tag:theconversation.com,2011:/us/topics/exoplanets-100/articlesExoplanets – The Conversation2024-03-22T14:32:05Ztag:theconversation.com,2011:article/2263612024-03-22T14:32:05Z2024-03-22T14:32:05ZStellar murder: when stars destroy and eat their own planets<figure><img src="https://images.theconversation.com/files/583649/original/file-20240322-22-txhykg.jpg?ixlib=rb-1.1.0&rect=3%2C0%2C1036%2C584&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/missions/chandra/nasas-chandra-planets-can-be-anti-aging-formula-for-stars/">NASA/CXC/M.Weiss</a></span></figcaption></figure><p>Our Sun is both our best friend and our worst enemy. On the one hand, we owe our very existence to our star. Earth and the other planets in the Solar System formed out of the same cloud of gas and dust as the Sun. </p>
<p>And without its light, there could be no life on this planet. On the other hand, there will come a day when the Sun ends all life on Earth and, eventually, destroys Earth itself.</p>
<p>The risks that stars can pose to their planets are highlighted by <a href="https://www.nature.com/articles/d41586-024-00847-6">a new study published in Nature</a>. The authors looked at stars similar to our Sun and found that at least one in 12 stars exhibits traces of metals in its atmosphere. These are thought to be the scars of planets and asteroids that have been ingested by the stars. </p>
<p>Planets should never feel too comfortable as they orbit their parent star, as there are at least two ways in which their star can betray their trust and bring about their violent demise. </p>
<h2>Tidal disruption</h2>
<p>The first is through a process called “tidal disruption”. As a planetary system forms, some planets will find themselves orbiting their star along paths that are either not quite circular or are slightly inclined relative to the plane of the star’s rotation. When that happens, the gravitational force exerted by the star on the planet will slowly correct the shape or the alignment of the wayward planet’s orbit. </p>
<p>In extreme cases, the gravitational force applied by the star will destabilise the planet’s orbit, slowly pulling it closer and closer. If the hapless planet strays too close, it will be torn apart by the star’s gravity. This happens because the side of the planet facing the star is slightly closer than the side facing away (the difference is the planet’s diameter). </p>
<p>The strength of the gravitational pull exerted by the star depends on the distance between it and the planet, so that the side of the planet facing the star feels a slightly stronger pull than the side facing away. </p>
<p>On Earth, this difference in the strength of the force of gravity creates the daily ebb and flow of the tides. In essence, the Sun is trying to deform Earth, but is far enough away that it only manages to pull on the waters of its oceans. But a planet dangerously close to its star will find its very crust and core being pulled apart by these tides. </p>
<p>If the planet is not too close to the star, its shape will merely be deformed into that of an egg. Just a little closer to the star, and the difference between the gravitational pull on its different sides will be enough to completely tear it apart, reducing it back to a cloud of gas and dust that spirals into the star and vaporises in its hellish fires.</p>
<p>The process of tidal disruption was first suggested some 50 years ago. For the last couple of decades, astronomers — including my group — have observed dozens of bright tidal disruption flares caused by <a href="https://science.nasa.gov/resource/tidal-disruption-event/">stars shredded by supermassive black holes</a> in the centres of galaxies. </p>
<figure class="align-center ">
<img alt="Planet and binary star." src="https://images.theconversation.com/files/583650/original/file-20240322-26-mpjqcm.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/583650/original/file-20240322-26-mpjqcm.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/583650/original/file-20240322-26-mpjqcm.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/583650/original/file-20240322-26-mpjqcm.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/583650/original/file-20240322-26-mpjqcm.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/583650/original/file-20240322-26-mpjqcm.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/583650/original/file-20240322-26-mpjqcm.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The new study in Nature looked specifically at stars orbiting each other in binary systems.</span>
<span class="attribution"><a class="source" href="https://images.nasa.gov/details/PIA21470">NASA/JPL-Caltech</a></span>
</figcaption>
</figure>
<p>Last year, for the first time, a group of astronomers reported observing a similar, dimmer flare that was consistent with <a href="https://www.nasa.gov/missions/neowise/caught-in-the-act-astronomers-detect-a-star-devouring-a-planet/">a planet being disrupted and consumed by its star</a>. </p>
<p>Tidal disruption of planets may be quite common, as shown by the new finding that at least 1 in 12 stars exhibits signs that <a href="https://www.nature.com/articles/d41586-024-00847-6">they have ingested planetary material</a>. </p>
<p>Other studies have found that between a quarter to half of all white dwarfs – the remnants of stars up to twice as massive as our Sun – sport similar scars. As their name implies, white dwarfs are white hot. With surface temperatures of tens of thousands of degrees, the hottest white dwarfs emit ultraviolet and X-ray light energetic enough to <a href="https://www.syfy.com/syfy-wire/a-dead-star-is-vaporizing-its-planets">vaporise their orbiting planets</a>.</p>
<h2>The end of Earth</h2>
<p>Rest assured; Earth won’t be destroyed via tidal disruption. Our planet’s end will come in about five billion years, when the Sun will transition into a red giant. </p>
<p>Stars are powered by <a href="https://www.energy.gov/science/doe-explainsnuclear-fusion-reactions#:%7E:text=Nuclear%20Fusion%20reactions%20power%20the,The%20leftover%20mass%20becomes%20energy.">the process known as fusion</a>, where two light elements are combined to make a heavier one. All stars start out their lives fusing the element hydrogen in their cores into the element helium. This fusion process both stabilises them against implosion, due to the incessant pull of gravity, and creates the light that makes them shine. Our Sun has been fusing hydrogen into helium for roughly 4.5 billion years. </p>
<p>But 4.5 billion years from now, the hydrogen in the Sun’s core will run out. All fusion in the core will stop, and gravity, unopposed, will force the star to contract. As the core contracts, it will heat up until the temperature is high enough for helium to fuse into carbon. </p>
<p>Fusion will once again stabilise the star. In the meantime, though, the outer envelopes of the star will expand and cool, giving the now giant star a redder hue. As the red giant Sun expands, it will <a href="https://www.scientificamerican.com/article/the-sun-will-eventually-engulf-earth-maybe/">engulf Mercury, Venus and Earth</a> – it may even reach all the way out to the orbit of Mars. </p>
<p>Earth may have another five billion years to go, but we will not be here to witness its extinction. As the Sun burns through its hydrogen stores, it steadily grows brighter: every billion years, its luminosity increases by about 10%. </p>
<p>A billion years from now, the Sun will be bright enough to <a href="https://theconversation.com/the-sun-wont-die-for-5-billion-years-so-why-do-humans-have-only-1-billion-years-left-on-earth-37379">boil away Earth’s oceans</a>. So, the next time you bask in the warm rays of the Sun, remember: it’s got it in for us.</p><img src="https://counter.theconversation.com/content/226361/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Or Graur receives funding from UKRI Science and Technology Facilities Council.. </span></em></p>There are several ways in which stars can destroy and swallow their own planets.Or Graur, Associate Professor of Astrophysics, University of PortsmouthLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2254842024-03-12T17:51:07Z2024-03-12T17:51:07ZOur survey of the sky is uncovering the secrets of how planets are born<figure><img src="https://images.theconversation.com/files/580926/original/file-20240311-22-5v1m89.jpeg?ixlib=rb-1.1.0&rect=22%2C44%2C2978%2C1165&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Discs giving birth to new planets, seen by the Very Large Telescope.</span> <span class="attribution"><span class="source">ESO/C. Ginski, A. Garufi, P.-G. Valegård et al.</span></span></figcaption></figure><p>When we look out to the stars, it is typically not a yearning for the distant depths of outer space that drives us. When we are looking out there, we are truly looking back at ourselves. We try to understand our place in the unimaginable vastness of the universe. </p>
<p>One of the most burning questions that drives us is how unique we are. Did life only emerge here on Earth or is our galaxy teaming with it? </p>
<p>The very first step in finding out is to understand how special the Earth really is – and, by extension, our entire Solar System. This requires knowledge about how solar systems actually form. And that’s exactly what <a href="https://www.eso.org/public/news/eso2405/">my colleagues and I have started to uncover</a> with a new series of studies of star-forming regions.</p>
<p>In the past decades, astronomers <a href="https://theconversation.com/explainer-how-do-you-find-exoplanets-24153">have spotted</a> more than 5,000 planets around distant stars – so called exoplanets. We now know that planets are so abundant that you can look up to almost any star in the night sky and be near certain that planets are circling around it. But what do these planets look like?</p>
<p>The first planet that was discovered around a star similar to the Sun came as a shock to us. It was a so-called <a href="https://exoplanets.nasa.gov/resources/1040/hot-jupiter/">hot Jupiter</a>, a massive gas giant that orbits its parent star on such a tight orbit that the length of a year is only four days. This is a truly alien world with no equal in our own solar system.</p>
<p>From this first groundbreaking discovery, astronomers have gone on and found tightly packed systems of super-Earths, rocky planets several times as massive as the Earth, as well as awesome gas giants in century-long orbits around their parent star. Of the many planetary systems that we have found, none equals our own solar system. In fact <a href="https://theconversation.com/more-than-1-000-new-exoplanets-discovered-but-still-no-earth-twin-59274">most of them are quite different.</a> </p>
<p>To understand how all of these different systems come to be, we have to turn to the very beginning. And that’s majestic discs of dust and gas that surround the youngest stars. These are the nurseries which will eventually bring forth new planetary systems. </p>
<p>These discs <a href="https://arxiv.org/abs/2002.00405">are enormous objects</a>, up to several hundred times as extended as the distance between the Earth and the Sun. Yet in the sky they appear tiny. This is because even the nearest ones, which are practically in our galactic backyard, are between 600 and 1,600 light years away.</p>
<p>That is a tiny distance when you consider that the Milky Way galaxy has a diameter of more than 100,000 light years, but it still means that light, the fastest thing in the universe, takes up to 1,600 years to reach us from there. </p>
<p>The typical size of one of these planetary nurseries, as seen from the Earth, would be an angle of 1 “arc-second” on sky, which is equivalent to a 3,600th part of a degree. To put it in perspective, it is like trying to observe a person standing on top of the Eiffel Tower from 500km away in the Dutch capital of Amsterdam. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/UGuIIeFipfk?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>To observe these discs we need the most advanced and largest telescopes. And we need sophisticated instruments that can correct for atmospheric turbulence which blurs our images. This is no mean feat of engineering, with the latest generation of instruments only being available since about a decade. </p>
<h2>New findings</h2>
<p>Using the European Southern Observatory’s “<a href="https://www.eso.org/public/unitedkingdom/teles-instr/paranal-observatory/vlt/">Very Large Telescope</a>”, the VLT, and the <a href="https://www.eso.org/sci/facilities/paranal/instruments/sphere.html">Sphere extreme adaptive optics camera</a>, we have now started to survey nearby young stars.</p>
<p>Our team, consisting of scientists from more than ten countries was able to observe more than 80 of these young stars in amazing detail – with our findings published in a <a href="https://www.eso.org/public/news/eso2405/">series of papers</a> in the journal Astronomy and Astrophysics.</p>
<p>All the images were taken in near infrared light, invisible to the human eye. They show the light from the distant young stars as it is reflected from the tiny dust particles in the discs. This dust is much like sand on the beach and will eventually clump together to form new planets. </p>
<p>What we found was an astonishing diversity of shape and form of these planetary nurseries. Some of them have huge ring systems, others large spiral arms. Some of them are smooth and calm, and yet others are caught in the middle of a storm as dust and gas from the surrounding star-forming clouds rains down on them. </p>
<p>While we expected some of this diversity, our survey shows for the first time that this holds true even within the same star-forming regions. So even planetary systems that form within the same neighbourhood might look quite different from one another.</p>
<figure class="align-center ">
<img alt="Planet-forming discs within the gas-rich cloud of Chamaeleon I, roughly 600 light-years from Earth." src="https://images.theconversation.com/files/581242/original/file-20240312-22-tc1s5x.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/581242/original/file-20240312-22-tc1s5x.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=430&fit=crop&dpr=1 600w, https://images.theconversation.com/files/581242/original/file-20240312-22-tc1s5x.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=430&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/581242/original/file-20240312-22-tc1s5x.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=430&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/581242/original/file-20240312-22-tc1s5x.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=540&fit=crop&dpr=1 754w, https://images.theconversation.com/files/581242/original/file-20240312-22-tc1s5x.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=540&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/581242/original/file-20240312-22-tc1s5x.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=540&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Planet-forming discs within the gas-rich cloud of Chamaeleon I, roughly 600 light-years from Earth.</span>
<span class="attribution"><span class="source">Ginski et, al 2024</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Finding such wide range of discs suggests that the huge diversity in exoplanets discovered so far is a consequence of this broad spectrum of planetary nurseries. </p>
<p>Unlike the Sun, most stars in our galaxy have companions, with two or more stars orbiting a shared centre of mass. When looking at the constellation of Orion, we found that stars in groups of two or more were less likely to have large planet-forming discs than lone stars. This is a useful thing to know when hunting for exo-planets. </p>
<p>Another interesting finding was how uneven the discs in this region were, suggesting they may host massive planets that warp the discs. </p>
<p>The next step in our research will be to connect specific planets to their nurseries, to understand how the different systems might have formed in detail. We also want to zoom in even closer in the innermost regions of these discs in which terrestrial planets like our own Earth might already be forming.</p>
<p>For this, we will use the next generation of telescopes spearheaded by the “<a href="https://elt.eso.org/">Extremely Large Telescope</a>” of the European Southern Observatory that is right now under construction in the Chilean Atacama desert. </p>
<p>There are many questions to answer. But thanks to our survey we now know that the very first step on the long way for life to emerge is an utterly beautiful one.</p><img src="https://counter.theconversation.com/content/225484/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Christian Ginski works for the University of Galway and frequently works with ESO facilities. </span></em></p>Astronomers have spotted a surprisingly diverse set of planet-forming disks.Christian Ginski, Lecturer of astronomy, University of GalwayLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2251452024-03-08T13:35:18Z2024-03-08T13:35:18ZDune: what the climate of Arrakis can tell us about the hunt for habitable exoplanets<p>Frank Herbert’s Dune is epic sci-fi storytelling with an environmental message at its heart. The novels and movies are set on the desert planet of Arrakis, which various characters dream of transforming into a greener world – much like some envision for Mars today. </p>
<p>We investigated Arrakis using a <a href="https://theconversation.com/dune-we-simulated-the-desert-planet-of-arrakis-to-see-if-humans-could-survive-there-170181">climate model</a>, a computer program similar to those used to give weather forecasts. We found the world that Herbert had created, well before climate models even existed, was remarkably accurate – and would be habitable, if not hospitable.</p>
<p>However, Arrakis wasn’t always a desert. In Dune lore, 91% of the planet was once covered by oceans, until some ancient catastrophe led to its desertification. What water remained was further removed by sand trout, an invasive species brought to Arrakis. These proliferated and carried liquid into cavities deep underground, leading to the planet becoming more and more arid.</p>
<p>To see what a large ocean would mean for the planet’s climate and habitability, we have now used the same climate model – putting in an ocean while changing no other factors. </p>
<p>When most of Arrakis is flooded, we calculate that the global average temperature would be reduced by 4°C. This is mostly because oceans add moisture to the atmosphere, which leads to more snow and certain types of cloud, both of which reflect the sun’s energy back into space. But it’s also because oceans on Earth and (we assume) on Arrakis emit “halogens” that <a href="https://www.nature.com/articles/s41586-023-06119-z">cool the planet</a> by depleting ozone, a potent greenhouse gas which Arrakis would have significantly more of than Earth.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/580451/original/file-20240307-18-5829gu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Map of Arrakis" src="https://images.theconversation.com/files/580451/original/file-20240307-18-5829gu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/580451/original/file-20240307-18-5829gu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=207&fit=crop&dpr=1 600w, https://images.theconversation.com/files/580451/original/file-20240307-18-5829gu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=207&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/580451/original/file-20240307-18-5829gu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=207&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/580451/original/file-20240307-18-5829gu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=261&fit=crop&dpr=1 754w, https://images.theconversation.com/files/580451/original/file-20240307-18-5829gu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=261&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/580451/original/file-20240307-18-5829gu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=261&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 authors gathered information from the books and the Dune Encyclopedia to build their original model. Then they added an ocean with 1,000 metres average depth.</span>
<span class="attribution"><span class="source">Farnsworth et al</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Unsurprisingly, the ocean world is a whopping 86 times wetter, as so much water evaporates from the oceans. This means plants can grow as water is no longer a finite resource, as it is on desert Arrakis.</p>
<h2>A wetter world would be more stable</h2>
<p>Oceans also reduce temperature extremes, as water heats and cools more slowly than land. (This is one reason Britain, surrounded by oceans, has relatively mild winters and summers, while places far inland tend to be <a href="https://weatherspy.net/?city=London&city=Winnipeg&metric=1">hotter in summer and very cold in winter</a>). The climate of an ocean planet is therefore more stable than a desert world. </p>
<p>In desert Arrakis, temperatures would reach 70°C or more, while in its ocean state, we put the highest recorded temperatures at about 45°C. That means the ocean Arrakis would be liveable even in summer. Forests and arable crops could grow outside of the (still cold and snowy) poles. </p>
<p>There is one downside, however. Tropical regions would be buffeted by large cyclones since the huge, warm oceans would contain lots of the energy and moisture required to drive hurricanes.</p>
<h2>The search for habitable planets</h2>
<p>All this isn’t an entirely abstract exercise, as scientists searching for habitable “exoplanets” in distant galaxies are looking for these sorts of things too. At the moment, we can only detect such planets using huge telescopes in space to search for those that are similar to Earth in size, temperature, available energy, ability to host water, and other factors. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/580454/original/file-20240307-28-l1ov3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Scatter chart of planets comparing habitability and similarity to Earth." src="https://images.theconversation.com/files/580454/original/file-20240307-28-l1ov3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/580454/original/file-20240307-28-l1ov3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=482&fit=crop&dpr=1 600w, https://images.theconversation.com/files/580454/original/file-20240307-28-l1ov3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=482&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/580454/original/file-20240307-28-l1ov3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=482&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/580454/original/file-20240307-28-l1ov3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=606&fit=crop&dpr=1 754w, https://images.theconversation.com/files/580454/original/file-20240307-28-l1ov3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=606&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/580454/original/file-20240307-28-l1ov3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=606&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Both desert and ocean Arrakis are considerably more habitable than any other planet we have discovered.</span>
<span class="attribution"><span class="source">Farnsworth et al</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>We know that desert worlds are probably more common than Earth-like planets in the universe. Planets with potentially life-sustaining oceans will usually be found in the so-called “Goldilocks zone”: far enough from the Sun to avoid being too hot (so further away than boiling hot Venus), but close enough to avoid everything being frozen (so nearer than Jupiter’s icy moon Ganymede). </p>
<p>Research has found this habitable zone is particularly <a href="https://www.liebertpub.com/doi/10.1089/ast.2010.0545">small for planets with large oceans</a>. Their water is at risk of either completely freezing, therefore making the planet even colder, or of evaporating as part of a runaway greenhouse effect in which a layer of water vapour prevents heat from escaping and the planet gets hotter and hotter. </p>
<p>The habitable zone is therefore much larger for desert planets, since at the outer edge they will have less snow and ice cover and will absorb more of their sun’s heat, while at the inner edge there is less water vapour and so less risk of a runaway greenhouse effect.</p>
<p>It’s also important to note that, though distance from their local star can give a general average temperature for a planet, such an average can be misleading. For instance, both desert and ocean Arrakis have a habitable average temperature, but the day-to-day temperature extremes on the ocean planet are much more hospitable. </p>
<p>Currently, even the most powerful telescopes cannot sense temperatures at this detail. They also cannot see in detail how the continents are arranged on distant planets. This again could mean the averages are misleading. For instance, while the ocean Arrakis we modelled would be very habitable, most of the land is in the polar regions which are under snow year-round – so the actual amount of inhabitable land is much less. </p>
<p>Such considerations could be important in our own far-future, when the Earth is projected to form a <a href="https://www.nature.com/articles/s41561-023-01259-3">supercontinent centred on the equator</a>. That continent would make the planet far too hot for mammals and other life to survive, potentially leading to mass extinction.</p>
<p>If the most likely liveable planets in the universe are deserts, they may well be very extreme environments that require significant technological solutions and resources to enable life – desert worlds will probably not have an oxygen-rich atmosphere, for instance.</p>
<p>But that won’t stop humans from trying. For instance, Elon Musk and SpaceX have grand ambitions to <a href="https://www.nytimes.com/2023/10/05/science/elon-musk-spacex-starship-mars.html">create a colony</a> on our closest desert world, Mars. But the many challenges they will face only emphasises how important our own Earth is as the cradle of civilisation – especially as ocean-rich worlds may not be as plentiful as we’d hope. If humans eventually colonise other worlds, they’re likely to have to deal with many of the same problems as the characters in Dune.</p>
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<p class="fine-print"><em><span>Alex Farnsworth works for the University of Bristol and receives funding from NERC and the Chinese Academy of Sciences.</span></em></p><p class="fine-print"><em><span>Sebastian Steinig works for the University of Bristol and receives funding from NERC.</span></em></p><p class="fine-print"><em><span>Michael Farnsworth 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>Climate scientists have simulated Arrakis as a desert and with its long-lost oceans.Alex Farnsworth, Senior Research Associate in Meteorology, University of BristolMichael Farnsworth, Research Lead Future Electrical Machines Manufacturing Hub, University of SheffieldSebastian Steinig, Research Associate in Paleoclimate Modelling, University of BristolLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2232472024-02-12T19:33:22Z2024-02-12T19:33:22ZNewborn gas planets may be surprisingly flat – new research<p>A new planet starts its life in a rotating circle of gas and dust, a cradle known as a <a href="https://esahubble.org/wordbank/circumstellar-disc/">protostellar disc</a>. My colleagues and I have used computer simulations to show that newborn gas planets in these discs are likely to have surprisingly flattened shapes. This finding, <a href="https://www.aanda.org/articles/aa/full_html/2024/02/aa48753-23/aa48753-23.html">published in Astronomy and Astrophysics Letters</a>, could add to our picture of exactly how planets form.</p>
<p>Observing protoplanets that have just formed and are still within their protostellar discs is extremely difficult. Until now only three such young protoplanets have been observed, with two of them in the same system, PDS 70.</p>
<p>We need to find systems that are young, and close enough for our telescopes to be able to detect the dim light from the planet itself and distinguish it from that of the disc. The whole process of planetary formation lasts only a few million years which is nothing more than a blink of an eye in astrophysical scales. This means we need to have luck to catch them in the act of forming.</p>
<p>Our research group performed computer simulations to determine the properties of gaseous protoplanets under a variety of thermal conditions in the planets’ cradles. </p>
<p>The simulations have enough resolution to be able to follow the evolution of a protoplanet in the disc from an early stage, when it is just a mere condensation within the disc. Such simulations are computationally demanding and were run on <a href="https://dirac.ac.uk/">DiRAC, the UK’s astrophysics supercomputing facility</a>.</p>
<p>Typically, multiple planets form within a disc. The study found that protoplanets have a shape known as oblate spheroids, like Smarties or M&M’s, rather than being spherical. They grow by drawing gas predominantly through their poles rather than their equators. </p>
<p>Technically, the planets in our Solar System are also oblate spheroids but their flattening is small. <a href="https://spaceplace.nasa.gov/planets-round/en/#:%7E:text=Mercury%20and%20Venus%20are%20the,bit%20thicker%20in%20the%20middle.">Saturn has a flattening of 10%, Jupiter 6%, whereas Earth a mere 0.3%</a>.</p>
<p>In comparison, the typical flattening of protoplanets is 90%. Such a flattening will affect the observed properties of protoplanets, and it needs to be taken into account when interpreting observations.</p>
<h2>How planets start off</h2>
<p>The most widely accepted theory for planet formation <a href="https://faculty.ucr.edu/%7Ekrice/coreacc.html#:%7E:text=The%20most%20commonly%20accepted%20mechanism,to%20accrete%20a%20gaseous%20envelope.">is that of “core accretion”</a>. According to this model, tiny dust particles smaller than sand collide with each other, group together and progressively grow into larger and larger bodies. This is effectively what happens to the dust under your bed when it isn’t cleaned. </p>
<p>Once a core of dust with enough massive forms, it draws gas from the disc to form a gas giant planet. This bottom-to-top approach would take a few million years. </p>
<p>The opposite, top-to-bottom approach, is the <a href="https://blog.planethunters.org/tag/disk-instability/">theory of disc instability</a>. In this model, the protostellar discs that attend young stars are gravitationally unstable. In other words, they are too heavy to be maintained and so fragment into pieces, which evolve into planets. </p>
<p>The theory of core accretion has been around for a long time and it can explain many aspects of how our Solar System formed. However, disc instability can better explain some of the exoplanetary systems we have discovered in recent decades, such as those where a gas giant planet orbits very very far from its host star.</p>
<p>The appeal of this theory is that planet formation happens very fast, within a few thousand years, which is consistent with observations that suggest planets exist in very young discs.</p>
<p>Our study focused on gas giant planets formed via the model of disc instability. They are flattened because they form from the compression of an already flat structure, the protostellar disc, but also because of how they rotate. </p>
<h2>No flat Earths</h2>
