tag:theconversation.com,2011:/uk/topics/exoplanet-discovery-35652/articlesExoplanet discovery – The Conversation2023-11-30T19:06:13Ztag: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>
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<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/1291622020-05-27T19:02:32Z2020-05-27T19:02:32ZHow Europe’s CHEOPS satellite will improve the hunt for exoplanets<figure><img src="https://images.theconversation.com/files/337727/original/file-20200526-106862-1sqt0ep.jpg?ixlib=rb-1.1.0&rect=23%2C5%2C3958%2C2233&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Artist's impression of CHEOPS in orbit above Earth. In this view the satellite's telescope cover is closed.</span> <span class="attribution"><a class="source" href="https://www.esa.int/ESA_Multimedia/Missions/CHEOPS/(offset)/200/(sortBy)/published/(result_type)/images">ESA / ATG medialab</a></span></figcaption></figure><p>While the planet has been on lockdown the last two months, a new space telescope called <a href="https://cheops.unibe.ch/">CHEOPS</a> opened its eyes, took its first pictures of the heavens and is now open for business. </p>
<p>The CHEOPS mission adds a unique twist in the science that the public normally associates with planet discovery missions like <a href="https://www.nasa.gov/mission_pages/kepler/main/index.html">Kepler</a> and <a href="https://www.nasa.gov/tess-transiting-exoplanet-survey-satellite">TESS</a>. Kepler and TESS produced <a href="http://doi.org/10.3847/1538-4365/aab4f9">many groundbreaking discoveries</a> and brought the number of known exoplanets into the thousands – so many that we’ve only scratched the surface of what we can learn from them. Consequently, rather than simply finding more planets, the primary objective of CHEOPS is to better understand the planets that we’ve already found.</p>
<p><a href="http://www.physics.unlv.edu/%7Ejsteffen/">I have been in the exoplanet field</a> for the better part of two decades. For most of that time I had the good fortune to work on NASA’s Kepler mission. Among Kepler’s major discoveries is the baffling array of planets that it found. Two prime examples are the thousands of planets whose sizes fall in the gap between Earth and Neptune. <a href="https://doi.org/10.1016/j.newar.2019.03.006">Kepler also found planets with orbits</a> that are only a few hours long. None of these planets has counterparts in the solar system. What these planets are like, how they form and how they arrived at their current state are matters of ongoing research. To better understand these planets, we need to have better measurements of their properties – their sizes, masses, composition and atmospheres. Astronomers will turn to CHEOPS to fill these gaps in our knowledge.</p>
<h2>CHEOPS mission overview</h2>
<p>A joint Swiss-ESA mission, CHEOPS, the “Characterizing Exoplanet Satellite,” will make key measurements of the size and albedo (reflectivity) of planets that orbit distant stars. CHEOPS launched in December of 2019 from the northern coast of South America, hitching a ride as a secondary passenger on a big Soyuz rocket.</p>
<p>The challenge with most of the planets discovered by the Kepler mission is that they orbit faint stars, making them difficult to observe with any telescope other than Kepler itself (which has finished its work and is no longer operating). CHEOPS, on the other hand, will observe planets orbiting bright stars that haven’t been studied with the level of detail once provided by Kepler, and that CHEOPS is now able to provide. These planets are more amenable to the wide variety of complementary observations from instruments on other telescopes – giving new insights into the nature of these recently discovered planets.</p>
<p>CHEOPS was placed in a “Sun-synchronous” orbit where it stays constantly above the Earth’s terminator – the line on the Earth that separates day from night. The satellite observes planets as they transit in front of their host stars using a 32-centimeter mirror. The telescope is 10 times smaller than Kepler, but since it will observe brighter stars, it can achieve a precision similar to Kepler – a fact demonstrated during its commissioning stage. And instead of continuously (and simultaneously) observing a hundred thousand stars in order to discover new planets, CHEOPS looks at individual targets when and where the planet is known to be there.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/337092/original/file-20200522-124836-15o5omi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/337092/original/file-20200522-124836-15o5omi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/337092/original/file-20200522-124836-15o5omi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/337092/original/file-20200522-124836-15o5omi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/337092/original/file-20200522-124836-15o5omi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/337092/original/file-20200522-124836-15o5omi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/337092/original/file-20200522-124836-15o5omi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/337092/original/file-20200522-124836-15o5omi.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">CHEOPS obtains its first exoplanet light curve.</span>
<span class="attribution"><a class="source" href="https://www.esa.int/ESA_Multimedia/Missions/CHEOPS/(result_type)/images">ESA/Airbus/CHEOPS</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>Science from the CHEOPS mission</h2>
<p>For the brightest Sun-like stars, CHEOPS can measure the sizes of planets as small as the Earth by seeing the fraction of the starlight that is blocked by the planet as it passes in front of the star. The improved measurements of planet sizes allow scientists to determine a planet’s density, giving insights into its composition and interior structure. They also establish the key relationship between planetary sizes and their masses, which tells us more about the traits shared by planets across many systems.</p>
