size%20Distribution.pdf">Saturn’s ring particles</a> shows us that as well as water ice, they also contain iron and organic material known as <a href="https://www.discovermagazine.com/the-sciences/what-are-tholins-the-mysterious-substance-that-turned-ultima-thule-red">tholins</a>, which give them a slight red colour. Some of these particles may be as small as a grain of sand but others are as large as a double-decker bus. </p>
<p>A new telescope, called the <a href="https://arxiv.org/pdf/1403.6849.pdf">James Webb Space Telescope</a>, will soon help us take a more detailed look at these ring systems and measure their spectra to find out more about what exactly they are made of. It’s possible that with this new telescope, we will even find rings around moons, not just planets. </p>
<hr>
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<hr><img src="https://counter.theconversation.com/content/171991/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Maggie Lieu has previously received funding from STFC. </span></em></p>Saturn, Jupiter, Neptune and Uranus all have rings.Maggie Lieu, Research Fellow, School of Physics and Astronomy, University of NottinghamLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1698052021-11-01T12:26:16Z2021-11-01T12:26:16ZA small telescope past Saturn could solve some mysteries of the universe better than giant telescopes near Earth<figure><img src="https://images.theconversation.com/files/429193/original/file-20211028-27-1f4qlx4.png?ixlib=rb-1.1.0&rect=0%2C186%2C2592%2C1593&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A telescope in the outer solar system would be able to do unique science that is impossible closer to the Sun.</span> <span class="attribution"><span class="source">Michael Zemcov</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>Dozens of space-based telescopes operate near Earth and provide incredible images of the universe. But imagine a telescope far away in the outer solar system, 10 or even 100 times farther from the Sun than Earth. The ability to look back at our solar system or peer into the darkness of the distant cosmos would make this a uniquely powerful scientific tool.</p>
<p><a href="https://www.rit.edu/directory/mbzsps-michael-zemcov">I’m an astrophysicist</a> who studies the formation of structure in the universe. Since the 1960s, scientists like me have been considering the important scientific questions we might be able to answer with a telescope placed in the outer solar system. </p>
<p>So what would such a mission look like? And what science could be done?</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/429160/original/file-20211028-25-3re5m6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing the Sun and all planets in a line." src="https://images.theconversation.com/files/429160/original/file-20211028-25-3re5m6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/429160/original/file-20211028-25-3re5m6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=227&fit=crop&dpr=1 600w, https://images.theconversation.com/files/429160/original/file-20211028-25-3re5m6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=227&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/429160/original/file-20211028-25-3re5m6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=227&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/429160/original/file-20211028-25-3re5m6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=286&fit=crop&dpr=1 754w, https://images.theconversation.com/files/429160/original/file-20211028-25-3re5m6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=286&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/429160/original/file-20211028-25-3re5m6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=286&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Where a telescope is located matters nearly as much as its power. In many cases, the farther from the Sun, the better.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Solar-System-blank.jpg#/media/File:Solar-System-blank.jpg">Beinahegut/WikimediaCommons</a></span>
</figcaption>
</figure>
<h2>A tiny telescope far from home</h2>
<p>The scientific strength of a telescope far from Earth would come primarily from its location, not its size. Plans for a telescope in the outer solar system would put it somewhere beyond the orbit of Saturn, roughly a billion or more miles from Earth. </p>
<p>We’d need only send a very small telescope – with a lens roughly the size of a small plate – to achieve some truly unique astrophysical insights. Such a telescope could be built to weigh less than 20 pounds (9 kilograms) and could be piggybacked on virtually any <a href="https://interstellarprobe.jhuapl.edu">mission to Saturn or beyond</a>. </p>
<p>Though small and simple compared with telescopes like <a href="https://hubblesite.org">Hubble</a> or <a href="https://www.jwst.nasa.gov/content/webbLaunch/index.html">James Webb</a>, such an instrument operating away from the bright light of the Sun could <a href="https://arxiv.org/pdf/1903.05729.pdf">make measurements</a> that are difficult or <a href="https://arxiv.org/pdf/1802.09536.pdf">outright impossible from a vantage point near the Earth</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/429192/original/file-20211028-13-1wgvq9a.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A picture and graphic showing a disc of dust around a central star." src="https://images.theconversation.com/files/429192/original/file-20211028-13-1wgvq9a.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/429192/original/file-20211028-13-1wgvq9a.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=302&fit=crop&dpr=1 600w, https://images.theconversation.com/files/429192/original/file-20211028-13-1wgvq9a.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=302&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/429192/original/file-20211028-13-1wgvq9a.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=302&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/429192/original/file-20211028-13-1wgvq9a.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=379&fit=crop&dpr=1 754w, https://images.theconversation.com/files/429192/original/file-20211028-13-1wgvq9a.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=379&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/429192/original/file-20211028-13-1wgvq9a.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=379&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 Sun has a disc of dust and gas surrounding it, much like the pinkish haze seen in this image and graphical representation of a nearby red dwarf star and its dust cloud.</span>
<span class="attribution"><a class="source" href="https://hubblesite.org/contents/media/images/2013/20/3181-Image.html?news=true">NASA/ESA/J. Debes</a></span>
</figcaption>
</figure>
<h2>Outside looking in</h2>
<p>Unfortunately for astronomers, getting a selfie of the solar system is a challenge. But being able to see the solar system from an outside vantage point would reveal a lot of information, in particular about the shape, distribution and composition of the dust cloud that surrounds the Sun. </p>
<p>Imagine a street lamp on a foggy evening – by standing far away from the lamp, the swirling mists are visible in a way that someone <a href="https://doi.org/10.3847/25c2cfeb.2f064292">standing under the streetlight could never see</a>.</p>
<p>For years astrophysicists have been able to take images of and study the dust discs in solar systems <a href="https://roman.gsfc.nasa.gov/science/Astro2020/ChenChristineH.pdf?version=1&modificationDate=1628623860142&api=v2">around other stars in the Milky Way</a>. But these stars are very far away, and there are <a href="https://www.science.org/content/article/cosmic-conundrum-disks-gas-and-dust-supposedly-form-planets-don-t-seem-have-goods">limits to what astronomers can learn about them</a>. Using observations looking back toward the Sun, astronomers could compare the shape, features and composition of these distant dust clouds with detailed data on Earth’s own solar system. This data would fill gaps in knowledge about solar dust clouds and make it possible to understand the history of production, migration and destruction of dust in other solar systems that there is no hope of traveling to in person.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/429164/original/file-20211028-20-129axtv.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A picture of thousands of galaxies." src="https://images.theconversation.com/files/429164/original/file-20211028-20-129axtv.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/429164/original/file-20211028-20-129axtv.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/429164/original/file-20211028-20-129axtv.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/429164/original/file-20211028-20-129axtv.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/429164/original/file-20211028-20-129axtv.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/429164/original/file-20211028-20-129axtv.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/429164/original/file-20211028-20-129axtv.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"></a>
<figcaption>
<span class="caption">The universe is full of galaxies – as seen in this image called the Hubble Ultra Deep Field – and measuring the cumulative light from these is hard to do from Earth.</span>
<span class="attribution"><a class="source" href="https://svs.gsfc.nasa.gov/30946">NASA/JPL</a></span>
</figcaption>
</figure>
<h2>Deep darkness of space</h2>
<p>Another benefit of placing a telescope far from the Sun is the lack of reflected light. The disc of dust in the plane of the planets reflects the Sun’s light back at Earth. This creates a haze that is between <a href="https://ned.ipac.caltech.edu/level5/March17/Cooray/Cooray1.html#1.4">100 and 1,000 times brighter than light from other galaxies</a> and obscures views of the cosmos from near Earth. Sending a telescope outside of this dust cloud would place it in a much darker region of space making it easier to measure the light coming from outside the solar system.</p>
<p>Once there, the telescope could measure the brightness of the ambient light of the universe over a wide range of wavelengths. This could provide insights into how <a href="https://ned.ipac.caltech.edu/level5/Madau2/Mad_contents.html">matter condensed into the first stars and galaxies</a>. It would also enable researchers to test models of the universe by comparing the predicted sum of light from all galaxies with a precise measurement. Discrepancies could point to problems with models of structure formation in the universe or perhaps to <a href="https://royalsocietypublishing.org/doi/10.1098/rsos.150555">exotic new physics</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/429166/original/file-20211028-5568-22i40f.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A blue horseshoe of light surrounding an orange galaxy." src="https://images.theconversation.com/files/429166/original/file-20211028-5568-22i40f.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/429166/original/file-20211028-5568-22i40f.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=396&fit=crop&dpr=1 600w, https://images.theconversation.com/files/429166/original/file-20211028-5568-22i40f.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=396&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/429166/original/file-20211028-5568-22i40f.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=396&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/429166/original/file-20211028-5568-22i40f.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=498&fit=crop&dpr=1 754w, https://images.theconversation.com/files/429166/original/file-20211028-5568-22i40f.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=498&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/429166/original/file-20211028-5568-22i40f.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=498&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">From far enough away, it would be possible to use the Sun as a giant lens, similar to the gravitational lensing seen here as light from a distant blue galaxy is bent around a nearer orange galaxy seen in the center.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Gravitational_lens#/media/File:A_Horseshoe_Einstein_Ring_from_Hubble.JPG">ESA/Hubble/NASA</a></span>
</figcaption>
</figure>
<h2>Into the unknown</h2>
<p>Finally, increasing a telescope’s distance from the Sun would also allow astronomers to do unique science that takes advantage of an <a href="https://hubblesite.org/contents/articles/gravitational-lensing">effect called gravitational lensing</a>, in which a massive object distorts the path light takes as it moves past an object.</p>
<p>One use of gravitational lensing is to <a href="https://theconversation.com/rogue-planets-hunting-the-galaxys-most-mysterious-worlds-149588">search for and weigh rogue planets</a> – planets that roam interstellar space after being ejected from their home solar systems. Since rogue planets don’t emit light on their own, astrophysicists can look for their <a href="https://www.universetoday.com/138141/gravitational-microlensing-method/">effect on the light from background stars</a>. To differentiate between the distance of the lensing object and its mass requires observations from a second location far from Earth.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/429162/original/file-20211028-13882-66luob.gif?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An image showing how a planet will bend the light from a distant star." src="https://images.theconversation.com/files/429162/original/file-20211028-13882-66luob.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/429162/original/file-20211028-13882-66luob.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=337&fit=crop&dpr=1 600w, https://images.theconversation.com/files/429162/original/file-20211028-13882-66luob.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=337&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/429162/original/file-20211028-13882-66luob.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=337&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/429162/original/file-20211028-13882-66luob.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/429162/original/file-20211028-13882-66luob.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/429162/original/file-20211028-13882-66luob.gif?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">Gravitational lensing caused by a planet passing in front of a distant star will bend light from that star, and that can also be used to detect dark planets that have been ejected from solar systems.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Gravitational_lens.gif#/media/File:Gravitational_lens.gif">NASA Ames/JPL-Caltech/T. Pyle via WikimediaCommons</a></span>
</figcaption>
</figure>
<p>In 2011, scientists used a camera on the EPOXI mission to the asteroid belt to discover and weigh a <a href="https://doi.org/10.1088/0004-637X/741/1/22">Neptune-sized object floating free among stars in the Milky Way galaxy</a>. Only a few rogue planets have been found, but astronomers suspect they are very common and could hold clues to the <a href="https://www.abc.net.au/news/2021-07-07/free-floating-planets-nasa-kepler-space-telescope/100273040">formation of solar systems and prevalence of planets around stars</a>.</p>
<p>But perhaps the most interesting use for a telescope in the outer solar system would be the potential to use the <a href="https://www.planetary.org/space-images/solar-gravity-lens-telescope">gravitational field of the Sun itself as a giant lens</a>. This kind of measurement may allow astrophysicists to actually map planets in other star systems. Perhaps one day we will be able to name continents on an Earth-like planet around a distant star.</p>
<p>[<em>Get the best of The Conversation, every weekend.</em> <a href="https://theconversation.com/us/newsletters/weekly-highlights-61?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=weeklybest">Sign up for our weekly newsletter</a>.]</p>
<h2>Coming soon?</h2>
<p>Since Pioneer 10 became the first human-made object to cross Jupiter’s orbit in 1973, there have been only a handful of astrophysical studies done from beyond the orbit of Earth. Missions to the outer solar system are rare, but many teams of scientists are doing <a href="https://www.universetoday.com/138141/gravitational-microlensing-method/">studies to show how an extrasolar telescope project would work</a> and what could be learned from one. </p>
<p>Every 10 years or so, leaders in the astrophysics and astronomy fields gather to set goals for the following decade. That plan for the 2020s is scheduled to be released on Nov. 4, 2021. In it, I expect to see discussions about the next telescope that could revolutionize astronomy. Taking a telescope to the outer solar system, while ambitious, is well within the technological ability of NASA or other space agencies. I hope that one day soon a tiny telescope out on a lonely mission in dark reaches of the solar system will provide us incredible insights into the universe.</p><img src="https://counter.theconversation.com/content/169805/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Michael Zemcov receives funding from the National Aeronautics and Space Administration and the National Science Foundation.</span></em></p>Such a mission could be developed soon, allowing astrophysicists to take selfies of the solar system and use the Sun’s gravity as a lens to peer deep into space.Michael Zemcov, Associate Professor of Physics, Rochester Institute of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1649032021-09-07T12:54:21Z2021-09-07T12:54:21ZWhy are planets round?<figure><img src="https://images.theconversation.com/files/413571/original/file-20210728-23-c5bsvh.jpg?ixlib=rb-1.1.0&rect=362%2C137%2C5018%2C3690&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Earth is round.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/boy-holding-up-a-large-globe-outdoors-royalty-free-image/1279305617?adppopup=true">Alistair Berg/DigitalVision 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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<span class="caption"></span>
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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>Why are planets round? – Daniel B., La Crosse, Wisconsin</strong></p>
</blockquote>
<hr>
<p>The <a href="https://www.aps.org/publications/apsnews/200606/history.cfm">ancient Greeks proved</a> over 2,000 years ago that the Earth was round and figured out how big it was by using simple observations of the Sun. </p>
<p>But how do people know this today? When you drop anything, gravity causes it to fall directly toward the center of the Earth, at least until it hits the ground. <a href="https://plato.stanford.edu/entries/newton-principia/">Gravity</a> is a force that is caused by nearly everything that has mass. <a href="https://plato.stanford.edu/entries/newton-principia/">Mass</a> is a measure of how much material there is in anything. It could be in the form of rocks, water, metal, people – anything. Everything material has mass, and therefore everything causes gravity. Gravity always pulls toward the center of mass. </p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1171426852340207617"}"></div></p>
<p>The Earth and all planets are round because when the <a href="https://phys.org/news/2015-01-planets.html">planets formed</a>, they were composed of molten material – essentially very hot liquid. Since gravity always points toward the center of a mass, it squeezed the stuff the Earth is made of equally in all directions and formed a ball. When the Earth cooled down and became a solid, it was a round ball. If the Earth didn’t spin, then it would have been a perfectly round planet. Scientists call something that is perfectly round in all directions a “sphere.” </p>
<p>The gas cloud that the Earth was made from was slowly rotating in one direction around an axis. The top and bottom of this <a href="https://www.nationalgeographic.org/encyclopedia/axis/">axis are the north and south poles of Earth</a>.</p>
<p>Now, hold out your right hand. Point your thumb on your right hand straight up, and curl your fingers around the direction of rotation. Your thumb is pointing toward the North pole. The equator is defined as the plane, halfway between the North and South Poles. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/413592/original/file-20210728-15-1x6e081.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Three young girls playing on a playground carousel" src="https://images.theconversation.com/files/413592/original/file-20210728-15-1x6e081.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/413592/original/file-20210728-15-1x6e081.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/413592/original/file-20210728-15-1x6e081.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/413592/original/file-20210728-15-1x6e081.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/413592/original/file-20210728-15-1x6e081.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/413592/original/file-20210728-15-1x6e081.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/413592/original/file-20210728-15-1x6e081.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">Centrifugal force in action on this carousel.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/kids-on-carousal-in-playground-royalty-free-image/82980840?adppopup=true">Todd Warnock/DigitalVision via Getty Images</a></span>