<p>Although these protoplanets overall are very flattened, their cores, which will eventually evolve into gas giant planets as we know them, are less flattened – only by about 20%. This is just twice the flattening of Saturn. With time they are expected to become more spherical.</p>
<p>Rocky planets, like Earth and Mars, cannot form via disc instability. They are thought to form by slowly assembling dust particles to pebbles, rocks, kilometre-sized objects and eventually planets. They are too dense to be significantly flattened even when they are newly born. There is no possibility that Earth was flattened at such a high degree when it as young.</p>
<p>But our study does support a role for disc instability in the case of some worlds in some planetary systems.</p>
<p>We are now moving from the era of exoplanet discoveries to the era of exoplanet characterisation. Many new observatories are set to become operational. These will help discover more protoplanets embedded in their discs. Predictions from computer models are also becoming more sophisticated. </p>
<p>The comparison between these theoretical models and observations is bringing us closer and closer to understanding the origins of our Solar System.</p><img src="https://counter.theconversation.com/content/223247/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Dimitris Stamatellos receives funding from the Science and Technology Facilities Council (STFC).</span></em></p>The observation could fill in gaps in our knowledge about planet formation.Dimitris Stamatellos, Associate Professor in Astrophysics, University of Central LancashireLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2198922024-02-05T13:30:46Z2024-02-05T13:30:46ZUS Moon landing marks new active phase of lunar science, with commercial launches of landers that will study solar wind and peer into the universe’s dark ages<figure><img src="https://images.theconversation.com/files/567940/original/file-20240104-21-s3p58r.jpg?ixlib=rb-1.1.0&rect=4%2C17%2C2991%2C1868&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The dark, far side of the Moon is the perfect place to conduct radio astronomy. </span> <span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/LunarEclipse/704e3da2df90473486270e23aa73419d/photo?Query=moon&mediaType=photo&sortBy=&dateRange=Anytime&totalCount=399&digitizationType=Digitized&currentItemNo=12&vs=true&vs=true">AP Photo/Rick Bowmer</a></span></figcaption></figure><p>For the first time since 1972, NASA <a href="https://www.intuitivemachines.com/im-1">landed a craft on the surface of the Moon</a> in February 2024. But the agency didn’t do it alone – instead, it partnered with commercial companies. Thanks to new technologies and <a href="https://www.nasa.gov/commercial-lunar-payload-services/">public-private partnerships</a>, the scientific projects brought to the Moon on this craft and on future missions like it will open up new realms of scientific possibility. </p>
<p>As parts of several projects launching this year, teams of scientists, including myself, will conduct radio astronomy from the south pole and the far side of the Moon.</p>
<p>NASA’s <a href="https://www.nasa.gov/commercial-lunar-payload-services/">commercial lunar payload services program</a>, or CLPS, will use uncrewed landers to conduct NASA’s first science experiments from the Moon in over 50 years. The CLPS program differs from past space programs. Rather than NASA building the landers and operating the program, commercial companies will do so in a public-private partnership. NASA identified <a href="https://www.nasa.gov/commercial-lunar-payload-services/clps-providers/">about a dozen companies</a> to serve as vendors for landers that will go to the Moon. </p>
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<figcaption><span class="caption">CLPS will send science payloads to the Moon in conjunction with the Artemis program’s crewed missions.</span></figcaption>
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<p>NASA buys space on these landers for <a href="https://science.nasa.gov/lunar-science/clps-deliveries/">science payloads</a> to fly to the Moon, and the companies design, build and insure the landers, as well as contract with rocket companies for the launches. Unlike in the past, NASA is one of the customers and not the sole driver. </p>
<h2>Peregrine and Odysseus, the first CLPS landers</h2>
<p>The first two CLPS payloads are scheduled to launch during the first two months of 2024. There’s the <a href="https://science.nasa.gov/lunar-science/clps-deliveries/to2-astrobotic/">Astrobotics payload</a>, which launched Jan. 8 before its lander, named Peregrine, <a href="https://www.space.com/astrobotic-peregrine-moon-lander-headed-to-earth">experienced a fuel issue</a> that cut its journey to the Moon short. </p>
<p>Next, there’s the <a href="https://science.nasa.gov/lunar-science/clps-deliveries/op-to2-intuitive-machines/">Intuitive Machines payload</a>. Intuitive Machines’ lander, named Odysseus, <a href="https://www.intuitivemachines.com/im-1">landed near the south pole of the Moon</a> on Feb. 22, 2024. NASA has also planned a <a href="https://science.nasa.gov/lunar-science/clps-deliveries/">few additional landings</a> – about two or three per year – for each of the next few years.</p>
<p>I’m a <a href="https://www.colorado.edu/faculty/burns/">radio astronomer</a> and co-investigator on NASA’s <a href="https://www.colorado.edu/ness/projects/radiowave-observations-lunar-surface-photoelectron-sheath-rolses">ROLSES program</a>, otherwise known as Radiowave Observations at the Lunar Surface of the photoElectron Sheath. ROLSES was built by the NASA Goddard Space Flight Center and is led by <a href="https://science.gsfc.nasa.gov/sci/bio/natchimuthuk.gopalswamy-1">Natchimuthuk Gopalswamy</a>. </p>
<p>The ROLSES instrument landed on the Moon as <a href="https://www.intuitivemachines.com/_files/ugd/7c27f7_51f84ee63ea744a9b7312d17fefa9606.pdf">one of six NASA payloads</a> on the Intuitive Machines lander in February. Between ROLSES and another mission scheduled for the lunar far side in two years, LuSEE-Night, our teams will land NASA’s first two radio telescopes on the Moon by 2026. </p>
<h2>Radio telescopes on the Moon</h2>
<p>The Moon – particularly the far side of the Moon – is an ideal place to do radio astronomy and study signals from extraterrestrial objects such as the Sun and the Milky Way galaxy. On Earth, the ionosphere, which <a href="https://theconversation.com/earths-magnetic-field-protects-life-on-earth-from-radiation-but-it-can-move-and-the-magnetic-poles-can-even-flip-216231">contains Earth’s magnetic field</a>, distorts and absorbs radio signals below the <a href="https://www.fcc.gov/general/fm-radio">FM band</a>. These signals might get scrambled or may not even make it to the surface of the Earth.</p>
<p>On Earth, there are also TV signals, satellite broadcasts and defense radar systems <a href="https://theconversation.com/radio-interference-from-satellites-is-threatening-astronomy-a-proposed-zone-for-testing-new-technologies-could-head-off-the-problem-199353">making noise</a>. To do higher sensitivity observations, you have to go into space, away from Earth. </p>
<p>The Moon is what scientists call <a href="https://www.sciencefocus.com/space/what-is-tidal-locking">tidally locked</a>. One side of the Moon is always facing the Earth – the “<a href="https://www.rmg.co.uk/stories/topics/what-man-moon">man in the Moon</a>” side – and the other side, <a href="https://theconversation.com/whats-on-the-far-side-of-the-moon-111306">the far side</a>, always faces away from the Earth. The Moon has no ionosphere, and with about 2,000 miles of rock between the Earth and the far side of the Moon, there’s no interference. It’s radio quiet. </p>
<p>For our first mission with ROLSES, which launched in February 2024, we will collect data about environmental conditions on the Moon near its south pole. On the Moon’s surface, <a href="https://theconversation.com/solar-storms-can-destroy-satellites-with-ease-a-space-weather-expert-explains-the-science-177510">solar wind</a> directly strikes the lunar surface and creates a charged gas, called <a href="https://www.psfc.mit.edu/vision/what_is_plasma">a plasma</a>. Electrons lift off the negatively charged surface to form a highly ionized gas. </p>
<p>This doesn’t happen on Earth because <a href="https://theconversation.com/earths-magnetic-field-protects-life-on-earth-from-radiation-but-it-can-move-and-the-magnetic-poles-can-even-flip-216231">the magnetic field deflects</a> the solar wind. But there’s no global magnetic field on the Moon. With a low frequency radio telescope like ROLSES, we’ll be able to measure that plasma for the first time, which could help scientists figure out how to keep astronauts safe on the Moon. </p>
<p>When astronauts walk around on the surface of the Moon, they’ll pick up different charges. It’s like walking across the carpet with your socks on – when you reach for a doorknob, a spark can come out of your finger. The same kind of discharge happens on the Moon from the charged gas, but it’s potentially more harmful to astronauts. </p>
<h2>Solar and exoplanet radio emissions</h2>
<p>Our team is also going to use ROLSES to look at the Sun. The Sun’s surface releases shock waves that send out highly energetic particles and low radio frequency emissions. We’ll use the radio telescopes to measure these emissions and to see bursts of low-frequency radio waves from shock waves within the solar wind.</p>
<p>We’re also going to examine the Earth from the surface of the Moon and use that process as a template for <a href="https://theconversation.com/nasas-tess-spacecraft-is-finding-hundreds-of-exoplanets-and-is-poised-to-find-thousands-more-122104">looking at radio emissions from exoplanets</a> that may harbor life <a href="https://theconversation.com/are-there-any-planets-outside-of-our-solar-system-164062">in other star systems</a>. </p>
<p>Magnetic fields are important for life because they shield the planet’s surface from the <a href="https://theconversation.com/the-scorching-winds-on-the-surface-of-the-sun-and-how-were-forecasting-them-44098">solar/stellar wind</a>. </p>
<p>In the future, our team hopes to use specialized arrays of antennas on the far side of the Moon to observe nearby stellar systems that are known to have exoplanets. If we detect the same kind of radio emissions that come from Earth, this will tell us that the planet has a magnetic field. And we can measure the strength of the magnetic field to figure out whether it’s strong enough to shield life.</p>
<h2>Cosmology on the Moon</h2>
<p>The Lunar Surface Electromagnetic Experiment at Night, or <a href="https://www.colorado.edu/ness/projects/lunar-surface-electromagnetics-experiment-night-lusee-night">LuSEE-Night</a>, will fly in early 2026 to the far side of the Moon. LuSEE-Night marks scientists’ first attempt to do cosmology on the Moon.</p>
<p>LuSEE-Night is a novel collaboration between NASA and the Department of Energy. Data will be sent back to Earth using a communications satellite in lunar orbit, <a href="https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/A_pathway_for_communicating_at_the_Moon">Lunar Pathfinder</a>, which is funded by the European Space Agency.</p>
<p>Since the far side of the Moon is <a href="https://cosmicdawn.astro.ucla.edu/lunar_telescopes.html">uniquely radio quiet</a>, it’s the best place to do cosmological observations. During the two weeks of lunar night that happen every 14 days, there’s no emission coming from the Sun, and there’s no ionosphere. </p>
<p>We hope to study an unexplored part of the early universe called the <a href="https://www.astronomy.com/science/the-beginning-to-the-end-of-the-universe-the-cosmic-dark-ages/">dark ages</a>. The dark ages refer to before and just after the formation of the very first stars and galaxies in the universe, which is beyond what the <a href="https://webb.nasa.gov/">James Webb Space Telescope</a> can study.</p>
<p>During the dark ages, the universe was less than 100 million years old – today the universe is 13.7 billion years old. The universe was full of hydrogen <a href="https://theconversation.com/after-our-universes-cosmic-dawn-what-happened-to-all-its-original-hydrogen-65527">during the dark ages</a>. That hydrogen radiates through the universe at low radio frequencies, and when new stars turn on, they ionize the hydrogen, producing a radio signature in the spectrum. Our team hopes to measure that signal and learn about how the earliest stars and galaxies in the universe formed.</p>
<p>There’s also a lot of potential new physics that we can study in this last unexplored cosmological epoch in the universe. We will investigate the nature of <a href="https://theconversation.com/dark-matter-the-mystery-substance-physics-still-cant-identify-that-makes-up-the-majority-of-our-universe-85808">dark matter</a> and early <a href="https://theconversation.com/explainer-the-mysterious-dark-energy-that-speeds-the-universes-rate-of-expansion-40224">dark energy</a> and test our fundamental models of physics and cosmology in an unexplored age.</p>
<p>That process is going to start in 2026 with the LuSEE-Night mission, which is both a fundamental physics experiment and a cosmology experiment.</p>
<p><em>This is an updated version of an article originally published on Feb. 5, 2024.</em></p><img src="https://counter.theconversation.com/content/219892/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jack Burns receives funding from NASA.</span></em></p>Projects under NASA’s CLPS program – including the Odysseus lander that made it to the lunar surface – will probe unexplored questions about the universe’s formation.Jack Burns, Professor of Astrophysical and Planetary Sciences, University of Colorado BoulderLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2190542024-02-02T13:17:20Z2024-02-02T13:17:20ZOrbital resonance − the striking gravitational dance done by planets with aligning orbits<figure><img src="https://images.theconversation.com/files/571696/original/file-20240126-29-xc09zr.jpg?ixlib=rb-1.1.0&rect=19%2C4%2C1578%2C792&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Planets can gravitationally affect each other when their orbits line up. </span> <span class="attribution"><a class="source" href="https://exoplanets.nasa.gov/trappist1/">NASA/JPL-Caltech</a></span></figcaption></figure><p>Planets orbit their parent stars while separated by enormous distances – in our solar system, planets are like <a href="https://science.nasa.gov/learning-resources/how-big-is-the-solar-system/">grains of sand</a> in a region the size of a football field. The time that planets take to orbit their suns have no specific relationship to each other. </p>
<p>But sometimes, their orbits display striking patterns. For example, astronomers studying <a href="https://exoplanets.nasa.gov/news/1771/discovery-alert-watch-the-synchronized-dance-of-a-6-planet-system/">six planets orbiting a star</a> 100 light years away have just found that they orbit their star with an almost rhythmic beat, in perfect synchrony. Each pair of planets completes their orbits in times that are the ratios of whole numbers, allowing the planets to align and exert a gravitational push and pull on the other during their orbit.</p>
<p>This type of gravitational alignment is called <a href="https://www.aanda.org/glossary/175-orbital-resonance">orbital resonance</a>, and it’s like a harmony between distant planets.</p>
<p>I’m an <a href="https://scholar.google.com/citations?user=OrRLRQ4AAAAJ&hl=en">astronomer</a> who studies and writes about <a href="https://wwnorton.com/books/9780393343861">cosmology</a>. Researchers have discovered <a href="https://exoplanets.nasa.gov/">over 5,600 exoplanets</a> in the past 30 years, and their extraordinary diversity continues to surprise astronomers.</p>
<h2>Harmony of the spheres</h2>
<p>Greek mathematician <a href="https://www.auroraorchestra.com/2019/05/pythagoras-the-music-of-the-spheres/">Pythagoras</a> discovered the principles of musical harmony 2,500 years ago by analyzing the sounds of blacksmiths’ hammers and plucked strings. </p>
<p>He believed mathematics was at the heart of the natural world and proposed that the Sun, Moon and planets each emit unique hums based on their orbital properties. He thought this “music of the spheres” would be imperceptible to the human ear.</p>
<p>Four hundred years ago, <a href="https://www.skyscript.co.uk/kepler.html">Johannes Kepler</a> picked up this idea. He proposed that musical intervals and harmonies described the motions of the six known planets at the time. </p>
<p>To Kepler, the solar system had two basses, Jupiter and Saturn; a tenor, Mars; two altos, Venus and Earth; and a soprano, Mercury. These roles reflected how long it took each planet to orbit the Sun, lower speeds for the outer planets and higher speeds for the inner planets. </p>
<p>He called the book he wrote on these mathematical relationships “<a href="https://archive.org/details/ioanniskepplerih00kepl">The Harmony of the World</a>.” While these ideas have some similarities to the concept of orbital resonance, planets don’t actually make sounds, since <a href="https://theconversation.com/why-isnt-there-any-sound-in-space-an-astronomer-explains-why-in-space-no-one-can-hear-you-scream-217885">sound can’t travel through the vacuum of space</a>.</p>
<h2>Orbital resonance</h2>
<p><a href="https://www.aanda.org/glossary/175-orbital-resonance">Resonance happens when</a> planets or moons have orbital periods that are <a href="https://www.youtube.com/watch?v=qDHKveVSc0Y">ratios of whole numbers</a>. The orbital period is the time taken for a planet to make one complete circuit of the star. So, for example, two planets orbiting a star would be in a 2:1 resonance when one planet takes twice as long as the other to orbit the star. Resonance is seen in only <a href="https://arxiv.org/abs/1703.03634">5% of planetary systems</a>.</p>
<figure class="align-center ">
<img alt="A simple animated diagram showing a planet, as a dot, with three smaller dots making circles around it, and occasionally flashing when two of the three line up." src="https://images.theconversation.com/files/571674/original/file-20240126-17-ofefj2.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/571674/original/file-20240126-17-ofefj2.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=403&fit=crop&dpr=1 600w, https://images.theconversation.com/files/571674/original/file-20240126-17-ofefj2.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=403&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/571674/original/file-20240126-17-ofefj2.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=403&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/571674/original/file-20240126-17-ofefj2.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=506&fit=crop&dpr=1 754w, https://images.theconversation.com/files/571674/original/file-20240126-17-ofefj2.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=506&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/571674/original/file-20240126-17-ofefj2.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=506&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Orbital resonance, as seen with Jupiter’s moons, happens when planetary bodies’ orbits line up – for example, Io orbits Jupiter four times in the time it takes Europa to orbit twice and Ganymede to orbit once.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/File:Galilean_moon_Laplace_resonance_animation_2.gif">WolfmanSF/Wikimedia Commons</a></span>
</figcaption>
</figure>
<p>In the solar system, Neptune and Pluto are in a 3:2 resonance. There’s also a <a href="https://www.planetary.org/space-images/orbital-resonances-of-galilean-moons">triple resonance</a>, 4:2:1, among Jupiter’s three moons: Ganymede, Europa and Io. In the time it takes Ganymede to orbit Jupiter, Europa orbits twice and Io orbits four times. Resonances occur naturally, when planets happen to have orbital periods that are the ratio of whole numbers. </p>
<p>Musical intervals describe the relationship between two musical notes. In the musical analogy, important <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/Music/mussca.html">musical intervals</a> based on ratios of frequencies are the fourth, 4:3, the fifth, 3:2, and the octave, 2:1. Anyone who plays the <a href="https://globalguitarnetwork.com/perfect-intervals/">guitar or the piano</a> might recognize these intervals.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/2V3bvZu2Xqo?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Musical intervals can be used to create scales and harmony.</span></figcaption>
</figure>
<p>Orbital resonances can change <a href="https://theconversation.com/earth-isnt-the-only-planet-with-seasons-but-they-can-look-wildly-different-on-other-worlds-216874">how gravity influences</a> two bodies, causing them to speed up, slow down, stabilize on their orbital path and sometimes have their orbits disrupted.</p>
<p>Think of pushing a <a href="https://astrobites.org/2018/07/05/small-black-hole-meets-big-black-hole/">child on a swing</a>. A planet and a swing both have a natural frequency. Give the child a push that matches the swing motion and they’ll get a boost. They’ll also get a boost if you push them every other time they’re in that position, or every third time. But push them at random times, sometimes with the motion of the swing and sometimes against, and they get no boost. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/qDHKveVSc0Y?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Orbital resonance can cause planets or asteroids to speed up or start to wobble.</span></figcaption>
</figure>
<p>For planets, the boost can keep them continuing on their orbital paths, but it’s much more likely to disrupt their orbits.</p>
<h2>Exoplanet resonance</h2>
<p>Exoplanets, or planets outside the solar system, show striking examples of resonance, not just between two objects but also between resonant “chains” involving three or more objects. </p>
<hr>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/567788/original/file-20240103-23-yg479z.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A square box with the words 'Art & Science Collide' and a drawing of a lightbulb with its wire filament in the shape of a brain, surrounded by a circle." src="https://images.theconversation.com/files/567788/original/file-20240103-23-yg479z.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/567788/original/file-20240103-23-yg479z.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/567788/original/file-20240103-23-yg479z.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/567788/original/file-20240103-23-yg479z.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/567788/original/file-20240103-23-yg479z.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/567788/original/file-20240103-23-yg479z.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/567788/original/file-20240103-23-yg479z.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Art & Science Collide series.</span>
</figcaption>
</figure>
<p><em><strong><a href="https://theconversation.com/us/topics/art-in-science-series-2024-149583">This article is part of Art & Science Collide</a></strong>, a series examining the intersections between art and science.</em></p>
<p><em>You may be interested in:</em></p>
<p><a href="https://theconversation.com/literature-inspired-my-medical-career-why-the-humanities-are-needed-in-health-care-217357">Literature inspired my medical career: Why the humanities are needed in health care</a></p>
<p><a href="https://theconversation.com/i-wrote-a-play-for-children-about-integrating-the-arts-into-stem-fields-heres-what-i-learned-about-encouraging-creative-interdisciplinary-thinking-218001">I wrote a play for children about integrating the arts into STEM fields – here’s what I learned about interdisciplinary thinking</a> </p>
<p><a href="https://theconversation.com/pictures-have-been-teaching-doctors-medicine-for-centuries-a-medical-illustrator-explains-how-218998">Pictures have been teaching doctors medicine for centuries − a medical illustrator explains how</a></p>
<hr>
<p>The star <a href="http://oklo.org/2010/06/23/a-second-laplace-resonance/">Gliese 876</a> has three planets with orbit period ratios of 4:2:1, just like Jupiter’s three moons. <a href="https://skyandtelescope.org/astronomy-news/kepler-finds-planets-in-tight-dance/">Kepler 223</a> has four planets with ratios of 8:6:4:3. </p>
<p>The red dwarf <a href="https://arxiv.org/abs/2212.08695">Kepler 80</a> has five planets with ratios of 9:6:4:3:2, and <a href="https://www.esa.int/ESA_Multimedia/Images/2021/01/Infographic_of_the_TOI-178_planetary_system">TOI 178</a> has six planets, of which five are in a resonant chain with ratios of 18:9:6:4:3. </p>
<p><a href="https://www.sci.news/astronomy/trappist-1-planetary-harmonies-04851.html">TRAPPIST-1</a> is the record holder. It has seven Earth-like planets, two of which <a href="https://theconversation.com/ultracool-dwarf-star-hosts-three-potentially-habitable-earth-sized-planets-just-40-light-years-away-58695">might be habitable</a>, with orbit ratios of 24:15:9:6:4:3:2. </p>
<p>The newest example of a resonant chain is the <a href="https://www.digitaltrends.com/space/exoplanet-orbital-resonance-chain/">HD 110067</a> system. It’s about 100 light years away and has six sub-Neptune planets, a common type of exoplanet, with orbit ratios of 54:36:24:16:12:9. The discovery is interesting because most resonance chains are unstable and disappear over time. </p>
<p>Despite these examples, resonant chains are rare, and <a href="https://www.astronomy.com/science/astronomers-find-six-planets-orbiting-in-resonance/">only 1% of all planetary systems display them</a>. Astronomers think that planets form in resonance, but small gravitational nudges from passing stars and wandering planets erase the resonance over time. With HD 110067, the resonant chain has survived for billions of years, offering a rare and pristine view of the system as it was when it formed.</p>
<h2>Orbit sonification</h2>
<p>Astronomers use <a href="https://science.howstuffworks.com/sonification.htm">a technique called sonification</a> to translate complex visual data into sound. It gives people a different way to appreciate the beautiful images from the <a href="https://science.nasa.gov/mission/hubble/multimedia/sonifications/">Hubble Space Telescope</a>, and it has been applied to <a href="https://www.system-sounds.com/">X-ray data and gravitational waves</a>.</p>
<p>With exoplanets, sonification can convey the mathematical relationships of their orbits. Astronomers at the European Southern Observatory created what they call “<a href="https://www.youtube.com/watch?v=-WevvRG9ysY">music of the spheres</a>” for the TOI 178 system by associating a sound on a pentatonic scale to each of the five planets. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/-WevvRG9ysY?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Music from planetary orbits, created by astronomers at the European Southern Observatory.</span></figcaption>
</figure>
<p>A <a href="https://www.youtube.com/watch?v=WS5UxLHbUKc">similar musical translation</a> has been done for the TRAPPIST-1 system, with the orbital frequencies scaled up by a factor of 212 million to bring them into audible range. </p>
<p>Astronomers have also <a href="https://www.youtube.com/watch?v=2rrODAG7nmI&t=3s">created a sonification</a> for the HD 110067 system. People may not agree on whether these renditions sound like actual music, but it’s inspiring to see Pythagoras’ ideas realized after 2,500 years.</p><img src="https://counter.theconversation.com/content/219054/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Impey receives funding from the National Science Foundation. </span></em></p>Orbital resonance is kind of like musical harmony, but systems that display it are far more rare than songs with harmonic melodies.Chris Impey, University Distinguished Professor of Astronomy, University of ArizonaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2193962024-01-21T23:31:52Z2024-01-21T23:31:52ZThe Solar System used to have nine planets. Maybe it still does? Here’s your catch-up on space today<figure><img src="https://images.theconversation.com/files/566534/original/file-20231219-25-4dyqky.jpg?ixlib=rb-1.1.0&rect=31%2C15%2C5161%2C3230&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>Some of us remember August 24 2006 like it was yesterday. It was the day Pluto got booted from the exclusive “planets club”.</p>
<p>I (Sara) was 11 years old, and my entire class began lunch break by passionately chanting “Pluto is a planet” in protest of the information we’d just received. It was a touching display. At the time, 11-year-old me was outraged – even somewhat inconsolable. Now, a much older me wholeheartedly accepts: Pluto is not a planet. </p>
<p>Similar to Sara, I (Rebecca) vividly remember Pluto’s re-designation to dwarf status. For me, it wasn’t so much that the celestial body had been reclassified. That is science, after all, and things change with new knowledge. Rather, what got to me was how the astronomy community handled the PR. </p>
<p>Even popular astronomers known for their public persona stumbled through mostly <a href="https://www.npr.org/templates/story/story.php?storyId=100145890">unapologetic explanations</a>. It was a missed opportunity. What was poorly communicated as a demotion was actually the discovery of new exciting members of our Solar System, of which <a href="https://www.loc.gov/everyday-mysteries/astronomy/item/why-is-pluto-no-longer-a-planet/">Pluto was the first</a>. </p>
<p>The good news is astronomers have better media support now, and there’s a lot of amazing science to catch up on. Let’s go over what you might have missed.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/566535/original/file-20231219-19-8m96pv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/566535/original/file-20231219-19-8m96pv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/566535/original/file-20231219-19-8m96pv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/566535/original/file-20231219-19-8m96pv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/566535/original/file-20231219-19-8m96pv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/566535/original/file-20231219-19-8m96pv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/566535/original/file-20231219-19-8m96pv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/566535/original/file-20231219-19-8m96pv.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">Pluto didn’t meet the criteria of a fully fledged planet. But there may still be a 9th planet in our Solar System waiting to be found.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<h2>A throwback to a shocking demotion</h2>
<p>Pluto’s fate was almost certainly sealed the day Eris was discovered in 2005. Like Pluto, Eris orbits in the outskirts of our Solar System. Although it has a smaller radius than Pluto, it has <a href="https://astronomy.swin.edu.au/cosmos/m/Mass">more mass</a>.</p>
<p>Astronomers concluded that discovering objects such as Pluto and Eris would only become more common as our telescopes became more powerful. They were right. Today there are five known <a href="https://theconversation.com/new-dwarf-planet-in-the-outer-solar-system-62354">dwarf planets</a> in the Solar System. </p>
<p>The conditions for what classifies a “planet” as opposed to a “dwarf planet” were <a href="https://science.nasa.gov/solar-system/planets/what-is-a-planet/">set by the International Astronomical Union</a>. To cut a long story short, Pluto wasn’t being targeted back in 2006. It just didn’t meet all three criteria for a fully fledged planet:</p>
<ol>