<p>In addition to planet sizes, CHEOPS can measure a planet’s “phase curve,” the variation in brightness due to the changing profile of the planet as it orbits its host star (like the changing phases of the Moon). The phase curve tells us how much light is reflected by the planet and, therefore, some of the properties of its surface, atmosphere and clouds. This information, in turn, can tell us more about the conditions that might exist under the cloud tops and at a planet’s surface. Finally, since CHEOPS targets are bright, they are good candidates for detailed observations of their atmospheres using large ground-based and space-based telescopes (like the <a href="https://www.eso.org/public/usa/teles-instr/elt/">Extremely Large Telescope</a> and the <a href="https://www.jwst.nasa.gov/">James Webb Space Telescope</a>).</p>
<p>Ultimately, by better understanding the properties of planets orbiting other stars, astronomers can better understand the nature of the planets in our own solar system. We will better see how our planetary siblings fit into the broader context of planets in the galaxy and how our formation and history is similar to, or different from, these alien worlds.</p>
<p>[<em>You’re smart and curious about the world. So are The Conversation’s authors and editors.</em> <a href="https://theconversation.com/us/newsletters/weekly-highlights-61?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=weeklysmart">You can get our highlights each weekend</a>.]</p><img src="https://counter.theconversation.com/content/129162/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jason Steffen receives funding from NASA and the National Science Foundation. </span></em></p>The primary objective of CHEOPS is to better understand the planets that we’ve already found. And its mission is now in full swing.Jason Steffen, Assistant Professor of Physics and Astronomy, University of Nevada, Las VegasLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1292902020-01-07T00:43:45Z2020-01-07T00:43:45ZAn Earth-sized planet found in the habitable zone of a nearby star<figure><img src="https://images.theconversation.com/files/308458/original/file-20200103-11891-16j6k7w.jpg?ixlib=rb-1.1.0&rect=26%2C17%2C5865%2C3413&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An artist's impression of an exoplanet in the habitable zone around a star.</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/feature/goddard/2019/nasa-s-hubble-finds-water-vapor-on-habitable-zone-exoplanet-for-1st-time">ESA/Hubble, M. Kornmesser</a></span></figcaption></figure><p>A few months ago a group of NASA exoplanet astronomers, who are in the business of discovering planets around other stars, called me into a secret meeting to tell me about a planet that had captured their interest. Because <a href="https://scholar.google.com/citations?user=SVYEFJcAAAAJ&hl=en">my expertise</a> lies in modeling the climate of exoplanets, they asked me to figure out whether this new planet was habitable – a place where liquid water might exist. </p>
<p>These NASA colleagues, <a href="https://science.gsfc.nasa.gov/sed/bio/joshua.e.schlieder">Josh Schlieder</a> and his students <a href="https://astro.uchicago.edu/people/emily-gilbert.php">Emily Gilbert</a>, <a href="https://science.gsfc.nasa.gov/sed/bio/thomas.barclay">Tom Barclay</a> and <a href="https://science.gsfc.nasa.gov/sed/bio/elisa.quintana">Elisa Quintana</a>, had been studying data from TESS (<a href="https://www.nasa.gov/tess-transiting-exoplanet-survey-satellite">Transiting Exoplanet Survey Satellite</a>) when they discovered what may be TESS’ first known Earth-sized planet in a zone where liquid water could exist on the surface of a terrestrial planet. This is very exciting news because this new planet is relatively close to Earth, and it may be possible to observe its atmosphere with either the <a href="https://www.jwst.nasa.gov/">James Webb Space Telescope</a> or ground-based large telescopes. </p>
<h2>Habitable zone planets</h2>
<p>The host star of the planet that <a href="https://arxiv.org/abs/2001.00952">Gilbert’s team discovered</a> is called TESS of Interest number 700, or TOI-700. Compared to the Sun, it is a small, dim star. It is 40% the size, only about 1/50 of the Sun’s brightness and is located about 100 light-years from Earth in the constellation Dorado, which is visible from our Southern Hemisphere. For comparison, the nearest star to us, Proxima Centauri, is 4.2 light-years away from Earth. To get a sense of these distances, if you were to travel on the fastest spacecraft (<a href="http://parkersolarprobe.jhuapl.edu">Parker Solar Probe</a>) to reach Proxima Centauri, it would take nearly 20,000 years.</p>
<p>There are three planets around TOI-700: b, c and d. Planet d is Earth-size, within the star’s habitable zone and orbits TOI-700 every 37 days. My colleagues wanted me to create a climate model for Planet d using the known properties of the star and planet. Planets b and c are Earth-size and mini-Neptune-size, respectively. However, they orbit much closer to their host star, receiving 5 times and 2.6 times the starlight that our own Earth receives from the Sun. For comparison, Venus, a dry and hellishly hot world with surface temperature of approximately 860 degrees Fahrenheit, receives twice the sunlight of Earth.</p>
<p>Until about a decade ago, only two habitable zone planets of any size were known to astronomers: Earth and Mars. Within the last decade, however, thanks to discoveries made through both ground-based telescopes and the <a href="https://www.nasa.gov/mission_pages/kepler/main/index.html">Kepler mission</a> (which also looked for exoplanets from 2009 to 2019, but is now retired), astronomers have discovered about a dozen terrestrial-sized exoplanets. These are between half and two times larger than the Earth within the habitable zones of their host stars. </p>
<p>Despite the relatively large number of small exoplanet discoveries to date, the majority of stars are between 600 to 3,000 light-years away from Earth – too far and dim for detailed follow-up observation. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/QU0qsIGS6MQ?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">TESS has discovered its first Earth-size planet in its star’s habitable zone, the range of distances where conditions may be just right to allow the presence of liquid water on the surface.</span></figcaption>
</figure>
<h2>Why is liquid water important for habitability?</h2>
<p>Unlike Kepler, TESS’ mission is to search for planets around the Sun’s nearest neighbors: those bright enough for follow-up observations. </p>