</figcaption>
</figure>
<p>If you ever played on a merry-go-round, you know that the spinning merry-go-round tends to throw you off. The faster it spins, the harder it is to stay on. This tendency to be flung off is called <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/centrifugal-force">centrifugal force</a> and pushes the mass on the equator outward. This makes the planet bulge at the equator.</p>
<p>The faster the spin, the more unround it becomes. Then, when it cools and hardens, it retains that shape. If a molten planet starts off spinning faster, it would be less round and have a bigger bulge. </p>
<p>The <a href="https://phys.org/news/2015-08-planet-saturn.html">planet Saturn</a> is very oblate – non-spherical – because it rotates very fast. Because of gravity, all planets are round, and because they rotate at different rates, some have fatter equators than their poles. So the shape of the planet and the speed and direction that it rotates depends on the initial condition of the material out of which it forms.</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/164903/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>James Webb is affiliated with American Astronomical Society -full member
Planetary society - member
National Space Society- member
Southern Cross Astronomical Society lifetime member</span></em></p>Gravity, mass and centrifugal force all contribute to the final shape of a planet.James Webb, Professor and Director, Stocker AstroScience Center for Physics; Stocker AstroScience Center, Florida International UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1660462021-08-23T10:48:52Z2021-08-23T10:48:52ZThe five most impressive geological structures in the solar system<figure><img src="https://images.theconversation.com/files/417379/original/file-20210823-13-aqa2uc.jpg?ixlib=rb-1.1.0&rect=9%2C0%2C1581%2C1505&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Ligeia Mare on Titan.</span> <span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Ligeia_Mare#/media/File:Ligeia_Mare_in_false_color_(PIA17031).jpg">NASA/JPL-Caltech/ASI/Cornell -</a></span></figcaption></figure><p>When we talk about amazing geological features, we often limit ourselves to those on Earth. But as a geologist, I think that’s crazy – there are so many structures on other worlds that can excite and inspire, and that can put processes on our own planet into perspective.</p>
<p>Here, in no particular order, are the five geological structures in the solar system (excluding Earth) that most impress me.</p>
<h2>The grandest canyon</h2>
<p>I left out the solar system’s biggest volcano, <a href="https://theconversation.com/monster-volcanoes-on-mars-how-space-rocks-are-helping-us-solve-their-mysteries-85045">Olympus Mons</a> on Mars, so I could include that planet’s most spectacular canyon, <a href="https://www.space.com/20446-valles-marineris.html">Valles Marineris</a>. Being 3,000km long, hundreds of kilometres wide and up to eight kilometres deep, this is best seem from space. If you were lucky enough to stand on one rim, the opposite rim would be way beyond the horizon. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/416017/original/file-20210813-17-1pochz0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Image of Marineris seen in a colour-coded topographic view." src="https://images.theconversation.com/files/416017/original/file-20210813-17-1pochz0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/416017/original/file-20210813-17-1pochz0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=191&fit=crop&dpr=1 600w, https://images.theconversation.com/files/416017/original/file-20210813-17-1pochz0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=191&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/416017/original/file-20210813-17-1pochz0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=191&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/416017/original/file-20210813-17-1pochz0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=240&fit=crop&dpr=1 754w, https://images.theconversation.com/files/416017/original/file-20210813-17-1pochz0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=240&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/416017/original/file-20210813-17-1pochz0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=240&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Valles Marineris seen in a colour-coded topographic view as if from 5,000 km above the surface (left), and imaged by the High Resolution Stereo Camera on Esa’s Mars Express (right).</span>
<span class="attribution"><span class="source">Google Earth and NASA/USGS/ESA/DLR/FU Berlin (G. Neukum)</span></span>
</figcaption>
</figure>
<p>It was probably initiated by fracturing when an adjacent volcanic region (called <a href="https://astronomynow.com/tag/tharsis-volcanic-dome/">Tharsis</a>) began to bulge upwards, but was widened and deepened by a series of catastrophic floods that climaxed more than 3 billion years ago.</p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/plate-tectonics-new-findings-fill-out-the-50-year-old-theory-that-explains-earths-landmasses-55424">Plate tectonics: new findings fill out the 50-year-old theory that explains Earth's landmasses</a>
</strong>
</em>
</p>
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<h2>Venus’ fold mountains</h2>
<p>We are going to learn a lot more about Venus in the 2030s when <a href="https://theconversation.com/nasa-has-announced-two-missions-to-venus-by-2030-heres-why-thats-exciting-162133">two Nasa missions</a> and <a href="https://www.esa.int/Science_Exploration/Space_Science/ESA_selects_revolutionary_Venus_mission_EnVision">one from Esa (European Space Agency)</a> arrive. Venus is nearly the same size, mass and density as the Earth, causing <a href="https://theconversation.com/venus-has-very-few-volcanoes-weirdly-this-might-be-why-its-as-hot-as-hell-78363">geologists to puzzle</a> over why it lacks Earth-style plate tectonics and why (or indeed whether) it has comparatively little active volcanism. How does the planet get its heat out?</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/416030/original/file-20210813-25-ofb1wa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Image of the fold mountains on Venus." src="https://images.theconversation.com/files/416030/original/file-20210813-25-ofb1wa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/416030/original/file-20210813-25-ofb1wa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=438&fit=crop&dpr=1 600w, https://images.theconversation.com/files/416030/original/file-20210813-25-ofb1wa.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=438&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/416030/original/file-20210813-25-ofb1wa.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=438&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/416030/original/file-20210813-25-ofb1wa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=551&fit=crop&dpr=1 754w, https://images.theconversation.com/files/416030/original/file-20210813-25-ofb1wa.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=551&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/416030/original/file-20210813-25-ofb1wa.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=551&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Fold mountains in Ovda Regio, Venus. The insert is a similar view of part of the Applachians in central Pennsylvania.</span>
<span class="attribution"><span class="source">NASA/JPL</span></span>
</figcaption>
</figure>
<p>I find it reassuring that at least some aspects of Venus’ geology look familiar. For example, the northern margin of the highlands named <a href="https://www.jpl.nasa.gov/images/venus-ovda-regio">Ovda Regio</a> looks strikingly similar, apart from the lack of rivers cutting through the eroded, fold-like pattern, to “fold mountains” on Earth such as the <a href="https://www.nationalgeographic.org/encyclopedia/fold-mountain/">Appalachians</a>, which are the result of a <a href="https://www.nationalgeographic.org/encyclopedia/fold-mountain/">collision between continents</a>.</p>
<h2>Blasted Mercury</h2>
<p>I’m cheating a little with my next example, because it is both one of the solar system’s largest impact basins and an explosive volcano within it. Mercury’s 1,550km diameter <a href="https://solarsystem.nasa.gov/resources/2266/mercurys-caloris-basin/">Caloris basin</a> was formed by a major asteroid impact about 3.5 billion years ago, and soon after that its floor was flooded by lavas. </p>
<p>Some time later, a series of explosive eruptions blasted kilometres-deep holes through the solidified lavas near the edge of the basin where the lava cap was thinnest. These sprayed volcanic ash particles out over a range of tens of kilometres. One such deposit, named Agwo Facula, surrounds the explosive vent that I have chosen as my example. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/416045/original/file-20210813-13-osbbma.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Images of Mercury's Caloris basin." src="https://images.theconversation.com/files/416045/original/file-20210813-13-osbbma.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/416045/original/file-20210813-13-osbbma.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=298&fit=crop&dpr=1 600w, https://images.theconversation.com/files/416045/original/file-20210813-13-osbbma.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=298&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/416045/original/file-20210813-13-osbbma.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=298&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/416045/original/file-20210813-13-osbbma.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=374&fit=crop&dpr=1 754w, https://images.theconversation.com/files/416045/original/file-20210813-13-osbbma.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=374&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/416045/original/file-20210813-13-osbbma.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=374&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Right: most of Mercury’s Caloris basin, its floor covered by dull, orange lava. Brighter orange patches are remnants of explosive eruptions. Lower left: close-up inside the red box of an explosive volcanic deposit. Upper left: details of the vent interior.</span>
<span class="attribution"><span class="source">NASA/JHUAPL/CIW</span></span>
</figcaption>
</figure>
<p>Explosive eruptions are driven by the force of expanding gas, and are a <a href="https://theconversation.com/mysterious-red-spots-on-mercury-get-names-but-what-are-they-95114">surprising find on Mercury</a>, whose proximity to the Sun was previously expected to have starved it of such volatile substances – the heat would have made them boil off. Scientists suspect that there were in fact several explosive eruptions, possibly spaced over a prolonged timescale. This means that gas-forming volatile materials (whose composition will remain uncertain until <a href="https://theconversation.com/europe-blasts-off-to-mercury-heres-the-rocket-science-104641">Esa’s BepiColombo</a> mission starts work in 2026) were repeatedly available in Mercury’s magmas.</p>
<h2>The tallest cliff?</h2>
<p>In soil or vegetation-rich regions on Earth, cliffs offer the largest exposures of clean rock. Although <a href="https://www.bbc.co.uk/news/uk-england-dorset-56773648">dangerous to approach</a>, they reveal an uninterrupted cross-section of rock and can be great for fossil hunting. Because geologists love them so much, I give you the seven kilometres-high <a href="https://spaceplace.nasa.gov/cliff-jumping/en/">Verona Rupes</a>. This is a feature on Uranus’s small moon <a href="https://solarsystem.nasa.gov/moons/uranus-moons/miranda/in-depth/">Miranda</a> that is often described as “the tallest cliff in the solar system”, including on a <a href="https://science.nasa.gov/verona-rupes-tallest-known-cliff-solar-system">recent Nasa website</a>. This even goes so far as to remark that if you were careless enough to take a tumble off the top, it would take you 12 minutes to fall to the bottom. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/415845/original/file-20210812-15866-1l1jbhp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Images of Verona Rupes." src="https://images.theconversation.com/files/415845/original/file-20210812-15866-1l1jbhp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/415845/original/file-20210812-15866-1l1jbhp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=592&fit=crop&dpr=1 600w, https://images.theconversation.com/files/415845/original/file-20210812-15866-1l1jbhp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=592&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/415845/original/file-20210812-15866-1l1jbhp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=592&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/415845/original/file-20210812-15866-1l1jbhp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=744&fit=crop&dpr=1 754w, https://images.theconversation.com/files/415845/original/file-20210812-15866-1l1jbhp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=744&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/415845/original/file-20210812-15866-1l1jbhp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=744&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Verona Rupes, about 50km long and several km high, but not actually so cliff-like as it appears as seen by Voyager 2 during its 1986 flyby.</span>
<span class="attribution"><span class="source">NASA/JPL</span></span>
</figcaption>
</figure>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/mysterious-red-spots-on-mercury-get-names-but-what-are-they-95114">Mysterious red spots on Mercury get names – but what are they?</a>
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<p>This is nonsense, because Verona Rupes is nowhere near vertical. The only images we have of it are from <a href="https://solarsystem.nasa.gov/missions/voyager-2/in-depth/">Voyager 2</a>, captured during its 1986 fly by of Uranus. It is undeniably impressive, being almost certainly a geological fault where one block of Miranda’s icy crust (the outermost “shell” of the planet) has moved downwards against the adjacent block. </p>
<p>However, the obliqueness of the view is deceptive, making it impossible to be sure of the face’s steepness – it probably slopes at less than 45 degrees. If you stumbled at the top, I doubt you’d even slide to the bottom. The face appears to be very smooth in the best, but rather low resolution image that we have, but at Miranda’s -170°C daytime temperature, water-ice has a <a href="https://www.zmescience.com/science/ice-slippery-h-bonds-8731058/">high friction</a> and is not slippery at all.</p>
<h2>Titan’s drowned coastline</h2>
<p>For my final example I could happily have chosen virtually anywhere on Pluto, but instead I have opted for a hauntingly Earth-like coastline on Saturn’s largest moon, <a href="https://theconversation.com/flying-on-saturns-moon-titan-what-we-could-discover-with-nasas-new-dragonfly-mission-119823">Titan</a>. Here, a large depression in Titan’s water-ice “bedrock” hosts a sea of liquid methane named <a href="https://www.esa.int/ESA_Multimedia/Images/2013/06/Ligeia_Mare">Ligeia Mare</a>.</p>
<p>Valleys carved by methane rivers draining into the sea have evidently become flooded as the sea level rose. This complexly indented coastline reminds me strongly of Oman’s <a href="https://www.bbc.com/travel/article/20120323-omans-sleepy-peninsula">Musandam peninsula</a>, on the south side of the Straits of Hormuz. There, the local crust has been warped downwards because of the ongoing collision between Arabian and the Asian mainlands. Has something similar happened on Titan? We don’t know yet, but the way that the coastal geomorphology changes around Ligeia Mare suggests to me that its drowned valleys are more than a straightforward result of rising liquid levels.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/416316/original/file-20210816-28-tx30nn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Images of Ligeia Mare and The Musandam peninsula side by side." src="https://images.theconversation.com/files/416316/original/file-20210816-28-tx30nn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/416316/original/file-20210816-28-tx30nn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=319&fit=crop&dpr=1 600w, https://images.theconversation.com/files/416316/original/file-20210816-28-tx30nn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=319&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/416316/original/file-20210816-28-tx30nn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=319&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/416316/original/file-20210816-28-tx30nn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=401&fit=crop&dpr=1 754w, https://images.theconversation.com/files/416316/original/file-20210816-28-tx30nn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=401&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/416316/original/file-20210816-28-tx30nn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=401&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Left: Part of Titan’s Ligeia Mare, showing a coastline with valleys drowned by a sea of liquid methane. Right: The Musandam peninsula, Arabia, where coastal valleys are similarly drowned, but by a saltwater sea.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech/ASI/Cornell and Expedition 63, International Space Station (ISS)</span></span>
</figcaption>
</figure>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/titan-first-global-map-uncovers-secrets-of-a-potentially-habitable-moon-of-saturn-126985">Titan: first global map uncovers secrets of a potentially habitable moon of Saturn</a>
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<hr>
<p>Rock and liquid water on Earth, frigid water-ice and liquid methane on Titan - it makes little difference. Their mutual interactions are the same, and so we see geology repeating itself on different worlds.</p><img src="https://counter.theconversation.com/content/166046/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Rothery is Professor of Planetary Geosciences at the Open University. He is co-leader of the European Space Agency's Mercury Surface and Composition Working Group, and a Co-Investigator on MIXS (Mercury Imaging X-ray Spectrometer) that is now on its way to Mercury on board the European Space Agency's Mercury orbiter BepiColombo. He has received funding from the UK Space Agency and the Science & Technology Facilities Council for work related to Mercury and BepiColombo, and from the European Commission under its Horizon 2020 programme for work on planetary geological mapping (776276 Planmap). He is author of Planet Mercury - from Pale Pink Dot to Dynamic World (Springer, 2015), Moons: A Very Short Introduction (Oxford University Press, 2015) and Planets: A Very Short Introduction (Oxford University Press, 2010). He is Educator on the Open University's free learning Badged Open Course (BOC) on Moons and its equivalent FutureLearn Moons MOOC, and chair of the Open University's level 2 course on Planetary Science and the Search for Life.</span></em></p>From the tallest cliff in the solar system to its largest impact basin, geological processes on other worlds are very similar to those on our own planet.David Rothery, Professor of Planetary Geosciences, The Open UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1523702020-12-21T17:13:00Z2020-12-21T17:13:00ZThe ‘Christmas Star’ appears again: Jupiter and Saturn align in the ‘great conjunction’ on Dec. 21, 2020<figure><img src="https://images.theconversation.com/files/376184/original/file-20201221-15-1sejjhd.jpg?ixlib=rb-1.1.0&rect=40%2C62%2C2690%2C1931&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">On Dec. 21, Jupiter and Saturn will be so close together they will almost appear to be touching.</span> <span class="attribution"><span class="source">(Unsplash)</span></span></figcaption></figure><p>Jupiter and Saturn lined up on Dec. 21, so close together that they appeared as one bright shining star. Many referred to it as the “Christmas Star.” It’s the <a href="https://www.scientificamerican.com/article/jupiter-and-saturns-great-conjunction-is-the-best-in-800-years-heres-how-to-see-it/">closest the two planets have appeared together in about 800 years</a>, and won’t occur again until 2080.</p>
<p>This conjunction of Jupiter and Saturn may have an even closer tie to the Biblical story of the birth of Jesus Christ than its occurrence so close to Christmas this year. As noted by Johannes Kepler in the 17th century, a similar conjunction occurred in 7 BCE and could be the astronomical origin of the Star of Bethlehem that guided the wise men.</p>