<li>it must orbit a star (in our Solar System this would be the Sun)</li>
<li>it must be big enough that gravity has forced it into a spherical shape</li>
<li>it must be big enough that its own gravity has cleared away any other objects of a similar size near its orbit.</li>
</ol>
<p>The third criterion was Pluto’s downfall. It hasn’t cleared its neighbouring region of other objects. </p>
<p>So is our Solar System fated to have just eight planets? Not necessarily. There may be another one waiting to be found. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/ive-always-wondered-why-are-the-stars-planets-and-moons-round-when-comets-and-asteroids-arent-160541">I've always wondered: why are the stars, planets and moons round, when comets and asteroids aren't?</a>
</strong>
</em>
</p>
<hr>
<h2>Is there a Planet Nine out there?</h2>
<p>With the discovery of new and distant dwarf planets, astronomers eventually realised the dwarf planets’ motions around the Sun didn’t quite add up. </p>
<p>We can use complicated <a href="https://www.caltech.edu/about/news/caltech-researchers-find-evidence-real-ninth-planet-49523">simulations in supercomputers</a> to model how gravitational interactions would play out in a complex environment such as our Solar System. </p>
<p>In 2016, California Institute of Technology astronomers Konstantin Batygin and Mike Brown concluded – after modelling the dwarf planets and their observed paths – that mathematically there ought be a ninth planet out there.</p>
<p>Their <a href="https://www.caltech.edu/about/news/caltech-researchers-find-evidence-real-ninth-planet-49523">modelling</a> determined this planet would have to be about ten times the mass of Earth, and located some 90 billion kilometres away from the Sun (about 15 times farther then Pluto). It’s a pretty bold claim, and some remain sceptical.</p>
<p>One might assume it’s easy to determine whether such a planet exists. Just point a telescope towards where you think it is and look, right? If we can see galaxies billions of light years away, shouldn’t we be able to spot a ninth planet in our own Solar System?</p>
<p>Well, the issue lies in how (not) bright this theoretical planet would be. Best estimates suggest it sits at the depth limit of Earth’s largest telescopes. In other words, it could be 600 times fainter than Pluto.</p>
<p>The other issue is we don’t know exactly where to look. Our Solar System is <em>really</em> big, and it would take a significant amount of time to cover the entire sky region in which Planet Nine might be hiding. To further complicate things, there’s only a small window each year during which conditions are just right for this search. </p>
<p>That isn’t stopping us from looking, though. In 2021, a team using the Atacama Cosmology Telescope (a millimetre-wave radio telescope) published the results from their <a href="https://iopscience.iop.org/article/10.3847/1538-4357/ac2307">search for a ninth planet’s</a> movement in the outskirts of the Solar System. </p>
<p>While they weren’t able to confirm its existence, they provided ten candidates for further follow-up. We may only be a few years from knowing what lurks in the outskirts of our planetary neighbourhood.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/566540/original/file-20231219-17-8m96pv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/566540/original/file-20231219-17-8m96pv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/566540/original/file-20231219-17-8m96pv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/566540/original/file-20231219-17-8m96pv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/566540/original/file-20231219-17-8m96pv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/566540/original/file-20231219-17-8m96pv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/566540/original/file-20231219-17-8m96pv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/566540/original/file-20231219-17-8m96pv.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">The ACT sits at an altitude of 5,190 meters in Chile’s Atacama desert. Here, the lack of atmospheric water vapour helps to increase its accuracy.</span>
<span class="attribution"><a class="source" href="https://www.nist.gov/measuring-cosmos/atacama-cosmology-telescope">NIST/ACT Collaboration</a></span>
</figcaption>
</figure>
<h2>Finding exoplanets</h2>
<p>Even though we have telescopes that can reveal galaxies from the universe’s earliest years, we still can’t easily directly image planets outside of our Solar System, also called exoplanets. </p>
<p>The reason can be found in fundamental physics. Planets emit very dim red wavelengths of light, so we can only see them clearly when they’re reflecting the light of their star. The farther away a planet is from its star, the harder it is to see. </p>
<p>Astronomers knew they’d have to find other ways to look for planets in foreign star systems. Before Pluto was reclassified they had already detected the <a href="https://exoplanets.nasa.gov/resources/2084/greetings-from-your-first-exoplanet.">first exoplanet</a>, 51 Pegasi B, using a <a href="https://www.planetary.org/articles/color-shifting-stars-the-radial-velocity-method">radial velocity method</a>. </p>
<p>This gas giant world is large enough, and close enough to its star, that the gravitational tug of war between the two can be detected all the way from Earth. However, this method of discovery is tedious and challenging from Earth’s surface. </p>
<p>So astronomers came up with another way to find exoplanets: the transit method. When Mercury or Venus pass in front of the Sun, they block a small amount of the Sun’s light. With powerful telescopes, we can look for this phenomenon in distant star systems as well. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/566539/original/file-20231219-15-rhodbm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/566539/original/file-20231219-15-rhodbm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/566539/original/file-20231219-15-rhodbm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=619&fit=crop&dpr=1 600w, https://images.theconversation.com/files/566539/original/file-20231219-15-rhodbm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=619&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/566539/original/file-20231219-15-rhodbm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=619&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/566539/original/file-20231219-15-rhodbm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=778&fit=crop&dpr=1 754w, https://images.theconversation.com/files/566539/original/file-20231219-15-rhodbm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=778&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/566539/original/file-20231219-15-rhodbm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=778&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">In August, the TESS telescope took this snapshot of the Large Magellanic Cloud (right) and the bright star R Doradus (left).</span>
<span class="attribution"><span class="source">NASA/MIT/TESS</span></span>
</figcaption>
</figure>
<p>We do this via the <a href="https://science.nasa.gov/mission/kepler">Kepler</a> space telescope and the Transiting Exoplanet Survey Satellite (<a href="https://science.nasa.gov/mission/tess">TESS</a>). Both have observed tens of thousands of stars and discovered thousands of new planets – dozens of which are about the same size as Earth. </p>
<p>But these observatories can only tell us a planet’s size and distance from its star. They can’t tell us if a planet <a href="https://theconversation.com/do-aliens-exist-we-asked-five-experts-161811">might be hosting life</a>. For that we’d need the James Webb Space Telescope.</p>
<h2>Looking for life</h2>
<p>The James Webb Space Telescope (JWST) has just wrapped up its first year and a half of science. Among its many achievements is the detection of molecules in the atmospheres of exoplanets, a feat made possible by the transit method. </p>
<p>One of these exoplanets, WASP-17, is also known as a “hot Jupiter”. It seems to have been plucked from a page in a sci-fi novel, with evidence for <a href="https://webbtelescope.org/contents/media/images/2023/140/01HC3B0DZNEMRQT3KQ6X4ZMNN2">quartz nanocrystals</a> in its clouds. </p>
<hr>
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<em>
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Read more:
<a href="https://theconversation.com/10-times-this-year-the-webb-telescope-blew-us-away-with-new-images-of-our-stunning-universe-194739">10 times this year the Webb telescope blew us away with new images of our stunning universe</a>
</strong>
</em>
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<p>Meanwhile, the <a href="https://exoplanets.nasa.gov/what-is-an-exoplanet/planet-types/super-earth/">super-Earth</a> <a href="https://www.nasa.gov/universe/exoplanets/webb-discovers-methane-carbon-dioxide-in-atmosphere-of-k2-18-b/">K2-18b</a> (a Kepler find) shows signs of methane and carbon dioxide. But while such discoveries are amazing, the magic ingredient <a href="https://www.nhm.ac.uk/discover/eight-ingredients-life-in-space.html#:%7E:text=Liquid%20water%20is%20an%20essential,substances%20than%20most%20other%20liquids.">necessary for life</a> still eludes us: water vapour.</p>
<p>The field of planetary studies is evolving and 2024 looks promising. Maybe JWST will finally produce signs of water vapour in an exoplanet atmosphere. Who knows, we might even have a ninth planet surprise us all, filling the void left by Pluto. </p>
<p>Stay tuned for exciting science to come.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/566536/original/file-20231219-21-vpjm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/566536/original/file-20231219-21-vpjm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/566536/original/file-20231219-21-vpjm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/566536/original/file-20231219-21-vpjm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/566536/original/file-20231219-21-vpjm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/566536/original/file-20231219-21-vpjm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/566536/original/file-20231219-21-vpjm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/566536/original/file-20231219-21-vpjm.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">Small bodies on the very fringes of our Solar System are essentially invisible to us – but advanced new techniques and technologies are changing this.</span>
<span class="attribution"><span class="source">NASA/Jasmin Moghbeli</span></span>
</figcaption>
</figure><img src="https://counter.theconversation.com/content/219396/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>When most of us left school there were still 9 planets – but we’ve come a long way since Pluto’s demotion. Here’s what’s next on the space agenda.Sara Webb, Lecturer, Centre for Astrophysics and Supercomputing, Swinburne University of TechnologyRebecca Allen, Coordinator Swinburne Astronomy Online | Program Lead of Microgravity Experimentation, Space Technology and Industry Institute, Swinburne University of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2168742024-01-10T13:28:57Z2024-01-10T13:28:57ZEarth isn’t the only planet with seasons, but they can look wildly different on other worlds<figure><img src="https://images.theconversation.com/files/561980/original/file-20231127-27-h9xkjy.jpg?ixlib=rb-1.1.0&rect=0%2C6%2C2055%2C1445&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Nearby planets can affect how one planet 'wobbles' on its spin axis, which contributes to seasons. </span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/orbits-of-planets-in-the-solar-system-royalty-free-illustration/1148112202?phrase=planets+orbit&adppopup=true">Mark Garlick/Science Photo Library via Getty Images</a></span></figcaption></figure><p>Spring, summer, fall and winter – the seasons on Earth change every few months, around the same time every year. It’s easy to take this cycle for granted here on Earth, but not every planet has a regular change in seasons. So why does Earth have regular seasons when other planets don’t? </p>
<p><a href="https://scholar.google.com/citations?user=vxyrNXoAAAAJ&hl=en">I’m an astrophysicist</a> who studies the movement of planets and the causes of seasons. Throughout my research, I’ve found that Earth’s regular pattern of seasons is unique. The <a href="https://theconversation.com/how-the-earths-tilt-creates-short-cold-january-days-173403">rotational axis that Earth spins on</a>, along the North and South poles, <a href="https://en.wikipedia.org/wiki/Axial_tilt">isn’t quite aligned</a> with the vertical axis perpendicular to Earth’s orbit around the Sun. </p>
<p>That slight tilt has big implications for everything from seasons to glacier cycles. The magnitude of that tilt can even determine whether a planet is habitable to life. </p>
<h2>Seasons on Earth</h2>
<p>When a planet has perfect alignment between the axis it orbits on and the rotational axis, the amount of sunlight it receives is fixed as it orbits around the Sun – assuming its orbital shape is a circle. Since seasons come from variations in how much sunlight reaches the planet’s surface, a planet that’s perfectly aligned wouldn’t have seasons. But Earth isn’t perfectly aligned on its axis.</p>
<p>This small misalignment, called an obliquity, is <a href="https://en.wikipedia.org/wiki/Axial_tilt">around 23 degrees</a> from vertical for Earth. So, the Northern Hemisphere experiences more intense sunlight during the summer, when the Sun is positioned more directly above the Northern Hemisphere.</p>
<p>Then, as the Earth continues to orbit around the Sun, the amount of sunlight the Northern Hemisphere receives gradually decreases as the Northern Hemisphere tilts away from the Sun. This causes winter. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/566402/original/file-20231218-21-biar6k.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing the Earth as a blue circle on the left and on the right, with a blue arrow tilted a few degrees towards the right cutting through it, and a green arrow tilted up cutting through it. The angle between the two arrows is red, labeled 'obliquity.' In the middle is a drawing of the Sun." src="https://images.theconversation.com/files/566402/original/file-20231218-21-biar6k.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/566402/original/file-20231218-21-biar6k.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/566402/original/file-20231218-21-biar6k.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/566402/original/file-20231218-21-biar6k.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/566402/original/file-20231218-21-biar6k.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/566402/original/file-20231218-21-biar6k.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/566402/original/file-20231218-21-biar6k.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The obliquity marks the difference between the Earth’s spin axis (blue) and the vertical from orbit (green). The Northern Hemisphere experiences summer when the tilt lines it up directly with light from the Sun.</span>
<span class="attribution"><span class="source">Gongjie Li</span></span>
</figcaption>
</figure>
<p>The planets spinning on their axes and orbiting around the Sun look kind of like spinning tops – they spin around and wobble because of gravitational pull from the Sun. As a top spins, you might notice that it doesn’t just stay perfectly upright and stationary. Instead, it may start to tilt or wobble slightly. This tilt is what astrophysicists call <a href="https://www.britannica.com/science/precession-of-the-equinoxes">spin precession</a>.</p>
<p>Because of these wobbles, Earth’s obliquity isn’t perfectly fixed. These small variations in tilt can have <a href="https://www.jstor.org/stable/1746691">big effects on the Earth’s climate</a> when combined with small changes to Earth’s orbit shape. </p>
<p>The wobbling tilt and any natural variations to the shape of Earth’s orbit can change the amount and distribution of sunlight reaching Earth. These small changes contribute to the planet’s larger temperature shifts over thousands to hundreds of thousands of years. This can, in turn, <a href="https://climate.nasa.gov/news/2948/milankovitch-orbital-cycles-and-their-role-in-earths-climate/">drive ice ages and periods of warmth</a>.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/DD_8Jm5pTLk?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Earth’s seasons result from a variety of factors, including orbit and axial tilt.</span></figcaption>
</figure>
<h2>Translating obliquity into seasons</h2>
<p>So how do obliquity variations affect the seasons on a planet? Low obliquity, meaning the rotational spin axis is aligned with the planet’s orientation as it orbits around the Sun, <a href="https://climate.nasa.gov/news/2948/milankovitch-orbital-cycles-and-their-role-in-earths-climate/">leads to</a> stronger sunlight on the equator and low sunlight near the pole, like on Earth. </p>
<p>On the other hand, a high obliquity – meaning the planet’s rotational spin axis points toward or away from the Sun – <a href="https://climate.nasa.gov/news/2948/milankovitch-orbital-cycles-and-their-role-in-earths-climate/">leads to</a> extremely hot or cold poles. At the same time, the equator gets cold, as the Sun does not shine above the equator all year round. This leads to drastically varying seasons at high latitudes and low temperatures at the equator. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/566405/original/file-20231218-19-pudn6j.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A planet with a reversed zonation is represented by a blue circle next to a drawing of a sun, with a green oval representing the planet's orbit around the sun. A blue arrow pointing towards the sun represents the planet's spin axis, and a green arrow point up represents the planet's orbit direction." src="https://images.theconversation.com/files/566405/original/file-20231218-19-pudn6j.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/566405/original/file-20231218-19-pudn6j.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/566405/original/file-20231218-19-pudn6j.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/566405/original/file-20231218-19-pudn6j.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/566405/original/file-20231218-19-pudn6j.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/566405/original/file-20231218-19-pudn6j.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/566405/original/file-20231218-19-pudn6j.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">When a planet’s spin axis is tilted far from the vertical axis, it has a high obliquity. That means the equator barely gets any sunlight and the North Pole faces right at the Sun.</span>
<span class="attribution"><span class="source">Gongjie Li</span></span>
</figcaption>
</figure>
<p>When a planet has an obliquity of more than 54 degrees, that planet’s equator grows icy and <a href="https://doi.org/10.1016/0012-8252(93)90004-Q">the pole becomes warm</a>. This is called <a href="https://doi.org/10.1016/0012-8252(93)90004-Q">a reversed zonation</a>, and it’s the opposite of what Earth has. </p>
<p>Basically, if an obliquity has large and unpredictable variations, the seasonal variations on the planet become wild and hard to predict. A dramatic, large obliquity variation can turn the whole planet into a snowball, <a href="https://doi.org/10.1093/mnras/stab3179">where it’s all covered by ice</a>. </p>
<h2>Spin orbit resonances</h2>
<p>Most planets are not the only planets in their solar systems. Their planetary siblings can disturb each other’s orbit, which can lead to variations in the shape of their orbits and their orbital tilt. </p>
<p>So, planets in orbit look kind of like tops spinning on the roof of a car that’s bumping down the road, where the car represents the orbital plane. When the rate – or frequency, as scientists call it – at which the tops are precessing, or spinning, matches the frequency at which the car is bumping up and down, something called a <a href="https://doi.org/10.1038/361615a0">spin-orbit resonance</a> occurs.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/561691/original/file-20231126-23-xe830c.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing a planet, shown as a blue circle with an arrow through it representing a tilted, spinning axis, orbiting around the Sun, with another planet's orbit overlapping with it, causing the orbit to tilt up and down." src="https://images.theconversation.com/files/561691/original/file-20231126-23-xe830c.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/561691/original/file-20231126-23-xe830c.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/561691/original/file-20231126-23-xe830c.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/561691/original/file-20231126-23-xe830c.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/561691/original/file-20231126-23-xe830c.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/561691/original/file-20231126-23-xe830c.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/561691/original/file-20231126-23-xe830c.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The orbits of planets close by and the precession motion of a planet on its axis can affect seasonal patterns.</span>
<span class="attribution"><span class="source">Gongjie Li</span></span>
</figcaption>
</figure>
<p>Spin-orbit resonances can cause these obliquity variations, which is when a planet wobbles on its axis. Think about pushing a kid on a swing. When you push at just the right time – or at the resonant frequency – they’ll swing higher and higher.</p>
<p>Mars wobbles more on its axis than Earth does, even though the two are tilted about the same amount, and that actually has to do with the Moon orbiting around Earth. Earth and Mars have a <a href="https://doi.org/10.1038/361608a0">similar spin precession frequency</a>, which matches the orbital oscillation – the ingredients for a spin-orbit resonance. </p>
<p>But Earth has a massive Moon, which pulls on Earth’s spin axis and drives it to precess faster. This slightly faster precession prevents it from experiencing spin orbit resonances. So, the Moon stabilizes Earth’s obliquity, and Earth doesn’t wobble on its axis as much as Mars does. </p>
<h2>Exoplanet seasons</h2>
<p><a href="https://theconversation.com/are-there-any-planets-outside-of-our-solar-system-164062">Thousands of exoplanets</a>, or planets outside our solar system, have been discovered over the past few decades. My research group wanted to understand how habitable these planets are, and whether these exoplanets also have wild obliquities, or whether they have moons to stabilize them like Earth does. </p>
<p>To investigate this, my group has led the first investigation on <a href="https://doi.org/10.3847/1538-3881/aabfd1">the spin-axis variations of exoplanets</a>. </p>
<p>We investigated <a href="https://doi.org/10.3847/1538-3881/aabfd1">Kepler-186f</a>, which is the first discovered Earth-sized planet in a habitable zone. <a href="https://theconversation.com/an-earth-sized-planet-found-in-the-habitable-zone-of-a-nearby-star-129290">The habitable zone</a> is an area around a star where liquid water can exist on the surface of the planet and life may be able to emerge and thrive.</p>
<p>Unlike Earth, Kepler-186f is located far from the other planets in its solar system. As a result, these other planets have only a weak effect on its orbit and movement. So, Kepler-186f generally <a href="https://doi.org/10.3847/1538-3881/aabfd1">has a fixed obliquity</a>, similar to Earth. Even without a large moon, it doesn’t have wildly changing or unpredictable seasons like Mars.</p>
<p>Looking forward, more research into exoplanets will help scientists understand what seasons look like throughout the vast diversity of planets in the universe.</p><img src="https://counter.theconversation.com/content/216874/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Gongjie Li receives funding from NASA.</span></em></p>You might hate winter, but at least you know what to expect every year. Other planets have wobbly axes that lead to wild, unpredictable seasons.Gongjie Li, Assistant Professor of Physics, Georgia Institute of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2178612023-11-30T19:06:13Z2023-11-30T19:06:13ZMassive planet too big for its own sun pushes astronomers to rethink exoplanet formation<figure><img src="https://images.theconversation.com/files/562186/original/file-20231128-23-oz4tck.jpg?ixlib=rb-1.1.0&rect=0%2C8%2C1997%2C1488&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">LHS 3154b, a newly discovered massive planet that should be too big to exist. </span> <span class="attribution"><span class="source">The Pennsylvania State University</span></span></figcaption></figure><p>Imagine you’re a farmer searching for eggs in the chicken coop – but instead of a chicken egg, you find an ostrich egg, much larger than anything a chicken could lay.</p>
<p>That’s a little how <a href="https://scholar.google.com/citations?user=cSnTlM4AAAAJ&hl=en">our team</a> <a href="https://scholar.google.com/citations?user=lN5yvjMAAAAJ&hl=en">of astronomers</a> <a href="https://science.psu.edu/astrp/people/mmd6393">felt when we</a> <a href="https://doi.org/10.1126/science.abo0233">discovered a massive planet</a>, more than 13 times heavier than Earth, around a cool, dim red star, nine times less massive than Earth’s Sun, in 2023. </p>
<p>The smaller star, called an M star, is not only smaller than the Sun in Earth’s solar system, but it’s 100 times less luminous. Such a star should not have the necessary amount of material in its planet-forming disk to birth such a massive planet.</p>
<h2>The Habitable Zone Planet Finder</h2>
<p>Over the past decade, our team designed and built a new instrument at Penn State capable of detecting the light from these dim, cool stars at wavelengths beyond the sensitivity of the human eye – in the near-infrared – where such cool stars <a href="https://www.e-education.psu.edu/astro801/book/export/html/1755">emit most of their light</a>. </p>
<p>Attached to the 10-meter Hobby-Eberly Telescope in West Texas, our instrument, dubbed the <a href="https://hpf.psu.edu/">Habitable Zone Planet Finder</a>, can measure the subtle change in a star’s velocity as a planet gravitationally tugs on it. This technique, called the Doppler radial velocity technique, is <a href="https://theconversation.com/rarity-of-jupiter-like-planets-means-planetary-systems-exactly-like-ours-may-be-scarce-52116">great for detecting exoplanets</a>. </p>
<p>“<a href="https://exoplanets.nasa.gov/">Exoplanet</a>” is a combination of the words extrasolar and planet, so the term applies to any planet-sized body in orbit around a star that isn’t Earth’s Sun.</p>
<p>Thirty years ago, Doppler radial velocity observations enabled the discovery of <a href="https://exoplanets.nasa.gov/exoplanet-catalog/7001/51-pegasi-b/">51 Pegasi b</a>, the first known exoplanet orbiting a Sunlike star. In the ensuing decades, astronomers like us have improved this technique. These <a href="https://noirlab.edu/public/projects/neid/">increasingly more precise</a> measurements have an important goal: to enable the discovery of rocky planets in <a href="https://exoplanets.nasa.gov/search-for-life/habitable-zone/">habitable zones</a>, the regions around stars where liquid water can be sustained on the planetary surface. </p>
<p>The Doppler technique doesn’t yet have the capabilities to discover habitable zone planets the mass of the Earth around stars the size of the Sun. But the cool and dim M stars show a larger Doppler signature for the same Earth-size planet. The lower mass of the star leads to it getting tugged more by the orbiting planet. And the lower luminosity leads to a <a href="https://exoplanets.nasa.gov/resources/2255/what-is-the-habitable-zone/">closer-in habitable zone</a> and a shorter orbit, which also makes the planet easier to detect. </p>
<p>Planets around these smaller stars were the planets our team designed the Habitable Zone Planet Finder to discover. Our new discovery, <a href="https://doi.org/10.1126/science.abo0233">published in the journal Science</a>, of a massive planet orbiting closely around the cool dim M star LHS 3154 – the ostrich egg in the chicken coop – came as a real surprise.</p>
<h2>LHS 3154b: The planet that should not exist</h2>
<p><a href="https://theconversation.com/astronomers-have-learned-lots-about-the-universe-but-how-do-they-study-astronomical-objects-too-distant-to-visit-214320">Planets form in disks</a> composed of gas and dust. These disks pull together dust grains that grow into pebbles and eventually combine to form a solid planetary core. Once the core is formed, the planet can gravitationally pull in the solid dust, as well as surrounding gas such as hydrogen and helium. But it needs a lot of mass and materials to do this successfully. This way to form planets is called <a href="https://earthhow.com/planet-formation/">core accretion</a>.</p>
<p>A star as low mass as LHS 3154, nine times less massive than the Sun, should have a correspondingly low-mass planet forming disk. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/eSdZR4zT_UM?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">An artist’s rendering of LHS 3154b. Video Credit: Abby Minnich.</span></figcaption>
</figure>
<p>A typical disk around such a low-mass star should simply not have enough solid materials or mass to be able to make a core heavy enough to create such a planet. From computer simulations our team conducted, we concluded that such a planet needs a disk at least 10 times more massive than typically assumed <a href="https://doi.org/10.48550/arXiv.1608.03621">from direct observations of planet-forming disks</a>.</p>
<p>A different planet formation theory, <a href="https://astrobites.org/2011/02/28/planet-formation-at-wide-orbits-through-gravitational-instability/">gravitational instability</a> – where gas and dust in the disk undergo a direct collapse to form a planet – also struggles to explain the formation of such a planet without a very massive disk.</p>
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<h2>Planets around the most common stars</h2>
<p>Cool, dim M stars are <a href="https://www.stsci.edu/contents/newsletters/2020-volume-37-issue-01/how-well-do-we-understand-m-dwarfs">the most common stars in our galaxy</a>. In DC comics lore, <a href="https://theconversation.com/how-astronomers-could-find-the-real-planet-krypton-56646">Superman’s home world</a>, <a href="https://www.theguardian.com/culture/us-news-blog/2012/nov/05/neil-degrasse-tyson-superman-planet">planet Krypton, orbited an M dwarf star</a>. </p>
<p>Astronomers know, from discoveries made with Habitable Zone Planet Finder and other instruments, that giant planets in close-in orbits around the most massive M stars are <a href="https://doi.org/10.48550/arXiv.2303.00659">at least 10 times rarer</a> than those around Sunlike stars. And we know of no such massive planets in close orbits around the least massive M stars – until the discovery of LHS 3154b. </p>
<p>Understanding how planets form around our coolest neighbors will help us understand both how planets form in general and how rocky worlds around the most numerous types of stars form and evolve. This line of research could also help astronomers understand whether M stars are capable of supporting life.</p><img src="https://counter.theconversation.com/content/217861/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Suvrath Mahadevan receives external funding from NSF, NASA, and the Heising-Simons Foundation, as well as research funding and support from Penn State.