<p>Between April 2018 and now, TESS discovered more than 1,500 planet candidates. Most are more than twice the size of Earth with orbits of less than 10 days. Earth, of course, takes 365 days to orbit around our Sun. As a result, the planets receive significantly more heat than Earth receives from the Sun and are too hot for liquid water to exist on the surface. </p>
<p>Liquid water is essential for habitability. It provides a medium for chemicals to interact with each other. While it is possible for exotic life to exist at higher pressures, or hotter temperatures – like the extremophiles found near hydro-thermal vents or the microbes found half a mile beneath the West Antarctic ice sheet – those discoveries were possible because humans were able to directly probe those extreme environments. They would not have been detectable from space. </p>
<p>When it comes to finding life, or even habitable conditions, beyond our solar system, humans depend entirely upon remote observations. Surface liquid water may create habitable conditions that can potentially promote life. These life forms can then interact with the atmosphere above, creating remotely detectable bio-signatures that Earth-based telescopes can detect. These bio-signatures could be current Earth-like gas compositions (oxygen, ozone, methane, carbon dioxide and water vapor), or the composition of ancient Earth 2.7 billion years ago (mostly methane and carbon dioxide, and no oxygen).</p>
<p>We know one such planet where this has already happened: Earth. Therefore, astronomers’ goal is to find those planets that are about Earth-size, orbiting at those distances from the star where water could exist in liquid form on the surface. These planets will be our primary targets to hunt for habitable worlds and signatures of life outside our solar system.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/308701/original/file-20200106-123381-1lx7dio.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/308701/original/file-20200106-123381-1lx7dio.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/308701/original/file-20200106-123381-1lx7dio.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/308701/original/file-20200106-123381-1lx7dio.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/308701/original/file-20200106-123381-1lx7dio.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/308701/original/file-20200106-123381-1lx7dio.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/308701/original/file-20200106-123381-1lx7dio.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/308701/original/file-20200106-123381-1lx7dio.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The three planets of the TOI 700 system orbit a small, cool M dwarf star. TOI 700 d is the first Earth-size habitable-zone world discovered by TESS.</span>
<span class="attribution"><span class="source">NASA's Goddard Space Flight Center</span></span>
</figcaption>
</figure>
<h2>Possible climates for planet TOI-700 d</h2>
<p>To prove that TOI-700 d is real, Gilbert’s team needed to confirm using data from a different type of telescope. TESS detects planets when they cross in front of the star, causing a dip in the starlight. However, such dips could also be created by other sources, such as spurious instrumental noise or binary stars in the background eclipsing each other, creating false positive signals. Independent observations came from <a href="https://exoplanets.cfa.harvard.edu/people/joseph-rodriguez">Joey Rodriguez</a> at Center for Astrophysics at Harvard University. Rodriguez and his team <a href="https://arxiv.org/abs/2001.00954">confirmed the TESS detection of TOI-700 d</a> with the <a href="http://www.spitzer.caltech.edu/">Spitzer telescope</a>, and removed any remaining doubt that it is a genuine planet.</p>
<p>My student <a href="https://science.gsfc.nasa.gov/sed/bio/gabrielle.engelmann-suissa">Gabrielle Engelmann-Suissa</a> and I used our modeling software to figure out what type of <a href="https://arxiv.org/abs/2001.00955">climate might exist on planet TOI-700 d</a>. Because we do not yet know what kind of gases this planet may actually have in its atmosphere, we use our climate models to explore possible gas combinations that would support liquid oceans on its surface. Engelmann-Suissa, with the help of my longtime collaborator <a href="https://www.researchgate.net/profile/Eric_Wolf3">Eric Wolf</a>, tested various scenarios including the current Earth atmosphere (77% nitrogen, 21% oxygen, remaining methane and carbon dioxide), the composition of Earth’s atmosphere 2.7 billion years ago (mostly methane and carbon dioxide) and even a Martian atmosphere (a lot of carbon dioxide) as it possibly existed 3.5 billion years ago. </p>
<p>Based on our models, we found that if the atmosphere of planet TOI-700 d contains a combination of methane or carbon dioxide or water vapor, the planet could be habitable. Now our team needs to confirm these hypotheses with the James Webb Space Telescope. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/308466/original/file-20200103-11914-1nt7jrs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/308466/original/file-20200103-11914-1nt7jrs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=202&fit=crop&dpr=1 600w, https://images.theconversation.com/files/308466/original/file-20200103-11914-1nt7jrs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=202&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/308466/original/file-20200103-11914-1nt7jrs.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=202&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/308466/original/file-20200103-11914-1nt7jrs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=254&fit=crop&dpr=1 754w, https://images.theconversation.com/files/308466/original/file-20200103-11914-1nt7jrs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=254&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/308466/original/file-20200103-11914-1nt7jrs.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=254&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Bacteria living in harsh conditions like this geothermal basin in Yellowstone National Park provide clues about habitable zones on other planets.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/scenic-view-colorful-geothermal-basin-yellowstone-174313916">1tomm/Shutterstock.com</a></span>
</figcaption>
</figure>
<h2>Strange new worlds and their climates</h2>