<p>But there are notable differences between the two events, and the full story has several interesting ties to the history of astronomy, starting with the origins of the word “planet,” which <a href="https://www.etymonline.com/word/planet">comes from the Greek word meaning “wanderer.”</a></p>
<p>The planets have always been recognizable to astronomers, not only because they are relatively bright points of light among the stars, but because of their unique wandering nature. This posed a problem to ancient astronomers, which lasted more than 2,000 years and was only resolved during the Scientific Revolution.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/376231/original/file-20201221-15-dgnu5g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Sunset view of planets" src="https://images.theconversation.com/files/376231/original/file-20201221-15-dgnu5g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/376231/original/file-20201221-15-dgnu5g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=406&fit=crop&dpr=1 600w, https://images.theconversation.com/files/376231/original/file-20201221-15-dgnu5g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=406&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/376231/original/file-20201221-15-dgnu5g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=406&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/376231/original/file-20201221-15-dgnu5g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=511&fit=crop&dpr=1 754w, https://images.theconversation.com/files/376231/original/file-20201221-15-dgnu5g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=511&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/376231/original/file-20201221-15-dgnu5g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=511&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 graphic made from a simulation program, showing a view of the 2020 great conjunction through the naked eye just after sunset at approximately 5:15 p.m. (EST) on Dec. 21.</span>
<span class="attribution"><span class="source">(NASA)</span></span>
</figcaption>
</figure>
<h2>The motion of the planets</h2>
<p>As the Earth spins on its axis every 24 hours, the sun, moon, stars and planets all appear to move across our sky, rising in the East and setting in the West. But because the planets orbit the sun, all travelling in counterclockwise directions when viewed from above the North Pole, to us on Earth the sun and planets all appear to move with respect to the background stars. </p>
<p>As Earth moves around the sun, the sun in turn appears to move slowly to the East, by about a degree each day as it travels through the <a href="https://earthsky.org/space/what-is-the-ecliptic">Zodiac constellations</a>. Mercury and Venus move from one side of the sun to the other as they circle it. And the outer planets of the solar system — Mars, Jupiter and Saturn are visible to the naked eye — appear to move East through the stars as they orbit the sun.</p>
<p>But a peculiar thing happens to the positions of the outer planets when the Earth passes between them and the sun: They appear to briefly reverse direction, and travel West, against the background stars. This <a href="https://earthsky.org/space/what-is-retrograde-motion">apparent retrograde motion</a> is caused by a parallax shift that occurs for the same reason your thumb hops back and forth if you hold it fixed in front of your face and wink first with one eye, then the other; it’s an optical illusion caused by a shift in our perspective.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/376170/original/file-20201221-17-ww488o.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/376170/original/file-20201221-17-ww488o.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/376170/original/file-20201221-17-ww488o.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=623&fit=crop&dpr=1 600w, https://images.theconversation.com/files/376170/original/file-20201221-17-ww488o.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=623&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/376170/original/file-20201221-17-ww488o.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=623&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/376170/original/file-20201221-17-ww488o.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=783&fit=crop&dpr=1 754w, https://images.theconversation.com/files/376170/original/file-20201221-17-ww488o.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=783&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/376170/original/file-20201221-17-ww488o.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=783&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 Earth-centred model of planetary motions could explain why other planets sometimes appeared to be moving backwards. Nicolaus Copernicus proposed a sun-centred theory in 1543.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Ptolemaic_system.png">(Muhammad/Wikimedia)</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>While the Ancient Greeks had considered this explanation of the retrograde motions of planets, they mainly preferred an alternate, <a href="http://galileo.rice.edu/sci/theories/ptolemaic_system.html">Earth-centred model</a> in which the planets move around a fixed Earth on small circular orbits, the centres of which went around larger, Earth-centred circles. Thus, as the planets orbited an empty point in space while that point went around the Earth, the planets would occasionally stop and move backwards in their motion against the background stars. </p>
<p>Astronomers mainly described the solar system in this Earth-centred way until Nicolaus Copernicus proposed a <a href="https://earthobservatory.nasa.gov/features/OrbitsHistory">sun-centred theory in 1543</a>. Copernicus’s theory didn’t do any better job of describing planetary motion than the Earth-centred models did, but the idea gained traction.</p>
<p>The German 17th-century astronomer Johannes Kepler eventually found the key to describing planetary motion in a sun-centred system. Rather than orbiting the sun in circles, Kepler found the <a href="https://solarsystem.nasa.gov/resources/310/orbits-and-keplers-laws/">planets moved in ellipses</a>, a distinction that allowed him to precisely predict their observed positions. </p>
<h2>Christmas Star</h2>
<p>A conjunction is said to happen when two astronomical objects pass each other due to their movement along the direction of the stars’ daily rotation. Since solar system objects do not all move within precisely the same plane, conjunctions can sometimes happen with a wide separation. Since Jupiter orbits the sun every 11.9 years while Saturn’s orbit takes 29.5 years, it happens that a conjunction of Jupiter and Saturn — called a “great conjunction” due to its rarity — occurs roughly every 20 years.</p>
<figure class="align-center ">
<img alt="Night sky with two bright planets." src="https://images.theconversation.com/files/376190/original/file-20201221-23-1y3eslv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/376190/original/file-20201221-23-1y3eslv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/376190/original/file-20201221-23-1y3eslv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/376190/original/file-20201221-23-1y3eslv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/376190/original/file-20201221-23-1y3eslv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/376190/original/file-20201221-23-1y3eslv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/376190/original/file-20201221-23-1y3eslv.jpg?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">Conjunction of Jupiter (top) and Venus (bottom) in 2015.</span>
<span class="attribution"><span class="source">(Mike Pennington)</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Most great conjunctions are not particularly notable. But occasionally, like this year, Jupiter and Saturn cross paths so close to each other that they can be barely distinguishable to the naked eye. Or sometimes the two planets cross paths when they are opposite the sun, so their apparent retrograde motion results in a triple conjunction, as was the case in 7 BCE.</p>
<p>In 1604, while he was working in Prague, <a href="https://www.nature.com/articles/462987a">Kepler observed the tight arrangement of three planets — Mars, Saturn and Jupiter — and a bright new star, a supernova, that would slowly fade over the course of a year</a>. This occurrence inspired him to consider a similar set of events that might have led the wise men to Bethlehem in time for Jesus Christ’s birth. </p>
<p>Knowing that Herod the Great had died in 4 BCE, he placed the birth of Christ before that date. And using his knowledge of planetary motion, he found that Jupiter and Saturn underwent a triple conjunction in 7 BCE, that conjunctions of Mars with each planet in 6 BCE were shortly followed by conjunctions of the planets with the sun. Kepler <a href="http://articles.adsabs.harvard.edu//full/1937JRASC..31..417B/0000421.000.html">suggested that these solar conjunctions aligned with the conception of Christ and that the wise men arrived the following year to witness Christ’s birth beneath the Star of Bethlehem</a>.</p>
<h2>Significance of the great conjunction</h2>
<p>On Dec. 21 of this year, Jupiter and Saturn were only one-tenth of a degree apart, well within the field of any telescope’s view. With this year’s event, it is worth keeping in mind the historical significance previous conjunctions have had. </p>
<p>Kepler’s fascination with planetary motion led, only a handful of years later, to his discovery that planets follow elliptical paths around the sun. And Kepler’s discovery would, before the end of that century, <a href="https://www.pbs.org/wgbh/nova/newton/principia.html">inspire Newton’s work on his most important contribution</a>, the great <em>Philosophiae Naturalis Principia Mathematica</em>, where he laid down his ideas on the law of gravity, and which forever changed the world of science. </p>
<p>Without fear of exaggeration, it’s possible to link the wandering motion of the planets — never more clearly on display than when we can simultaneously see Saturn’s rings and the Galilean moons of Jupiter through a telescope — with the discovery that Earth is a planet within a solar system in which motions are dominated by a universal gravitation that acts between all massive bodies.</p>
<p><em>This is a corrected version of a story originally published on Dec. 21. The earlier story said a conjunction aligned with Immaculate Conception instead of the conception of Christ.</em></p><img src="https://counter.theconversation.com/content/152370/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Daryl Janzen does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>From the birth of Jesus Christ to Newton’s discovery of gravity, great conjunctions of Jupiter and Saturn have many notable connections in human history.Daryl Janzen, Observatory Manager and Instructor, Astronomy, University of SaskatchewanLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1522242020-12-18T13:26:06Z2020-12-18T13:26:06ZWhat you need to know about this year’s winter solstice and the great conjunction<p><em>Editor’s note: Dr. William Teets is the director of Vanderbilt University’s Dyer Observatory. In this interview, he explains what does and doesn’t happen during the winter solstice on Dec. 21. Another cosmic phenomenon is also going to occur on the same day called “<a href="https://www.nasa.gov/feature/the-great-conjunction-of-jupiter-and-saturn/">the great conjunction</a>,” where Saturn and Jupiter, both of which can be seen with the naked eye, will appear extremely close to one another.</em></p>
<h2>What happens on the winter solstice?</h2>
<p>The winter solstice this year happens on Dec. 21. This is when the Sun appears the lowest in the Northern Hemisphere sky and is at its farthest southern point over Earth – directly over the Tropic of Capricorn. For folks living at 23.5 degrees south latitude, not only does this day mark their summer solstice, but they also see the Sun directly over them at local noon. After that, the Sun will start to creep back north again. </p>
<p><img src="https://cdn.theconversation.com/static_files/files/1401/sun_over_here_2.gif?1608652248"></p>
<p>The sequence of images below shows the path of the Sun through the sky at different times of the year. You can see how the Sun is highest in the Northern Hemisphere sky in June, lowest in December, and halfway in between these positions in March and September during the equinoxes.</p>
<p><img src="https://cdn.theconversation.com/static_files/files/1389/Comp_1.gif?1608247458"></p>
<h2>The winter solstice is the shortest day in the Northern Hemisphere but not the day with the latest sunrise and earliest sunset. How is that possible?</h2>
<p>The winter solstice doesn’t coincide with the latest sunrise or the earliest sunset. Those actually occur about two weeks before and two weeks after the winter solstice. This is because we are changing our distance from the sun due to our elliptical, not circular, orbit, which changes the speed at which we orbit. </p>
<p>If you were to look at where the Sun is at exactly the same time of day over different days of the year, you would see that it’s not always in the same spot. Yes, the Sun is higher in the summer and lower in the winter, but it also moves from side to side of the average noontime position, which also plays a role in when the Sun rises and sets. </p>
<p>One should also keep in mind that the seasons are due to the Earth’s axial tilt, not our distance from the Sun. Believe it or not, we are closest to the Sun in January.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/375778/original/file-20201217-23-sp6uaa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Analemma of the sun over Callanish, Scotland." src="https://images.theconversation.com/files/375778/original/file-20201217-23-sp6uaa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/375778/original/file-20201217-23-sp6uaa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=693&fit=crop&dpr=1 600w, https://images.theconversation.com/files/375778/original/file-20201217-23-sp6uaa.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=693&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/375778/original/file-20201217-23-sp6uaa.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=693&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/375778/original/file-20201217-23-sp6uaa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=870&fit=crop&dpr=1 754w, https://images.theconversation.com/files/375778/original/file-20201217-23-sp6uaa.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=870&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/375778/original/file-20201217-23-sp6uaa.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=870&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 photograph of the position of the Sun, taken at the same time on different days throughout the year, shows a figure-eight pattern known as an analemma. This photo was taken in Callanish, Scotland.</span>
<span class="attribution"><a class="source" href="https://apod.nasa.gov/apod/ap180923.html">Giuseppe Petricca, NASA</a></span>
</figcaption>
</figure>
<h2>What is ‘the great conjunction’?</h2>
<p><img src="https://cdn.theconversation.com/static_files/files/1387/travelling.gif?1608244561"></p>
<p>Saturn and Jupiter have appeared fairly close together in our sky throughout the year. But on Dec. 21, Saturn and Jupiter will appear so close together that some folks may have a difficult time seeing them as two objects. </p>
<p>If you have a pair of binoculars, you’ll easily be able to spot both planets. In even a small telescope, you’d see both planets at the same time in the same field of view, which is really unheard of. That’s what makes this conjunction so rare. Jupiter and Saturn appear to meet up about every 20 years. Most of the time, however, they’re not nearly as close together as we’re going to see them on Monday, Dec. 21. </p>
<p>For a comparison, there was a great conjunction back in 2000, but the two planets were separated by about two full-Moon widths. This year, the orbits will bring them to where they appear to be about one-fifth of a full-Moon diameter. </p>
<p><img src="https://cdn.theconversation.com/static_files/files/1388/december.gif?1608244618"></p>
<p>We have been encouraging folks to go out and look at these planets using just their eyes between now and Dec. 21. You’ll actually be able to see how much they appear to move over the course of a single day. </p>
<p>The next time they will get this close together in our sky won’t be for another 60 years, so this is going to be a once-in-a-lifetime event for many people. In fact, the last time they got this close together was in the year <a href="https://whenthecurveslineup.com/2020/02/20/1623-the-great-conjunction-of-jupiter-and-saturn/">1623</a>, but it was really difficult, if not impossible, to see them then because they appeared much closer to the Sun and set soon after it. Go back another 400 years to <a href="https://thehill.com/changing-america/opinion/529835-the-great-conjunction-of-jupiter-and-saturn-the-dawn-of-a-new-era">1226</a> and this would have been the last time that we would have had a good view of this type of conjunction.</p>
<h2>What advice would you give to people who want to see the great conjunction?</h2>
<p>If weather permits at <a href="https://dyer.vanderbilt.edu/">Dyer Observatory</a>, we’ll be streaming a live view of the conjunction from one of the observatory’s telescopes, and I’ll be available to answer questions. Even if you don’t have a telescope or a pair of binoculars, definitely go out and check out this very rare alignment with your own eyes. Remember that they set soon after sunset, so be ready to view right at dusk!</p>
<p>[<em>Understand new developments in science, health and technology, each week.</em> <a href="https://theconversation.com/us/newsletters/science-editors-picks-71/?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=science-understand">Subscribe to The Conversation’s science newsletter</a>.]</p><img src="https://counter.theconversation.com/content/152224/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>William Teets does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The 2020 winter solstice is also when Saturn and Jupiter appear closest to each other for 60 years, Here’s what you need to know about both the events.William Teets, Acting Director and Astronomer, Dyer Observatory, Vanderbilt UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1463582020-09-18T11:50:53Z2020-09-18T11:50:53ZThe four most promising worlds for alien life in the solar system<figure><img src="https://images.theconversation.com/files/358659/original/file-20200917-14-1qdn4n4.jpg?ixlib=rb-1.1.0&rect=36%2C36%2C1238%2C782&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">NASA's Curiosity Rover takes a selfie on Mars in June, 2018.</span> <span class="attribution"><a class="source" href="https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA22486">NASA/JPL-Caltech/MSSS</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>The Earth’s biosphere contains all the known ingredients necessary for life as we know it. Broadly speaking these are: liquid water, at least one source of energy, and an inventory of biologically useful elements and molecules.</p>
<p>But the recent discovery of possibly biogenic phosphine <a href="https://theconversation.com/venus-could-it-really-harbour-life-new-study-springs-a-surprise-145981">in the clouds of Venus</a> reminds us that at least some of these ingredients exist elsewhere in the solar system too. So where are the other most promising locations for extra-terrestrial life?</p>
<h2>Mars</h2>
<p>Mars is one of the most Earth-like worlds in the solar system. It has a 24.5-hour day, polar ice caps that expand and contract with the seasons, and a large array of surface features that were sculpted by water during the planet’s history.</p>
<figure class="align-center ">
<img alt="Red planet Mars in space with polar ice caps visible" src="https://images.theconversation.com/files/358594/original/file-20200917-24-fwl0h9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/358594/original/file-20200917-24-fwl0h9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/358594/original/file-20200917-24-fwl0h9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/358594/original/file-20200917-24-fwl0h9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/358594/original/file-20200917-24-fwl0h9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/358594/original/file-20200917-24-fwl0h9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/358594/original/file-20200917-24-fwl0h9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Mars has polar ice caps.</span>
<span class="attribution"><a class="source" href="https://upload.wikimedia.org/wikipedia/commons/0/02/OSIRIS_Mars_true_color.jpg">ESA & MPS for OSIRIS Team MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA)</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>The detection of <a href="https://www.sciencemag.org/news/2018/07/liquid-water-spied-deep-below-polar-ice-cap-mars">a lake beneath</a> the southern polar ice cap and methane in the Martian atmosphere (which varies with the seasons and even the <a href="https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GL083800">time of day</a>) make Mars a very interesting candidate for life. Methane is significant as it can be produced by biological processes. But the actual source for the methane on Mars is not yet known.</p>