</span></em></p><p class="fine-print"><em><span>Guðmundur Kári Stefánsson receives funding from NSF, NASA and the Heising-Simons Foundation.</span></em></p><p class="fine-print"><em><span>Megan Delamer receives funding from NSF, NASA, and Heising-Simons Foundation. </span></em></p>A newly discovered planet that should be too big to have formed around a tiny star is throwing into question what researchers know about planet formation.Suvrath Mahadevan, Verne M. Willaman Professor of Astronomy & Astrophysics, Penn StateGuðmundur Kári Stefánsson, NASA Hubble Fellow, Department of Astrophysical Sciences, Princeton UniversityMegan Delamer, Graduate Student, Department of Astronomy, Penn StateLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2170122023-11-08T16:41:22Z2023-11-08T16:41:22ZHow we’re building the world’s biggest optical telescope to crack some of the greatest puzzles in science<figure><img src="https://images.theconversation.com/files/557968/original/file-20231107-25-fl42fz.jpg?ixlib=rb-1.1.0&rect=237%2C89%2C5185%2C3533&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">ESO’s Extremely Large Telescope.</span> <span class="attribution"><span class="source">ESO/wikipedia</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>Astronomers get to ask some of the most fundamental questions there are, ranging from whether we’re alone in the cosmos to what the nature of the mysterious dark energy and dark matter making up most of the universe is.</p>
<p>Now a large group of astronomers from all over the world is building the biggest optical telescope ever – the <a href="https://elt.eso.org/">Extremely Large Telescope (ELT)</a> — in Chile. Once construction is completed in 2028, it could provide answers that transform our knowledge of the universe. </p>
<hr>
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<p>With its 39-metre diameter primary mirror, the ELT will contain the largest, most perfect reflecting surface ever made. Its light-collecting power will exceed that of all other large telescopes combined, enabling it to detect objects millions of times fainter than <a href="https://supernova.eso.org/exhibition/0805/">the human eye can see</a>.</p>
<p>There are several reasons why we need such a telescope. Its incredible sensitivity will let it image some of the first galaxies ever formed, with light that has travelled for 13 billion years to reach the telescope. Observations of such distant objects may allow us to refine our understanding of cosmology and the nature of <a href="https://theconversation.com/dark-matter-should-we-be-so-sure-it-exists-heres-how-philosophy-can-help-184109">dark matter</a> and <a href="https://theconversation.com/the-experiments-trying-to-crack-physics-biggest-question-what-is-dark-energy-52917">dark energy</a>.</p>
<h2>Alien life</h2>
<p>The ELT may also offer an answer to the most fundamental question of all: are we alone in the universe? The ELT is expected to be the first telescope to track down Earth-like exoplanets — planets that orbit other stars but have a similar mass, orbit and proximity to their host as Earth. </p>
<p>Occupying the so-called Goldilocks zone, these Earth-like planets will orbit their star at just the right distance for water to neither boil nor freeze – providing the conditions for life to exist.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/557768/original/file-20231106-15-g3l1kl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Size comparison between the ELT and other telescope domes." src="https://images.theconversation.com/files/557768/original/file-20231106-15-g3l1kl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/557768/original/file-20231106-15-g3l1kl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=113&fit=crop&dpr=1 600w, https://images.theconversation.com/files/557768/original/file-20231106-15-g3l1kl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=113&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/557768/original/file-20231106-15-g3l1kl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=113&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/557768/original/file-20231106-15-g3l1kl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=142&fit=crop&dpr=1 754w, https://images.theconversation.com/files/557768/original/file-20231106-15-g3l1kl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=142&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/557768/original/file-20231106-15-g3l1kl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=142&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Size comparison between the ELT and other telescope domes.</span>
<span class="attribution"><span class="source">ESO/wikipeida</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>The ELT’s camera will have six times better resolution than that of the <a href="https://webb.nasa.gov/">James Webb Space Telescope</a>, allowing it to take the clearest images yet of exoplanets. But fascinating as these pictures will be, they will not tell the whole story.</p>
<p>To learn if life is likely to exist on an exoplanet, astronomers must complement imaging with spectroscopy. While images reveal shape, size and structure, spectra tell us about the speed, temperature and even the chemistry of astronomical objects.</p>
<p>The ELT will contain not one, but four spectrographs — instruments that disperse light into its constituent colours, much like the iconic prism on the Pink Floyd’s The <a href="https://theconversation.com/the-dark-side-of-the-moon-at-50-an-album-artwork-expert-on-pink-floyds-music-marketing-revolution-200932">Dark Side of the Moon</a> album cover.</p>
<p>Each about the size of a minibus, and carefully environmentally controlled for stability, these spectrographs underpin all of the ELT’s key science cases. For giant exoplanets, the <a href="https://elt.eso.org/instrument/HARMONI/">Harmoni instrument</a> will analyse light that has travelled through their atmospheres, looking for the signs of water, oxygen, methane, carbon dioxide and other gases that indicate the existence of life.</p>
<p>To detect much smaller Earth-like exoplanets, the more specialised <a href="https://elt.eso.org/instrument/ANDES/">Andes instrument</a> will be needed. With a cost of around €35 million (£30 million), Andes will be able to detect tiny changes in the wavelength of light.</p>
<p>From previous satellite missions, astronomers already have a good idea of where to look in the sky for exoplanets. Indeed, there have been several thousand confirmed or “candidate” exoplanets detected using <a href="https://theconversation.com/explainer-how-do-you-find-exoplanets-24153">the “transit method”</a>. Here, a space telescope stares at a patch of sky containing thousands of stars and looks for tiny, periodic dips in their intensities, caused when an orbiting planet passes in front of its star.</p>
<p>But Andes will use a different method to hunt for other Earths. As an exoplanet orbits its host star, <a href="https://www.eso.org/public/unitedkingdom/videos/eso1035g/">its gravity tugs on the star, making it wobble</a>. This movement is incredibly small; Earth’s orbit causes the Sun to oscillate at just 10 centimetres per second — the walking speed of a tortoise. </p>
<p>Just as the pitch of an ambulance siren rises and falls as it travels towards and away from us, the wavelength of light observed from a wobbling star increases and decreases as the planet traces out its orbit.</p>
<figure class="align-center ">
<img alt="Artist's impression of ELT." src="https://images.theconversation.com/files/557969/original/file-20231107-19-l8m44m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/557969/original/file-20231107-19-l8m44m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=426&fit=crop&dpr=1 600w, https://images.theconversation.com/files/557969/original/file-20231107-19-l8m44m.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=426&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/557969/original/file-20231107-19-l8m44m.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=426&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/557969/original/file-20231107-19-l8m44m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=535&fit=crop&dpr=1 754w, https://images.theconversation.com/files/557969/original/file-20231107-19-l8m44m.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=535&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/557969/original/file-20231107-19-l8m44m.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=535&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Artist’s impression of ELT.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Extremely_Large_Telescope#/media/File:ELT_concept.jpg">ESO/L. Calçada/wikipedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Remarkably, Andes will be able to detect this minuscule change in the light’s colour. Starlight, while essentially continuous (“white”) from the ultraviolet to the infrared, contains bands where atoms in the outer region of the star absorb specific wavelengths as the light escapes, appearing dark in the spectra. </p>
<p>Tiny shifts in the positions of these features — around 1/10,000th of a pixel on the Andes sensor — may, over months and years, reveal the periodic wobbles. This could ultimately help us to find an Earth 2.0.</p>
<p>At Heriot-Watt University, we are piloting <a href="https://www.hw.ac.uk/news/articles/2023/planet-hunting-systems-for-the-extremely.htm">the development of a laser system</a> known as a frequency comb, that will enable Andes to reach such exquisite precision. Like the millimetre ticks on a ruler, the laser will calibrate the Andes spectrograph by providing a spectrum of light structured as thousands of regularly spaced wavelengths.</p>
<p>This scale will remain constant over decades, mitigating the measurement errors that occur from environmental changes in temperature and pressure.</p>
<p>With the ELT’s construction cost coming in at €1.45 billion, some will question the value of the project. But astronomy has a significance that spans millennia and transcends cultures and national borders. It is only by looking far outside our Solar System that we can gain a perspective beyond the here and now.</p><img src="https://counter.theconversation.com/content/217012/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Derryck Reid receives funding from the UK Science and Technology Facilities Council (STFC).</span></em></p>From improving our understanding of dark matter to revealing the location of Earth 2.0, the Extremely Large Telescope promises answers to some of the biggest scientific questions of our time.Derryck Telford Reid, Professor of Physics, Heriot-Watt UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2157312023-10-18T16:17:31Z2023-10-18T16:17:31ZClouds of quartz detected high in a distant planet’s atmosphere – here’s what this tells us about other worlds<figure><img src="https://images.theconversation.com/files/554062/original/file-20231016-15-uqj0xs.png?ixlib=rb-1.1.0&rect=5%2C0%2C3828%2C2155&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Artists impression of what WASP-17b could look like, based on
data gathered by Mid-Infrared Instrument (MIRI) and other ground- and space-based
telescopes, including the Hubble and Spitzer space telescopes. </span> <span class="attribution"><span class="source">NASA, ESA, CSA, Ralf Crawford (STScI)</span></span></figcaption></figure><p><a href="https://www.britannica.com/science/quartz">Quartz</a>, also known as silica, is everywhere. This mineral is in the screen of the laptop or phone you’re reading this article on. It’s used to make computer chips, which are in everything from medical equipment to washing machines. It can be melted to <a href="https://en.wikipedia.org/wiki/Fused_quartz">produce glass</a>.</p>
<p>Chemically, quartz is silicon dioxide: one silicon atom attached to two oxygen atoms. It’s a major <a href="https://uwaterloo.ca/earth-sciences-museum/resources/detailed-rocks-and-minerals-articles/quartz#:%7E:text=Quartz%20is%20an%20almost%20pure,oxygen%20together%20with%20other%20elements.">component of the Earth’s crust</a>, the ground beneath our feet.</p>
<p>This remarkable material has <a href="https://iopscience.iop.org/article/10.3847/2041-8213/acfc3b">now been discovered</a> floating in the atmosphere of a giant planet 1,300 light-years from Earth.
This planet is called <a href="https://exoplanets.nasa.gov/exoplanet-catalog/5371/wasp-17-b/">WASP-17b</a> and belongs to a class of planet known as a “<a href="https://exoplanets.nasa.gov/resources/1040/hot-jupiter/">hot Jupiter</a>”. WASP-17b is an exoplanet, which is a world orbiting a star that’s not the Sun.</p>
<p>The new study provides an important insight into the sometimes extreme and unfamiliar conditions present on worlds around other stars. We think of quartz as a hard substance, but the heat and pressure on WASP-17b can transform this mineral into a gas. The crystals then form out of this gas in the upper atmosphere.</p>
<p>Much like Jupiter, it’s composed mainly of hydrogen and helium. However, it orbits close to its parent star, completing a full circuit (a year on WASP-17b) in just 3.7 Earth days. The proximity to its star super-heats WASP-17b to temperatures of over 1,500°C (2,700°F). This temperature is so high that most materials, such as rocks or ice, will exist on WASP-17b only as gases. </p>
<p>We made observations of the planet using Earth’s <a href="https://webb.nasa.gov/">largest space telescope, the James Webb Space Telescope (JWST)</a>. We looked at WASP-17b as it passed in front of its star from our point of view, a phenomenon <a href="https://exoplanets.nasa.gov/faq/31/whats-a-transit/">called a transit</a>. We then measured the starlight as it filtered through the planet’s atmosphere.</p>
<p>By breaking up that starlight <a href="https://exoplanets.nasa.gov/resources/58/isolating-a-planets-spectrum/">into different wavelengths</a>, we could see changes in how the atmosphere absorbs and interacts with that light. Each atom and molecule in the atmosphere imparts a unique fingerprint on the light, and we can use computer models to disentangle these fingerprints, linking them to particular chemical compounds. </p>
<h2>Extreme conditions</h2>
<p>Using <a href="https://jwst-docs.stsci.edu/jwst-mid-infrared-instrument">JWST’s Mid-Infrared Instrument (MIRI)</a>, which measures light at infrared wavelengths, we revealed evidence for very tiny quartz crystals (nanocrystals) forming high-altitude clouds in the atmosphere of WASP-17b.</p>
<p>The pressure where the quartz crystals form, high in the atmosphere, is only about one-thousandth of what we experience on Earth’s surface. Combined with the temperatures of around 1,500°C, the conditions allow solid crystals to form directly from gas, without going through a liquid phase first.</p>
<p>This shows us that other planetary systems like this one, for example, in which gas giant planets orbit close to their parent stars, can have quite different characteristics to our Solar System. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/554064/original/file-20231016-17-9btowm.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Transmission spectrum from WASP-17b." src="https://images.theconversation.com/files/554064/original/file-20231016-17-9btowm.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/554064/original/file-20231016-17-9btowm.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=384&fit=crop&dpr=1 600w, https://images.theconversation.com/files/554064/original/file-20231016-17-9btowm.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=384&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/554064/original/file-20231016-17-9btowm.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=384&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/554064/original/file-20231016-17-9btowm.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=482&fit=crop&dpr=1 754w, https://images.theconversation.com/files/554064/original/file-20231016-17-9btowm.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=482&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/554064/original/file-20231016-17-9btowm.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=482&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Measured transmission spectrum of WASP-17b from JWST MIRI. The purple line shows the modelled quartz clouds with the yellow line showing what it would look like without them.</span>
<span class="attribution"><span class="source">NASA, ESA, CSA, Ralf Crawford (STScI), data and models: Grant et al. 2023, Astrophysical Journal Letters</span></span>
</figcaption>
</figure>
<p>The fine quartz crystals in the atmosphere of WASP-17b, which measure just one millionth of a centimetre, can help us unravel more information about this exoplanet and the nature of its atmosphere. Potentially, it could provide us with a detailed understanding of the planet’s chemistry.</p>
<p>We have previously detected silicates in the atmospheres of <a href="https://www.nasa.gov/news-release/silicate-stardust-traces-histories-of-dust-in-the-galaxy/">stars</a>, astronomical objects called <a href="https://arxiv.org/abs/2209.00620">brown dwarfs</a> and <a href="https://arxiv.org/abs/2209.00620">giant young exoplanets</a>. However, these are often in the form of magnesium silicate and not pure silica. Silica can take on many forms depending on the additional atoms of material that contaminate it, slightly changing its properties. </p>
<p>Instead, on WASP-17b, we are seeing the likely building blocks of silicates in the form of tiny “seed” particles of pure silica absorbing and scattering the light, causing a spike in our measurements. </p>
<p>We combined these measurements with those from the <a href="https://hubblesite.org/home">Hubble Space Telescope</a>, which measured the planet at optical rather than infrared wavelengths. When we fed the data into computer models, they told us the atmospheric particles are just nanometres across, 10,000 times smaller than the width of a human hair.</p>
<p>The prevalence of silicates throughout the universe suggests they should be there in all exoplanets in some form or another, but in the exoplanets that can be most easily examined with current tools they have previously eluded our detection.</p>
<p>While exoplanets have captured the imaginations of scientists and the public alike, of the <a href="https://exoplanetarchive.ipac.caltech.edu/docs/counts_detail.html">some 5,500 known today</a>, only a fraction can be explored in detail. But advanced telescopes such as JWST are allowing us to find out more than ever before about worlds located tens, hundreds and thousands of light years away.</p><img src="https://counter.theconversation.com/content/215731/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Hannah Wakeford is an Associate Professor at the University of Bristol and receives funding from UK Research and Innovation (UKRI) under the UK government’s Horizon Europe funding guarantee formerly ERC Starting Grant (grant number EP/Y006313/1).
HRW acknowledges the significant harm caused to members of the LGBTQIA+ community in the Department of State and Nasa, while under the leadership of James Webb as Under Secretary of State and Nasa Administrator, respectively.</span></em></p>The atmosphere is a reflection of extreme conditions on the super-heated planet.Hannah Wakeford, Associate professor, University of BristolLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2154662023-10-11T15:14:41Z2023-10-11T15:14:41ZThe afterglow of an explosive collision between giant planets may have been detected in a far-off star system<figure><img src="https://images.theconversation.com/files/553243/original/file-20231011-25-y5wvfs.jpeg?ixlib=rb-1.1.0&rect=2%2C0%2C1914%2C1431&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A visualisation of the huge, glowing planetary body produced by a planetary collision.</span> <span class="attribution"><a class="source" href="https://www.eurekalert.org/multimedia/1001427">Mark Garlick</a>, <span class="license">Author provided</span></span></figcaption></figure><p>The afterglow of a massive collision between two giant planets may have been detected for the first time. The wreckage of the collision could eventually cool and form an entirely new planet. If the observation is confirmed, it provides an amazing opportunity to watch the birth of a new world in real time and open a window into how planets form.</p>
<p>In December 2021, astronomers watching an otherwise unremarkable sun-like star <a href="https://astronomerstelegram.org/?read=14879">saw it begin to flicker</a>. For a few months, the visible light (the light we can see with our eyes) from this star continued to change. At times it would almost disappear, before returning to its previous brightness. </p>
<p>The star, which sits roughly 1,800 light years from Earth, was given the identifier ASASSN-21qj, after the <a href="https://www.astronomy.ohio-state.edu/asassn/">ASASN-SN astronomy survey</a> that first observed the star’s dimming. </p>
<p>Seeing stars dim like this is not uncommon. It’s generally attributed to material passing between the star and Earth. ASASSN-21qj may just have been added to a growing list of similar observations had it not been for an amateur astronomer, <a href="https://science.nasa.gov/people/arttu-sainio/">Arttu Sainio</a>. Sainio pointed out on social media that some two and a half years before the star’s light was seen to fade, the emission of infrared light coming from its location rose by roughly 4%. </p>
<p>Infrared light is most strongly emitted by objects at relatively high temperatures of a few hundred degrees Celsius. This posed the questions: were these two observations related and, if so, what the heck was going on around ASASSN-21qj?</p>
<h2>Planetary cataclysm</h2>
<p>Publishing our findings <a href="https://www.nature.com/articles/s41586-023-06573-9">in Nature</a>, we propose that both sets of observations could be explained by a cataclysmic collision between two planets. Giant impacts, as such collisions are known, are thought to be common in the final stages of the formation of planets. They dictate the final sizes, compositions, and thermal states of planets and mould the orbits of objects in those planetary systems. </p>
<p>In our solar system, giant impacts are thought to be responsible for the <a href="https://science.nasa.gov/uranus/facts/">odd tilt of Uranus</a>, the <a href="https://science.nasa.gov/mercury/facts/">high density of Mercury</a> and the <a href="https://news.uchicago.edu/explainer/formation-earth-and-moon-explained#moonform">existence of Earth’s Moon</a>. However, until now, we had little direct evidence of giant impacts ongoing in the galaxy. </p>
<figure class="align-center ">
<img alt="Artist's impression of the WISE telescope." src="https://images.theconversation.com/files/553260/original/file-20231011-19-jdcjpm.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/553260/original/file-20231011-19-jdcjpm.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=337&fit=crop&dpr=1 600w, https://images.theconversation.com/files/553260/original/file-20231011-19-jdcjpm.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=337&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/553260/original/file-20231011-19-jdcjpm.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=337&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/553260/original/file-20231011-19-jdcjpm.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/553260/original/file-20231011-19-jdcjpm.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/553260/original/file-20231011-19-jdcjpm.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Nasa’s WISE telescope observed an increase in the infrared light coming from the star.</span>
<span class="attribution"><a class="source" href="https://photojournal.jpl.nasa.gov/catalog/PIA17254">NASA/JPL-Caltech</a></span>
</figcaption>
</figure>
<p>In order to explain the observations, a collision would have needed to release more energy in the first few hours after impact than would be emitted from the star. Material from the colliding bodies would have been superheated and melted, vaporised or both.</p>
<p>The impact would have formed a hot, glowing mass of material hundreds of times larger than the original planets. The infrared brightening of ASASSN-21qj was observed by <a href="https://www.jpl.nasa.gov/missions/wide-field-infrared-survey-explorer-wise">Nasa’s WISE space telescope</a>. WISE only looks at the star every 300 days or so, and probably missed the initial flash of light from the impact. </p>
<p>However, the expanded planetary body produced by the impact will take a long time, perhaps millions of years, to cool and shrink to something we might recognise as a new planet. Initially, when this “post-impact body” was at its greatest extent, the light emitted from it could still be as high as several percent of emission from the star. Such a body could have produced the infrared brightening that we saw.</p>
<p>The impact would also have ejected great plumes of debris into a range of different orbits around the star. A fraction of this debris would have been vaporised by the shock of the impact, later condensing to form clouds of tiny ice and rock crystals. Over time, some of this clumpy cloud of material passed between ASASSN-21qj and Earth, blocking out a fraction of the visible light from the star and producing the erratic dimming. </p>
<figure class="align-center ">
<img alt="Neptune." src="https://images.theconversation.com/files/553274/original/file-20231011-25-9485zg.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/553274/original/file-20231011-25-9485zg.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=599&fit=crop&dpr=1 600w, https://images.theconversation.com/files/553274/original/file-20231011-25-9485zg.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=599&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/553274/original/file-20231011-25-9485zg.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=599&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/553274/original/file-20231011-25-9485zg.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=753&fit=crop&dpr=1 754w, https://images.theconversation.com/files/553274/original/file-20231011-25-9485zg.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=753&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/553274/original/file-20231011-25-9485zg.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=753&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The planets may have been similar to Neptune in the solar system.</span>
<span class="attribution"><a class="source" href="https://photojournal.jpl.nasa.gov/catalog/PIA01492">NASA/JPL</a></span>
</figcaption>
</figure>
<p>If our interpretation of the events is correct, studying this star system could help us understand a key mechanism of planet formation. Even from the limited set of observations we have so far, we have learned some very interesting things. </p>
<p>Firstly, to emit the amount of energy observed, the post-impact body must have been many hundreds of times the size of Earth. To create a body that large, the planets that collided must each have been several times the mass of Earth – possibly as large as the <a href="https://www.lpi.usra.edu/opag/outer_planets.pdf">“ice giant”</a> planets Uranus and Neptune. </p>
<p>Secondly, we estimate the temperature of the post-impact body to be around 700°C. For the temperature to be that low, the colliding bodies could not have been entirely made of rock and metal. </p>
<h2>Ice giants</h2>
<p>The outer regions of at least one of the planets must have contained elements with low boiling temperatures, such as in water. We therefore think that we have seen a collision between two Neptune-like worlds that are rich in ice. </p>
<p>The delay that was seen between the emission of infrared light and the observation of debris crossing the star suggests that the collision took place quite far away from the star – further away than the Earth is from the Sun. Such a system, in which there are ice giants far from the star, is more similar to our solar system than to many of the tightly-packed planetary systems astronomers often observe around other stars.</p>
<p>The most exciting aspect of this is that we can continue to watch the system evolve for many decades and test our conclusions. Future observations, using telescopes such as <a href="https://webbtelescope.org/home">Nasa’s JWST</a>, will determine the sizes and compositions of particles in the debris cloud, identify the chemistry of the upper layers of the post-impact body and track how this hot mass of debris cools down. We may even see new moons emerge. </p>
<p>These observations can inform our theories, helping us understand how giant impacts shape planetary systems. So far the only examples we’ve had are the echoes of impacts in our own solar system. We will now be able to watch the birth of a new planet in real time.</p><img src="https://counter.theconversation.com/content/215466/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Simon Lock receives funding from the UK Natural Environment Research Council (grant NE/V014129/1).</span></em></p><p class="fine-print"><em><span>Zoe Leinhardt receives funding from UK Science and Technology Facilities Council (grant number ST/V000454/1). </span></em></p><p class="fine-print"><em><span>Matthew Kenworthy does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The discovery provides a way to study the birth of an entirely new planet in real time.Simon Lock, NERC Research Fellow, School of Earth Sciences, University of BristolMatthew Kenworthy, Associate professor in Astronomy, Leiden UniversityZoe Leinhardt, Associate Professor, School of Physics, University of BristolLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2135282023-09-15T17:36:07Z2023-09-15T17:36:07ZNASA report finds no evidence that UFOs are extraterrestrial<figure><img src="https://images.theconversation.com/files/548453/original/file-20230915-27-9mccw0.jpg?ixlib=rb-1.1.0&rect=7%2C14%2C4690%2C2810&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">NASA's UAP study team and newly appointed director of UAP research represent growing efforts to study and declassify UFO-related data. </span> <span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/f277d5676ab5460186317c9f8fd11427?ext=true">AP Photo/Terry Renn</a></span></figcaption></figure><p>NASA’s <a href="https://www.nasa.gov/feature/nasa-announces-unidentified-anomalous-phenomena-study-team-members/">independent study team</a> released its highly anticipated <a href="https://science.nasa.gov/science-pink/s3fs-public/atoms/files/UAP%20Independent%20Study%20Team%20-%20Final%20Report_0.pdf">report</a> on UFOs on Sept. 14, 2023. </p>
<p>In part to move beyond the <a href="https://www.politico.com/news/2022/05/17/pentagon-dod-ufos-00032929">stigma often attached to UFOs</a>, where military pilots fear ridicule or job sanctions if they report them, UFOs are now characterized by the U.S. government as UAPs, or unidentified anomalous phenomena.</p>
<p>Bottom line: The study team found no evidence that reported UAP observations are extraterrestrial.</p>
<p>I’m a <a href="https://www.as.arizona.edu/people/faculty/chris-impey">professor of astronomy</a> who has written extensively on <a href="https://www.cambridge.org/core/books/living-cosmos/11D69005D09D25581AE4E6684EC8A3C1">astrobiology</a> and the <a href="https://www.cambridge.org/core/books/talking-about-life/696F47F802931AE9021CA72083313579">scientists</a> who search for life in the universe. I have long been <a href="https://theconversation.com/im-an-astronomer-and-i-think-aliens-may-be-out-there-but-ufo-sightings-arent-persuasive-150498">skeptical of the claim</a> that UFOs represent visits by aliens to Earth.</p>
<h2>From sensationalism to science</h2>
<p>During a <a href="https://uk.sports.yahoo.com/video/nasa-announces-findings-ufo-report-160301583.html">press briefing</a>, NASA Administrator <a href="https://www.nasa.gov/feature/nasa-administrator-bill-nelson/">Bill Nelson</a> noted that NASA has scientific programs to search for <a href="https://mars.nasa.gov/msr/">traces of life on Mars</a> and the <a href="https://theconversation.com/to-search-for-alien-life-astronomers-will-look-for-clues-in-the-atmospheres-of-distant-planets-and-the-james-webb-space-telescope-just-proved-its-possible-to-do-so-184828">imprints of biology</a> in the atmospheres of exoplanets. He said he wanted to shift the UAP conversation from sensationalism to one of science.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1702321823692832843"}"></div></p>
<p>With this statement, Nelson was alluding to some of the more outlandish claims about UAPs and UFOs. At a <a href="https://theconversation.com/whistleblower-calls-for-government-transparency-as-congress-digs-for-the-truth-about-ufos-210435">congressional hearing in July</a>, former Pentagon intelligence officer <a href="https://www.space.com/us-hiding-evidence-alien-intelligence-ufo-whistleblower-claims">David Grusch testified</a> that the American government has been hiding evidence of crashed UAPs and alien biological specimens. <a href="https://www.politico.com/news/2023/07/28/pentagon-ufo-boss-congress-hearing-00108822">Sean Kirkpatrick</a>, head of the Pentagon office charged with investigating UAPs, has denied these claims.</p>
<p>And the same week NASA’s report came out, <a href="https://www.reuters.com/world/americas/mexican-congress-holds-hearing-ufos-featuring-purported-alien-bodies-2023-09-13/">Mexican lawmakers</a> were shown by journalist Jaime Maussan two tiny, 1,000-year-old bodies that he claimed were the remains of “non-human” beings. Scientists have called this <a href="https://www.livescience.com/62045-alien-mummies-explained.html">claim fraudulent</a> and say the mummies may have been looted from gravesites in Peru. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/ZAW1l5Q1e9c?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">A controversial journalist presented the Mexican government with 1,000-year-old bodies that he claimed were aliens.</span></figcaption>
</figure>
<h2>Conclusions from the report</h2>
<p>The NASA study team report sheds little light on whether some UAPs are extraterrestrial. In his comments, the chair of the study team, astronomer <a href="https://www.astro.princeton.edu/%7Edns/">David Spergel</a> stated that the team had seen “no evidence to suggest that UAPs are extraterrestrial in origin.” </p>