<p>The climate simulations our NASA team has completed suggest that an Earth-like atmosphere and gas pressure isn’t adequate to support liquid water on its surface. If we put the same quantity of greenhouse gases as we have on Earth on TOI-700 d, the surface temperature on this planet would still be below freezing. </p>
<p>Our own atmosphere supports a liquid ocean on Earth now because our star is quite big and brighter than TOI-700. One thing is for sure: All of our teams’ modeling indicates that the climates of planets around small and dim stars like TOI-700 are very unlike what we see on our Earth. </p>
<p>The field of exoplanets is now in a transitional era from discovering them to characterizing their atmospheres. In the history of astronomy, new techniques enable new observations of the universe including surprises like the discovery of hot-Jupiters and mini-Neptunes, which have no equivalent in our solar system. The stage is now set to observe the atmospheres of these planets to see which ones have conditions that support life. </p>
<p>[ <em>You’re smart and curious about the world. So are The Conversation’s authors and editors.</em> <a href="https://theconversation.com/us/newsletters/weekly-highlights-61?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=weeklysmart">You can get our highlights each weekend</a>. ]</p><img src="https://counter.theconversation.com/content/129290/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ravi kumar Kopparapu receives funding from NASA.</span></em></p>NASA scientists have discovered a new planet orbiting around a nearby star that is in a habitable zone. But does this planet have liquid oceans that can support life?Ravi Kumar Kopparapu, Research Scientist of Planetary Studies, NASALicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1245592019-12-19T13:49:57Z2019-12-19T13:49:57ZA real-life deluminator for spotting exoplanets by reflected starlight<figure><img src="https://images.theconversation.com/files/306421/original/file-20191211-95153-m2drqo.jpg?ixlib=rb-1.1.0&rect=4%2C13%2C696%2C709&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An artist's conception of WASP-18b, a giant exoplanet that orbits very close to its star.</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/chandra/multimedia/wasp18-2014.html">X-ray: NASA/CXC/SAO/I.Pillitteri et al; Optical: DSS</a></span></figcaption></figure><p>Perhaps you remember the opening scene of “Harry Potter and the Sorcerer’s Stone” that took place on Privet Drive. A bearded man pulled a mysterious device, called a deluminator, from his dark robe and one by one the lights from the street lamps flew into it.</p>
<p>For the last decade or more, Muggles around the world – including me – have been busy designing and perfecting a similar device called a coronagraph. It blocks light from stars so scientists can take pictures of planets orbiting them – the exoplanets.</p>
<p>More than 500 years ago <a href="https://www.britannica.com/biography/Giordano-Bruno">Italian friar Giordano Bruno</a> postulated that stars in the night sky were like our Sun with planets orbiting them, some of which likely harbored life. Starting in the 1990s, using ground-based and satellite observations astronomers have gathered evidence of the existence of <a href="https://exoplanetarchive.ipac.caltech.edu">thousands of extra-solar planets</a> or exoplanets. The discovery of exoplanets earned the <a href="https://www.nobelprize.org/prizes/physics/2019/summary/">2019 Nobel Prize in Physics</a>.</p>
<p>The next major milestone in exoplanetary research is imaging and characterizing Jupiter-sized exoplanets in visible light because imaging Earth-size planets is much more difficult. However, imaging exo-Jupiters would show that astromomers have all necessary tools to image and characterize Earth-size planets in the habitable zones of nearby stars, where life might exist. Space missions capable of imaging exo-Earths in their habitable zones, such as Habitable Exoplanet Observatory or <a href="https://www.jpl.nasa.gov/habex/">HabEx</a> and Large UV/Optical/IR Surveyor or <a href="https://asd.gsfc.nasa.gov/luvoir/">LUVOIR</a>, are currently being designed by scientists and engineers around the globe and are at least a decade away from their flight.</p>
<p>In preparation for these flagship-class missions, it is critical that key technologies and software tools are developed and validated. A coronagraph is essential to all of these imaging efforts.</p>
<p><a href="https://www.uml.edu/Research/LoCSST/default.aspx">I am a professor of physics</a> and lead a research group that has designed many experiments that have flown on NASA missions. For the last decade or so, our team has been developing technologies needed to directly image and characterize exoplanets around nearby stars and test them aboard rockets and balloons before they can be selected for flight on major space missions. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/306410/original/file-20191211-95153-cfe0qs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/306410/original/file-20191211-95153-cfe0qs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/306410/original/file-20191211-95153-cfe0qs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/306410/original/file-20191211-95153-cfe0qs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/306410/original/file-20191211-95153-cfe0qs.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/306410/original/file-20191211-95153-cfe0qs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/306410/original/file-20191211-95153-cfe0qs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/306410/original/file-20191211-95153-cfe0qs.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">This artist’s conception depicts the Kepler-10 star system. The Kepler mission has discovered two planets around this star. Kepler-10b (dark spot against yellow star) is, to date, the smallest known rocky exoplanet outside our solar system. The larger object in the foreground is Kepler-c. Both planets would be blistering hot worlds.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/mission_pages/kepler/multimedia/images/Kepler-10_family_portrait.html">NASA/Ames/JPL-Caltech</a></span>
</figcaption>
</figure>
<h2>Imaging exoplanets in visible light</h2>