<p>It is possible that life may have gained a foothold, given the <a href="https://advances.sciencemag.org/content/4/6/eaar3330">evidence</a> that the planet once had a much more benign environment. Today, Mars has a very thin, dry atmosphere comprised almost entirely of carbon dioxide. This offers scant protection from solar and cosmic radiation. If Mars has managed to retain some reserves of water beneath its surface, it is not impossible that life may still exist. </p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/life-on-mars-europe-commits-to-groundbreaking-mission-to-bring-back-rocks-to-earth-128328">Life on Mars? Europe commits to groundbreaking mission to bring back rocks to Earth</a>
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<h2>Europa</h2>
<p>Europa was discovered by Galileo Galilei in 1610, along with Jupiter’s three other larger moons. It is slightly smaller than Earth’s moon and orbits the gas giant at a distance of some 670,000km once every 3.5 days. Europa is constantly squeezed and stretched by the competing gravitational fields of Jupiter and the other <a href="https://www.universetoday.com/44796/galilean-moons/">Galilean moons</a>, a process known as tidal flexing. </p>
<p>The moon is believed to be a geologically active world, like the Earth, because the strong tidal flexing heats its rocky, metallic interior and keeps it partially molten.</p>
<figure class="align-center ">
<img alt="Jupiter's white with brown streaks moon Europa in space," src="https://images.theconversation.com/files/358637/original/file-20200917-14-1hfzvc8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/358637/original/file-20200917-14-1hfzvc8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=444&fit=crop&dpr=1 600w, https://images.theconversation.com/files/358637/original/file-20200917-14-1hfzvc8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=444&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/358637/original/file-20200917-14-1hfzvc8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=444&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/358637/original/file-20200917-14-1hfzvc8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=557&fit=crop&dpr=1 754w, https://images.theconversation.com/files/358637/original/file-20200917-14-1hfzvc8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=557&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/358637/original/file-20200917-14-1hfzvc8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=557&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Europa’s icy surface is a good sign for alien hunters.</span>
<span class="attribution"><a class="source" href="https://photojournal.jpl.nasa.gov/catalog/PIA19048">NASA/JPL-Caltech/SETI Institute</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>The surface of Europa is a vast expanse of water ice. Many scientists think that beneath the frozen surface is a layer of liquid water – a global ocean – which is prevented from freezing by the heat from flexing and which maybe over 100km deep. </p>
<p>Evidence for this ocean includes geysers erupting through <a href="https://www.nature.com/articles/s41550-019-0933-6">cracks in the surface ice</a>, a <a href="http://ffden-2.phys.uaf.edu/webproj/212_spring_2015/Justin_Long/Justin_Long/magnetic.html">weak magnetic field</a> and <a href="https://www.sciencedirect.com/science/article/abs/pii/S0019103599961870?via%3Dihub">chaotic terrain</a> on the surface, which could have been deformed by ocean currents swirling beneath. This icy shield insulates the subsurface ocean from the extreme cold and vacuum of space, as well as Jupiter’s ferocious radiation belts.</p>
<p>At the bottom of this ocean world it is conceivable that we might find <a href="https://oceanservice.noaa.gov/facts/vents.html">hydrothermal vents</a> and ocean floor volcanoes. On Earth, such features often support very rich and diverse ecosystems.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/europa-there-may-be-life-on-jupiters-moon-and-two-new-missions-will-pave-the-way-for-finding-it-122551">Europa: there may be life on Jupiter's moon and two new missions will pave the way for finding it</a>
</strong>
</em>
</p>
<hr>
<h2>Enceladus</h2>
<p>Like Europa, <a href="https://solarsystem.nasa.gov/moons/saturn-moons/enceladus/in-depth/">Enceladus</a> is an ice-covered moon with a subsurface ocean of liquid water. Enceladus orbits Saturn and first came to the attention of scientists as a potentially habitable world following the <a href="https://solarsystem.nasa.gov/resources/806/bursting-at-the-seams-the-geyser-basin-of-enceladus/">surprise discovery</a> of enormous geysers near the moon’s south pole.</p>
<p>These jets of water escape from large cracks on the surface and, given Enceladus’ weak gravitational field, spray out into space. They are clear evidence of an underground store of liquid water.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"906891543780323328"}"></div></p>
<p>Not only was water detected in these geysers but also an array of organic molecules and, crucially, tiny grains of rocky silicate particles that can only be present if the sub-surface ocean water was in physical contact with the rocky ocean floor at a <a href="https://solarsystem.nasa.gov/missions/cassini/science/enceladus/">temperature of at least 90˚C</a>. This is very strong evidence for the existence of hydrothermal vents on the ocean floor, providing the chemistry needed for life and localised sources of energy. </p>
<h2>Titan</h2>
<p>Titan is the largest moon of Saturn and the only moon in the solar system with a substantial atmosphere. It contains a thick orange haze of complex organic molecules and a methane weather system in place of water – complete with seasonal rains, dry periods and surface sand dunes created by wind.</p>
<figure class="align-center ">
<img alt="Yellow/orange moon Titan in space" src="https://images.theconversation.com/files/358645/original/file-20200917-16-17xgwya.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/358645/original/file-20200917-16-17xgwya.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/358645/original/file-20200917-16-17xgwya.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/358645/original/file-20200917-16-17xgwya.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/358645/original/file-20200917-16-17xgwya.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/358645/original/file-20200917-16-17xgwya.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/358645/original/file-20200917-16-17xgwya.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Titan’s atmosphere makes it look like a fuzzy orange ball.</span>
<span class="attribution"><a class="source" href="https://photojournal.jpl.nasa.gov/catalog/PIA14602">NASA/JPL-Caltech/Space Science Institute</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>The atmosphere consists mostly of nitrogen, an important chemical element used in the construction of proteins in all known forms of life. Radar observations have detected the presence of <a href="https://theconversation.com/titan-first-global-map-uncovers-secrets-of-a-potentially-habitable-moon-of-saturn-126985">rivers and lakes</a> of liquid methane and ethane and possibly the presence of cryovolcanoes – volcano-like features that erupt liquid water rather than lava. This suggests that Titan, like Europa and Enceladus, has a sub-surface reserve of liquid water.</p>
<p>At such an enormous distance from the Sun, the surface temperatures on Titan are a frigid -180˚C – way too cold for liquid water. However, the bountiful chemicals available on Titan has raised speculation that lifeforms – potentially with fundamentally different chemistry to terrestrial organisms – <a href="https://www.space.com/8547-strange-discovery-titan-leads-speculation-alien-life.html">could exist</a> there.</p><img src="https://counter.theconversation.com/content/146358/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>The clouds of Venus may harbour alien life. But where else?Gareth Dorrian, Post Doctoral Research Fellow in Space Science, University of BirminghamLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1303182020-01-29T13:00:18Z2020-01-29T13:00:18ZCurious Kids: why are some planets surrounded by rings?<figure><img src="https://images.theconversation.com/files/311372/original/file-20200122-117933-hxjvkf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Saturn is one of a few planets in our solar system surrounded by rings.</span> <span class="attribution"><span class="source">Vadim Sadovski/Shutterstock/Elements of this image furnished by NASA</span></span></figcaption></figure><p><em>Curious Kids is a series for children in which we ask experts to answer questions from kids.</em></p>
<p><strong>Why do Uranus and other planets have rings around them? (Lesedi, 6, Soweto)</strong></p>
<p>For a very long time, Saturn was thought to be the only planet in our solar system with rings. The rings around Saturn were discovered by an astronomer called <a href="https://www.britannica.com/biography/Galileo-Galilei">Galileo Galilei</a> nearly 400 years ago. He used a very simple telescope that he constructed himself from lenses and pointed it at the planets in the night sky. One of the first objects he looked at was Saturn. At first he thought that Saturn had two large moons on either side of the planet because his telescope wasn’t very good and only produced very blurry images.</p>
<p>Since then, astronomers – who study the universe and everything in it, like planets – have used bigger and better telescopes to find rings around all of the outer gas giant planets: Jupiter, Saturn, Neptune and Uranus. These planets, unlike others in our system, consist largely of gas. </p>
<p>We’re not sure how the rings work or how they formed, but there are a few theories.</p>
<h2>Different theories</h2>
<p>The first <a href="https://www.universetoday.com/127197/127197/">theory</a> states that the rings formed at the same time as the planet. Some particles of gas and dust that the planets are made of were too far away from the core of the planet and could not be squashed together by gravity. They remained behind to form the ring system. </p>
<p>The second <a href="https://www.planetsforkids.org/why-does-saturn-have-rings.html">theory</a>, and my personal favourite, is that the rings were formed when two of the moons of the planet, which had formed at the same time as the planet, somehow got disturbed in their orbits and eventually crashed into each other (an orbit is the circular path that the moon travels on around the planet). The stuff that was left behind in this huge smash could not come together again to form a new moon. Instead, it spread out into the ring systems we see today.</p>
<p>Since we don’t have the answers yet, we keep exploring and testing different theories.</p>
<p>What we do know is that the rings around the various planets are all slightly different from one another, but they all share some characteristics too.</p>
<p>First, they are all much wider than they are thick. The rings of Saturn, for example, are about <a href="https://solarsystem.nasa.gov/planets/saturn/in-depth/">280,000km wide</a> (stretching away from the planet) but only 200 metres thick. That’s like having a normal pancake on your plate for breakfast that is 14km wide.</p>
<p>The other thing that all rings systems share is that they are all made of small particles of ice and rock. The smallest of these particles are no bigger than dust grains, while the largest of the particles are about 20 metres in diameter – about the size of a school hall. All the rings around the planets also contain gaps that are sometimes many kilometres wide and at first nobody could figure out why. We later learned that the gaps were caused by small <a href="https://www.universetoday.com/849/gaps-in-saturns-rings/">moons</a> that had gobbled up all the material in that particular part of the ring system.</p>
<p>The biggest difference between the rings of Saturn and the other gas giant planets is that the particles that make up the rings of Saturn are very good at reflecting the light from the sun back towards the Earth. That means they appear to be very bright, which is why we can see the rings from Earth using a normal telescope. The extremely large number of particles trapped in the rings of Saturn also make the rings much bigger and wider; that’s another reason they’re easier to see than the rings of the other gas giant planets.</p>
<p>The particles that make up the rings of Uranus and Neptune contain elements that were darkened by the sun. These dark particles look very similar to pieces of coal or charcoal like you’d use to make a fire. This makes them much more difficult to see because they don’t reflect as much of the sun’s light back to us.</p>
<h2>New discoveries</h2>
<p>This is an exciting time for astronomy. More and more satellites and space probes are being launched from all over the <a href="https://www.planetary.org/explore/space-topics/space-missions/missions-beyond-mars.html">world</a>, which allows us to investigate the outer planets of our solar system. That means astronomers will have the chance to study these rings – and one day, hopefully, we’ll be able to answer all of your questions and more.</p>
<p><em>Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to africa-curiouskids@theconversation.com. Please tell us your name, age, and which city you live in. We won’t be able to answer every question but we will do our best.</em></p><img src="https://counter.theconversation.com/content/130318/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Dr Rudi Kuhn 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>We’re not sure how the rings work or how they formed, but there are a few theories.Dr Rudi Kuhn, SALT Astronomer, South African Astronomical ObservatoryLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1241582019-12-16T13:43:04Z2019-12-16T13:43:04ZPlanetary confusion – why astronomers keep changing what it means to be a planet<figure><img src="https://images.theconversation.com/files/300167/original/file-20191104-88409-13vd5ta.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">In 2015, NASA’s New Horizons spacecraft looked back toward the sun and captured this near-sunset view of the rugged, icy mountains and flat ice plains extending to Pluto’s horizon. </span> <span class="attribution"><a class="source" href="https://www.nasa.gov/image-feature/pluto-s-majestic-mountains-frozen-plains-and-foggy-hazes">NASA/JHUAPL/SwRI</a></span></figcaption></figure><p>As an astronomer, the question I hear the most is why isn’t Pluto a planet anymore? More than 10 years ago, astronomers famously voted to change <a href="https://www.nytimes.com/2006/08/24/science/space/25pluto.html">Pluto’s classification</a>. But the question still comes up. </p>
<p>When I am asked directly if I think Pluto is a planet, I tell everyone my answer is no. It all goes back to the origin of the word “planet.” It comes from the Greek phrase for “wandering stars.” Back in ancient times before the telescope was invented, the mathematician and astronomer Claudius Ptolemy called stars “fixed stars” to distinguish them from the seven wanderers that move across the sky in a very specific way. <a href="https://www.loc.gov/collections/finding-our-place-in-the-cosmos-with-carl-sagan/articles-and-essays/modeling-the-cosmos/ancient-greek-astronomy-and-cosmology">These seven objects are the Sun, the Moon, Mercury, Venus, Mars, Jupiter and Saturn</a>.</p>
<p>When people started using the word “planet,” they were referring to those seven objects. Even Earth was not originally called a planet – but the Sun and Moon were. </p>
<p>Since people use the word “planet” today to refer to many objects beyond the original seven, it’s no surprise we argue about some of them.</p>
<p>Although I am trained as an astronomer and I studied more distant objects like stars and galaxies, I have an interest in the objects in our Solar System because I teach several classes on planetary science.</p>
<h2>Asteroids, the first demoted planets</h2>
<p>The word “planet” is used to describe <a href="https://www.skyandtelescope.com/observing/ice-giants-neptune-and-uranus/">Uranus and Neptune</a>, which were discovered in 1781 and 1846 respectively, because they move in the same way that the other “wandering stars” move. Like Saturn and Jupiter, if you look at them through a telescope, they appear bigger than stars, so they were recognized to be more like planets than stars. </p>
<p>Not long after the discovery of Uranus, astronomers discovered additional wandering objects – these were named <a href="https://www.esa.int/About_Us/Welcome_to_ESA/ESA_history/Asteroids_The_discovery_of_asteroids">Ceres, Pallas, Juno and Vesta</a>. At the time they were considered planets, too. Through a telescope they look like pinpoints of light and not disks. With a small telescope, even <a href="http://www.astronomy.com/observing/sky-this-month/2018/08/neptune-at-its-best">distant Neptune appears fuzzier than a star</a>. Even though these other, new objects were called planets at first, astronomers thought they needed a different name since they appear more star-like than planet-like. </p>
<p>William Herschel (who discovered Uranus) is often said to have named them “asteroids” which means “star-like,” but <a href="https://www.skyandtelescope.com/astronomy-news/why-do-we-call-them-asteroids/">recently, Clifford Cunningham</a> claimed that the person who coined that name was Charles Burney Jr., a preeminent Greek scholar. </p>
<p>Today, just like the word “planet,” we use the word “asteroid” differently. Now it refers to objects that are rocky in composition, mostly found between Mars and Jupiter, mostly irregularly shaped, smaller than planets, but bigger than meteoroids. Most people assume there is a strict definition for what makes an object an asteroid. But there isn’t, just like there never was for the word “planet.”</p>
<p>In the 1800s the large asteroids were called planets. Students at the time likely learned that the planets were Mercury, Venus, Earth, Mars, Ceres, Vesta, Pallas, Juno, Jupiter, Saturn, Uranus and, eventually, Neptune. Most books today write that asteroids are different than planets, but there is a <a href="https://arxiv.org/abs/1805.04115">debate among astronomers</a> about whether the term “asteroid” was originally used to mean a small type of planet, rather than a different type of object altogether. </p>
<h2>How are moons different than planets?</h2>
<p>These days, scientists consider properties of these celestial objects to figure out whether an object is a planet or not. For example, you might say that shape is important; planets should be mostly spherical, while asteroids can be lumpy. As astronomers try to fix these definitions to make them more precise, we then create new problems. If we use roundness as an important distinction for objects, what should we call moons? Should moons be considered planets if they are round and asteroids if they are not round? Or are they somehow different from planets and asteroids altogether? </p>
<p>I would argue we should again look to how the word “moon” came to refer to objects that orbit planets. </p>
<p>When astronomers talk about the Moon of Earth, we capitalize the word “Moon” to indicate that it’s a proper name. That is, <a href="http://curious.astro.cornell.edu/observational-astronomy/seti-and-extraterrestrial-life/159-our-solar-system/the-sun/the-solar-system/4-what-are-the-names-of-the-earth-moon-sun-and-solar-system-beginner">the Earth’s moon has the name, Moon</a>. For much of human history, it was the only Moon known, so there was no need to have a word that referred to one celestial body orbiting another. This changed when <a href="http://galileo.rice.edu/sci/observations/jupiter_satellites.html">Galileo discovered four large objects orbiting Jupiter</a>. These are now called Io, Europa, Ganymede and Callisto, the moons of Jupiter. </p>
<p>This makes people think the technical definition of moon is a satellite of another object, and so we call lots of objects that orbit Mars, Jupiter, Saturn, Uranus, Neptune, Pluto, Eris, Makemake, Ida and a <a href="https://stardate.org/radio/program/2018-08-28">large number of other asteroids</a> moons. When you start to look at the variety of moons, some, like Ganymede and Titan, are larger than Mercury. Some are similar in size to the object they orbit. Some are small and irregularly shaped, and some have odd orbits. </p>