<p>Of the more than 800 unclassified sightings collected by the Department of Defense’s <a href="https://www.defense.gov/News/Releases/Release/Article/3100053/dod-announces-the-establishment-of-the-all-domain-anomaly-resolution-office/">All-domain Anomaly Resolution Office</a> and reported at the NASA panel’s <a href="https://interestingengineering.com/science/nasas-quest-for-unidentified-anomalies-among-ufos">first public meeting</a> back in May 2023, only “a small handful cannot be immediately identified as known human-made or natural phenomena,” according to <a href="https://science.nasa.gov/science-pink/s3fs-public/atoms/files/UAP%20Independent%20Study%20Team%20-%20Final%20Report_0.pdf">the report</a>. </p>
<p>Many of the <a href="https://www.nytimes.com/2022/10/28/us/politics/ufo-military-reports.html">recent sightings</a> can be attributed to weather balloons and airborne clutter. Historically, <a href="http://www.ianridpath.com/ufo/astroufo1.html">most UFOs are astronomical objects</a> such as meteors, <a href="https://cneos.jpl.nasa.gov/fireballs/intro.html">fireballs</a> and <a href="https://www.jsonline.com/story/news/local/2023/03/02/venus-and-jupiter-appeared-close-sparking-concern-of-ufos-or-aliens/69963097007/">the planet Venus</a>. </p>
<p>Some sightings represent <a href="https://www.nytimes.com/2022/10/28/us/politics/ufo-military-reports.html">surveillance operations</a> by foreign powers, which is why the U.S. military considers this <a href="https://theconversation.com/whistleblower-calls-for-government-transparency-as-congress-digs-for-the-truth-about-ufos-210435">a national security issue</a>.</p>
<p>The report does offer recommendations to NASA on how to move these investigations forward.</p>
<p>Most of the UAP data considered by the study team comes from U.S. military aircraft. Analysis of this data is “hampered by poor sensor calibration, the lack of multiple measurements, the lack of sensor metadata, and the lack of baseline data.” The ideal set of measurements would include optical imaging, infrared imaging, and radar data, but very few reports have all these.</p>
<p>The NASA study team described in the report the types of data that can shed more light on UAPs. The authors note the importance of reducing the stigma that can cause both military and commercial pilots to feel that they cannot freely report sightings. The stigma stems from decades of <a href="https://theconversation.com/are-we-alone-the-question-is-worthy-of-serious-scientific-study-98843">conspiracy theories tied to UFOs</a>. </p>
<p>The NASA study team suggests gathering sightings by commercial pilots using the Federal Aviation Administration and combining these with classified sightings not included in the report. Team members did not have security clearance, so they could look only at the subset of military sightings that were unclassified. At the moment, there is no anonymous nationwide UAP reporting mechanism for commercial pilots.</p>
<p>With access to these classified sightings and a structured mechanism for commercial pilots to report sightings, the <a href="https://www.aaro.mil/">All-domain Anomaly Resolution Office</a> – the military office charged with leading the analysis effort – could have the most data. </p>
<p><a href="https://www.nasa.gov/press-release/update-nasa-shares-uap-independent-study-report-names-director">NASA also announced</a> the appointment of a new director of research on UAPs. This position will oversee the creation of a database with resources to evaluate UAP sightings. </p>
<h2>Looking for a needle in a haystack</h2>
<p>Parts of the briefing resembled a primer on the scientific method. Using analogies, officials described the analysis process as looking for a needle in a haystack, or separating the wheat from the chaff. The officials said they needed a consistent and rigorous methodology for characterizing sightings, as a way of homing in on something truly anomalous.</p>
<p>Spergel said the study team’s goal was to characterize the hay – or the mundane phenomena – and subtract it to find the needle, or the potentially exciting discovery. He noted that artificial intelligence can help researchers comb through massive datasets to find rare, anomalous phenomena. AI is already being used this way in <a href="https://theconversation.com/ai-is-helping-astronomers-make-new-discoveries-and-learn-about-the-universe-faster-than-ever-before-204351">many areas of astronomy research</a>.</p>
<p>The speakers noted the importance of transparency. Transparency is important because UFOs have long been associated with <a href="https://www.nytimes.com/2021/06/24/us/politics/ufo-report-us-pentagon.html">conspiracy theories and government cover-ups</a>. Similarly, much of the discussion during the congressional <a href="https://www.cnn.com/2023/07/26/politics/ufo-house-hearing-congress/index.html">UAP hearing</a> in July focused on a need for transparency. All scientific data that NASA gathers is made public on various websites, and officials said they intend to do the same with the nonclassified UAP data. </p>
<p>At the <a href="https://uk.sports.yahoo.com/video/nasa-announces-findings-ufo-report-160301583.html">beginning of the briefing</a>, Nelson gave his opinion that there were perhaps a trillion instances of life beyond Earth. So, it’s plausible that there is intelligent life out there. But the report says that when it comes to UAPs, extraterrestrial life must be the hypothesis of last resort. It quotes Thomas Jefferson: “Extraordinary claims require extraordinary evidence.” That evidence does not yet exist.</p><img src="https://counter.theconversation.com/content/213528/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Impey receives funding from the National Science Foundation.</span></em></p>Months after a military officer made sensational claims about unexplained objects in the skies, NASA released a report loosely outlining a scientific approach for analyzing UAP reports.Chris Impey, University Distinguished Professor of Astronomy, University of ArizonaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2133942023-09-13T13:57:15Z2023-09-13T13:57:15ZPossible hints of life found on distant planet – how excited should we be?<figure><img src="https://images.theconversation.com/files/547762/original/file-20230912-19-lzosd4.jpeg?ixlib=rb-1.1.0&rect=5%2C0%2C3811%2C2160&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The exoplanet K2-18b might host a water ocean.</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/goddard/2023/webb-discovers-methane-carbon-dioxide-in-atmosphere-of-k2-18b">Credits: Illustration: NASA, CSA, ESA, J. Olmsted (STScI), Science: N. Madhusudhan (Cambridge University)</a></span></figcaption></figure><p>Data from the <a href="https://webb.nasa.gov/">James Webb Space Telescope</a> (JWST) has shown that an exoplanet around a star in the constellation Leo has some of the chemical markers that, on Earth, are associated with living organisms. But these are vague indications. So how likely is it that this exoplanet harbours alien life?</p>
<p>Exoplanets are worlds that orbit stars other than the Sun. The planet in question is named <a href="http://www.exoplanetkyoto.org/exohtml/K2-18.html">K2-18b</a>. It’s so named because it was the first planet found to orbit the red dwarf star K2-18. There is a K2-18c as well – the second planet to be discovered. The star itself is dimmer and cooler than the Sun, meaning that, to get the same level of light as we do on Earth, the planet would need to be much closer to its star than we are. </p>
<p>The system is roughly 124 light years away, which is close in astronomical terms. So what are conditions like on this exoplanet? This is a difficult question to answer. We have telescopes and techniques powerful enough to tell us what the star is like, and how far away the exoplanet is, but we can’t capture direct images of the planet. We can work out a few basics, however. </p>
<p>Working out how much light hits K2-18b is important for assessing the planet’s potential for life. K2-18b orbits closer to its star than Earth does: it’s at roughly 16% of the distance from Earth to the Sun. Another measurement we need is the star’s power output: the total amount of energy it radiates per second. K2-18’s power output is 2.3% that of the Sun. </p>
<p>Using geometry, we can work out that K2-18b receives about 1.22 kilowatts (kW) in solar power per square metre. <a href="https://www.sws.bom.gov.au/Educational/2/1/12">This is similar</a> to the 1.36 kW of incoming light we receive on Earth. Although there’s less energy coming from K2-18, it evens out because the planet is closer. So far, so good. However, the incoming light calculation doesn’t take into account clouds or how reflective the planet’s surface is.</p>
<figure class="align-center ">
<img alt="JWST" src="https://images.theconversation.com/files/548036/original/file-20230913-19-odwob3.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/548036/original/file-20230913-19-odwob3.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/548036/original/file-20230913-19-odwob3.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/548036/original/file-20230913-19-odwob3.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/548036/original/file-20230913-19-odwob3.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/548036/original/file-20230913-19-odwob3.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/548036/original/file-20230913-19-odwob3.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Artist’s impression of the James Webb Space Telescope (JWST).</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/feature/ames/webb">NASA</a></span>
</figcaption>
</figure>
<p>When we consider life on other planets, a popular term to use is the <a href="https://exoplanets.nasa.gov/search-for-life/habitable-zone/">habitable zone</a>, which means that at an average surface temperature, water will be in a liquid state – as this condition is considered essential for life. In 2019, the Hubble Space Telescope determined that K2-18b showed signs of <a href="https://www.nature.com/articles/s41550-019-0878-9#change-history">water vapour</a>, suggesting that liquid water would be present on the surface. It is currently thought that there are large oceans on the planet.</p>
<p>This caused a ripple of excitement at the time, but without further evidence it was just an interesting result. Now we have reports that JWST has identified carbon dioxide, methane and – possibly – the compound dimethyl sulfide (DMS) <a href="https://www.nasa.gov/goddard/2023/webb-discovers-methane-carbon-dioxide-in-atmosphere-of-k2-18b">in the atmosphere</a>. The tentative detection of DMS is significant because it is only produced on Earth by <a href="https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/dimethyl-sulfide">algae</a>. We currently know of no way it can be naturally produced without a life-form.</p>
<h2>Is there life on K2-18b?</h2>
<p>All these indications seem to suggest that K2-18b might be the place to go to find alien life. It is not quite as simple as that, though, as we have no idea how accurate the results are. The method used to determine what is in the atmosphere of an exoplanet involves light from a different source (usually a star or galaxy) passing through the edge of the atmosphere that is then observed by us. Any chemical compounds will <a href="https://webbtelescope.org/contents/media/images/01FEE26XVSM851DHPVCE1KB4S2">absorb light in specific wavelengths</a> which can then be identified. </p>
<p>Imagine it as looking at a light bulb through a glass tumbler. You can see through it perfectly when empty. If you fill it with water, you can still see through pretty well, but there are some optical effects and colouration, which are the equivalent of hydrogen and dust clouds in space. Now imagine you poured in red food dye – this might be the equivalent of the main chemical constituent in a planet’s atmosphere. </p>
<p>But most atmospheres are made up of many chemicals. The equivalent of looking for any one of them would be like pouring 50 – likely many more – coloured food dyes, in different amounts, into your tumbler and trying to identify how much of one particular colour is present. It is an incredibly difficult task with plenty of room for subjective assessment and errors. In addition, the light going through the atmosphere contains a signal of the star’s chemical constituents – further complicating the analysis.</p>
<figure class="align-center ">
<img alt="Atmospheric composition of K2-18 b." src="https://images.theconversation.com/files/547763/original/file-20230912-17-ds12z4.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/547763/original/file-20230912-17-ds12z4.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/547763/original/file-20230912-17-ds12z4.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/547763/original/file-20230912-17-ds12z4.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/547763/original/file-20230912-17-ds12z4.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/547763/original/file-20230912-17-ds12z4.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/547763/original/file-20230912-17-ds12z4.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">The chemical composition of K2-18b’s atmosphere.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/goddard/2023/webb-discovers-methane-carbon-dioxide-in-atmosphere-of-k2-18b">Credits: Illustration: NASA, CSA, ESA, R. Crawford (STScI), J. Olmsted (STScI), Science: N. Madhusudhan (Cambridge University)</a></span>
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<p>Only a few years ago there was a surge of interest in <a href="https://www.nytimes.com/2020/09/14/science/venus-life-clouds.html">whether life existed on Venus</a>, as observations had indicated the presence of phosphine gas, which can be produced by microbes. </p>
<p>However, this finding was later successfully refuted by <a href="https://arxiv.org/pdf/2010.09761.pdf">several studies</a>. If there can be confusion about what is in the atmosphere of a planet that’s just next door, in astronomical terms, it’s easy to see why analysing a planet that’s many times further away is a difficult task.</p>
<h2>What can we take from this?</h2>
<p>The chances of life on exoplanet K2-18b are low but not impossible. These results will likely not change anybody’s opinions or beliefs about extraterrestrial life. Instead, they do demonstrate the advancing ability to look into worlds that are not our own and find more information. </p>
<figure class="align-center ">
<img alt="Rho Ophiuchi" src="https://images.theconversation.com/files/548021/original/file-20230913-21-su4cro.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/548021/original/file-20230913-21-su4cro.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=562&fit=crop&dpr=1 600w, https://images.theconversation.com/files/548021/original/file-20230913-21-su4cro.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=562&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/548021/original/file-20230913-21-su4cro.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=562&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/548021/original/file-20230913-21-su4cro.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=706&fit=crop&dpr=1 754w, https://images.theconversation.com/files/548021/original/file-20230913-21-su4cro.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=706&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/548021/original/file-20230913-21-su4cro.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=706&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">JWST image of Rho Ophiuchi, the closest star-forming region to Earth.</span>
<span class="attribution"><a class="source" href="https://webbtelescope.org/contents/media/images/2023/128/01H449193V5Q4Q6GFBKXAZ3S03?news=true">NASA, ESA, CSA, STScI, Klaus Pontoppidan (STScI)</a></span>
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<p>The power of JWST is not only in producing incredible pictures, but in providing <a href="https://webbtelescope.org/contents/news-releases/2023/news-2023-103.html">more detailed</a> and accurate data on celestial objects themselves. Knowing which exoplanets host water and which do not could provide information on how the Earth formed. </p>
<p>Studying the atmospheres of gas giant exoplanets can inform the study of similar worlds in the Solar System, such as Jupiter and Saturn. And identifying levels of CO2 indicates how an extreme greenhouse effect might affect a planet. This is the real power of studying the composition of planetary atmospheres.</p><img src="https://counter.theconversation.com/content/213394/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ian Whittaker does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The results are intriguing, but analysing the atmospheres of exoplanets is no easy task.Ian Whittaker, Senior Lecturer in Physics, Nottingham Trent UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2134582023-09-13T07:13:57Z2023-09-13T07:13:57ZSigns of life? Why astronomers are excited about carbon dioxide and methane in the atmosphere of an alien world<figure><img src="https://images.theconversation.com/files/547922/original/file-20230913-23-zphpi7.jpeg?ixlib=rb-1.1.0&rect=28%2C5%2C3805%2C2149&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">NASA / CSA / ESA / J. Olmsted (STScI) / Science: N. Madhusudhan (Cambridge University)</span></span></figcaption></figure><p>Are we alone? This question is nearly as old as humanity itself. Today, this question in astronomy focuses on finding life beyond our planet. Are we, as a species, and as a planet, alone? Or is there life somewhere else?</p>
<p>Usually the question inspires visions of weird, green versions of humans. However, life is more than just us: animals, fish, plants and even bacteria are all the kinds of things we seek signs of in space.</p>
<p>One thing about life on Earth is that it leaves traces in the chemical makeup of the atmosphere. So traces like that, which are visible from a long way away, are something we look for when we’re hunting aliens. </p>
<p>Scientists in the United Kingdom and the United States <a href="https://arxiv.org/abs/2309.05566">have just reported</a> some very interesting chemical traces in the atmosphere of a planet called K2-18b, which is about 124 light-years from Earth. In particular, they may have detected a substance which on Earth is only produced by living things. </p>
<h2>Meet exoplanet K2-18b</h2>
<p>K2-18b is an interesting exoplanet – a planet that orbits another star. Discovered in 2015 by the Kepler Space Telescope’s K2 mission, it is a type of planet called a sub-Neptune. As you probably guessed, these are smaller than Neptune in our own Solar System.</p>
<p>The planet is about eight and a half times heavier than Earth, and orbits a type of star called a red dwarf, which is much cooler than our Sun. However, K2-18b orbits much closer to its star than Neptune does – in what we call the habitable zone. This is the area that is not too hot and not too cold, where liquid water can exist (instead of freezing to ice or boiling into steam).</p>
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<p>Earth is what is called a rocky planet (for obvious reasons), but sub-Neptunes are gas planets, with much larger atmospheres containing lots of hydrogen and helium. Their atmosphere can also contain other elements.</p>
<p>Which brings us to the excitement around K2-18b. </p>
<h2>How to fingerprint an atmosphere</h2>
<p>The planet was first discovered by the Kepler Space Telescope, which was monitoring distant stars and hoping for planets to pass in front of them. When a planet does pass between us and a star, the star becomes momentarily dimmer – which is what tells us a planet is there.</p>
<p>By measuring how big the dip in brightness is, how long it takes for the planet to pass in front of the star, and how often it happens, we can work out the size and orbit of the planet. This technique is great at finding planets, but it doesn’t tell us about their atmospheres – which is a key piece of information to understand if they hold life or are habitable.</p>
<p>NASA’s James Webb Space Telescope – the big space telescope launched at the end of 2021 – has now observed and measured the atmosphere of this exoplanet. </p>
<p>The telescope did this by measuring the colour of light so finely, it can detect traces of specific atoms and molecules. This process, called spectroscopy, is like measuring the fingerprint of elements. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/547994/original/file-20230913-15-44y44s.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A chart showing the absorption of different wavelengths of light by the atmosphere of K2-18b, and which wavelengths correspond to different substances in the atmosphere." src="https://images.theconversation.com/files/547994/original/file-20230913-15-44y44s.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/547994/original/file-20230913-15-44y44s.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/547994/original/file-20230913-15-44y44s.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/547994/original/file-20230913-15-44y44s.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/547994/original/file-20230913-15-44y44s.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/547994/original/file-20230913-15-44y44s.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/547994/original/file-20230913-15-44y44s.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>
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<span class="caption">The atmosphere of the exoplanet K2-18b showed strong signs of methane and carbon dioxide, as well as a weak indication of dimethyl sulfide.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/goddard/2023/webb-discovers-methane-carbon-dioxide-in-atmosphere-of-k2-18b">NASA / CSA / ESA / R. Crawford (STScI) / J. Olmsted (STScI) / N. Madhusudhan (Cambridge University)</a></span>
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</figure>
<p>Each element and molecule has its own colour signature. If you can look at the colour signature, you can do a bit of detective work, and work out what elements or compounds are in the planet.</p>
<p>While the planet does not have its own light, astronomers waited for when K2-18b passed in front of its star, and measured the starlight as it went through the planet’s atmosphere, allowing the team to detect fingerprints of substances in the atmosphere.</p>
<h2>Alien marine farts?</h2>
<p>The new study found a lot of carbon dioxide and methane. This is interesting as this is like what is found on Earth, Mars, and Venus in our Solar System – rather than Neptune.</p>
<p>However, it also found a small amount of dimethyl sulfide. Dimethyl sulfide is an interesting molecule, made up of carbon, hydrogen, and sulfur.</p>
<p>On Earth, it’s generally a bit smelly. But it’s also closely linked to life.</p>
<p>The only process we know that creates dimethyl sulfide on our planet is life. In particular, marine life and plankton emit it in the form of flatulence.</p>
<p>So yes, scientists are excited by the potential idea of alien marine farts. If it is real. And linked to life.</p>
<h2>The search continues</h2>
<p>While on Earth, dimethyl sulfide is linked to life, on other planets it may somehow be related to geological or chemical processes.</p>
<p>After all, K2-18b is something like Neptune – a planet we do not really know a lot about. Just last month, researchers discovered that <a href="https://www.sciencedirect.com/science/article/abs/pii/S0019103523002440">clouds on Neptune are strongly linked</a> to the Sun’s 11-year cycle of activity. We have a lot to learn about planets and their atmospheres.</p>
<p>Also, the measurement of dimethyl sulfide is very subtle – not nearly as strong as the carbon dioxide and methane. This means more detailed measurements, to improve the strength of the signal, are required. </p>
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Read more:
<a href="https://theconversation.com/the-webb-telescope-has-released-its-very-first-exoplanet-image-heres-what-we-can-learn-from-it-189876">The Webb telescope has released its very first exoplanet image – here's what we can learn from it</a>
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<p>Other telescopes may need to join the effort. Instruments on the Very Large Telescope in Chile are able to measure the atmospheres of planets around other stars – as is a new instrument called Veloce on the Anglo Australian Telescope at Siding Spring Observatory in Australia.</p>
<p>And new space telescopes, like Europe’s PLATO which is under construction, will also help us get a better look at alien atmospheres.</p>
<p>So while the signs of dimethyl sulfide on K2-18b may not be linked to life, they are still an exciting prospect. There is plenty more to explore.</p><img src="https://counter.theconversation.com/content/213458/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Brad E Tucker receives funding from the Australian Research Council and Australian Capital Territory Government. </span></em></p>The James Webb Space Telescope has detected key carbon-bearing molecules on the potential ocean world K2-18b, including tantalising hints of a substance produced by tiny plankton on Earth.Brad E Tucker, Astrophysicist/Cosmologist, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2078302023-07-13T20:05:32Z2023-07-13T20:05:32ZWe’ve detected a star barely hotter than a pizza oven – the coldest ever found to emit radio waves<figure><img src="https://images.theconversation.com/files/534486/original/file-20230628-29-v7zc7u.png?ixlib=rb-1.1.0&rect=673%2C3%2C1365%2C1015&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/LSR_J1835%2B3259#/media/File:Powerful_Auroras_Found_at_Brown_Dwarf_(19641761103).jpg, https://www.pexels.com/photo/stars-1257860/">Composite: Chuck Carter / Gregg Hallinan (Caltech) and Philippe Donn (Pexels)</a></span></figcaption></figure><p>We have identified the coldest star ever found to produce radio waves – a brown dwarf too small to be a regular star and too massive to be a planet.</p>
<p>Our findings, published today in the <a href="https://iopscience.iop.org/article/10.3847/2041-8213/ace188">Astrophysical Journal Letters</a>, detail the detection of pulsed radio emission from this star, called WISE J0623.</p>
<p>Despite being roughly the same size as Jupiter, this dwarf star has a magnetic field much more powerful than our Sun’s. It’s joining the ranks of just a small handful of known ultra-cool dwarfs that generate repeating radio bursts.</p>
<h2>Making waves with radio stars</h2>
<p>With over 100 billion stars in our Milky Way galaxy, it might surprise you astronomers have detected radio waves from fewer than 1,000 of them. One reason is because radio waves and optical light are generated by different physical processes.</p>
<p>Unlike the thermal (heat) radiation coming from the hot outer layer of a star, radio emission is the result of particles called electrons speeding up and interacting with magnetised gas around the star.</p>
<p>Because of this we can use the radio emission to learn about the atmospheres and magnetic fields of stars, which ultimately could tell us more about the potential for life to survive on any planets that orbit them. </p>
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<a href="https://theconversation.com/the-webb-telescope-has-released-its-very-first-exoplanet-image-heres-what-we-can-learn-from-it-189876">The Webb telescope has released its very first exoplanet image – here's what we can learn from it</a>
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<p>Another factor is the sensitivity of radio telescopes which, historically, could only detect sources that were very bright. </p>
<p>Most of the detections of stars with radio telescopes over the past few decades have been flares from highly active stars or energetic bursts from the interaction of binary (two) star systems. But with the improved sensitivity and coverage of new radio telescopes, we can detect less luminous stars such as cool <a href="https://astronomy.swin.edu.au/cosmos/B/brown+dwarf">brown dwarfs</a>.</p>
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<img alt="Images of star, brown dwarfs and planets comparing their masses." src="https://images.theconversation.com/files/532586/original/file-20230619-23-l44kho.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/532586/original/file-20230619-23-l44kho.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/532586/original/file-20230619-23-l44kho.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/532586/original/file-20230619-23-l44kho.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/532586/original/file-20230619-23-l44kho.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/532586/original/file-20230619-23-l44kho.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/532586/original/file-20230619-23-l44kho.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Mass comparison of stars, brown dwarfs and planets (not to scale).</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech</span></span>
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<p>WISE J0623 has a temperature of around 700 Kelvin. That’s equivalent to 420°C or about the same temperature as a commercial pizza oven – pretty hot by human standards, but quite cold for a star.</p>
<p>These cool brown dwarfs can’t sustain the levels of atmospheric activity that generates radio emission in hotter stars, making stars like WISE J0623 harder for radio astronomers to find.</p>
<h2>How did we find the coolest radio star?</h2>
<p>This is where the new <a href="https://www.csiro.au/askap">Australian SKA Pathfinder</a> radio telescope comes in. This is located at Inyarrimanha Ilgari Bundara, the CSIRO Murchison Radio-astronomy Observatory in Western Australia, and has an array of 36 antennas, each 12 metres in diameter.</p>
<p>The telescope can see large regions of the sky in a single observation and has already surveyed nearly 90% of it. From this survey we have identified close to three million radio sources, most of which are <a href="https://theconversation.com/some-black-holes-are-anything-but-black-and-weve-found-more-than-75-000-of-the-brightest-ones-169938">active galactic nuclei</a> – black holes at the centres of distant galaxies.</p>
<p>So how do we tell which of these millions of sources are radio stars? One way is to look for something called “circularly polarised radio emission”.</p>
<p><iframe id="tc-infographic-881" class="tc-infographic" height="400px" src="https://cdn.theconversation.com/infographics/881/69a906363dc78254a227172888b6ecc69ffa3723/site/index.html" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>Radio waves, like other electromagnetic radiation, oscillate as they move through space. Circular polarisation occurs when the electric field of the wave rotates in a spiralling or corkscrew motion as it propagates.</p>
<p>For our search we used the fact that the only astronomical objects known to emit a significant fraction of circularly polarised light are stars and <a href="https://theconversation.com/weve-used-a-new-technique-to-discover-the-brightest-radio-pulsar-outside-our-own-galaxy-180508">pulsars</a> (rotating neutron stars).</p>
<p>By selecting only highly circularly polarised radio sources from <a href="https://theconversation.com/weve-mapped-a-million-previously-undiscovered-galaxies-beyond-the-milky-way-take-the-virtual-tour-here-148442">an earlier survey of the sky</a>, we found WISE J0623. You can see using the slider in the figure above that once you switch to polarised light, there is only one object visible.</p>
<h2>What does this discovery mean?</h2>
<p>Was the radio emission from this star some rare one-off event that happened during our 15 minute observation? Or could we detect it again?</p>
<p><a href="https://ui.adsabs.harvard.edu/abs/2008ApJ...684..644H">Previous research</a> has shown that radio emission detected from other cool brown dwarfs was tied to their magnetic fields and generally repeated at the same rate as the star rotates.</p>
<p>To investigate this we did follow-up observations with CSIRO’s <a href="https://www.csiro.au/en/about/facilities-collections/atnf/australia-telescope-compact-array">Australian Telescope Compact Array</a>, and with the <a href="https://www.sarao.ac.za/science/meerkat/">MeerKAT</a> telescope operated by the South African Radio Astronomy Observatory.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/532595/original/file-20230619-17-n1mp6a.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/532595/original/file-20230619-17-n1mp6a.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/532595/original/file-20230619-17-n1mp6a.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=519&fit=crop&dpr=1 600w, https://images.theconversation.com/files/532595/original/file-20230619-17-n1mp6a.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=519&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/532595/original/file-20230619-17-n1mp6a.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=519&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/532595/original/file-20230619-17-n1mp6a.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=652&fit=crop&dpr=1 754w, https://images.theconversation.com/files/532595/original/file-20230619-17-n1mp6a.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=652&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/532595/original/file-20230619-17-n1mp6a.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=652&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The bottom panel shows the brightness of polarised light over time. The top panel shows emission at different radio frequencies.</span>
<span class="attribution"><span class="source">Author Provided.</span></span>
</figcaption>
</figure>
<p>These new observations showed that every 1.9 hours there were two bright, circularly polarised bursts from WISE J0623 followed by a half an hour delay before the next pair of bursts.</p>
<p>WISE J0623 is the coolest brown dwarf detected via radio waves and is the first case of persistent radio pulsations. Using this same search method, we expect future surveys to detect even cooler brown dwarfs.</p>
<p>Studying these missing link dwarf stars will help improve our understanding of stellar evolution and how giant exoplanets (planets in other solar systems) develop magnetic fields.</p>