<p>Even though we know about the existence of over 4,000 exoplanets, most were detected using indirect methods such as the dimming the light of the parent star when a planet passes in front and blocks some of its light – just like the <a href="https://www.jpl.nasa.gov/edu/events/2019/11/11/watch-the-transit-of-mercury-2019/">recent transit of Mercury</a>. This is the technique employed by the <a href="https://www.nasa.gov/mission_pages/kepler/overview/index.html">Kepler</a> and Transiting Exoplanet Survey Satellite or <a href="https://www.nasa.gov/tess-transiting-exoplanet-survey-satellite%20missions">TESS</a> missions. The 2019 Nobel Prize winners used <a href="https://www.universetoday.com/138014/radial-velocity-method/">another indirect method</a>, that relies on the measurement of minute and periodic motion of stars caused by planets orbiting them. But a photograph of an exoplanet, with characteristics similar to those in our Solar System, has not yet been taken.</p>
<p>Imaging exoplanets is hard. For example, even a huge planet like Jupiter is a billion times dimmer than the Sun. And when seen from far away, the Earth is 10 times dimmer than Jupiter. But the difficulty of imaging exoplanets is not because they are dim – large telescopes including the Hubble Space Telescope have imaged much fainter objects. </p>
<p>The challenge of imaging exoplanets has to do with taking a picture of a very faint object that is close to a much brighter one. Since the stars and their planets are far away, when photographed they appear as one bright spot in the sky, just like the headlights of a car look like one bright light from a distance. So, the challenge of imaging even the nearest exoplanet is akin to a person in California taking a picture of a fly 10 feet away from the bright light of a lighthouse in Massachusetts. </p>
<p>My research group recently flew a high-altitude balloon experiment named <a href="http://doi.org/10.1117/1.JATIS.1.4.044001">Planetary Imaging Concept Testbed Using a Recoverable Experiment – Coronagraph (PICTURE-C)</a> that tested the coronagraph’s ability to work in space to image exoplanets and their environments. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/298853/original/file-20191028-114005-1i5bmsb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/298853/original/file-20191028-114005-1i5bmsb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/298853/original/file-20191028-114005-1i5bmsb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/298853/original/file-20191028-114005-1i5bmsb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/298853/original/file-20191028-114005-1i5bmsb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/298853/original/file-20191028-114005-1i5bmsb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/298853/original/file-20191028-114005-1i5bmsb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The completed payload being readied on the morning of its flight.</span>
<span class="attribution"><span class="source">UMass Lowell</span></span>
</figcaption>
</figure>
<h2>Key components of PICTURE-C instrument</h2>
<p>PICTURE-C’s coronagraph creates artificial eclipses to dim or eliminate starlight without dimming the planets that the stars illuminate. It is designed to capture faint asteroid belt like objects very close to the central star.</p>
<p>While a coronagraph is necessary for direct imaging of exoplanets, our 6,000 pound device also includes deformable mirrors to correct the shape of the the telescope mirrors that get distorted due to changes in gravity, temperature fluctuations and other manufacturing imperfections. </p>
<p>Finally, the entire device has to be held steady in space for relatively long periods of time. A specially NASA-designed gondola called Wallops Arc Second Pointer (WASP) carried PICTURE-C and got us part way. An internal image stabilization system designed by my colleagues provided the “steady hand” necessary.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/306885/original/file-20191213-85417-1uvyvd.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/306885/original/file-20191213-85417-1uvyvd.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/306885/original/file-20191213-85417-1uvyvd.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=337&fit=crop&dpr=1 600w, https://images.theconversation.com/files/306885/original/file-20191213-85417-1uvyvd.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=337&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/306885/original/file-20191213-85417-1uvyvd.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=337&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/306885/original/file-20191213-85417-1uvyvd.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=423&fit=crop&dpr=1 754w, https://images.theconversation.com/files/306885/original/file-20191213-85417-1uvyvd.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=423&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/306885/original/file-20191213-85417-1uvyvd.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=423&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">PICTURE-C in flight with its telescope pointed at a star and the cloud-covered Earth illuminated by sunlight.</span>
<span class="attribution"><span class="source">Supriya Chakrabarti</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>The maiden flight of PICTURE-C</h2>
<p>After many tests to demonstrate that all systems were ready for flight our team launched PICTURE-C on the morning of September 29, 2019 from Ft. Sumner, New Mexico.</p>
<p>After the 20-hour test flight confirming that all systems worked well, PICTURE-C returned to the Earth using its parachute to land softly. The experiment has been recovered and returned to our laboratory. PICTURE-C wasn’t supposed to actually discover any exoplanets on its first test run. But it will fly again on another balloon when it will photograph several stars to explore if any of them have asteroid belts. These would be easier to see, and if we are lucky, it will snap a shot of a Jupiter-sized planet in September 2020.</p>
<p>[ <em><a href="https://theconversation.com/us/newsletters?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=expertise">Expertise in your inbox. Sign up for The Conversation’s newsletter and get a digest of academic takes on today’s news, every day.</a></em> ]</p><img src="https://counter.theconversation.com/content/124559/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Supriya Chakrabarti receives funding from NASA.