<p>So they are not all just like Earth’s Moon. If we try to fix the definition for what is a moon and how that differs from a planet and asteroid, we are likely going to have to reconsider the classification of some of these objects, too. You can argue that Titan has more properties in common with the planets than Pluto does, for example. You can also argue that every single particle in Saturn’s rings is an individual moon, which would mean that Saturn has billions upon billions of moons.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/300166/original/file-20191104-88419-3j0wfr.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/300166/original/file-20191104-88419-3j0wfr.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/300166/original/file-20191104-88419-3j0wfr.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/300166/original/file-20191104-88419-3j0wfr.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/300166/original/file-20191104-88419-3j0wfr.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/300166/original/file-20191104-88419-3j0wfr.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/300166/original/file-20191104-88419-3j0wfr.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/300166/original/file-20191104-88419-3j0wfr.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">Family portrait of Pluto’s moons: This composite image shows a sliver of Pluto’s large moon, Charon, and all four of Pluto’s small moons.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/image-feature/charon-and-the-small-moons-of-pluto">NASA/JHUAPL/SwRI</a></span>
</figcaption>
</figure>
<h2>Planets around other stars</h2>
<p>The most recent naming challenge astronomers face arose when they discovering planets far from our Solar System orbiting around distant stars. These objects have been called extrasolar planets, exosolar planets or <a href="http://exoplanets.org/">exoplanets</a>. </p>
<p>Astronomers are currently searching for <a href="https://arxiv.org/abs/1904.10618">exomoons</a> orbiting exoplanets. Exoplanets are being discovered that have properties unlike the planets in our Solar System, so astronomers have started putting them in categories like “hot Jupiter,” “warm Jupiter,” “super-Earth” and “mini-Neptune.” </p>
<p>Ideas for how planets form also suggest that there are planetary objects that have been flung out of orbit from their parent star. This means there are <a href="https://exoplanets.nasa.gov/resources/28/free-floating-planets-may-be-more-common-than-stars/">free-floating planets</a> not orbiting any star. Should planetary objects that are flung out of a solar system also get ejected from the elite club of planets? </p>
<p>When I teach, I end this discussion with a recommendation. Rather than arguing over planet, moon, asteroid and exoplanet, I think we need to do what Herschel and Burney did and coin a new word. For now, I use “world” in my class, but I do not offer a rigorous definition of what makes something a world and what does not. Instead, I tell my students that all of these objects are of interest to study. </p>
<h2>The Sun was once a planet</h2>
<p>A lot of people seem to feel that scientists wronged Pluto by changing its classification. I look at it that Pluto was only originally called a planet because of an accident; scientists were looking for planets beyond Neptune, and when they found Pluto they called it a planet, even though its observable properties should have led them to call it an asteroid. </p>
<p>As our understanding of this object has grown, I feel like the evidence now leads me to call Pluto something besides planet. There are other scientists who disagree, feeling Pluto still should be classified as a planet. </p>
<p>But remember: The Greeks started out calling the Sun a planet given how it moved on the sky. We now know that the properties of the Sun show it to belong in a very different category from the planets; it’s a star, not a planet. If we can stop calling the Sun a planet, why can’t we do the same to Pluto?</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/300165/original/file-20191104-88387-brm58q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/300165/original/file-20191104-88387-brm58q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/300165/original/file-20191104-88387-brm58q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/300165/original/file-20191104-88387-brm58q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/300165/original/file-20191104-88387-brm58q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/300165/original/file-20191104-88387-brm58q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/300165/original/file-20191104-88387-brm58q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/300165/original/file-20191104-88387-brm58q.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">The Kepler-90 planets have a similar configuration to our solar system with small planets found orbiting close to their star, and the larger planets found farther away.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/image-feature/ames/kepler-90-system-planet-sizes">NASA/Ames Research Center/Wendy Stenzel</a></span>
</figcaption>
</figure>
<p>[ <em>Like what you’ve read? Want more?</em> <a href="https://theconversation.com/us/newsletters?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=likethis">Sign up for The Conversation’s daily newsletter</a>. ]</p><img src="https://counter.theconversation.com/content/124158/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Christopher Palma does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Many people are still upset that Pluto was demoted from being a planet. But definitions of various celestial objects are fairly fluid. So whether it is an asteroid or moon or planet is up for debate.Christopher Palma, Associate Dean for Undergraduate Students and Teaching Professor of Astronomy & Astrophysics, Penn StateLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1269852019-11-20T15:02:44Z2019-11-20T15:02:44ZTitan: first global map uncovers secrets of a potentially habitable moon of Saturn<figure><img src="https://images.theconversation.com/files/302643/original/file-20191120-467-1jdql0z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Titan imaged in the near infrared by the Cassini orbiter on November 13, 2015. </span> <span class="attribution"><span class="source">NASA/JPL/University of Arizona/University of Idaho</span></span></figcaption></figure><p>There are just three moons in our solar system that measure more than 5,000km across. Of these, Jupiter’s moons Ganymede and Callisto are airless and have ancient heavily cratered surfaces. But Saturn’s largest moon, Titan, abounds in landscapes that are eerily Earth-like – and it may even harbour life.</p>
<p>But we have had a rather limited view of what’s lurking beneath the thick atmosphere of this mysterious world. A new study, <a href="https://nature.com/articles/s41550-019-0917-6">published in Nature Astronomy</a>, however, unveils the first geomorphologic map to cover the whole of Titan. This is important because it shows how Titan’s various kinds of terrain relate to each other. </p>
<p>Despite the fact that Titan’s “bedrock” is ice, its surface is so cold (-180°C) that the ice is sufficiently strong and rigid to behave just like rock on Earth. Furthermore, Titan is the only moon with a dense atmosphere, having a surface pressure that is one and a half times that of Earth’s.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/302003/original/file-20191115-66941-10ciwu5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/302003/original/file-20191115-66941-10ciwu5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=207&fit=crop&dpr=1 600w, https://images.theconversation.com/files/302003/original/file-20191115-66941-10ciwu5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=207&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/302003/original/file-20191115-66941-10ciwu5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=207&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/302003/original/file-20191115-66941-10ciwu5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=260&fit=crop&dpr=1 754w, https://images.theconversation.com/files/302003/original/file-20191115-66941-10ciwu5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=260&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/302003/original/file-20191115-66941-10ciwu5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=260&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Near-infrared image of Titan’s surface brightness.</span>
<span class="attribution"><a class="source" href="https://photojournal.jpl.nasa.gov/catalog/PIA22770">NASA/JPL-Caltech/Univ. Arizona</a></span>
</figcaption>
</figure>
<p>In common with Earth, by far the most abundant atmospheric gas on Titan is nitrogen. The moon’s second most abundant gas is methane, which makes Titan Earth-like in a different but very remarkable way. The gaseous methane can condense to form clouds from which droplets of liquid methane can fall like rain. Methane rainfall erodes the surface, carves out channels, and drains into depressions to form methane seas and lakes. Evaporation back into the atmosphere completes the cycle, so Titan has a methane cycle to match Earth’s <a href="https://en.m.wikipedia.org/wiki/Water_cycle">water cycle</a>.</p>
<p>Despite two Titan flybys by NASA’s Voyager probes in 1980 and 1981, we knew little about the moon’s surface until the <a href="https://theconversation.com/bittersweet-feeling-as-cassini-mission-embarks-on-its-grand-finale-ahead-of-death-plunge-76670">Cassini spacecraft</a> arrived to orbit Saturn between 2005 and 2017. This is because sunlight causes the molecules of methane high in Titan’s atmosphere to <a href="https://theconversation.com/saturns-moon-titan-may-harbour-simple-life-forms-and-reveal-how-organisms-first-formed-on-earth-81527">link into larger molecules</a>, making a high-altitude smog that the Voyager cameras could not see through. </p>
<p>But Cassini was equipped to cope with this, carrying an imaging radar system and near-infrared and thermal infrared cameras that could detect radiation reflected or emitted from the ground in specific wavelengths that the smog does little to obstruct. Cassini also sent a <a href="https://sci.esa.int/web/education/-/45751-the-huygens-probe-lands-on-titan">lander called Huygens</a> down to the surface by parachute, giving us unimpeded visual views from below the clouds – albeit of only a small area.</p>
<h2>A global map</h2>
<p>The most detailed images to inform the new geological map come from the radar. These cover slightly less than half the globe so, to achieve global coverage, other Cassini data had to be used to fill in the gaps. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/301732/original/file-20191114-26211-xlys2m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/301732/original/file-20191114-26211-xlys2m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/301732/original/file-20191114-26211-xlys2m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=340&fit=crop&dpr=1 600w, https://images.theconversation.com/files/301732/original/file-20191114-26211-xlys2m.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=340&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/301732/original/file-20191114-26211-xlys2m.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=340&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/301732/original/file-20191114-26211-xlys2m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=428&fit=crop&dpr=1 754w, https://images.theconversation.com/files/301732/original/file-20191114-26211-xlys2m.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=428&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/301732/original/file-20191114-26211-xlys2m.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=428&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Global map of Titan’s major geomorphologic units.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/">NASA/JPL/ASU</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Six major units are on the global map, depicted at a scale of 1:20 million. Plains make up 65% of the globe, these are smooth and dark, possibly because of smog-derived sooty particles on the ground. In a belt hugging the equator, the plains are overlaid by extensive fields of dunes (17% of the globe by area), sculpted by winds that blow from west to east. </p>
<p>These dunes are not sand grains made of quartz as they would be on Earth, nor grains of water ice, but particles made from organic molecules that presumably originated from the atmosphere in the same way as the dark colouring of the plains (derived from smog).</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/302014/original/file-20191115-66971-oxw5mm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/302014/original/file-20191115-66971-oxw5mm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/302014/original/file-20191115-66971-oxw5mm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/302014/original/file-20191115-66971-oxw5mm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/302014/original/file-20191115-66971-oxw5mm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/302014/original/file-20191115-66971-oxw5mm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/302014/original/file-20191115-66971-oxw5mm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/302014/original/file-20191115-66971-oxw5mm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A 400km wide area of Titan seen by imaging radar.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech/ASI</span></span>
</figcaption>
</figure>
<p>Exposed icy bedrock is apparent in places where neither plains nor dunes have covered it. This is divided into a “hummocky” unit (14% of the globe) characterised by hilly and mountainous ground. There are some branching valleys here (including some seen by the Huygens lander), but such valleys are more extensively developed in a unit named “labyrinth” (1.5% of the globe), which is perhaps ice mixed with organic material that has been more strongly cut by methane rivers.</p>
<p>Impact craters occupy just 0.4% of the globe, and there are only 23 that are more than 20km in diameter. Their scarcity attests to Titan’s active geology – erosion of high ground, burial under sediments, and possibly erasure by volcanism (spewing out ice instead of molten rock).</p>
<h2>Land of lakes</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/301739/original/file-20191114-26217-r97f8r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/301739/original/file-20191114-26217-r97f8r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/301739/original/file-20191114-26217-r97f8r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=331&fit=crop&dpr=1 600w, https://images.theconversation.com/files/301739/original/file-20191114-26217-r97f8r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=331&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/301739/original/file-20191114-26217-r97f8r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=331&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/301739/original/file-20191114-26217-r97f8r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=415&fit=crop&dpr=1 754w, https://images.theconversation.com/files/301739/original/file-20191114-26217-r97f8r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=415&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/301739/original/file-20191114-26217-r97f8r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=415&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Area within 35 degrees of each of Titan’s poles. There are many more lakes in the north than in the south.</span>
<span class="attribution"><span class="source">Lopes et al. (2019), nature</span></span>
</figcaption>
</figure>
<p>Titan’s polar regions contain over 650 lakes or seas covering 1.5% of the total surface area. Some are currently dry, but many are filled by liquid methane. Parts of the shoreline of the second largest lake, named Ligeia Mare, which is 400km across and up to 170 metres deep, have an odd shape suggesting that either the lake level has risen, or that parts of the land surface have sunk due to tectonic forces. Elsewhere, and on other lakes, there are shoreline features suggestive of wave action and river deltas.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/301748/original/file-20191114-26250-1xpzmeq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/301748/original/file-20191114-26250-1xpzmeq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/301748/original/file-20191114-26250-1xpzmeq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=543&fit=crop&dpr=1 600w, https://images.theconversation.com/files/301748/original/file-20191114-26250-1xpzmeq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=543&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/301748/original/file-20191114-26250-1xpzmeq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=543&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/301748/original/file-20191114-26250-1xpzmeq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=683&fit=crop&dpr=1 754w, https://images.theconversation.com/files/301748/original/file-20191114-26250-1xpzmeq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=683&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/301748/original/file-20191114-26250-1xpzmeq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=683&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Ligeia Mare with a shoreline symptomatic of a drowned landscape of river valleys.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech/ASI/Cornell</span></span>
</figcaption>
</figure>
<p>If Titan is home to any microbial life, this is much more likely to be in Titan’s <a href="https://phys.org/news/2019-07-habitability-titan-ocean.html">water ocean</a> deep in its interior, rather than at the surface. But understanding the distribution of landscapes documented in the global map is a vital step towards understanding the environments and history of this amazing world. </p>
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<strong>
Read more:
<a href="https://theconversation.com/flying-on-saturns-moon-titan-what-we-could-discover-with-nasas-new-dragonfly-mission-119823">Flying on Saturn’s moon Titan: what we could discover with NASA's new Dragonfly mission</a>
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</em>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/how-geological-maps-made-the-apollo-moon-landings-worthwhile-117539">How geological maps made the Apollo moon landings worthwhile</a>
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</em>
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<img src="https://counter.theconversation.com/content/126985/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Rothery is co-leader of the European Space Agency's Mercury Surface and Composition Working Group, and a Co-Investigator on MIXS (Mercury Imaging X-ray Spectrometer) that is now on its way to Mercury on board the European Space Agency's Mercury orbiter BepiColombo. He has received funding from the UK Space Agency and the Science & Technology Facilities Council for work related to Mercury BepiColombo, and is currently funded by the European Commission under its Horizon 2020 programme for work on planetary geological mapping (776276 Planmap). He is author of Planet Mercury - from Pale Pink Dot to Dynamic World (Springer, 2015), Moons: A Very Short Introduction (Oxford University Press, 2015) and Planets: A Very Short Introduction (Oxford University Press, 2010). He is Educator on the Open University's free learning Badged Open Course (BOC) on Moons and its equivalent FutureLearn Moons MOOC, and chair of the Open University's level 2 course on Planetary Science and the Search for Life.</span></em></p>Saturn’s largest moon has been fully mapped for the first time.David Rothery, Professor of Planetary Geosciences, The Open UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1248882019-10-09T19:01:09Z2019-10-09T19:01:09ZSaturn has more moons than Jupiter – but why are we only finding out about them now?<figure><img src="https://images.theconversation.com/files/296139/original/file-20191009-3917-1xqo5je.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C2393%2C1354&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">This Hubble Space Telescope image of Saturn and a few of its moons shows how hard it can be to spot the gas giant's tiny orbiting companions.</span> <span class="attribution"><a class="source" href="https://www.spacetelescope.org/images/heic1814d/">NASA / ESA / Hubble</a></span></figcaption></figure><p>With the discovery of 20 more moons orbiting Saturn, the ringed planet has overtaken Jupiter as host to the most moons in the Solar System. Saturn now has 82 known moons, whereas Jupiter has a paltry 79. </p>
<p>Announced at the International Astronomical Union’s Minor Planet Centre by a <a href="https://carnegiescience.edu/news/saturn-surpasses-jupiter-after-discovery-20-new-moons-and-you-can-help-name-them">team of astronomers</a> from the Carnegie Institute for Science led by Scott S. Sheppard, the discovery is the latest advance in the 400-year history of our understanding of the satellites of our neighbouring planets.</p>
<p>As technology has improved, we have observed more and more of these tiny, distant worlds – and we can be reasonably confident there are still plenty waiting to be discovered. </p>
<h2>How do we even know Saturn has moons?</h2>
<p>Although most planets of the Solar System are visible to the naked eye and have been known to humans since antiquity, it wasn’t until Galileo Galilei turned a telescope on Jupiter in 1610 that we discovered Earth was not alone in having an orbiting companion.</p>