<hr>
<p><em>We acknowledge the Wajarri Yamatji as the traditional owners of the Murchison Radio-astronomy Observatory site where Australian SKA Pathfinder is located, and the Gomeroi people as the traditional owners of the Australian Telescope Compact Array site.</em></p><img src="https://counter.theconversation.com/content/207830/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Tara Murphy works for the University of Sydney and receives funding from the Australian Research Council.</span></em></p><p class="fine-print"><em><span>Kovi Rose 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 detected the coldest star ever found to emit radio waves using the Australian SKA Pathfinder telescope.Kovi Rose, Astrophysics PhD Candidate, University of SydneyTara Murphy, Professor, University of SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2060552023-07-12T12:39:24Z2023-07-12T12:39:24ZA new, thin-lensed telescope design could far surpass James Webb – goodbye mirrors, hello diffractive lenses<figure><img src="https://images.theconversation.com/files/536371/original/file-20230707-21-kxopc5.jpeg?ixlib=rb-1.1.0&rect=44%2C44%2C1209%2C599&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A light, cheap space telescope design would make it possible to put many individual units in space at once.</span> <span class="attribution"><span class="source">Katie Yung, Daniel Apai /University of Arizona and AllThingsSpace /SketchFab</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>Astronomers have discovered more than <a href="https://exoplanets.nasa.gov/discovery/exoplanet-catalog/">5,000 planets outside of the solar system</a> to date. The grand question is whether <a href="https://theconversation.com/to-search-for-alien-life-astronomers-will-look-for-clues-in-the-atmospheres-of-distant-planets-and-the-james-webb-space-telescope-just-proved-its-possible-to-do-so-184828">any of these planets are home to life</a>. To find the answer, astronomers will likely need <a href="https://nap.nationalacademies.org/catalog/26141/pathways-to-discovery-in-astronomy-and-astrophysics-for-the-2020s">more powerful telescopes</a> than exist today.</p>
<p>I am an <a href="https://scholar.google.com/citations?user=2SCIYjIAAAAJ&hl=en&oi=ao">astronomer who studies astrobiology</a> and planets around distant stars. For the last seven years, I have been co-leading a team that is developing a new kind of space telescope that could collect a hundred times more light than the <a href="https://theconversation.com/the-most-powerful-space-telescope-ever-built-will-look-back-in-time-to-the-dark-ages-of-the-universe-169603">James Webb Space Telescope</a>, the biggest space telescope ever built.</p>
<p>Almost all space telescopes, including Hubble and Webb, collect light using mirrors. Our proposed telescope, the <a href="https://nautilus-array.space/">Nautilus Space Observatory</a>, would replace large, heavy mirrors with a novel, thin lens that is much lighter, cheaper and easier to produce than mirrored telescopes. Because of these differences, it would be possible to launch many individual units into orbit and create a powerful network of telescopes.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/536355/original/file-20230707-21-3gvtcx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A blue planet with clouds." src="https://images.theconversation.com/files/536355/original/file-20230707-21-3gvtcx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/536355/original/file-20230707-21-3gvtcx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/536355/original/file-20230707-21-3gvtcx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/536355/original/file-20230707-21-3gvtcx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/536355/original/file-20230707-21-3gvtcx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/536355/original/file-20230707-21-3gvtcx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/536355/original/file-20230707-21-3gvtcx.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">Exoplanets, like TOI-700d shown in this artist’s conception, are planets beyond our solar system and are prime candidates in the search for life.</span>
<span class="attribution"><a class="source" href="https://www.jpl.nasa.gov/spaceimages/images/largesize/PIA23408_hires.jpg">NASA's Goddard Space Flight Center</a></span>
</figcaption>
</figure>
<h2>The need for larger telescopes</h2>
<p>Exoplanets – planets that orbit stars other than the Sun – are prime targets in the search for life. Astronomers need to use giant space telescopes that collect huge amounts of light to <a href="https://exoplanets.nasa.gov/discovery/missions/#first-planetary-disk-observed">study these faint and faraway objects</a>. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/536356/original/file-20230707-23-pdn1e5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A massive circular gold mirror with people standing in the foreground." src="https://images.theconversation.com/files/536356/original/file-20230707-23-pdn1e5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/536356/original/file-20230707-23-pdn1e5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=899&fit=crop&dpr=1 600w, https://images.theconversation.com/files/536356/original/file-20230707-23-pdn1e5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=899&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/536356/original/file-20230707-23-pdn1e5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=899&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/536356/original/file-20230707-23-pdn1e5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1130&fit=crop&dpr=1 754w, https://images.theconversation.com/files/536356/original/file-20230707-23-pdn1e5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1130&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/536356/original/file-20230707-23-pdn1e5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1130&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 James Webb Space Telescope is just barely able to search exoplanets for signs of life.</span>
<span class="attribution"><a class="source" href="http://jwst.nasa.gov/multimedia.html">NASA</a></span>
</figcaption>
</figure>
<p>Existing telescopes can detect exoplanets as small as Earth. However, it takes a lot more sensitivity to begin to learn about the chemical composition of these planets. Even Webb is just barely powerful enough to search <a href="https://doi.org/10.3847/1538-3881/ab21e0">certain exoplanets for clues of life</a> – namely <a href="https://theconversation.com/to-search-for-alien-life-astronomers-will-look-for-clues-in-the-atmospheres-of-distant-planets-and-the-james-webb-space-telescope-just-proved-its-possible-to-do-so-184828">gases in the atmosphere</a>. </p>
<p>The James Webb Space Telescope cost more than <a href="https://www.gao.gov/products/gao-18-273">US$8 billion and took over 20 years to build</a>. The next flagship telescope is not expected to fly before 2045 and is estimated to <a href="https://www.science.org/content/article/nasa-unveils-initial-plan-multibillion-dollar-telescope-find-life-alien-worlds">cost $11 billion</a>. These ambitious telescope projects are always expensive, laborious and produce a single powerful – but very specialized – observatory.</p>
<h2>A new kind of telescope</h2>
<p>In 2016, aerospace giant <a href="https://www.northropgrumman.com">Northrop Grumman</a> invited me and 14 other professors and NASA scientists – all experts on exoplanets and the search for extraterrestrial life – to Los Angeles to answer one question: What will exoplanet space telescopes look like in 50 years?</p>
<p>In our discussions, we realized that a major bottleneck preventing the construction of more powerful telescopes is the challenge of making larger mirrors and getting them into orbit. To bypass this bottleneck, a few of us came up with the idea of revisiting an old technology called diffractive lenses. </p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/536361/original/file-20230707-29-i85svw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A cross section of two lenses, with the one on the left showing a jagged surface and the one on the right a rounded surface." src="https://images.theconversation.com/files/536361/original/file-20230707-29-i85svw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/536361/original/file-20230707-29-i85svw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=897&fit=crop&dpr=1 600w, https://images.theconversation.com/files/536361/original/file-20230707-29-i85svw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=897&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/536361/original/file-20230707-29-i85svw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=897&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/536361/original/file-20230707-29-i85svw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1127&fit=crop&dpr=1 754w, https://images.theconversation.com/files/536361/original/file-20230707-29-i85svw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1127&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/536361/original/file-20230707-29-i85svw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1127&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Diffractive lenses, left, are much thinner compared to similarly powerful refractive lenses, right.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Fresnel_lens#/media/File:Fresnel_lens.svg">Pko/Wikimedia Commons</a></span>
</figcaption>
</figure>
<p>Conventional lenses use refraction to focus light. <a href="https://theconversation.com/can-rainbows-form-in-a-circle-fun-facts-on-the-physics-of-rainbows-202952">Refraction is when light changes direction</a> as it passes from one medium to another – it is the reason light bends when it enters water. In contrast, diffraction is when light bends around corners and obstacles. A cleverly arranged pattern of steps and angles on a glass surface can form a diffractive lens. </p>
<p>The first such lenses were invented by the French scientist Augustin-Jean Fresnel in 1819 to provide lightweight lenses for <a href="https://wwnorton.com/books/9780393350890">lighthouses</a>. Today, similar diffractive lenses can be found in many small-sized consumer optics – from <a href="https://global.canon/en/v-square/34.html">camera lenses</a> to <a href="https://doi.org/10.1889/1.2206112">virtual reality headsets</a>. </p>
<p>Thin, simple diffractive lenses are <a href="http://cplire.ru:8080/2902/1/OGRW_2014_Proceedings.pdf#page=77">notorious for their blurry images</a>, so they have never been used in astronomical observatories. But if you could improve their clarity, using diffractive lenses instead of mirrors or refractive lenses would allow a space telescope to be much cheaper, lighter and larger.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/536359/original/file-20230707-17-kdihhg.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A person holding a round, thin piece of glass." src="https://images.theconversation.com/files/536359/original/file-20230707-17-kdihhg.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/536359/original/file-20230707-17-kdihhg.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=389&fit=crop&dpr=1 600w, https://images.theconversation.com/files/536359/original/file-20230707-17-kdihhg.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=389&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/536359/original/file-20230707-17-kdihhg.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=389&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/536359/original/file-20230707-17-kdihhg.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=488&fit=crop&dpr=1 754w, https://images.theconversation.com/files/536359/original/file-20230707-17-kdihhg.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=488&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/536359/original/file-20230707-17-kdihhg.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=488&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">One of the benefits of diffractive lenses is that they can remain thin while increasing in diameter.</span>
<span class="attribution"><span class="source">Daniel Apai/University of Arizona</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>A thin, high-resolution lens</h2>
<p>After the meeting, I returned to the University of Arizona and decided to explore whether modern technology could produce diffractive lenses with better image quality. Lucky for me, <a href="https://profiles.arizona.edu/person/milster">Thomas Milster</a> – one of the world’s leading experts on diffractive lens design – works in the building next to mine. We formed a team and got to work.</p>
<p>Over the following two years, our team invented a new type of diffractive lens that required new manufacturing technologies to etch a complex pattern of tiny grooves onto a piece of clear glass or plastic. The specific pattern and shape of the cuts focuses incoming light to a single point behind the lens. The new design produces a <a href="https://doi.org/10.1364/OSAC.410187">near-perfect quality image</a>, far better than previous diffractive lenses. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/536358/original/file-20230707-25-gj9ryc.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A triangular piece of glass with subtle etchings reflecting in the light." src="https://images.theconversation.com/files/536358/original/file-20230707-25-gj9ryc.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/536358/original/file-20230707-25-gj9ryc.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/536358/original/file-20230707-25-gj9ryc.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/536358/original/file-20230707-25-gj9ryc.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/536358/original/file-20230707-25-gj9ryc.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/536358/original/file-20230707-25-gj9ryc.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/536358/original/file-20230707-25-gj9ryc.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A diffractive lens bends light using etchings and patterns on its surface.</span>
<span class="attribution"><span class="source">Daniel Apai/University of Arizona</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Because it is the surface texture of the lens that does the focusing, not the thickness, you can easily make the lens bigger while <a href="https://doi.org/10.1364/FIO.2020.JTu7A.1">keeping it very thin and lightweight</a>. Bigger lenses collect more light, and low weight means <a href="https://doi.org/10.3847/1538-3881/ab2631">cheaper launches to orbit</a> – both great traits for a space telescope.</p>
<p>In August 2018, our team produced the first prototype, a 2-inch (5-centimeter) diameter lens. Over the next five years, we further improved the image quality and increased the size. We are now completing a 10-inch (24-cm) diameter lens that will be more than 10 times lighter than a conventional refractive lens would be.</p>
<h2>Power of a diffraction space telescope</h2>
<p>This new lens design makes it possible to rethink how a space telescope might be built. In 2019, our team published a concept called the <a href="https://doi.org/10.3847/1538-3881/ab2631">Nautilus Space Observatory</a>. </p>
<p>Using the new technology, our team thinks it is possible to build a 29.5-foot (8.5-meter) diameter lens that would be only about 0.2 inches (0.5 cm) thick. The lens and support structure of our new telescope could weigh around 1,100 pounds (500 kilograms). This is more than three times lighter than a Webb–style mirror of a similar size and would be bigger than Webb’s 21-foot (6.5-meter) diameter mirror. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/536353/original/file-20230707-21-pbljxz.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A spherical object in space with a lens on one side." src="https://images.theconversation.com/files/536353/original/file-20230707-21-pbljxz.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/536353/original/file-20230707-21-pbljxz.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/536353/original/file-20230707-21-pbljxz.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/536353/original/file-20230707-21-pbljxz.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/536353/original/file-20230707-21-pbljxz.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/536353/original/file-20230707-21-pbljxz.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/536353/original/file-20230707-21-pbljxz.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The thin lens allowed the team to design a lighter, cheaper telescope, which they named the Nautilus Space Observatory.</span>
<span class="attribution"><span class="source">Daniel Apai/University of Arizona</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>The lenses have other benefits, too. First, they are <a href="https://doi.org/10.1117/12.2633573">much easier and quicker</a> <a href="https://theconversation.com/how-do-you-build-a-mirror-for-one-of-the-worlds-biggest-telescopes-49927">to fabricate than mirrors</a> and can be made en masse. Second, lens-based telescopes work well even when not aligned perfectly, making these telescopes easier to <a href="https://doi.org/10.1117/12.2633760">assemble</a> and fly in space than mirror-based telescopes, which require extremely precise alignment.</p>
<p>Finally, since a single Nautilus unit would be light and relatively cheap to produce, it would be possible to put dozens of them into orbit. Our current design is in fact not a single telescope, but a constellation of 35 individual telescope units.</p>
<p>Each individual telescope would be an independent, highly sensitive observatory able to collect more light than Webb. But the real power of Nautilus would come from turning all the individual telescopes toward a single target. </p>
<p>By combining data from all the units, Nautilus’ light-collecting power would equal a telescope nearly 10 times larger than Webb. With this powerful telescope, astronomers could search hundreds of exoplanets for atmospheric gases that may <a href="https://theconversation.com/to-search-for-alien-life-astronomers-will-look-for-clues-in-the-atmospheres-of-distant-planets-and-the-james-webb-space-telescope-just-proved-its-possible-to-do-so-184828">indicate extraterrestrial life</a>.</p>
<p>Although the Nautilus Space Observatory is still a long way from launch, our team has made a lot of progress. We have shown that all aspects of the technology work in small-scale prototypes and are now focusing on building a 3.3-foot (1-meter) diameter lens. Our next steps are to send a small version of the telescope to the edge of space on a high-altitude balloon.</p>
<p>With that, we will be ready to propose a revolutionary new space telescope to NASA and, hopefully, be on the way to exploring hundreds of worlds for signatures of life.</p><img src="https://counter.theconversation.com/content/206055/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Daniel Apai receives funding from NASA, NSF, and the Gordon and Betty Moore Foundation. He works for The University of Arizona.</span></em></p>Space telescopes are limited in size due to the difficulties and cost of getting into orbit. By revamping an old optical technology, researchers are working on a lightweight and thin telescope design.Daniel Apai, Associate Dean for Research and Professor of Astronomy and Planetary Sciences, University of ArizonaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2086492023-06-28T20:04:03Z2023-06-28T20:04:03ZAstronomers puzzled by ‘planet that shouldn’t exist’<figure><img src="https://images.theconversation.com/files/534458/original/file-20230627-17-bpm2lk.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C1920%2C1080&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Julian Baum</span></span></figcaption></figure><p>The search for planets outside our Solar System – exoplanets – is one of the most rapidly growing fields in astronomy. Over the past few decades, more than 5,000 exoplanets have been detected and astronomers now estimate that on average there is at least one planet per star in our galaxy.</p>
<p>Many current research efforts aim at detecting Earth-like planets suitable for life. These endeavours focus on so-called “main sequence” stars like our Sun – stars which are powered by fusing hydrogen atoms into helium in their cores, and remain stable for billions of years. More than 90% of all known exoplanets so far have been detected around main-sequence stars.</p>
<p>As part of an international team of astronomers, we studied a star that looks much like our Sun will in billions of years’ time, and found it has a planet which by all rights it should have devoured. In <a href="https://www.nature.com/articles/s41586-023-06029-0">research</a> published today in Nature, we lay out the puzzle of this planet’s existence – and propose some possible solutions.</p>
<h2>A glimpse into our future: red giant stars</h2>
<p>Just like humans, stars undergo changes as they age. Once a star has used up all its hydrogen in the core, the core of the star shrinks and the outer envelope expands as the star cools. </p>
<p>In this “red giant” phase of evolution, stars can grow to more than 100 times their original size. When this happens to our Sun, in about 5 billion years, we expect it will grow so large it will engulf Mercury, Venus, and possibly Earth.</p>
<p>Eventually, the core becomes hot enough for the star to begin fusing helium. At this stage the star shrinks back to about 10 times its original size, and continues stable burning for tens of millions of years.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-how-do-you-find-exoplanets-24153">Explainer: how do you find exoplanets?</a>
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</em>
</p>
<hr>
<p>We know of hundreds of planets orbiting red giant stars. One of these is called <a href="https://exoplanets.nasa.gov/exoplanet-catalog/7100/8-ursae-minoris-b/">8 Ursae Minoris b</a>, a planet with around the mass of Jupiter in an orbit that keeps it only about half as far from its star as Earth is from the Sun.</p>
<p>The planet was discovered in 2015 by a team of Korean astronomers using the “Doppler wobble” technique, which measures the gravitational pull of the planet on the star. In 2019, the International Astronomical Union <a href="https://www.nameexoworlds.iau.org/_files/ugd/6358ac_5eebee4eba4f41b7a9f6201123673a24.pdf">dubbed</a> the star Baekdu and the planet Halla, after the tallest mountains on the Korean peninsula.</p>
<h2>A planet that should not be there</h2>
<p>Analysis of new data about Baekdu collected by NASA’s Transiting Exoplanet Survey Satellite (<a href="https://www.nasa.gov/tess-transiting-exoplanet-survey-satellite/">TESS</a>) space telescope has yielded a surprising discovery. Unlike other red giants we have found hosting exoplanets on close-in orbits, Baekdu has already started fusing helium in its core.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/nasas-planet-hunting-spacecraft-tess-is-now-on-its-mission-to-search-for-new-worlds-94291">NASA's planet-hunting spacecraft TESS is now on its mission to search for new worlds</a>
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</em>
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<p>Using the techniques of <a href="https://exoplanets.nasa.gov/news/1516/symphony-of-stars-the-science-of-stellar-sound-waves/">asteroseismology, which studies waves inside stars</a>, we can determine what material a star is burning. For Baekdu, the frequencies of the waves unambiguously showed it has commenced burning helium in its core.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/534474/original/file-20230628-19-njdov.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/534474/original/file-20230628-19-njdov.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/534474/original/file-20230628-19-njdov.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=331&fit=crop&dpr=1 600w, https://images.theconversation.com/files/534474/original/file-20230628-19-njdov.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=331&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/534474/original/file-20230628-19-njdov.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=331&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/534474/original/file-20230628-19-njdov.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=416&fit=crop&dpr=1 754w, https://images.theconversation.com/files/534474/original/file-20230628-19-njdov.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=416&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/534474/original/file-20230628-19-njdov.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=416&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Sound waves inside a star can be used to determine whether it is burning helium.</span>
<span class="attribution"><span class="source">Gabriel Perez Diaz / Instituto de Astrofisica de Canarias</span></span>
</figcaption>
</figure>
<p>The discovery was puzzling: if Baekdu is burning helium, it should have been much bigger in the past – so big it should have engulfed the planet Halla. How is it possible Halla survived?</p>
<p>As is often the case in scientific research, the first course of action was to rule out the most trivial explanation: that Halla never really existed. </p>
<p>Indeed, some apparent discoveries of planets orbiting red giants using the Doppler wobble technique have later been shown to be illusions <a href="https://ui.adsabs.harvard.edu/abs/2018AJ....155..120H/abstract">created by long-term variations in the behaviour of the star itself</a>. </p>
<p>However, follow-up observations ruled out such a false-positive scenario for Halla. The Doppler signal from Baekdu has remained stable over the last 13 years, and close study of other indicators showed no other possible explanation for the signal. Halla is real – which returns us to the question of how it survived engulfment. </p>
<h2>Two stars become one: a possible survival scenario</h2>
<p>Having confirmed the existence of the planet, we arrived at two scenarios which could explain the situation we see with Baekdu and Halla. </p>
<p>At least half of all stars in our galaxy did not form in isolation like our Sun, but are part of binary systems. If Baekdu once was a binary star, Halla may have never faced the danger of engulfment. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/534475/original/file-20230628-23-52qepf.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/534475/original/file-20230628-23-52qepf.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=509&fit=crop&dpr=1 600w, https://images.theconversation.com/files/534475/original/file-20230628-23-52qepf.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=509&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/534475/original/file-20230628-23-52qepf.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=509&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/534475/original/file-20230628-23-52qepf.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=640&fit=crop&dpr=1 754w, https://images.theconversation.com/files/534475/original/file-20230628-23-52qepf.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=640&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/534475/original/file-20230628-23-52qepf.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=640&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">If the star Baekdu used to be a binary, there are two scenarios which can explain the survival of the planet Halla.</span>
<span class="attribution"><span class="source">Brooks G. Bays, Jr, SOEST/University of Hawai'i</span></span>
</figcaption>
</figure>
<p>A merger of these two stars may have prevented the expansion of either star to a size large enough to engulf planet Halla. If one star became a red giant on its own, it would have engulfed Halla – however, if it merged with a companion star it would jump straight to the helium-burning phase without getting big enough to reach the planet. </p>
<p>Alternatively, Halla may be a relatively newborn planet. The violent collision between the two stars may have produced a cloud of gas and dust from which the planet could have formed. In other words, the planet Halla may be a recently born “second generation” planet. </p>
<p>Whichever explanation is correct, the discovery of a close-in planet orbiting a helium-burning red giant star demonstrates that nature finds ways for exoplanets to appear in places where we might least expect them. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/534470/original/file-20230627-35262-ufsunt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An illustration of a planet in a ring of dust and debris around a star." src="https://images.theconversation.com/files/534470/original/file-20230627-35262-ufsunt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/534470/original/file-20230627-35262-ufsunt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/534470/original/file-20230627-35262-ufsunt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/534470/original/file-20230627-35262-ufsunt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/534470/original/file-20230627-35262-ufsunt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/534470/original/file-20230627-35262-ufsunt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/534470/original/file-20230627-35262-ufsunt.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">The planet Halla may have formed from debris created by the merger of two stars.</span>
<span class="attribution"><span class="source">W. M. Keck Observatory / Adam Makarenko</span></span>
</figcaption>
</figure><img src="https://counter.theconversation.com/content/208649/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Daniel Huber receives funding from the Australian Research Council (ARC), the National Aeronautics and Space Administration (NASA), the National Science Foundation (NSF), and the Sloan Foundation. He is also affiliated with the University of Hawaiʻi. </span></em></p>The planet Halla looks like it should have been devoured by its host star, a red giant called Baekdu – but a secret in the star’s past may hold the answer to the planet’s present.Daniel Huber, Astronomer, University of SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2052652023-05-10T12:28:10Z2023-05-10T12:28:10ZAstronomers just saw a star eat a planet – an astrophysicist on the team explains the first-of-its-kind discovery<figure><img src="https://images.theconversation.com/files/525217/original/file-20230509-17-8m0pr7.jpg?ixlib=rb-1.1.0&rect=0%2C137%2C3460%2C2017&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">New research shows that the destructive merging of a star and a planet expels huge amounts of gas, as shown in this artist's impression.</span> <span class="attribution"><a class="source" href="https://www.nature.com/articles/d41586-023-01385-3">K. Miller/R. Hurt (Caltech/IPAC)</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>For the first time, astronomers have captured images that show a star consuming one of its planets. The star, named ZTF SLRN-2020, is located in the Milky Way galaxy, in the constellation Aquila. As the star swallowed its planet, the star brightened to 100 times its normal level, allowing the 26-person team of astronomers I worked with to <a href="https://doi.org/10.1038/s41586-023-05842-x">detect this event as it happened</a>.</p>
<p><a href="https://itc.cfa.harvard.edu/people/morgan-macleod">I am a theoretical astrophysicist</a>, and I developed the computer models that our team uses to interpret the data we collect from telescopes. Although we only see the effects on the star, not the planet directly, our team is confident that the event we witnessed was a star swallowing its planet. Witnessing such an event for the first time has confirmed the long-standing assumption that stars swallow their planets and has illuminated how this fascinating process plays out.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/524944/original/file-20230508-247807-drmefx.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A white domed building at sunset." src="https://images.theconversation.com/files/524944/original/file-20230508-247807-drmefx.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/524944/original/file-20230508-247807-drmefx.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/524944/original/file-20230508-247807-drmefx.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/524944/original/file-20230508-247807-drmefx.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/524944/original/file-20230508-247807-drmefx.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/524944/original/file-20230508-247807-drmefx.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/524944/original/file-20230508-247807-drmefx.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Zwicky Transient Facility in Southern California is one of the observatories that captured the flash of light caused by the star consuming its planet.</span>
<span class="attribution"><a class="source" href="https://www.ztf.caltech.edu/multimedia.html#">Caltech/Palomar</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
</figure>
<h2>Finding a flash in the dynamic night sky</h2>
<p>The team I work with searches for the bursts of light and gas that occur when two stars merge into a bigger, single star. To do this, we have been using data from the <a href="https://www.ztf.caltech.edu/">Zwicky Transient Facility</a>, a telescope located on Palomar Mountain in Southern California. It takes nightly images of broad swaths of the sky, and astronomers can then compare these images to find stars that change in brightness over time, or what are called astronomical transients.</p>
<p>Finding stars that change in brightness isn’t the challenge – it’s sorting out the cause behind any specific change to a star. As my colleague <a href="https://space.mit.edu/people/de-kishalay/">Kishalay De</a> likes to say, “There are plenty of things in the sky that go boom.” The trick to identifying stellar mergers is to combine visible light – like the data collected at Palomar – with infrared data from <a href="https://www.nasa.gov/mission_pages/WISE/main/index.html">NASA’s WISE space telescope</a>, which has been surveying the entire sky for the past decade.</p>