</span></em></p>Sometimes it is difficult to take a photograph of an exoplanet because the star illuminating it is too bright. Now there is a new ‘deluminator’ telescope that can block out the extra light.Supriya Chakrabarti, Professor of Physics, UMass LowellLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1249302019-10-08T21:49:46Z2019-10-08T21:49:46ZNobel Prize in Physics for two breakthroughs: Evidence for the Big Bang and a way to find exoplanets<figure><img src="https://images.theconversation.com/files/296084/original/file-20191008-128652-16ovxuu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Artist's rendering of a Jupiter-sized exoplanet and its host, a star slightly more massive than our sun. Image credit:</span> <span class="attribution"><a class="source" href="https://www.jpl.nasa.gov/news/news.php?feature=4674">ESO/NASA</a></span></figcaption></figure><p>Did the universe really begin with a Big Bang? And if so, is there evidence? Are there planets around other stars? Can they support life? </p>
<p>The 2019 Nobel Prize in Physics goes to three scientists who have provided deep insights into all of these questions. </p>
<p>James Peebles, <a href="https://phy.princeton.edu/people/p-james-peebles">an emeritus professor of physics</a> at Princeton University, won half the prize for a body of work he completed since the 1960s, when he and a team of physicists at Princeton attempted to detect the remnant radiation of the dense, hot ball of gas at the beginning of the universe: the Bang Bang. </p>
<p>The other half went to Michel Mayor, <a href="http://www.planetary.org/connect/our-experts/profiles/michel-mayor.html">an emeritus professor of physics from the University of Geneva</a>, together with Didier Queloz, <a href="http://obswww.unige.ch/%7Equeloz/Welcome.html">also a Swiss astrophysicist at the University of Geneva</a> and <a href="https://www.astro.phy.cam.ac.uk/directory/prof-didier-queloz">the University of Cambridge</a>. Both made breakthroughs with the discovery of the first planets orbiting other stars, also known as exoplanets, beyond our solar system.</p>
<p>I am an <a href="http://www.novastella.org">astrophysicist</a> and was delighted to hear of this year’s Nobel recipients, who had a profound impact on scientists’ understanding of the universe. A lot of my own work on exploding stars is guided by theories describing the structure of the universe that James Peebles himself laid down. </p>
<p>In fact, one might say that Peebles, of all this year’s Nobel winners, is the biggest star of the real “Big Bang Theory.” </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/296088/original/file-20191008-128681-quk6go.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/296088/original/file-20191008-128681-quk6go.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/296088/original/file-20191008-128681-quk6go.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=300&fit=crop&dpr=1 600w, https://images.theconversation.com/files/296088/original/file-20191008-128681-quk6go.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=300&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/296088/original/file-20191008-128681-quk6go.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=300&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/296088/original/file-20191008-128681-quk6go.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=377&fit=crop&dpr=1 754w, https://images.theconversation.com/files/296088/original/file-20191008-128681-quk6go.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=377&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/296088/original/file-20191008-128681-quk6go.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=377&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Nobel Prize winners in physics, from left, James Peebles in Princeton, N.J., Didier Queloz in London and Michel Mayor in Madrid.</span>
<span class="attribution"><a class="source" href="http://www.apimages.com/metadata/Index/Nobel-Physics/38f8572988cd40fdba43aab73b2a714b/29/0">AP Photo/Frank Augstein</a></span>
</figcaption>
</figure>
<h2>The real Big Bang Theory</h2>
<p>As Peebles and his Princeton team rushed to complete their discovery in 1964, they were scooped by two young scientists at nearby Bell Labs, <a href="https://www.nobelprize.org/prizes/physics/1978/penzias/biographical/">Arno Penzias</a> and <a href="https://www.nobelprize.org/prizes/physics/1978/wilson/biographical/">Robert Wilson</a>. The remaining radiation from the Big Bang was predicted to be microwave energy, in much the same form used by countertop ovens.</p>
<p>It was a serendipitous finding because Penzias and Wilson had constructed an antenna to detect this microwave radiation which was used in satellite communications. But they were mystified by a persistent source of noise in their measurements, like the fuzz of a radio tuned between stations. </p>
<p>Penzias and Wilson talked to Peebles and his colleagues and learned that this static they were hearing was the radiation left over from the Big Bang itself. Penzias and Wilson <a href="https://www.nobelprize.org/prizes/physics/1978/summary/">won the Nobel Prize in 1978</a> for their discovery, though Peebles and his team <a href="https://doi.org/10.1086/148306">provided the crucial interpretation</a>. </p>