<p>Galileo saw Jupiter’s four largest moons and could make out what we now know are Saturn’s rings. Decades later, with better telescopes, Christian Huygens and Giovanni Domenico Cassini observed Saturn’s moons. </p>
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<strong>
Read more:
<a href="https://theconversation.com/curious-kids-why-does-saturn-have-rings-121433">Curious Kids: why does Saturn have rings?</a>
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<p>It became clear that the giant planets are surrounded by multitudes of satellites, resembling smaller versions of the Solar System. By the middle of the 19th century, telescopes had improved enough that the first eight moons of Saturn – including Titan, the largest – had been viewed directly. </p>
<p>The introduction of photographic plates, which enabled the detection of fainter objects with long-exposure observations, helped astronomers increase their count of Saturn’s moons to 14. </p>
<h2>Closer inspections</h2>
<p>It was a long journey (literally) to the next big improvement in our view of Saturn’s moons. Many of the smaller moons were not discovered until the Voyager fly-by missions in the 1980s and the more recent 13-year stopover of the Cassini spacecraft in Saturn’s orbit. </p>
<p>Until these closer visits, we knew little about the moons aside from the fact that they existed.</p>
<p>One of Cassini’s goals was to explore Titan, which is the only moon in the Solar System with a thick, smoggy atmosphere. Another was to take a look at Saturn’s other mid-sized moons, including frozen Enceladus, which may hold an ocean of liquid water beneath its icy crust. </p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/a-look-back-at-cassinis-incredible-mission-to-saturn-before-its-final-plunge-into-the-planet-83226">A look back at Cassini's incredible mission to Saturn before its final plunge into the planet</a>
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<p>Cassini also discovered much smaller moons, so-called “shepherd moons” that interact with Saturn’s rings by carving gaps and wavy patterns as they pass through a rubble of rocks and snowballs. </p>
<h2>Bigger telescopes, more moons</h2>
<p>These close-up observations from space advanced our understanding of individual moons that stay near to Saturn. Recently, many more moons have been found in orbits much further from the planet. </p>
<p>These more distant moons could only be detected with large optical telescopes such as the Subaru telescope at Mauna Kea in Hawaii. The telescope is equipped with sensitive cameras that can detect some of the faint objects separated by millions of kilometres from Saturn. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/296112/original/file-20191009-128686-wdozxu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/296112/original/file-20191009-128686-wdozxu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=238&fit=crop&dpr=1 600w, https://images.theconversation.com/files/296112/original/file-20191009-128686-wdozxu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=238&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/296112/original/file-20191009-128686-wdozxu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=238&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/296112/original/file-20191009-128686-wdozxu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=300&fit=crop&dpr=1 754w, https://images.theconversation.com/files/296112/original/file-20191009-128686-wdozxu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=300&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/296112/original/file-20191009-128686-wdozxu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=300&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The new moons were discovered by comparing photos like this pair taken about an hour apart. While the background stars stay fixed, the moon – highlighted with orange bars – moves between frames.</span>
<span class="attribution"><span class="source">Scott Sheppard</span></span>
</figcaption>
</figure>
<p>To confirm that these objects are indeed associated with Saturn, astronomers have to observe them over days or even months to reconstruct the shape and size of the moon’s orbit. </p>
<h2>Many small moons are fragments of shattered large moons</h2>
<p>Such observations revealed a population of moons that are often described as “irregular” moons. They are split into three distinct groups: Inuit, Gallic, and Norse. They all have large, elliptical orbits at an angle to those of moons closer to the planet. </p>
<p>Each group is thought to have formed from a collision or fragmentation of a larger moon. The Norse group consists of some of the most distant moons of Saturn, which orbit in the opposite direction to the rotation of the planet. This suggests they could have formed elsewhere and were later captured by the gravitational force of Saturn. </p>
<p>Of the 20 new moons, 17 belong to the Norse group including the furthest known moon from the planet. Their estimated sizes are of the order of 5km in diameter. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/296111/original/file-20191009-128695-tsfl02.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/296111/original/file-20191009-128695-tsfl02.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/296111/original/file-20191009-128695-tsfl02.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/296111/original/file-20191009-128695-tsfl02.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/296111/original/file-20191009-128695-tsfl02.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/296111/original/file-20191009-128695-tsfl02.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/296111/original/file-20191009-128695-tsfl02.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/296111/original/file-20191009-128695-tsfl02.png?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">Most of the newly discovered moons have retrograde orbits, going in the opposite direction to Saturn’s spin.</span>
<span class="attribution"><a class="source" href="https://carnegiescience.edu/news/saturn-surpasses-jupiter-after-discovery-20-new-moons-and-you-can-help-name-them">Carnegie Institution for Science</a></span>
</figcaption>
</figure>
<h2>Have we found all the moons now?</h2>
<p>Are we likely to find even more moons around Saturn? Absolutely. </p>
<p>Some of the newly discovered moons are very faint and at the limit of detection with currently available instruments. New, bigger telescopes such as Giant Magellan Telescope will allow us to observe even fainter objects.</p>
<p>In the meantime, the 20 new moons need names. Carnegie Science has <a href="https://carnegiescience.edu/NameSaturnsMoons">invited everyone to help</a>.</p><img src="https://counter.theconversation.com/content/124888/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Lucyna Kedziora-Chudczer 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>Astronomers have found 20 new moons around Saturn, and will keep finding more as technology improves.Lucyna Kedziora-Chudczer, Program Manager / Adjunct Research Fellow, Swinburne University of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1214332019-09-09T03:24:02Z2019-09-09T03:24:02ZCurious Kids: why does Saturn have rings?<figure><img src="https://images.theconversation.com/files/286855/original/file-20190805-117866-dgviij.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C5000%2C2776&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Galileo thought Saturn looked a bit like the head of a teddy bear with two big ears. He thought it may be made of three planets. </span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/download/confirm/598786217?src=3gOjCUuRJ49ko3p_hhzRfg-1-10&studio=1&size=huge_jpg">www.shuttershock.com </a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</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>If you have a question you’d like an expert to answer, send it to curiouskids@theconversation.edu.au.</em> </p>
<hr>
<blockquote>
<p><strong>Why does Saturn have rings? – Isla, age 7, Killarney.</strong></p>
</blockquote>
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<p>Most people think many millions of years ago, Saturn didn’t have rings at all. Instead, it had a big moon moving around it.</p>
<p>Eventually, this moon came very close to Saturn while moving faster and faster around it. </p>
<p>This caused the moon to get pulled in two directions at once. It burst and broke into pieces that eventually spread around the planet into a flattened doughnut shape made of ice and rock. </p>
<p>The chunks kept smashing into each other, which made a lot of powdery dust and snow. Some chunks fell onto Saturn or floated off into space. That’s still happening today, and in the distant future the rings will disappear entirely.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/290468/original/file-20190902-175668-1b5jt8o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/290468/original/file-20190902-175668-1b5jt8o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=328&fit=crop&dpr=1 600w, https://images.theconversation.com/files/290468/original/file-20190902-175668-1b5jt8o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=328&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/290468/original/file-20190902-175668-1b5jt8o.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=328&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/290468/original/file-20190902-175668-1b5jt8o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=412&fit=crop&dpr=1 754w, https://images.theconversation.com/files/290468/original/file-20190902-175668-1b5jt8o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=412&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/290468/original/file-20190902-175668-1b5jt8o.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=412&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Pieces of ice and rock spread around the planet into a flattened doughnut.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/saturn-isolated-on-black-215681422?src=-1-17">Shutterstock</a></span>
</figcaption>
</figure>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-can-people-live-in-space-120334">Curious Kids: can people live in space?</a>
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<h2>Discovering Saturn’s rings</h2>
<p>We didn’t always know Saturn had rings. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/291032/original/file-20190905-175696-tmdxvu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/291032/original/file-20190905-175696-tmdxvu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/291032/original/file-20190905-175696-tmdxvu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=1230&fit=crop&dpr=1 600w, https://images.theconversation.com/files/291032/original/file-20190905-175696-tmdxvu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=1230&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/291032/original/file-20190905-175696-tmdxvu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=1230&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/291032/original/file-20190905-175696-tmdxvu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1545&fit=crop&dpr=1 754w, https://images.theconversation.com/files/291032/original/file-20190905-175696-tmdxvu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1545&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/291032/original/file-20190905-175696-tmdxvu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1545&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Here is a close up photo of Saturn’s rings.</span>
<span class="attribution"><span class="source">JPL/NASA</span></span>
</figcaption>
</figure>
<p>A few hundred years ago, an astronomer named Galileo looked at the sky through one of the first telescopes. When he used it to look at Saturn, he thought the planet looked a bit like the head of a teddy bear with two big ears. He thought it may be made of three planets. </p>
<p>Years later, astronomers used better telescopes and realised Saturn was surrounded by what looked like a large flat disk.</p>
<p>At first, astronomers thought the disk might actually touch Saturn. An astronomer named Christiaan Huygens thought the disk around Saturn was as solid as a pancake or a ring on a finger. </p>
<p>Another astronomer, Giovanni Cassini, was first to notice the ring had some gaps in it. </p>
<p>Now we know the rings are made of moon dust and rocks. And because Saturn is very far away from the Sun, it is a very cold planet. That means the rocks in Saturn’s rings are very icy. Some are even made entirely of ice, like snowballs.</p>
<p>Saturn’s rings are very bright because snow reflects sunlight strongly.</p>
<p>When people sent spaceships to other planets and took close-up photos, they discovered Jupiter, Uranus and Neptune also have rings. But these rings are very faint and hard to see from Earth. They also realised these planets have many moons – some smaller and some bigger than Earth’s Moon.</p>
<h2>Thank you and goodbye, Cassini</h2>
<p>If you are interested to learn more about Saturn and its beautiful rings, you might like to read about the <a href="https://www.nasa.gov/mission_pages/cassini/main/index.html">Cassini–Huygens</a> space research mission. It involved sending a spaceship (with no people on it) to Saturn. </p>
<p>It took about seven years for Cassini to get to Saturn. Then, for about 10 years, Cassini sent photographs and data back to Earth so we could learn as much as we could about Saturn before the spacecraft ran out of fuel. At the end of the mission, on Friday, September 15, 2017, Cassini dived into Saturn’s atmosphere. </p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-how-high-could-i-jump-on-the-moon-120865">Curious Kids: how high could I jump on the moon?</a>
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<p><em>Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to curiouskids@theconversation.edu.au</em> <em>Please tell us your name, age and which city you live in. We won’t be able to answer every question but we will do our best.</em></p><img src="https://counter.theconversation.com/content/121433/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Lucyna Kedziora-Chudczer 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>Most people think that many millions of years ago, Saturn didn’t have rings at all. Instead, it had a big moon moving around it. Eventually, the moon burst and broke into pieces.Lucyna Kedziora-Chudczer, Program Manager / Adjunct Research Fellow, Swinburne University of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1209452019-08-14T12:32:30Z2019-08-14T12:32:30ZA brief astronomical history of Saturn’s amazing rings<figure><img src="https://images.theconversation.com/files/287419/original/file-20190808-144892-1u8fsji.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">With giant Saturn hanging in the blackness and sheltering Cassini from the Sun's blinding glare, the spacecraft viewed the rings as never before.</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/multimedia/imagegallery/image_feature_1202.html">NASA/JPL/Space Science Institute</a></span></figcaption></figure><p>Many dream of what they would do had they a time machine. Some would travel 100 million years back in time, when dinosaurs roamed the Earth. Not many, though, would think of taking a telescope with them, and if, having done so, observe Saturn and its rings.</p>
<p>Whether our time-traveling astronomer would be able to observe Saturn’s rings is debatable. Have the rings, in some shape or form, existed since the beginnings of the solar system, 4.6 billion years ago, or are they a more recent addition? Had the rings even formed when the <a href="https://theconversation.com/more-bad-news-for-dinosaurs-chicxulub-meteorite-impact-triggered-global-volcanic-eruptions-on-the-ocean-floor-91053">Chicxulub asteroid</a> wiped out the dinosaurs?</p>
<p><a href="https://dornsife.usc.edu/cf/faculty-and-staff/faculty.cfm?pid=1063926">I am a space scientist</a> with a passion for teaching physics and astronomy, and Saturn’s rings have always fascinated me as they tell the story of how the eyes of humanity were opened to the wonders of our solar system and the cosmos.</p>
<h2>Our view of Saturn evolves</h2>
<p>When Galileo first observed Saturn through his telescope in 1610, he was still basking in the fame of <a href="https://www.forbes.com/sites/briankoberlein/2016/01/07/galileos-discovery-of-jupiters-moons-and-how-it-changed-the-world/#dd6cc0f46f07">discovering the four moons of Jupiter</a>. But Saturn perplexed him. Peering at the planet through his telescope, it first looked to him as a planet with two very large moons, then as a lone planet, and then again through his newer telescope, in 1616, as a planet with arms or handles.</p>
<p>Four decades later, <a href="https://www.britannica.com/biography/Christiaan-Huygens">Christiaan Huygens</a> first suggested that Saturn was a ringed planet, and what Galileo had seen were different views of Saturn’s rings. Because of the 27 degrees in the tilt of Saturn’s rotation axis relative to the plane of its orbit, the rings appear to tilt toward and away from Earth with the 29-year cycle of Saturn’s revolution about the Sun, giving humanity an ever-changing view of the rings.</p>
<p>But what were the rings made of? Were they solid disks as some suggested? Or were they made up of smaller particles? As more structure became apparent in the rings, as more gaps were found, and as the motion of the rings about Saturn was observed, astronomers realized that the rings were not solid, and were perhaps made up of a large number of moonlets, or small moons. At the same time, estimates for the thickness of the rings went from Sir William Herschel’s 300 miles in 1789, to Audouin Dollfus’ much more precise <a href="http://solarviews.com/eng/saturnbg.htm">estimate of less than two miles</a> in 1966. </p>
<p>Astronomers understanding of the rings changed dramatically with the <a href="https://solarsystem.nasa.gov/missions/pioneer-11/in-depth/">Pioneer 11</a> and twin Voyager missions to Saturn. <a href="https://voyager.jpl.nasa.gov/assets/images/galleries/images-voyager-took/saturn/6bg.jpg">Voyager’s now famous photograph of the rings</a>, backlit by the Sun, showed for the first time that what appeared as the vast A, B and C rings in fact comprised millions of smaller ringlets. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/287555/original/file-20190809-144868-1oi82mi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/287555/original/file-20190809-144868-1oi82mi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/287555/original/file-20190809-144868-1oi82mi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=469&fit=crop&dpr=1 600w, https://images.theconversation.com/files/287555/original/file-20190809-144868-1oi82mi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=469&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/287555/original/file-20190809-144868-1oi82mi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=469&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/287555/original/file-20190809-144868-1oi82mi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=589&fit=crop&dpr=1 754w, https://images.theconversation.com/files/287555/original/file-20190809-144868-1oi82mi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=589&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/287555/original/file-20190809-144868-1oi82mi.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">Voyager 2 false color image of Saturn’s B and C rings showing many ringlets.</span>
<span class="attribution"><a class="source" href="https://voyager.jpl.nasa.gov/assets/images/galleries/images-voyager-took/saturn/6bg.jpg">NASA</a></span>
</figcaption>
</figure>
<p>The Cassini mission to Saturn, having spent over a decade orbiting the ringed giant, gave planetary scientists even more spectacular and surprising views. The magnificent ring system of Saturn is between 10 meters and one kilometer thick. The combined mass of its particles, which are 99.8% ice and most of which are less than one meter in size, is about 16 quadrillion tons, less than 0.02% the mass of Earth’s Moon, and less than half the mass of Saturn’s moon <a href="https://doi.org/10.1126/science.aat2965">Mimas</a>. This has led some scientists to speculate whether the rings are a result of the breakup of one of Saturn’s moons or the capture and breakup of a stray comet. </p>
<h2>The dynamic rings</h2>
<p>In the four centuries since the invention of the telescope, rings have also been discovered around <a href="https://doi.org/10.1007/978-0-387-73981-6_4">Jupiter</a>, <a href="https://www.universetoday.com/19288/uranus-rings/">Uranus</a> and <a href="https://www.universetoday.com/21635/rings-of-neptune/">Neptune</a>, the giant planets of our solar system. The reason why the giant planets are adorned with rings and Earth and the other rocky planets are not was first proposed by Eduard Roche, a French astronomer in 1849. </p>
<p>A moon and its planet are always in a gravitational dance. Earth’s moon, by pulling on opposite sides of the Earth, causes the ocean tides. Tidal forces also affect planetary moons. If a moon ventures too close to a planet, these forces can overcome the gravitational “glue” holding the moon together and tear it apart.