<p>In 2020, the star ZTF SLRN-2020 suddenly became 100 times brighter in visible light over just 10 days. It then slowly started to fade back toward its normal brightness. About nine months before, the same object started to emit a lot of infrared light, too. This is exactly what it looks like when two stars merge together, with one critical difference – everything was scaled down. The brightness and total energy of this event were about a thousand times lower than any of the merging stellar pairs astronomers had found to date. </p>
<h2>When a star swallows its planets</h2>
<p>The idea that stars could engulf some of their planets has been a long-standing assumption in astronomy. Astronomers have long known that when stars <a href="https://www.teachastronomy.com/textbook/Star-Birth-and-Death/Nuclear-Reactions-in-Main-Sequence-Stars/">run out of hydrogen in their cores</a>, they get brighter and begin to <a href="https://www.teachastronomy.com/textbook/Star-Birth-and-Death/Red-Giants/">increase in size</a>.</p>
<p>Many planets have orbits that are <a href="https://doi.org/10.5281/zenodo.6368226">smaller than the eventual size of their parent stars</a>. So, when a star runs out of fuel and starts to expand, the planets nearby are inevitably consumed.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/525243/original/file-20230509-43918-15gi7w.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A graph showing two lines increasing to a peak near the same time with one increasing over a much shorter period of time." src="https://images.theconversation.com/files/525243/original/file-20230509-43918-15gi7w.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/525243/original/file-20230509-43918-15gi7w.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=305&fit=crop&dpr=1 600w, https://images.theconversation.com/files/525243/original/file-20230509-43918-15gi7w.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=305&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/525243/original/file-20230509-43918-15gi7w.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=305&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/525243/original/file-20230509-43918-15gi7w.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=383&fit=crop&dpr=1 754w, https://images.theconversation.com/files/525243/original/file-20230509-43918-15gi7w.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=383&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/525243/original/file-20230509-43918-15gi7w.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=383&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The star ZTF SLRN-2020 increased in brightness in both visible and infrared wavelengths of light, with the peak occurring on May 24, 2020.</span>
<span class="attribution"><span class="source">M. MacLeod</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Interpreting a stellar flash</h2>
<p>In the ZTF SLRN-2020 outburst, our team never saw the planet itself, only the brightening from when the star absorbed the planet. This is where combining theoretical models with the observational data allowed us to understand what the telescopes captured.</p>
<p>The merging of two stars into a single, bigger star is a <a href="https://doi.org/10.3847/1538-4357/835/2/282">dramatic event</a> that throws matter out into the stars’ surroundings. A large part of my career has focused on <a href="https://doi.org/10.3847/1538-4357/aacf08">modeling the way stellar gas moves</a> and crashes into itself and is expelled in these moments of intense interaction. </p>
<p>My work has shown that the total mass of matter ejected in a merging event is proportional to the <a href="https://doi.org/10.3847/1538-4357/ab89b6">size of the objects involved in the merger</a>. Merge two equally large stars and you see a huge disturbance. Merge one star with a much smaller companion and the event might throw out a tiny fraction of the total mass of the stars.</p>
<p>The energy released during ZTF SLRN-2020’s outburst was a thousand times lower than typical for a two-star merger. This implies that the object that merged with the star weighed a thousand times less than a normal star. This clue pointed our team toward a gas giant planet – like Jupiter in our own solar system, which weighs roughly a thousand times less than the Sun.</p>
<p>Compared to Jupiter, however, this planet must have <a href="https://doi.org/10.48550/arXiv.2210.15848">orbited much closer to the star</a>, with one revolution around the star only taking a few days. <a href="https://doi.org/10.1146/annurev-astro-082214-122246">About 1% of stars</a> share this configuration of a large planet orbiting incredibly close to its parent star. </p>
<p>Further, I think that this configuration of a big planet close to its star is important in generating the event our team saw. My past research suggests that smaller planets – or ones in more-distant orbits that only get consumed once a star has grown massively in size – might be <a href="https://doi.org/10.3847/2041-8213/aaa5fa">swallowed without a detectable flash</a>.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/nDi0JIRDXI0?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The planet around ZTF SLRN-2020 skimmed the stellar surface before eventually falling into the star.</span></figcaption>
</figure>
<h2>Learning from the real thing</h2>
<p>From our data and modeling for ZTF SLRN-2020, our team has been able to paint a much clearer picture of how stars and planets merge. First, the planet skims across the surface of the star for many years, slowly heating up and expelling material <a href="https://doi.org/10.1038/d41586-023-01385-3">from the star’s atmosphere</a>. As this gas expands and cools, some of it forms molecules and dust. This cloud of dust gives the star a progressively redder color and emits increasing amounts of infrared radiation.</p>
<p>In the case of ZTF SLRN-2020, the orbit of the planet shrank slowly at first, then faster and faster as the planet smashed through the denser layers of the star’s atmosphere. Eventually, in just a few final days, the planet plunged below the surface of the star and was torn apart by the heat and force of the collision. This rapid injection of energy supplied heat to power ZTF SLRN-2020’s 10-day, hundredfold increase in brightness. Following this climactic moment, the star began to fade, telling our team that the planet-swallowing process was over and that the star was beginning to go back to business as usual. </p>
<p>While the destructive event has passed, there is still much to be learned. Next week our team will start analyzing data from the <a href="https://webb.nasa.gov/">James Webb Space Telescope</a> in the hopes of learning about the chemistry of the gas that now surrounds ZTF SLRN-2020.</p><img src="https://counter.theconversation.com/content/205265/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Morgan MacLeod is grateful for support from the Clay Postdoctoral Fellowship at the Smithsonian Astrophysical Observatory and from the National Science Foundation. </span></em></p>Stars begin to expand when they run out of fuel and can become thousands of times larger, consuming any planets in the way. For the first time, astronomers have witnessed one such event.Morgan MacLeod, Postdoctoral Fellow in Theoretical Astrophysics, Harvard UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2037522023-04-13T20:08:42Z2023-04-13T20:08:42ZAstronomers have directly detected a massive exoplanet. The method could transform the search for life beyond Earth<figure><img src="https://images.theconversation.com/files/520725/original/file-20230413-14-kps5s1.jpg?ixlib=rb-1.1.0&rect=29%2C44%2C4877%2C3185&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>Finding life on other planets might well be the holy grail of astronomy, but the hunt for suitable host planets that can sustain life is a resource-intensive task.</p>
<p>The search for exoplanets (planets outside our Solar System) involves competing for time on Earth’s biggest telescopes – yet the hit rate of this search can be disappointingly low. </p>
<p>In a <a href="http://www.science.org/doi/10.1126/science.abo6192">new study</a> published today in Science, I and my international team of colleagues have combined different search techniques to discover a new giant planet. It could change the way we try to image planets in the future.</p>
<h2>Imaging planets is no small feat</h2>
<p>To satisfy our curiosity about our place in the universe, astronomers have developed many techniques to search for planets orbiting other stars. Perhaps the simplest of these is called direct imaging. But it’s not easy.</p>
<p>Direct imaging involves attaching a powerful camera to a large telescope and trying to detect light emitted, or reflected, from a planet. Stars are bright, and planets are dim, so it’s akin to searching for fireflies dancing around a spotlight. </p>
<p>It’s no surprise only about 20 planets have been found with this technique to date.</p>
<p>Yet direct imaging is of great value. It helps shed light on a planet’s atmospheric properties, such as its temperature and composition, in a way other detection techniques can’t.</p>
<h2>HIP99770b: a new gas giant</h2>
<p>Our direct imaging of a new planet, named HIP99770b, reveals a hot, giant and moderately cloudy planet. It orbits its star at a distance that falls somewhere between the orbital distances of Saturn and Uranus around our Sun. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/520712/original/file-20230413-26-kg7d4d.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/520712/original/file-20230413-26-kg7d4d.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/520712/original/file-20230413-26-kg7d4d.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=362&fit=crop&dpr=1 600w, https://images.theconversation.com/files/520712/original/file-20230413-26-kg7d4d.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=362&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/520712/original/file-20230413-26-kg7d4d.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=362&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/520712/original/file-20230413-26-kg7d4d.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=455&fit=crop&dpr=1 754w, https://images.theconversation.com/files/520712/original/file-20230413-26-kg7d4d.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=455&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/520712/original/file-20230413-26-kg7d4d.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=455&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 HIP99770 star is almost 14 times brighter than the Sun. But since its planet has an orbit larger than Saturn’s, the planet receives a similar amount of energy as Jupiter does from the Sun.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>With about 15 times the mass of Jupiter, HIP99770b is a real giant. However, it’s also more than 1,000°C, so it’s not a good prospect for a habitable world.</p>
<p>What the HIP99770 system does offer is an analogy to our own Solar System. It has a cold “debris disk” of ice and rock far out from the star, akin to a scaled-up version of the Kuiper Belt in our Solar System. </p>
<p>The main difference is that the HIP99770 system is dominated by one high-mass planet, rather than several smaller ones.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/520697/original/file-20230413-28-yujzdr.gif?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/520697/original/file-20230413-28-yujzdr.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/520697/original/file-20230413-28-yujzdr.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=599&fit=crop&dpr=1 600w, https://images.theconversation.com/files/520697/original/file-20230413-28-yujzdr.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=599&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/520697/original/file-20230413-28-yujzdr.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=599&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/520697/original/file-20230413-28-yujzdr.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=753&fit=crop&dpr=1 754w, https://images.theconversation.com/files/520697/original/file-20230413-28-yujzdr.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=753&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/520697/original/file-20230413-28-yujzdr.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=753&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Images of the HIP99770 system, taken with exoplanet imager SCExAO (Subaru Coronagraphic Extreme Adaptive Optics Project) coupled with data from the CHARIS instrument (Coronagraphic High-Resolution Imager and Spectrograph).</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>Searching with the light on</h2>
<p>We reached our findings by first detecting hints of a planet via indirect detection methods. We noticed the star was wobbling in space, which hinted at the presence of a planet in the vicinity with a large gravitational pull.</p>
<p>This motivated our direct imaging efforts; we were no longer searching in the dark.</p>
<p>The extra data came from the European Space Agency’s <a href="https://www.esa.int/Science_Exploration/Space_Science/Gaia">Gaia spacecraft</a>, which has been measuring the positions of nearly one billion stars since 2014. Gaia is sensitive enough to detect tiny variations of a star’s motion through space, such as those caused by planets. </p>
<p>We also supplemented these data with measurements from Gaia’s predecessor, Hipparcos. In total, we had 25 years’ worth of “astrometric” (positional) data to work with.</p>
<p>Previously, researchers <a href="https://iopscience.iop.org/article/10.3847/0004-637X/831/2/136/meta">have used indirect methods</a> to guide imaging that has discovered companion stars, but not planets.</p>
<p>It’s not their fault: massive stars such as HIP99770 – which is almost twice the mass of our Sun – are reluctant to give up their secrets. Otherwise-successful search techniques can rarely reach the levels of precision required to detect planets around such massive stars.</p>
<p>Our detection, which used both direct imaging and astrometry, demonstrates a more efficient way to search for planets. It’s the first time the direct detection of an exoplanet has been guided through initial indirect detection methods.</p>
<p>Gaia is expected to continue observing until at least 2025, and its archive will remain useful for decades to come.</p>
<h2>Mysteries remain</h2>
<p>Astrometry of HIP99770 suggests it belongs to the Argus association of stars – a group of stars that moves together through space. This would suggest the system is rather young, about 40 million years old. That would make it roughly one-hundredth of the age of our Solar System.</p>
<p>However, our analysis of the star’s pulsations, as well as models of the planet’s brightness, suggest an older age of between 120 million and 200 million years. If this is the case, HIP99770 might just be an interloper in the Argus group.</p>
<p>Now that it’s known to host a planet, astronomers will aim to further unravel the mysteries of HIP99770 and its immediate environment.</p>
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Read more:
<a href="https://theconversation.com/a-next-generation-gamma-ray-observatory-is-underway-to-probe-the-extreme-universe-191772">A 'next-generation' gamma-ray observatory is underway to probe the extreme Universe</a>
</strong>
</em>
</p>
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<img src="https://counter.theconversation.com/content/203752/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Simon Murphy receives funding from the Australian Research Council. He contributed to this research whilst at the University of Sydney, as well as at the University of Southern Queensland, where he now works as an ARC Future Fellow.</span></em></p>Astronomers are hot on the search for new exoplanets – planets that lie beyond our Solar System – which might show potential for sustaining life.Simon J. Murphy, Senior Lecturer, Astrophysics, University of Southern QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1982742023-03-08T13:41:07Z2023-03-08T13:41:07ZDistant star TOI-700 has two potentially habitable planets orbiting it – making it an excellent candidate in the search for life<figure><img src="https://images.theconversation.com/files/512978/original/file-20230301-18-2jg7dp.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C1859%2C1034&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The TOI-700 star system is home to four planets, including two in its habitable zone that could host liquid water.</span> <span class="attribution"><a class="source" href="https://www.jpl.nasa.gov/spaceimages/images/largesize/PIA23408_hires.jpg">NASA's Goddard Space Flight Center</a></span></figcaption></figure><p>NASA recently announced the <a href="https://doi.org/10.3847/2041-8213/acb599">discovery of a new, Earth-sized planet</a> in the habitable zone of a nearby star called TOI-700. <a href="https://sites.google.com/site/josepherodriguezjr/">We are</a> <a href="https://avanderburg.github.io/">two of</a> the astronomers who led the discovery of this planet, called TOI-700 e. TOI-700 e is just over 100 light years from Earth – too far away for humans to visit – but we do know that it is similar in size to the Earth, likely rocky in composition and could potentially support life.</p>
<p>You’ve probably heard about some of the <a href="https://exoplanets.nasa.gov/trappist1/">many</a> <a href="https://www.eso.org/public/news/eso1629/">other</a> <a href="https://www.nasa.gov/press-release/nasa-kepler-mission-discovers-bigger-older-cousin-to-earth">exoplanet</a> <a href="https://www.nasa.gov/image-feature/kepler-1649c-earth-size-habitable-zone-planet-hides-in-plain-sight">discoveries</a> in <a href="https://www.nasa.gov/mission_pages/kepler/news/kepscicon-briefing.html">recent</a> years. In fact, TOI-700 e is one of two potentially habitable planets just in the TOI-700 star system. </p>
<p>Habitable planets are those that are just the right distance from their star to have a surface temperature that could sustain liquid water. While it is always exciting to find a new, potentially habitable planet far from Earth, the focus of exoplanet research is shifting away from simply discovering more planets. Instead, researchers are focusing their efforts on finding and studying systems most likely to answer key questions about how planets form, how they evolve, and whether life might exist in the universe. TOI-700 e stands out from many of these other planet discoveries because it is well suited for future studies that could help answer big question about the conditions for life outside the solar system. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/xNeRqbw18Jk?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Specific methods for detecting exoplanets, like the transit method, which looks for a dip in the light coming from a distant star as a planet passes in front of it, have led to an explosion in the number of known exoplanets.</span></figcaption>
</figure>
<h2>From 1 to 5,000</h2>
<p>Astronomers discovered the first exoplanet around a Sun-like star <a href="https://doi.org/10.1038/378355a0">in 1995</a>. The field of exoplanet discovery and research has been rapidly evolving ever since.</p>
<p>At first, astronomers were finding only a <a href="https://www.hughosborn.co.uk/2015/02/09/a-history-of-planet-detection-in-one-animation/">few exoplanets each year</a>, but the combination of new cutting-edge facilities focused on <a href="https://www.nasa.gov/tess-transiting-exoplanet-survey-satellite">exoplanet science</a> with improved detection sensitivity have led to astronomers’ discovering hundreds of exoplanets each year. As detection methods and tools have improved, the amount of information scientists can learn about these planets has increased. In 30 years, scientists have gone from barely being able to detect exoplanets to <a href="https://theconversation.com/to-search-for-alien-life-astronomers-will-look-for-clues-in-the-atmospheres-of-distant-planets-and-the-james-webb-space-telescope-just-proved-its-possible-to-do-so-184828">characterizing key chemical clues in their atmospheres</a>, like water, using facilities like the James Webb Space Telescope.</p>
<p>Today, there are more than <a href="https://exoplanetarchive.ipac.caltech.edu/">5,000 known exoplanets</a>, ranging from gas giants to small rocky worlds. And perhaps most excitingly, astronomers have now found about a dozen exoplanets that are likely rocky and orbiting within the habitable zones of their respective stars.</p>
<p>Astronomers have even discovered a few systems – like TOI-700 – that have more than one planet orbiting in the habitable zone of their star. We call these keystone systems.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/512975/original/file-20230301-24-8pqinb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing a star with a green ring around it marking the habitable zone." src="https://images.theconversation.com/files/512975/original/file-20230301-24-8pqinb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/512975/original/file-20230301-24-8pqinb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=185&fit=crop&dpr=1 600w, https://images.theconversation.com/files/512975/original/file-20230301-24-8pqinb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=185&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/512975/original/file-20230301-24-8pqinb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=185&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/512975/original/file-20230301-24-8pqinb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=233&fit=crop&dpr=1 754w, https://images.theconversation.com/files/512975/original/file-20230301-24-8pqinb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=233&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/512975/original/file-20230301-24-8pqinb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=233&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 TOI-700 system has a large habitable zone, and the newly discovered TOI-700 e, not shown in this image, orbits the star along the inner edge of the habitable zone.</span>
<span class="attribution"><a class="source" href="https://www.jpl.nasa.gov/spaceimages/images/largesize/PIA23407_hires.jpg">NASA's Goddard Space Flight Center</a></span>
</figcaption>
</figure>
<h2>A pair of habitable siblings</h2>
<p>TOI-700 first made headlines when our team announced the discovery of <a href="https://doi.org/10.3847/1538-3881/aba4b2">three small planets orbiting the star</a> in early 2020. Using a <a href="https://doi.org/10.3847/1538-3881/aba4b3">combination of observations</a> from NASA’s <a href="https://exoplanets.nasa.gov/tess/">Transiting Exoplanet Surveying Satellite</a> mission and the <a href="https://www.nasa.gov/mission_pages/spitzer/main/index.html">Spitzer Space Telescope</a> we discovered these planets by measuring small dips in the amount of light coming from TOI-700. These dips in light are caused by planets passing in front of the small, cool, red dwarf star at the center of the system.</p>
<p>By taking precise measurements of the changes in light, we were able to determine that at least three small planets are in the TOI-700 system, with hints of a possible fourth. We could also determine that the third planet from the star, TOI-700 d, orbits within its star’s habitable zone, where the temperature of the planet’s surface could allow for liquid water. </p>
<p>The Transiting Exoplanet Surveying Satellite observed TOI-700 for another year, from July 2020 through May 2021, and using these observations <a href="https://doi.org/10.3847/2041-8213/acb599">our team found the fourth planet, TOI-700 e</a>. TOI-700 e is 95% the size of the Earth and, much to our surprise, orbits on the inner edge of the star’s habitable zone, between planets c and d. Our discovery of this planet makes TOI-700 one of only a few known systems with two Earth-sized planets orbiting in the habitable zone of their star. The fact that it is relatively close to Earth also makes it one of the most accessible systems in terms of future characterization.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/512981/original/file-20230301-24-v7fzr8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="James Webb Space Telescope against the backdrop of space." src="https://images.theconversation.com/files/512981/original/file-20230301-24-v7fzr8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/512981/original/file-20230301-24-v7fzr8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=467&fit=crop&dpr=1 600w, https://images.theconversation.com/files/512981/original/file-20230301-24-v7fzr8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=467&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/512981/original/file-20230301-24-v7fzr8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=467&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/512981/original/file-20230301-24-v7fzr8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=586&fit=crop&dpr=1 754w, https://images.theconversation.com/files/512981/original/file-20230301-24-v7fzr8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=586&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/512981/original/file-20230301-24-v7fzr8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=586&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">New tools, like the James Webb Space Telescope, can provide clues about life on distant planets, but with thousands of scientific questions to answer, efficient use of time is key.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:James_Webb_Space_Telescope.jpg#/media/File:James_Webb_Space_Telescope.jpg">Bricktop/Wikimedia Commons</a></span>
</figcaption>
</figure>
<h2>The bigger questions and tools to answer them</h2>
<p>With the successful launch of the James Webb Space Telescope, astronomers are now able to start <a href="https://www.nasa.gov/feature/goddard/2022/nasa-s-webb-reveals-an-exoplanet-atmosphere-as-never-seen-before">characterizing the atmospheric chemistry</a> of exoplanets and search for <a href="https://theconversation.com/to-search-for-alien-life-astronomers-will-look-for-clues-in-the-atmospheres-of-distant-planets-and-the-james-webb-space-telescope-just-proved-its-possible-to-do-so-184828">clues about whether life exists</a> on them. In the near future, a number of massive, ground-based telescopes will also help reveal further details about the composition of planets far from the solar system. </p>
<p>But even with powerful new telescopes, collecting enough light to learn these details requires pointing the telescope at a system for a <a href="https://arxiv.org/abs/1708.04239">long period of time</a>. With thousands of <a href="https://www.stsci.edu/jwst/science-execution/approved-programs/cycle-1-go">valuable scientific questions to answer</a>, astronomers need to know where to look. And that is the goal of our team, to find the most interesting and promising exoplanets to study with the Webb telescope and future facilities.</p>
<p>Earth is currently the only data point in the search for life. It is possible alien life could be vastly different from life as we know it, but for now, places similar to the home of humanity with liquid water on the surface offer a good starting point. We believe that keystone systems with multiple planets that are likely candidates for hosting life – like TOI-700 – offer the best use of observation time. By further studying TOI-700, our team will be able to learn more about what makes a planet habitable, how rocky planets similar to Earth form and evolve, and the mechanisms that shaped the solar system. The more astronomers know about how star systems like TOI-700 and our own solar system work, the better the chances of detecting life out in the cosmos.</p><img src="https://counter.theconversation.com/content/198274/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Joseph Rodriguez receives funding from the National Aeronautics and Space Administration and Michigan State University. </span></em></p><p class="fine-print"><em><span>Andrew Vanderburg receives funding from the National Aeronautics and Space Administration and the Massachusetts Institute of Technology. </span></em></p>With more than 5,000 known exoplanets, astronomers are shifting their focus from discovering additional distant worlds to identifying which are good candidates for further study.Joey Rodriguez, Assistant Professor of Physics and Astronomy, Michigan State UniversityAndrew Vanderburg, Assistant Professor of Physics, Massachusetts Institute of Technology (MIT)Licensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1986942023-02-01T12:08:35Z2023-02-01T12:08:35ZSeti: alien hunters get a boost as AI helps identify promising signals from space<figure><img src="https://images.theconversation.com/files/507097/original/file-20230130-12-qfen8v.jpg?ixlib=rb-1.1.0&rect=672%2C272%2C2956%2C1999&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The new study analysed data gathered at the Green Bank Observatory in West Virginia.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/green-bank-west-virginia-october-15-762059119">Shutterstock</a></span></figcaption></figure><p>An international team of researchers looking for signs of intelligent life in space have used artificial intelligence (AI) to reveal eight promising radio signals in data collected at a US observatory.</p>
<p>The results of their research, <a href="https://www.nature.com/articles/s41550-022-01872-z">published in Nature Astronomy</a> are remarkable. The team hasn’t yet carried out an exhaustive analysis, but the paper suggests the signals have many of the characteristics we would expect if they were artificially generated. In other words, they are the kinds of signals we might pick up from an extraterrestrial civilisation broadcasting into space.</p>
<p>A cursory review of the new paper suggest these are indeed promising signals. They’re much more compelling than what is perhaps the most famous Seti candidate, <a href="https://astronomy.com/news/2020/09/the-wow-signal-an-alien-missed-connectio">the “Wow!” signal</a>, radio emission bearing the hallmarks of an extraterrestrial origin that was collected by an Ohio telescope in 1977.</p>
<p>Realistically, it’s most likely that these eight new signals were generated by human technology. But the real story here is the effectiveness of AI and <a href="https://en.wikipedia.org/wiki/Deep_learning">the techniques used by the team to</a> dig out rare and interesting signals previously buried in the noise of human-generated <a href="https://public.nrao.edu/telescopes/radio-frequency-interference/">radio frequency interference,</a> such as mobile phones and GPS.</p>
<p>Astronomers working in the field of <a href="https://www.seti.org/primer-seti-seti-institute">Seti (the search for extraterrestrial intelligence)</a> must filter out interference produced by radio communications here on Earth.</p>
<p>In this case, Peter Ma from the University of Toronto and his colleagues unleashed a set of algorithms on a mountain of data collected by the <a href="https://greenbankobservatory.org">Green Bank Telescope in West Virginia</a>, US. The data was gathered through a Seti initiative called <a href="https://seti.berkeley.edu/listen/">Breakthrough Listen</a>, established in 2015 by the investor Yuri Milner and his wife Julia. </p>
<p>Here are the characteristics astronomers look for in signals that could be artificially-generated: firstly they are <a href="https://en.wikipedia.org/wiki/Narrowband">narrow-band</a>, which means that where the radio transmission is confined to only a few frequency channels. They also disappear as the telescope is moved to another direction in the sky, and they exhibit <a href="https://en.wikipedia.org/wiki/Doppler_effect">“Doppler drifting”</a>, where the frequency of the signal changes in a predictable way with time. We would expect Doppler drifting because both the transmitter — on a distant planet, for example — and the receiver, on Earth, are moving.</p>
<figure class="align-center ">
<img alt="Artist's impression of exoplanets" src="https://images.theconversation.com/files/507060/original/file-20230130-22-kadncw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/507060/original/file-20230130-22-kadncw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=449&fit=crop&dpr=1 600w, https://images.theconversation.com/files/507060/original/file-20230130-22-kadncw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=449&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/507060/original/file-20230130-22-kadncw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=449&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/507060/original/file-20230130-22-kadncw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=565&fit=crop&dpr=1 754w, https://images.theconversation.com/files/507060/original/file-20230130-22-kadncw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=565&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/507060/original/file-20230130-22-kadncw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=565&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Any artificial signals from deep space need to be distinguished from radio interference here on Earth.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/planets-deep-space-cosmos-nebula-stars-2057080619">Shutterstock</a></span>
</figcaption>
</figure>
<h2>Buried in the noise</h2>
<p>The Breakthrough Listen project’s <a href="https://seti.berkeley.edu/blc1/">first candidate signal</a>, called BLC1, was first announced in 2020. But it was <a href="https://www.nature.com/articles/s41550-021-01508-8">later traced</a> to transmissions associated with cheap electronic devices on this planet. The application of AI techniques to the Breakthrough Listen observing programme, however, is a potential game changer for the field. Even seasoned Seti researchers are beginning to think that we might be on the cusp of a momentous scientific breakthrough.</p>
<p>This may explain renewed interest by groups around the world that are planning for Seti success. For example, a <a href="https://seti.wp.st-andrews.ac.uk">Seti post-detection hub</a> has been set up at the University of St Andrews in Scotland. This will study how humans should react if we discover we are not alone in the Universe.</p>