<p>Peebles has also made decades of pivotal contributions to the study of the matter which pervades the cosmos but is invisible to telescopes, known as <a href="https://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy">dark matter</a>, and the equally mysterious energy of empty space, known as dark energy. He has done foundational work on the formation of galaxies, as well as to how the Big Bang gave rise to the first elements – hydrogen, helium, lithium – on the <a href="https://pubchem.ncbi.nlm.nih.gov/periodic-table/">periodic table</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/296085/original/file-20191008-128648-1ijlkkj.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/296085/original/file-20191008-128648-1ijlkkj.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/296085/original/file-20191008-128648-1ijlkkj.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=346&fit=crop&dpr=1 600w, https://images.theconversation.com/files/296085/original/file-20191008-128648-1ijlkkj.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=346&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/296085/original/file-20191008-128648-1ijlkkj.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=346&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/296085/original/file-20191008-128648-1ijlkkj.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=434&fit=crop&dpr=1 754w, https://images.theconversation.com/files/296085/original/file-20191008-128648-1ijlkkj.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=434&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/296085/original/file-20191008-128648-1ijlkkj.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=434&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">First discovery of an exoplanet just earned the Nobel Prize for Physics.</span>
<span class="attribution"><a class="source" href="https://exoplanets.nasa.gov/resources/289/infographic-profile-of-planet-51-pegasi-b/">NASA/JPL-Caltech</a></span>
</figcaption>
</figure>
<h2>Finding planets beyond our solar system</h2>
<p>For their Nobel Prize-winning work, Mayor and Queloz carried out a survey of nearby stars using a <a href="http://www.obs-hp.fr/www/guide/elodie/elodie-eng.html">custom-built instrument</a>. Using this instrument, they could detect the wobble of a star – a sign that it is being tugged by the gravity of an orbiting exoplanet. </p>
<p>In 1995, in a landmark discovery <a href="https://doi.org/10.1038/378355a0">published in the journal Nature</a>, they found a star in the constellation Pegasus rapidly wobbling across the sky, in response to an unseen planet with half the mass of Jupiter. This exoplanet, dubbed <a href="https://exoplanets.nasa.gov/resources/289/infographic-profile-of-planet-51-pegasi-b/">51 Pegasi b</a>, orbits close to its central star, well within the orbit of Mercury in our own solar system, and completes one full orbit in just four days. </p>
<p>This surprising discovery of a “hot Jupiter,” quite unlike any planet in our own solar system, excited the astrophysical community and inspired many other research groups, including the <a href="https://exoplanets.nasa.gov/keplerscience/">Kepler space telescope team</a>, to search for exoplanets. </p>
<p>These groups are using both the same wobble detection method as well as new methods, such as looking for light dips caused by exoplanets passing over nearby stars. Thanks to these research efforts, more than 4,000 exoplanets have now been discovered.</p>
<p>[ <em><a href="https://theconversation.com/us/newsletters?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=expertise">Expertise in your inbox. Sign up for The Conversation’s newsletter and get a digest of academic takes on today’s news, every day.</a></em> ]</p><img src="https://counter.theconversation.com/content/124930/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Robert T Fisher receives funding from NASA. </span></em></p>Scientists who discovered planets in far off stellar systems and the fundamentals of the Big Bang Theory have earned the 2019 Nobel Prize in Physics.Robert T. Fisher, Associate Professor of Physics, UMass DartmouthLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1241502019-09-26T18:03:27Z2019-09-26T18:03:27ZExoplanet discovery blurs the line between large planets and small stars<figure><img src="https://images.theconversation.com/files/294148/original/file-20190925-51414-15r5rmu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Dome at Calar Alto Observatory. </span> <span class="attribution"><span class="source">Pedro Amado/Marco Azzaro - IAA/CSIC</span></span></figcaption></figure><p>The discovery of yet another exoplanet <a href="https://theconversation.com/more-than-1-000-new-exoplanets-discovered-but-still-no-earth-twin-59274">is no longer news</a>. More than 4,000 planets around other stars have now been found since the detection of the first one in 1995. As astronomers long suspected, or at least hoped, it seems that planets are ubiquitous in stellar systems and there are probably more planets than stars in our galaxy. </p>
<p>But a new discovery of a large planet orbiting the small star GJ3512 is worth noting. The paper, <a href="https://science.sciencemag.org/cgi/doi/10.1126/science.aay7775">published in Science</a>, challenges our understanding of how planets form – and further blurs the line between small, cool stars <a href="https://en.wikipedia.org/wiki/Brown_dwarf">known as brown dwarfs and planets</a>.</p>
<p>The star itself is a <a href="http://astronomy.swin.edu.au/cosmos/R/Red+Dwarf">red dwarf</a>, about 30 light years away, with a luminosity less than 0.2% that of the sun. It has around 12% of the sun’s mass and 14% of its radius. Such cool, dim stars are in fact the most common stars in the galaxy, but only one in ten of the known exoplanets have been found to orbit red dwarfs. </p>