This causes the moon to break up and spread along its original orbit, forming a ring. </p>
<p>The <a href="https://www.britannica.com/science/Roche-limit">Roche limit</a>, the minimum safe distance for a moon’s orbit, is approximately 2.5 times the planet’s radius from the planet’s center. For enormous Saturn, this is a distance of 87,000 kilometers above its cloud tops and matches the location of Saturn’s outer F ring. For Earth, this distance is less than 10,000 kilometers above its surface. An asteroid or comet would have to venture very close to the Earth to be torn apart by tidal forces and form a ring around the Earth. Our own Moon is a very safe 380,000 kilometers away.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/287560/original/file-20190809-144873-yojp3b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/287560/original/file-20190809-144873-yojp3b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=253&fit=crop&dpr=1 600w, https://images.theconversation.com/files/287560/original/file-20190809-144873-yojp3b.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=253&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/287560/original/file-20190809-144873-yojp3b.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=253&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/287560/original/file-20190809-144873-yojp3b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=318&fit=crop&dpr=1 754w, https://images.theconversation.com/files/287560/original/file-20190809-144873-yojp3b.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=318&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/287560/original/file-20190809-144873-yojp3b.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=318&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 Cassini spacecraft about to make one of its dives between Saturn and its innermost rings as part of the mission’s grand finale.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/image-feature/illustration-of-cassini-spacecrafts-grand-finale-dive">NASA/JPL-Caltech</a></span>
</figcaption>
</figure>
<p>The thinness of planetary rings is caused by their ever-changing nature. A ring particle whose orbit is tilted with respect to the rest of the ring will eventually collide with other ring particles. In doing so, it will lose energy and settle into the plane of the ring. Over millions of years, all such errant particles either fall away or get in line, leaving only the very thin ring system people observe today.</p>
<p>During the last year of its mission, the Cassini spacecraft dived repeatedly through the 7,000 kilometer gap between the clouds of Saturn and its inner rings. These unprecedented observations made one fact very clear: <a href="https://doi.org/10.1126/science.aat3760">The rings are constantly changing</a>. Individual particles in the rings are continually jostled by each other. Ring particles are steadily raining down onto Saturn.</p>
<p>The shepherd moons Pan, Daphnis, Atlas, Pandora and Prometheus, measuring between eight and 130 kilometers across, quite literally shepherd the ring particles, <a href="https://doi.org/10.1126/science.aat2349">keeping them in their present orbits</a>. Density waves, caused by the motion of shepherd moons within the rings, jostle and reshape the rings. Small moonlets are forming from ring particles that coalesce together. All this indicates that the rings are ephemeral. Every second <a href="https://doi.org/10.1126/science.aat2382">up to 40 tons of ice from the rings</a> rain down on Saturn’s atmosphere. That means the rings may last only several tens to hundreds of millions of years. </p>
<p>Could a time-traveling astronomer have seen the rings 100 million years ago? One indicator for the age of the rings is their dustiness. Objects exposed to the dust permeating our solar system for long periods of time grow dustier and darker. </p>
<p>Saturn’s rings are extremely bright and dust-free, seeming to indicate that they <a href="https://www.scientificamerican.com/article/how-old-are-saturns-rings-the-debate-rages-on/">formed anywhere from 10 to 100 million years ago</a>, if astronomers’ understanding of how icy particles gather dust is correct. One thing is for certain. The rings our time-traveling astronaut would have seen would have looked very different from the way they do today. </p>
<p><em>This story has been corrected to reflect that it was Christiaan Huygens, not Giovanni Cassini, who first suggested that Saturn had rings.</em></p>
<p>[ <em>Like what you’ve read? Want more?</em> <a href="https://theconversation.com/us/newsletters?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=likethis">Sign up for The Conversation’s daily newsletter</a>. ]</p><img src="https://counter.theconversation.com/content/120945/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Vahe Peroomian does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Although the rings of Saturn may look like a permanent fixture of the planet, they are ever-changing. New analyses of the rings reveal how and when they were made, from what and whether they’ll last.Vahe Peroomian, Associate Professor of Physics and Astronomy, USC Dornsife College of Letters, Arts and SciencesLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1198232019-07-04T09:26:01Z2019-07-04T09:26:01ZFlying on Saturn’s moon Titan: what we could discover with NASA’s new Dragonfly mission<figure><img src="https://images.theconversation.com/files/282485/original/file-20190703-126340-166nr0f.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Artist's impression of the Dragonfly landing.</span> <span class="attribution"><span class="source">NASA</span></span></figcaption></figure><p>Flying on other worlds is the next leap in the exploration of our solar system. The <a href="https://www.nasa.gov/press-release/mars-helicopter-to-fly-on-nasa-s-next-red-planet-rover-mission/">Mars Helicopter</a> will piggyback on the <a href="https://mars.nasa.gov/mars2020/">NASA Mars 2020 rover mission</a> to demonstrate the technology. But this is only the start. The real prize will be the Dragonfly mission in 2026, sending a drone to Saturn’s largest moon, Titan – <a href="https://www.nasa.gov/press-release/nasas-dragonfly-will-fly-around-titan-looking-for-origins-signs-of-life/">as just announced by NASA</a>.</p>
<p>For a craft to become airborne, it needs air or, more generally, an atmosphere. Only a handful of objects in our solar system fit that bill. Titan boasts an atmosphere thicker than Earth’s, which has shrouded this world in mystery for a long time. Studies have shown Titan may be able to <a href="https://theconversation.com/saturns-moon-titan-may-harbour-simple-life-forms-and-reveal-how-organisms-first-formed-on-earth-81527">host primitive lifeforms</a> and is the ideal place to study how life may have arisen on our own planet.</p>
<p>Titan is the second largest moon in the solar system behind Jupiter’s <a href="https://solarsystem.nasa.gov/moons/jupiter-moons/ganymede/in-depth/">Ganymede</a>. In fact, Titan’s diameter of 5,149km is larger than the planet Mercury’s at 4,880km. Its atmosphere consists mainly of nitrogen (96%), similar to Earth’s atmosphere (80% nitrogen, the rest being oxygen and less than 1% of other trace gases). The <a href="https://theconversation.com/bittersweet-feeling-as-cassini-mission-embarks-on-its-grand-finale-ahead-of-death-plunge-76670">Cassini spacecraft</a> orbited Saturn from 2004 until 2017 and was the first to use radar and other instruments to peer underneath Titan’s clouds during numerous flybys. </p>
<p>The <a href="https://solarsystem.nasa.gov/missions/cassini/mission/spacecraft/huygens-probe/">Huygens probe</a> touched down on Titan’s surface in 2005. It revealed that Titan is the only world in our solar system other than Earth with a currently active hydrological cycle – complete with rain, rivers and lakes, some of them more than 100 metres deep. The only difference is that it is not water raining from the clouds.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/282655/original/file-20190704-51312-khs2y3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/282655/original/file-20190704-51312-khs2y3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/282655/original/file-20190704-51312-khs2y3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/282655/original/file-20190704-51312-khs2y3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/282655/original/file-20190704-51312-khs2y3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/282655/original/file-20190704-51312-khs2y3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/282655/original/file-20190704-51312-khs2y3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Titan imaged by Cassini.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech/Univ. Arizona/Univ. Idaho</span></span>
</figcaption>
</figure>
<p>Because Saturn and its moons are about ten times further from the sun than the Earth, temperatures there are so low (-179°C on average) that water is frozen solid at all times and behaves like rocks on Earth. Instead, hydrocarbons such as methane, a gas at temperatures typical for Earth, condense into a liquid that fills the lakes. Other complex organic (meaning carbon-based) molecules form in Titan’s atmosphere and fall like snow. This snow is then rearranged into dunes by wind.</p>
<p>The Dragonfly mission will land in 2034 in the relative safety of one of those dune fields called Shangri-La. From there, it will fly to different locations to investigate the nature of the organic material. One important aspect of the mission is to shed light on the processes that led to the origin of life on Earth. We know that macromolecules such as DNA and proteins formed from simpler organic molecules such as amino acids. But we haven’t pinned down the exact intermediate steps in this process – something that we may be able to observe on Titan. </p>
<h2>Current life?</h2>
<p>With all these building blocks around, there is speculation about whether life – for example, in the form of microorganisms – could exist on Titan. But how likely is this? It is thought that life at the very basic level needs at least three ingredients: liquid water, a carbon source and an energy source.</p>
<p>Though there is plenty of carbon around on Titan, the cold temperatures keep water in its solid form as ice and also limit the energy available. However, liquid water may exist below the frozen surface. We also know that water plumes erupting from neighbouring moon Enceladus do rain down onto Titan’s upper atmosphere, <a href="https://theconversation.com/saturns-moon-titan-may-harbour-simple-life-forms-and-reveal-how-organisms-first-formed-on-earth-81527">providing a key source of oxygen</a>.</p>
<p>There are many forms of microorganism that can live under extreme conditions on Earth – <a href="https://oceanservice.noaa.gov/facts/extremophile.html">so-called extremophiles</a>. But even among those, basic life functions seize at temperatures below -20°C. So for life to exist on Titan, we would need to stretch the envelope of suitable conditions we know from Earth quite far. But then again, life on Earth is the only example we know of to date and we may be limited in our imagination. Even if it looks only like a remote possibility, the Dragonfly mission will properly assess the habitability of Titan and look out for signs of potential life, past or present.</p>
<p>A compelling target to address both how life arose on Earth and whether it currently exists is the 80km diameter <a href="http://titancraters.blogspot.com/2016/01/selk.html">Selk impact crater</a>, which is one of the flight destinations. Here, the impact that created it in relatively recent times on the geological timescale melted water ice and provided energy in the form of heat to allow such reactions to take place.</p>
<p>Flying a drone on Titan promises to be an out-of-this-world experience that also takes us back in time!</p><img src="https://counter.theconversation.com/content/119823/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Christian Schroeder 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>Titan may host primitive lifeforms and could tell us how life arose on our own planet.Christian Schroeder, Senior Lecturer in Environmental Science and Planetary Exploration, University of StirlingLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1043872018-10-12T01:26:38Z2018-10-12T01:26:38ZFive in a row - the planets align in the night sky<figure><img src="https://images.theconversation.com/files/240207/original/file-20181011-154580-mzyulx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Enjoying the planets lined up in a row.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/derekbruff/7230149502/in/photolist-c1Upy3-2173RBW-5LkrX9-22EFTqu-rsBndP-dXfMAh-UzKZKG-5Lgdoe-23PZBsP-6jAqZw-5Lgce6-5LgbVe-22Jo5Fa-qCZcHL-5LkqNy-dXfMEC-96k4AR-PF9JN-zR2CmQ-8H7KKj-6CNbrM-d9274G-GiXZq-mx8BXq-5LgdsD-dqtmSq-5Lkrcs-J6dE2-Ggdbb6-5Lkpgy-5Lgcan-2td5k6-dXfMCE-GkTKGh-7gc2Bs-9k9ri5-r72E5m-7884h5-5LkrRq-qiVg2u-5Lgc2i-5Lgb8V-5LgbbX-rbYTwD-4bN7FU-4Anbdh-yV8tVL-qPwtJS-r6XyQv-7emdda/">Derek Bruff/flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span></figcaption></figure><p>For the second time this year, the five brightest planets can be seen at the same time. You can catch them by looking towards the western sky after sunset. The planets will form a line rising up from the horizon.</p>
<p>Mercury and Venus are low to the west, with bright Jupiter shining just above. Higher up in the northwestern sky is Saturn, and completing the set of five is the red planet Mars, high overhead. </p>
<p>On Friday October 12 a beautiful crescent Moon sits just to the right of Jupiter. Keep watching the planets night after night and you can track the progression of the Moon.</p>
<hr>
<p>
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Read more:
<a href="https://theconversation.com/more-bright-fast-radio-bursts-revealed-but-where-do-they-all-come-from-104488">More 'bright' fast radio bursts revealed, but where do they all come from?</a>
</strong>
</em>
</p>
<hr>
<p>As the Moon zips around Earth each month, its apparent motion in the sky is much faster than the more leisurely motion of the planets in their orbits around the Sun.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/240210/original/file-20181011-154573-1pigxwh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/240210/original/file-20181011-154573-1pigxwh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/240210/original/file-20181011-154573-1pigxwh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=534&fit=crop&dpr=1 600w, https://images.theconversation.com/files/240210/original/file-20181011-154573-1pigxwh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=534&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/240210/original/file-20181011-154573-1pigxwh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=534&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/240210/original/file-20181011-154573-1pigxwh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=671&fit=crop&dpr=1 754w, https://images.theconversation.com/files/240210/original/file-20181011-154573-1pigxwh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=671&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/240210/original/file-20181011-154573-1pigxwh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=671&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">After sunset around Australia, the five bright planets can be seen in the western sky this week.</span>
<span class="attribution"><span class="source">Museums Victoria/Stellarium</span></span>
</figcaption>
</figure>
<p>By Monday October 15, the Moon will have moved higher in the sky to sit near Saturn, and a few days later, on October 18, the Moon will partner with Mars.</p>
<p>That will also be a perfect evening to see the planets, as Venus and Mercury will be sitting side by side. Of all the five planets, Mercury is the faintest and therefore hardest to see, so having bright Venus as a signpost to Mercury is always an advantage.</p>
<p>In about a week’s time, Venus, which has been the bright <a href="https://www.universetoday.com/22570/venus-the-morning-star/">evening star</a> for most of this year, will move into the glare of the Sun and out of the night sky. </p>
<h2>Five planets, two groups</h2>
<p>The planets have been doing a merry dance in the night sky over the past few months. </p>
<p>Back in July, they also came together in the evening sky, but on that occasion they were stretched right across the sky. Mercury and Venus could be found in the west, while Jupiter, Saturn and Mars were rising in the east. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/240212/original/file-20181011-154555-mb2dnr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/240212/original/file-20181011-154555-mb2dnr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/240212/original/file-20181011-154555-mb2dnr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=1800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/240212/original/file-20181011-154555-mb2dnr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=1800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/240212/original/file-20181011-154555-mb2dnr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=1800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/240212/original/file-20181011-154555-mb2dnr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=2262&fit=crop&dpr=1 754w, https://images.theconversation.com/files/240212/original/file-20181011-154555-mb2dnr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=2262&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/240212/original/file-20181011-154555-mb2dnr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=2262&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 five planets were last seen together in the western sky, August 2016.</span>
<span class="attribution"><span class="source">Alex Cherney</span></span>
</figcaption>
</figure>
<p>As Mercury and Venus are the inner planets, orbiting closer to the Sun than Earth does, we only ever see these two low to the west after sunset, or low to the east before sunrise. They are the planets either following or leading the Sun.</p>
<p>In contrast, the outer planets of Mars, Jupiter and Saturn can drift right across the sky, which is exactly what they have been doing since July. The trio has moved from east to west, and now they join Mercury and Venus to put on the five-planet show. </p>
<h2>There’s more in store</h2>
<p>It may seem like a common occurrence, since the five planets have come together again in the space of just a few months. But it’s only possible because Jupiter and Saturn are currently on the same side of the Sun and therefore near each other, relatively speaking. </p>
<p>The five planets have come together twice this year and twice in 2016, but before that there was a decade when it just wasn’t possible. The two gas giants were too far apart.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/fWUbmdaDf-k?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Watch the planets come together.</span></figcaption>
</figure>
<p>As Jupiter and Saturn pair up in the sky, it’s only a matter of time before the other planets fall into the right configuration to bring them all together. </p>