<p>The International Academy of Astronautics (IAA) <a href="https://iaaseti.org/en/">Seti permanent committee</a> oversees the <a href="https://iaaseti.org/en/protocols/">Seti post-detection protocols</a>, which outline what steps scientists should take in the event of detecting a genuine signal. The IAA has opted to update the text of the protocols sometime later this year.</p>
<p>But the new study highlights a problem with previous signals of interest. When the team took another look at the stars associated with the eight narrow-band transmissions, they could no longer detect the signals. </p>
<p>It would not be surprising if many, and perhaps the vast majority of bona-fide Seti signals, were isolated events. After all, what are the chances that we point our telescopes in exactly the right direction, at the right time and with the right frequency on multiple occasions?</p>
<h2>Missing ingredients</h2>
<p>As I <a href="https://theconversation.com/seti-new-signal-excites-alien-hunters-heres-how-we-could-find-out-if-its-real-152498">argued here</a> a few years ago, Seti surveys would greatly benefit from employing multiple radio telescopes, operating in a manner that’s known as a <a href="https://public.nrao.edu/ask/how-does-a-radio-interferometer-work/">classical interferometer network</a>. </p>
<p>These telescope arrays (groups of several antennas observing together) generate huge amounts of data. With AI onboard, the challenge is perhaps more manageable than previously thought. </p>
<p>Breakthrough Listen is already using telescope arrays such as <a href="https://www.sarao.ac.za/science/meerkat/about-meerkat/">MeerKAT in South Africa</a> for Seti searches. In Europe, researchers have been experimenting with <a href="https://www.evlbi.org">arrays that span the globe</a>.</p>
<p>This European approach would help us isolate signals from human-made interference, give us multiple independent detections of individual events, and permit us to localise signals to individual stars and possibly orbiting planets. </p>
<p>Among the future projects is the <a href="https://www.skao.int/en">Square Kilometre Array</a>, an international project to build the two largest telescope arrays in the world, which will be based in Australia and South Africa. Another upcoming project is the <a href="https://ngvla.nrao.edu">next generation VLA (ngVLA)</a>, a series of linked telescope facilities that will be spread across the United States. These radio telescope arrays will be even more sensitive than current instruments.</p>
<p>It’s my belief — and indeed hope — that somewhere out there intelligent beings are waiting to be discovered. The AI revolution might be the missing ingredient that previous endeavours have lacked. In particular, AI algorithms will eventually evolve into powerful tools that no longer suffer from <a href="https://www.nist.gov/news-events/news/2022/03/theres-more-ai-bias-biased-data-nist-report-highlights">human biases</a>. </p>
<p>Lord Martin Rees, chairman of the Breakthrough Listen advisory board and the astronomer royal, has proposed that if we do find aliens they are likely to be <a href="https://theconversation.com/seti-why-extraterrestrial-intelligence-is-more-likely-to-be-artificial-than-biological-169966">intelligent machines</a> operating in the depths of space, unconstrained by the biological limitations placed on humans. </p>
<p>If we ever do find a bona-fide signal, it could just be that it’s mediated by machines on Earth and in space.</p><img src="https://counter.theconversation.com/content/198694/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Michael Garrett is on the advisory board of the Breakthrough Listen initiative and the Seti Institute.</span></em></p>Can artificial intelligence transform the search for alien intelligence?Michael Garrett, Sir Bernard Lovell chair of Astrophysics and Director of Jodrell Bank Centre for Astrophysics, University of ManchesterLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1952242022-11-24T20:14:01Z2022-11-24T20:14:01ZJames Webb space telescope uncovers chemical secrets of distant world – paving the way for studying Earth-like planets<figure><img src="https://images.theconversation.com/files/497034/original/file-20221123-22-xg8b05.jpg?ixlib=rb-1.1.0&rect=5%2C5%2C3822%2C2144&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Artist impression of WASP b and its star</span> <span class="attribution"><a class="source" href="https://www.esa.int/ESA_Multimedia/Images/2022/08/Artist_impression_of_WASP-39_b_and_its_star">NASA, ESA, CSA, and J. Olmsted (STScI)</a></span></figcaption></figure><p>Since the first planet orbiting a star other than the Sun was discovered in 1995, we have realised that planets and planetary systems are more diverse than we ever imagined. Such distant worlds – exoplanets – give us the opportunity to study how planets behave in different situations. And learning about their atmospheres is a crucial piece of the puzzle.</p>
<p>Nasa’s <a href="https://webb.nasa.gov/">James Webb space telescope</a> (JWST) is the largest telescope in space. Launched on Christmas Day 2021, it is the perfect tool for investigating these worlds. Now my colleagues and I have used the telescope for the first time to unveil the chemical make-up of an exoplanet. And <a href="https://www.mpg.de/19521589/Alderson_ERS_WASP39b_JWST_NIRSpec.pdf">the data</a>, <a href="https://arxiv.org/abs/2211.10488">released</a> <a href="https://arxiv.org/abs/2211.10489">in preprint</a> <a href="https://arxiv.org/abs/2211.10493">form</a> (meaning it has yet to be published in a peer-reviewed journal), <a href="https://exoplanets.nasa.gov/news/1715/nasas-webb-reveals-an-exoplanet-atmosphere-as-never-seen-before/">suggests some surprising results</a>.</p>
<p>Many exoplanets are too close to their parent stars for even this powerful telescope to distinguish them. But we can use the trick of watching as the planet passes in front of (transits) its star. During transit, the planet blocks a small fraction of the starlight, and an even tinier fraction of the starlight is filtered through the outer layers of the planet’s atmosphere. </p>
<p>Gases within the atmosphere absorb some of the light – leaving fingerprints on the starlight in the form of a reduction in brightness at certain colours, or wavelengths. JWST is particularly suited to exoplanet atmosphere studies because it is an infrared telescope. Most of the gases that are in an atmosphere – such as water vapour and carbon dioxide – absorb infrared rather than visible light.</p>
<figure class="align-center ">
<img alt="The image shows a graph with wavelength on the horizontal axis, increasing left to right, and the amount of light blocked on the vertical axis, increasing towards the top. The data resemble a bumpy line." src="https://images.theconversation.com/files/497079/original/file-20221123-12-ba99xt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/497079/original/file-20221123-12-ba99xt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=368&fit=crop&dpr=1 600w, https://images.theconversation.com/files/497079/original/file-20221123-12-ba99xt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=368&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/497079/original/file-20221123-12-ba99xt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=368&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/497079/original/file-20221123-12-ba99xt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=463&fit=crop&dpr=1 754w, https://images.theconversation.com/files/497079/original/file-20221123-12-ba99xt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=463&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/497079/original/file-20221123-12-ba99xt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=463&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">One of four separate measurements. Each bump corresponds to a different absorbing gas in the atmosphere.</span>
<span class="attribution"><span class="source">NASA, ESA, CSA, Joseph Olmsted (STScI)</span></span>
</figcaption>
</figure>
<p>I am part of an international team of exoplanet scientists that has been using JWST to study a roughly Jupiter-sized planet called <a href="https://exoplanets.nasa.gov/exoplanet-catalog/5673/wasp-39-b/">WASP-39b</a>. Unlike Jupiter, however, this world takes only a few days to orbit its star, so it is being cooked – reaching temperatures exceeding 827°C. This gives us the perfect opportunity to explore how a planetary atmosphere behaves in extreme temperature conditions. </p>
<p>We used JWST to recover the most complete spectrum yet of this fascinating planet. In fact, our work represents the first chemical inventory of the planet’s atmosphere.</p>
<p>We already knew that most of this large planet’s atmosphere had to be a mixture of hydrogen and helium – the lightest and most abundant gases in the universe. And the Hubble telescope has previously detected water vapour, sodium and potassium there.</p>
<p>Now, we’ve been able to confirm our detection and produce a measurement of the amount of water vapour. The data also suggests there are other gases including <a href="https://scied.ucar.edu/learning-zone/how-climate-works/carbon-dioxide">carbon dioxide</a>, <a href="https://www.gov.uk/government/publications/carbon-monoxide-properties-incident-management-and-toxicology/carbon-monoxide-general-information">carbon monoxide</a>, and unexpectedly, <a href="https://www.epa.gov/so2-pollution/sulfur-dioxide-basics">sulphur dioxide</a>.</p>
<p>Having measurements of how much of each of these gases is present in the atmosphere means we can estimate the relative amounts of the elements that make up the gases – hydrogen, oxygen, carbon and sulphur. Planets are formed in a disc of dust and gas around a young star, and we expect different amounts of these elements to be available to a baby planet at different distances from the star. </p>
<p>WASP-39b appears to have a relatively low amount of carbon relative to oxygen, indicating it probably formed at a greater distance from the star where it could have easily absorbed water ice from the disc (boosting its oxygen), compared with its current very close orbit. If this planet has migrated, it could help us develop our theories about planet formation, and would support the idea that the giant planets in our Solar System also did a fair bit of moving and shaking early on.</p>
<h2>A sulphurous key</h2>
<p>The amount of sulphur we detected relative to oxygen is quite high for WASP-39b. We’d expect sulphur in a young planetary system to be more concentrated in bits of rock and rubble than as an atmospheric gas. So this indicates that WASP-39b might have undergone an unusual amount of collisions with sulphur-containing chunks of rock. Some of that sulphur would be released as gas.</p>
<p>In a planet’s atmosphere, different chemicals react with each other at different rates depending on how hot it is. Usually, these settle into an equilibrium state, with the total amounts of each gas remaining stable as the reactions balance each other. We managed to predict what gases we would see in WASP-39b’s atmosphere for a range of starting points. But none of them came up with sulphur dioxide, instead expecting any sulphur to be locked up in a different gas, hydrogen sulphide.</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/497115/original/file-20221123-18-j3raez.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing the chemical process that converts hydrogen sulphide to sulphur dioxide." src="https://images.theconversation.com/files/497115/original/file-20221123-18-j3raez.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/497115/original/file-20221123-18-j3raez.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/497115/original/file-20221123-18-j3raez.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/497115/original/file-20221123-18-j3raez.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/497115/original/file-20221123-18-j3raez.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/497115/original/file-20221123-18-j3raez.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/497115/original/file-20221123-18-j3raez.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Photochemistry on WASP-39b.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech/Robert Hurt; Center for Astrophysics-Harvard & Smithsonian/Melissa Weiss</span></span>
</figcaption>
</figure>
<p>The missing piece of the chemical jigsaw puzzle was a process called <a href="https://arxiv.org/abs/2211.10490">photochemistry</a>. This is when the rates of certain chemical reactions are driven by energy from photons – packets of light – coming from the star, rather than by the temperature of the atmosphere. Because WASP-39b is so hot, and reactions generally speed up at higher temperatures, we didn’t expect photochemistry to be quite as important as it has turned out to be. </p>
<p>The data suggests that water vapour in the atmosphere is split apart by light into oxygen and hydrogen. These products would then react with the gas hydrogen sulphide, eventually stripping away the hydrogen and replacing it with oxygen to form sulphur dioxide.</p>
<h2>What’s next for JWST?</h2>
<p>Photochemistry is even more important on cooler planets that may be habitable – the ozone layer on our own planet is formed via a photochemical process. JWST will be observing the rocky worlds in the <a href="https://theconversation.com/solar-system-with-seven-earth-like-planets-found-around-nearby-star-heres-what-they-could-be-like-73394">Trappist-1 system</a> during its first year of operation. Some of these measurements have already been made – and all of these planets have temperatures more similar to Earth’s. </p>
<p>Some may even have the right temperature to have liquid water on the surface, and potentially life. Having a good understanding of how photochemistry influences atmospheric composition is going to be critical for interpreting the Webb telescope observations of the Trappist-1 system. This is especially important since an apparent chemical imbalance in an atmosphere might hint at the presence of life, so we need to be aware of other possible explanations for this. </p>
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Read more:
<a href="https://theconversation.com/four-ways-to-spot-hints-of-alien-life-using-the-james-webb-space-telescope-192445">Four ways to spot hints of alien life using the James Webb Space Telescope</a>
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<hr>
<p>The WASP-39b chemical inventory has shown us just how powerful a tool JWST is. We’re at the start of a very exciting era in exoplanet science, so stay tuned.</p><img src="https://counter.theconversation.com/content/195224/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Joanna Barstow receives funding from the Science and Technology Facilities Council. She is a Councillor and Trustee for the Royal Astronomical Society. </span></em></p>The James Webb space telescope is making the headlines again – this time completing its first chemical inventory of a distant, exotic world.Joanna Barstow, Ernest Rutherford Fellow, The Open UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1924472022-10-28T09:26:10Z2022-10-28T09:26:10ZZombie worlds: five spooky planets orbiting dead stars<figure><img src="https://images.theconversation.com/files/489593/original/file-20221013-17-wk1s48.jpeg?ixlib=rb-1.1.0&rect=0%2C0%2C3000%2C2398&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">PIA</span> <span class="attribution"><span class="source">NASA/JPL</span></span></figcaption></figure><p>All stars, including the Sun, have a finite lifetime. Stars shine by the process of nuclear fusion in which lighter atoms, such as hydrogen, fuse together to create heavier ones. This process releases vast quantities of energy which counteracts the ever-present inward pull of the star’s gravity. Ultimately, fusion helps stars to resist gravitational collapse. </p>
<p>This balance of forces is called “hydrostatic equilibrium”. However, there will come a time when the supply of fuel in the core of a star starts to run out and it eventually dies. Stars with more than about eight times the mass of the Sun will typically burn through their fuel in less than 100 million years. Once fusion ceases, the star collapses – generating a massive instantaneous final burst of nuclear fusion which causes the star to explode as a supernova. </p>
<p>Supernovas release enough energy to <a href="https://www.eso.org/public/images/ann11014a/">outshine the entire galaxy</a> in which they occur. What’s left afterwards are collapsed, dead stellar cores called neutron stars or, if the progenitor star was massive enough, a black hole. Any planets orbiting a star when it goes supernova would be <a href="https://getyarn.io/yarn-clip/0ea694af-2cb1-4a33-b0a5-b1b7f256ff4c/gif">obliterated</a>. Mysteriously though, <a href="https://academic.oup.com/mnras/article/512/2/2446/6542453?login=false">a handful</a> of “zombie planets” have been detected orbiting neutron stars. And they are some of the weirdest worlds in the cosmos.</p>
<p>Neutron stars are extremely dense, containing as much mass as the Sun squashed into a sphere only a few miles across. Some neutron stars emit beams of radio waves into space – and it is around these “pulsar” stars that planets have been found. As the pulsar spins, its radio beams sweep through space generating regular radio flashes. Pulsars were <a href="https://www.nature.com/articles/217709a0.pdf">discovered</a> in 1967 – you can listen to the sounds of the radio emission from some of them <a href="https://www.youtube.com/watch?v=gb0P6x_xDEU">here</a>.</p>
<p>The regularity of these radio pulses make pulsars ideal for hunting nearby planets. If a pulsar has a planet, they will both orbit a <a href="https://www.education.com/science-fair/article/barycenter-balancing-point/">shared gravitational centre</a>. This means the radio emission will be periodically stretched and compressed in a predictable fashion – allowing us to detect the planet.</p>
<h2>Phobetor, Draugr and Poltergeist</h2>
<p>Some 2,300 light years from Earth lies the pulsar <a href="https://exoplanets.nasa.gov/exoplanet-catalog/7134/psr-b125712-b/">PSR B1257+12</a>. It flashes 161 times per second and has been nicknamed “Lich” after an undead creature in western folklore. It is orbited by three rocky, terrestrial planets named Phobetor, Draugr and Poltergeist. </p>
<p>These planets hold a special place in the history of astronomy, as they were the first beyond our Solar System (exoplanets) to be <a href="https://www.sciencedirect.com/science/article/abs/pii/S1387647311000418">discovered</a> back in 1991. A few years ago, Nasa released this “zombie worlds” poster of them: </p>
<figure class="align-center ">
<img alt="Zombie world poster." src="https://images.theconversation.com/files/490353/original/file-20221018-14-d1hsi5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/490353/original/file-20221018-14-d1hsi5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=900&fit=crop&dpr=1 600w, https://images.theconversation.com/files/490353/original/file-20221018-14-d1hsi5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=900&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/490353/original/file-20221018-14-d1hsi5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=900&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/490353/original/file-20221018-14-d1hsi5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1131&fit=crop&dpr=1 754w, https://images.theconversation.com/files/490353/original/file-20221018-14-d1hsi5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1131&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/490353/original/file-20221018-14-d1hsi5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1131&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Zombie world poster.</span>
<span class="attribution"><span class="source">Credit: NASA/JPL-Caltech</span></span>
</figcaption>
</figure>
<p>Their discovery challenged ideas about planetary formation, which normally takes place as a new star forms. In contrast, these planets must have formed after the dying star’s supernova. It is not yet known with certainty how this happened. Material in a disk of debris orbiting the pulsar may have coalesced into planets after the supernova.</p>
<p>Draugr, named after an <a href="https://en.wikipedia.org/wiki/Draugr">undead creature in Norse mythology</a>, is the innermost of the three. It has about twice the mass of the Moon and is the least-massive planet currently known, orbiting Lich every 25 days. Its larger cousins, Poltergeist and Phobetor, orbit every 67 and 98 days respectively, and are each about four times the mass of Earth.</p>
<p>Pulsars have powerful magnetic fields which may allow electric currents to arc through space between the pulsar and an orbiting planet. So if any of these planets have atmospheres, they might constantly be bathed in the unearthly light of powerful aurora (similar to our northern lights).</p>
<p>If you were to stand on the surface of one of these zombie worlds, you would see, through the powerful hue of the aurora, the incandescent Lich in the sky projecting two powerful and tightly confined beams of light outwards in opposite directions into the blackness of space. Neutron stars can be extremely hot, carrying the residual heat left over from the supernova. Lich is nearly 30,000°C and the innermost of these worlds, Draugr, is likely to only be a few degrees below freezing at its surface.</p>
<h2>Diamond world</h2>
<p>Planet PSR J1719−1438b orbits a pulsar some 4,000 light years away, hurtling around its host in just over two hours. It is the densest planet yet discovered – so dense, in fact, that it is thought to be <a href="https://www.mpg.de/4406441/diamond_planet">composed largely of diamond</a>.</p>
<p>This “diamond world” is the <a href="https://arxiv.org/abs/1108.5201">remnant core</a> of a dead star called a <a href="https://imagine.gsfc.nasa.gov/science/objects/dwarfs2.html">white dwarf</a>. These are known to have a high carbon content (diamond is made of carbon) – but this particular white dwarf has lost 99.9% of its original mass, consumed by the powerful gravity of its nearby host pulsar.</p>
<p>This sphere of diamond is about half the size of Jupiter, and orbits PSR J1719-1438 at a distance of 600,000km (just 1.5 times further away than our Moon is from Earth). At such a close distance from its host pulsar, it is likely that this world has a very hot surface. </p>
<h2>Methuselah</h2>
<p>Orbiting the Milky Way (and many galaxies) are <a href="https://esahubble.org/wordbank/globular-cluster/#:%7E:text=Globular%20clusters%20are%20stable%2C%20tightly,and%20are%20tightly%20gravitationally%20bound.">globular star clusters</a> – spherical groups of up to a million stars each. These are some of the oldest stars in the universe.</p>
<p>The globular star cluster <a href="https://www.nasa.gov/feature/goddard/2017/messier-4">Messier M4</a> lies about 5,600 light years away and contains some 100,000 stars. Among these is a planet nicknamed Methuselah, after the son of Enoch in the Book of Genesis who supposedly lived for 969 years.</p>
<p>At the centre of the M4 star cluster is a pulsar and a white dwarf orbiting about their shared gravitational centre every 161 days. Given the short-lived nature of high-mass stars, the pulsar would have formed shortly after the formation of Messier 4 itself. </p>
<p>Methuselah also orbits this centre, but at a much more leisurely pace of once every 100 years or so, at a distance similar to that at which Uranus orbits our own Sun. It is a giant gas planet around 2.5 times the mass of Jupiter. Methuselah is believed to have formed as a normal planet around a Sun-like star within the first billion years of the formation of the universe. It was then captured into orbit around the host pulsar, which it has orbited ever since. </p>
<p>The high density of stars in globular clusters makes the chances of two stars having a close encounter quite high – and likewise the exchange of planets. Methuselah is the <a href="https://www.nasa.gov/centers/goddard/news/topstory/2003/0709hstssu.html">oldest known</a> planet in the cosmos, having formed an estimated 12.7 billion years ago along with all the stars in M4.</p>
<p>Pulsar planets are worlds of extremes, yet even they may not be the most bizarre. A small number of <a href="https://iopscience.iop.org/article/10.3847/1538-4357/ab4cf0">theoretical studies</a> have proposed the existence of planets orbiting black holes. So far, however, none have been found.</p><img src="https://counter.theconversation.com/content/192447/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>A handful of zombie planets have been spotted – thought to have been born after the death of their host stars.Gareth Dorrian, Post Doctoral Research Fellow in Space Science, University of BirminghamLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1924452022-10-21T17:04:48Z2022-10-21T17:04:48ZFour ways to spot hints of alien life using the James Webb Space Telescope<figure><img src="https://images.theconversation.com/files/490217/original/file-20221017-19-fs1i2r.jpg?ixlib=rb-1.1.0&rect=4%2C0%2C2982%2C1994&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An artist's impression of planet Gliese 667 Cc at sunset. </span> <span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Gliese_667_Cc#/media/File:Gliese_667_Cc_sunset.jpg">ESO/L. Calçada</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>The study of exoplanets, worlds which orbit stars other than our sun, is currently being transformed <a href="https://theconversation.com/james-webb-space-telescope-how-our-launch-of-worlds-most-complex-observatory-will-rest-on-a-nail-biting-knife-edge-173619">by the new James Webb Space Telescope</a> (JWST). We will shortly gain our first insight into conditions on rocky, potentially Earth-like worlds beyond our solar system. One of these distant worlds might host life. But could we detect it?</p>
<p>We may be able to spot signs of life in the composition of the planet’s atmosphere. We can use a technique called <a href="https://theconversation.com/its-all-in-the-atmosphere-exploring-planets-orbiting-distant-stars-62034">transmission spectroscopy</a> – which divides up light by its wavelength – to search for traces of different gases in starlight as it passes through a planet’s atmosphere. </p>
<p>Some starlight-absorbing gases might indicate the presence of life on the planet. We call these biosignatures. </p>
<h2>1. Oxygen and ozone</h2>
<p>Oxygen is probably the most obvious biosignature. Plants make it, we breathe it and the rock record shows that levels in Earth’s atmosphere <a href="https://theconversation.com/earths-oxygen-has-varied-dramatically-over-time-heres-how-our-data-could-help-us-spot-alien-life-192349">changed dramatically as life evolved</a>. The oxygen that we breathe is O<sub>2</sub>, two oxygen atoms stuck together. But another configuration of oxygen, O<sub>3</sub> or ozone, could also be observed with JWST. </p>
<p>So, if we detected one or both of these gases, would it be job done? Unfortunately not. Another scenario that could produce large amounts of atmospheric oxygen is a planet undergoing a “<a href="https://theconversation.com/venus-the-trouble-with-sending-people-there-191534">runaway greenhouse effect</a>”. Once a planet is hot enough for its water ocean to evaporate, the resulting water vapour in the atmosphere contributes to a greenhouse effect – super-heating the planet to levels that aren’t compatible with life – in a feedback loop. </p>
<p>Eventually, the planet becomes hot enough for water molecules to break apart into hydrogen and oxygen. Hydrogen molecules are light and can move fast enough to easily escape the planet’s gravity, whereas the more sluggish oxygen tends to stick around, ready to be detected and trick unsuspecting astronomers. </p>
<h2>2. Phosphine and ammonia</h2>
<p>The current focus of the search for life might be mostly on exoplanets, but there have also been recent developments closer to home. Phosphine – a gas that occurs naturally in hydrogen-dominated atmospheres like those of gas giants Jupiter and Saturn – was recently <a href="https://www.liebertpub.com/doi/10.1089/ast.2018.1954">detected in the atmosphere of Venus</a>. Interestingly, phosphine is considered to <a href="https://www.liebertpub.com/doi/10.1089/ast.2018.1954">be a potential biosignature</a>.</p>
<p>On Earth, phosphine is produced by microorganisms, for example in the intestinal tracts of animals. If no life is present, we wouldn’t expect phosphine to occur in large quantities in Venus-like atmospheres, which are dominated by carbon dioxide. That said, we can’t yet rule out other sources of phosphine on Venus.</p>
<p>Foul-smelling ammonia is another potential biosignature gas, also produced by animals on Earth. Like phosphine, it is prevalent on gas giant planets, but not expected to occur on rocky worlds in the absence of life. </p>
<p>However, detecting phosphine or ammonia in the atmosphere of a distant exoplanet is likely to be challenging. Both reach tiny concentrations of only a few parts per billion on Earth. So unless our potential extraterrestrials are much stinkier than Earth’s animals, we probably won’t be spotting them any time soon.</p>
<h2>3. Methane plus carbon dioxide</h2>
<p>Individual gases that are unambiguous biosignatures are few and far between, so we might be better off looking for a winning combination if we want to detect life. Large amounts of <a href="https://www.pnas.org/doi/10.1073/pnas.2117933119">methane</a>, produced by farting animals on Earth, plus carbon dioxide would be a good hint that there is something going on. </p>
<p>If there’s enough oxygen available, then carbon much prefers to hang around with oxygen as carbon dioxide (CO<sub>2</sub>, one carbon atom and two oxygen atoms), rather than form methane (CH<sub>4</sub>, one carbon atom and four hydrogen atoms). In an oxygen-rich environment, any carbon finding itself in a methane molecule quickly ditches its hydrogen buddies in favour of a couple of spare oxygens. </p>
<figure class="align-center ">
<img alt="Cartoon showing a carbon atom leaving four hydrogen atoms and heading towards a pair of oxygen atoms, saying 'Bye!' as it leaves." src="https://images.theconversation.com/files/490485/original/file-20221018-8364-beidg3.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/490485/original/file-20221018-8364-beidg3.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=339&fit=crop&dpr=1 600w, https://images.theconversation.com/files/490485/original/file-20221018-8364-beidg3.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=339&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/490485/original/file-20221018-8364-beidg3.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=339&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/490485/original/file-20221018-8364-beidg3.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=426&fit=crop&dpr=1 754w, https://images.theconversation.com/files/490485/original/file-20221018-8364-beidg3.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=426&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/490485/original/file-20221018-8364-beidg3.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=426&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">When it’s available, carbon prefers the company of oxygen.</span>
<span class="attribution"><span class="source">Author's own work.</span></span>
</figcaption>
</figure>
<p>So seeing lots of both methane and carbon dioxide coexisting would suggest that something – maybe bacteria – is constantly producing methane.</p>
<h2>4. Chemical imbalances</h2>
<p>We can apply the above argument to any combination of gases that shouldn’t happily coexist. Life disrupts the chemical equilibrium (balance) of its environment because it uses chemical reactions to generate energy. </p>
<p>On Earth, oxygen is transformed into carbon dioxide, but in a different type of atmosphere, with different chemicals available, life would use other processes to achieve the same goal. Methane-producing bacteria that live around hydrothermal vents deep in Earth’s oceans, for example, harvest chemical energy from minerals and chemical compounds. Looking for imbalances allows us to be open minded about what life elsewhere might look like.</p>
<h2>What happens if we spots signals of alien life?</h2>
<p>JWST is already <a href="https://www.nature.com/articles/s41586-022-05269-w">exceeding our expectations</a> for exoplanet atmosphere observations. As powerful as it is, though, rocky planets with mild temperatures and atmospheres dominated by nitrogen or carbon dioxide are still going to be challenging to study using transmission spectroscopy. The signals we expect from these planets are much weaker than those we have successfully observed in hot gas giant atmospheres. </p>
<p>If we are lucky enough to observe starlight-absorbing gases in the atmosphere of a rocky exoplanet – <a href="https://solarsystem.nasa.gov/resources/2686/exploring-alien-worlds-with-nasas-james-webb-space-telescope-trappist-1-system/">TRAPPIST-1e</a>, for example – we still have to measure how much of these gases are present to draw meaningful conclusions. This isn’t straightforward as the signals can overlap and need to be carefully disentangled.</p>
<p>Even if we do detect and accurately measure one of our possible biosignature gases, I don’t think we could claim to have detected alien life. JWST is only just opening up a new, rich laboratory of planetary atmospheres, and as we explore no doubt we will find many of our previous assumptions are proven wrong. </p>
<p>Jumping to conclusions about aliens every time we find something unusual would be premature. A JWST biosignature detection would be an interesting hint, with the promise of a great deal more work to do. As an astronomer, that’s exciting enough for me.</p><img src="https://counter.theconversation.com/content/192445/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Joanna Barstow receives funding from the Science and Technology Faciliites Council. She is a Councillor and Trustee of the Royal Astronomical Society.</span></em></p>New telescope allows us to study the atmospheres of planets orbiting stars other than our Sun in unprecedented detail.Joanna Barstow, Ernest Rutherford Fellow, The Open UniversityLicensed as Creative Commons – attribution, no derivatives.