<p>The next time this occurs will be in July 2020, but it will be harder to see compared to this week. The planets will be stretched across the sky rather than all clustered together in the west as they are right now.</p>
<p>So it’s still special to spot the five planets coming together. There’s great satisfaction in being able to tick off all five planets in a single viewing. </p>
<h2>Up for a challenge?</h2>
<p>Not only are the five easy-to-see planets visible in the evening sky, but they are joined by Uranus and Neptune to complete the planetary set.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/240215/original/file-20181011-154577-8ygoaj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/240215/original/file-20181011-154577-8ygoaj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/240215/original/file-20181011-154577-8ygoaj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=300&fit=crop&dpr=1 600w, https://images.theconversation.com/files/240215/original/file-20181011-154577-8ygoaj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=300&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/240215/original/file-20181011-154577-8ygoaj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=300&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/240215/original/file-20181011-154577-8ygoaj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=377&fit=crop&dpr=1 754w, https://images.theconversation.com/files/240215/original/file-20181011-154577-8ygoaj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=377&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/240215/original/file-20181011-154577-8ygoaj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=377&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Voyager 2 flew by Uranus in 1986 and Neptune in 1989 capturing stunning close-up images.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech (Uranus) and NASA (Neptune)</span></span>
</figcaption>
</figure>
<p>These two ice giants that orbit beyond Saturn are modern-day planets. They were not known in ancient times because their discovery needed the <a href="https://www.universetoday.com/18886/discovery-of-uranus/">aid of a telescope</a> and an <a href="http://earthsky.org/human-world/today-in-science-discovery-of-neptune">understanding of gravity</a> to know how the Solar System works.</p>
<p>But while they may not be seen with the naked eye, Uranus is low in the east at sunset and Neptune is higher up, about midway to Mars. </p>
<p>Practised observers, viewing the sky from a dark country site, have been able to see Uranus with the naked eye by knowing exactly where to look. Through binoculars, Uranus appears like a faint star but a good telescope will show its slightly bluish disc. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/aboriginal-traditions-describe-the-complex-motions-of-planets-the-wandering-stars-of-the-sky-97938">Aboriginal traditions describe the complex motions of planets, the 'wandering stars' of the sky</a>
</strong>
</em>
</p>
<hr>
<p>It is best to wait until later in the evening, when Uranus has risen higher, to try to observe it. But now is an ideal time, as the planet is approaching <a href="https://in-the-sky.org/news.php?id=20181024_12_100">opposition on October 24</a>, when it will be at its best. </p>
<p>Neptune is about the same size as Uranus but much further away, making it harder to see. Even with a modest telescope it appears as a bluish star, while the right observing conditions and a high-quality telescope are needed to reveal Neptune’s disc. </p>
<p>Lastly, and not to be left out, even the dwarf planet Pluto joins the crowd. It’s much too small and distant to be seen but currently sits about midway between Saturn and Mars. </p>
<p>Even with a high-quality telescope Pluto only ever appears as a faint star-like object, and it will be a challenge for most (myself included) to find it in its current position among all the stars near the bright Milky Way.</p>
<p>If you are up for the challenge, a free astronomy program such as <a href="https://stellarium.org/">Stellarium</a> is ideal to help locate the planets. But it’s just as rewarding to enjoy the five bright planets, observed since ancient times, briefly coming together in the western sky.</p><img src="https://counter.theconversation.com/content/104387/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Tanya Hill 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 five planets visible to the naked eye since ancient times are putting on a dazzling display this month, in a night-sky dance along with the Moon.Tanya Hill, Honorary Fellow of the University of Melbourne and Senior Curator (Astronomy), Museums Victoria Research InstituteLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1001622018-07-20T07:25:21Z2018-07-20T07:25:21ZCapturing the shadow of Saturn’s moon Titan from right here on Earth<figure><img src="https://images.theconversation.com/files/228551/original/file-20180720-142423-5iics4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">NASA's Cassini spacecraft captures Saturn's largest moon, Titan, passes in front of the planet and its rings.</span> <span class="attribution"><a class="source" href="https://saturn.jpl.nasa.gov/resources/5441/titan-up-front/">NASA/JPL-Caltech/Space Science Institute</a></span></figcaption></figure><p><a href="https://solarsystem.nasa.gov/moons/saturn-moons/titan/overview/">Titan</a> is <a href="https://solarsystem.nasa.gov/planets/saturn/overview/">Saturn</a>’s largest moon, and it is more like a planet than a moon in many respects.</p>
<p>It has a thick atmosphere as well as wind, rivers, lakes made of hydrocarbons such as methane, and a liquid water ocean. Understanding its atmosphere may help us in the search for life on other planets.</p>
<p>Hence the excitement this July when a rare opportunity was available to further study Titan, from right here on Earth. On July 18 at 11:05pm (WAST, Western Australian time) Titan passed in front of a faint star, as seen by observers across most of Australia.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/the-secrets-of-titan-cassini-searched-for-the-building-blocks-of-life-on-saturns-largest-moon-83441">The secrets of Titan: Cassini searched for the building blocks of life on Saturn's largest moon</a>
</strong>
</em>
</p>
<hr>
<p>This event, known as an <a href="https://www.space.com/33946-occultations.html">occultation</a>, lasted only a few minutes and about 2% of the star’s light was blocked by Titan’s atmosphere.</p>
<p>The effect was so small it required large telescopes and a special camera to record it. But the data gathered should have profound implications for our understanding of an atmosphere on another world.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/228381/original/file-20180719-142423-dk5z13.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/228381/original/file-20180719-142423-dk5z13.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/228381/original/file-20180719-142423-dk5z13.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=405&fit=crop&dpr=1 600w, https://images.theconversation.com/files/228381/original/file-20180719-142423-dk5z13.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=405&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/228381/original/file-20180719-142423-dk5z13.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=405&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/228381/original/file-20180719-142423-dk5z13.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=509&fit=crop&dpr=1 754w, https://images.theconversation.com/files/228381/original/file-20180719-142423-dk5z13.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=509&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/228381/original/file-20180719-142423-dk5z13.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=509&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Saturn’s moon Titan compared (by diameter) to the Earth and its Moon.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Titan,_Earth_%26_Moon_size_comparison.jpg">Wikimedia/The Conversation</a></span>
</figcaption>
</figure>
<h2>Examining Titan’s atmosphere</h2>
<p>Scientists have developed a very clever technique to examine Titan’s atmosphere using stellar occultations. As Titan enters and exits an occultation, the star’s light would illuminate the atmosphere from behind, but be blocked by the moon itself. </p>
<p>Scientists then record subtle changes in brightness of the star over a few minutes, which represents a profile of the atmosphere’s density with height. </p>
<p>This method was used to study Titan’s atmosphere before, during a stellar occultation in 2003.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/228150/original/file-20180718-142405-1mq54j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/228150/original/file-20180718-142405-1mq54j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/228150/original/file-20180718-142405-1mq54j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=417&fit=crop&dpr=1 600w, https://images.theconversation.com/files/228150/original/file-20180718-142405-1mq54j.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=417&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/228150/original/file-20180718-142405-1mq54j.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=417&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/228150/original/file-20180718-142405-1mq54j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=524&fit=crop&dpr=1 754w, https://images.theconversation.com/files/228150/original/file-20180718-142405-1mq54j.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=524&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/228150/original/file-20180718-142405-1mq54j.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=524&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Artist’s concept of Cassini’s June 4, 2010, flyby of Saturn’s moon Titan.</span>
<span class="attribution"><a class="source" href="https://www.jpl.nasa.gov/news/news.php?feature=2625">NASA/JPL</a></span>
</figcaption>
</figure>
<p>But in 2005, when <a href="https://saturn.jpl.nasa.gov/">Cassini’s</a> Huygens lander arrived at Titan and descended to its surface, the atmospheric profile measured from its instruments did not match that derived from the 2003 occultation. This fuelled the question of how variable is the state of Titan’s atmosphere.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/228164/original/file-20180718-142417-1hgve61.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/228164/original/file-20180718-142417-1hgve61.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/228164/original/file-20180718-142417-1hgve61.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=765&fit=crop&dpr=1 600w, https://images.theconversation.com/files/228164/original/file-20180718-142417-1hgve61.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=765&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/228164/original/file-20180718-142417-1hgve61.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=765&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/228164/original/file-20180718-142417-1hgve61.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=961&fit=crop&dpr=1 754w, https://images.theconversation.com/files/228164/original/file-20180718-142417-1hgve61.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=961&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/228164/original/file-20180718-142417-1hgve61.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=961&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Composite of Titans surface taken by Huygens at different heights.</span>
<span class="attribution"><span class="source">ESA/NASA/JPL/University of Arizona</span></span>
</figcaption>
</figure>
<p>Since the Cassini mission ended in 2017, NASA’s Karsten Schindler said there was keen interest in any new atmospheric observations from occultations:</p>
<blockquote>
<p>Occultations remain the only means to study Titan’s upper atmosphere and its evolution for the foreseeable future.</p>
</blockquote>
<h2>Countdown to the July occultation</h2>
<p>So how were the latest observations made, and how was the data gathered?</p>
<p>From the air, the plan was for the July 18 occultation to be recorded by a camera mounted on a telescope of the Stratospheric Observatory of Infrared Astronomy <a href="https://www.nasa.gov/mission_pages/SOFIA/index.html">(SOFIA)</a> on board a Boeing 747 aircraft.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/228145/original/file-20180718-142435-pzv82d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/228145/original/file-20180718-142435-pzv82d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/228145/original/file-20180718-142435-pzv82d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=347&fit=crop&dpr=1 600w, https://images.theconversation.com/files/228145/original/file-20180718-142435-pzv82d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=347&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/228145/original/file-20180718-142435-pzv82d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=347&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/228145/original/file-20180718-142435-pzv82d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=436&fit=crop&dpr=1 754w, https://images.theconversation.com/files/228145/original/file-20180718-142435-pzv82d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=436&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/228145/original/file-20180718-142435-pzv82d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=436&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">SOFIA takes off from Christchurch International Airport in 2017.</span>
<span class="attribution"><span class="source">SOFIA/ Waynne Williams</span></span>
</figcaption>
</figure>
<p>That’s right: a telescope mounted inside a modified passenger plane imaging an object more than 1 billion kilometres away! SOFIA would fly above the clouds between Australia and New Zealand.</p>
<p>From the ground, several facilities across Australia were to attempt to record the occultation.</p>
<p>The University of Western Australia’s <a href="http://www.zt.ems.uwa.edu.au/">Zadko Telescope</a>, located about 80km north of Perth (see map, below), was identified by NASA as a ground facility sensitive enough to contribute to the project. </p>
<iframe src="https://www.google.com/maps/embed?pb=!1m14!1m12!1m3!1d2388.822095869977!2d115.71176221504176!3d-31.356613427959715!2m3!1f0!2f0!3f0!3m2!1i1024!2i768!4f13.1!5e1!3m2!1sen!2sau!4v1532067433110" width="100%" height="500" frameborder="0" style="border:0" allowfullscreen=""></iframe>
<p>The most obvious deal breaker was the weather. July is one of the wettest months at the Zadko telescope site. But, as we found out, there were other unforseen challenges. </p>
<h2>Three days to occultation</h2>
<p>NASA’s Karsten Schindler arrived at the UWA research site, at Gingin, on Monday July 16, armed with a case filled with delicate cameras, cables and electronics.</p>
<p>The camera was the key to record the event. The current Zadko telescope camera cannot record fast enough to capture the rapid changes in brightness of the occulted star. </p>
<p>The Zadko Telescope was fitted out with a fast shooting (a frame every few seconds), NASA camera, more like a movie camera than a standard astronomical camera. After hours of installation, the new imaging system needed to be tested.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/228387/original/file-20180719-142420-f10uxn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/228387/original/file-20180719-142420-f10uxn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/228387/original/file-20180719-142420-f10uxn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/228387/original/file-20180719-142420-f10uxn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/228387/original/file-20180719-142420-f10uxn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/228387/original/file-20180719-142420-f10uxn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/228387/original/file-20180719-142420-f10uxn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/228387/original/file-20180719-142420-f10uxn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Ground occultation team: John Kennwell, Arie Verveer, Karsten Schindler with the Zadko Telescope in the background.</span>
</figcaption>
</figure>
<p>Unfortunately, the observatory roof would not open because of a faulty sensor. No Monday test, but hey, we still had Tuesday to test the system? Onsite engineers scrambled to fix the sensor ready for Tuesday.</p>
<h2>Two days to occultation</h2>
<p>On Tuesday, I received the following text message from the site.</p>
<blockquote>
<p>11:07pm: Rain sensor working but clouded out … cheers Arie. So no chance testing the camera and weather forecast for Wednesday was bleak.</p>
</blockquote>
<h2>The day of occultation</h2>
<p>Despite the cloud and nearly constant rain showers, team occulation (Karsten, Arie and John) were on site ready to start pointing the telescope and activate the imaging. </p>
<p>“Up to 10pm it was still raining,” Karsten told me the next morning. “Then a miracle happened.”</p>
<p>Less than an hour before the event, and he said the weather changed.</p>
<p>“The clouds seemed to vaporise away, leaving a totally cloudless sky with 100% visibility. I have never seen anything like it.” </p>
<p>The team swung into action, pointing the telescope at the target star, focusing the camera. At the designated occulation time 11:05pm, Karsten hit the image acquisition button, enabling the camera to take hundreds of images over a few minutes.</p>
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Read more:
<a href="https://theconversation.com/what-cassinis-mission-revealed-about-saturns-known-and-newly-discovered-moons-83430">What Cassini's mission revealed about Saturn's known and newly discovered moons</a>
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<p>Eager to see if the data contained the signature of an occulation, the team performed a preliminary analysis within minutes. Yes, there was a clear occulation signature, a big dip in the brightness of the star at exactly the predicted time of the occulation.</p>
<p>Next morning I was informed that SOFIA had also captured the event. </p>
<p>The data recorded from the Australian ground stations and by SOFIA will be analysed over the coming weeks and published in peer reviewed journals.</p>
<p>But one thing the journals won’t highlight is the excitement of the observation, and the enormous effort by a few individuals who helped acquire this data that should hopefully give us a better understanding of the atmosphere of Titan.</p><img src="https://counter.theconversation.com/content/100162/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Coward receives funding from the Australian Research Council Center of Excellence: OzGrav CE170100004
</span></em></p>Titan is more than a billion kilometres from our Sun but occasionally it’s shadow can be seen here on Earth, with the right technology. That’s what scientists gathered in Western Australia to observe.David Coward, Associate professor, The University of Western AustraliaLicensed as Creative Commons – attribution, no derivatives.