<p>This is likely to be a selection effect. Red dwarfs are so dim that it is hard to detect their planets with the “<a href="https://theconversation.com/explainer-how-do-you-find-exoplanets-24153">Doppler shift method”</a>. This relies on detecting how the wavelength of the starlight gets periodically shifted (to blue or red) by a tiny amount as the unseen planet orbits, tugging the star to and fro. Several of the other planets that have been discovered orbiting red dwarf stars have instead been found by the transit method – looking at how a star’s light dims as a planet passes in front of it.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/294151/original/file-20190925-51452-wrm207.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/294151/original/file-20190925-51452-wrm207.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=436&fit=crop&dpr=1 600w, https://images.theconversation.com/files/294151/original/file-20190925-51452-wrm207.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=436&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/294151/original/file-20190925-51452-wrm207.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=436&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/294151/original/file-20190925-51452-wrm207.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=548&fit=crop&dpr=1 754w, https://images.theconversation.com/files/294151/original/file-20190925-51452-wrm207.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=548&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/294151/original/file-20190925-51452-wrm207.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=548&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Comparison of GJ 3512 to the Solar System and other nearby red-dwarf planetary systems.</span>
<span class="attribution"><span class="source">Guillem Anglada-Escude - IEEC, SpaceEngine.org</span></span>
</figcaption>
</figure>
<p>What makes the new discovery stand out is that the planet, dubbed GJ3512b, is a gas giant in a 204-day elliptical orbit. The planet has a mass of at least half that of Jupiter and its diameter is likely to be around 70% that of the star it orbits. It is therefore one of the largest planets known to be orbiting such a small star in such a wide orbit – and this poses a problem for understanding how it formed. </p>
<h2>Planet formation</h2>
<p>Our solar system was born out of a “<a href="https://theconversation.com/a-disc-of-dust-and-gas-found-around-a-newborn-planet-could-be-the-birthplace-of-moons-118260">protoplanetary disc</a>” – a cloud containing dense gas and dust surrounding our newly formed sun. </p>
<p>The most commonly accepted explanation for how the gas giant planets formed is that rocky icy cores were created by the accumulation of smaller bodies in the outer regions of the disc. This went on until these cores had built up to around ten Earth masses. At this point, they were able to gather a hydrogen and helium envelope before the planets migrated to the inner edge of the disc, or the disc dispersed. </p>
<p>This is how gas giant planets are believed to form in most exoplanetary systems, including so-called <a href="https://theconversation.com/uk-satellite-twinkle-will-reveal-atmospheres-of-distant-exoplanets-44945">“hot-Jupiters” discovered</a> in close, orbits around their stars. But it’s hard to see how planets could form in this way around a low mass star – the disc would not be massive enough. </p>
<p>An alternative scenario is likely to have happened in the case of GJ3512b – and potentially many other planetary systems out there. Here, it seems the planet may have formed by direct fragmentation of the protoplanetary disc. That means part of the disc collapsed and condensed (changing from gas to a liquid and thereafter solid) into a large body, without the need to build up by accumulation of smaller rocks. This is similar to the way in which <a href="https://www.scientificamerican.com/article/how-is-a-star-born/">stars themselves normally form</a>. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/294153/original/file-20190925-51401-nivgg8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/294153/original/file-20190925-51401-nivgg8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/294153/original/file-20190925-51401-nivgg8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/294153/original/file-20190925-51401-nivgg8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/294153/original/file-20190925-51401-nivgg8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/294153/original/file-20190925-51401-nivgg8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/294153/original/file-20190925-51401-nivgg8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">3.5-m telescope at the Calar Alto observatory where the CARMENES spectrograph is installed.</span>
<span class="attribution"><span class="source">Pedro Amado/Marco Azzaro - IAA/CSIC</span></span>
</figcaption>
</figure>
<p>The team behind the new study report further evidence for this formation route from hints of a second giant exoplanet in the system (tentatively called GJ3512c) with an orbital period in excess of 1,400 days. This might also explain the unusually eccentric orbit of GJ3512b, which may have resulted from interactions between the two planets soon after the planets formed. This process would have ejected a third planet from the system. And if three large planets once existed around such a small star, the only way they could have formed is by direct fragmentation of the disc.</p>
<h2>Star versus planet</h2>
<p>The discovery of this system also has implications <a href="https://www.space.com/42790-brown-dwarfs-coolest-stars-hottest-planets.html">for the debate</a> over what constitutes a <a href="https://en.wikipedia.org/wiki/Brown_dwarf">brown dwarf star</a> and what constitutes a planet. Brown dwarfs are stars that failed to initiate nuclear fusion in their cores, and so have a mass below about 8% that of the sun or roughly 85 Jupiter masses. </p>
<p>The lowest mass brown dwarfs known have masses as small as 12 times that of Jupiter, while the highest mass planets known have masses up to 30 times that of Jupiter. So, if the most massive planets are heavier than the least massive stars – what is it that distinguishes a star from a planet?</p>
<p>One answer is to say that stars form like stars do, and planets form like planets do, so mass is to some extent irrelevant. The problem is that normally we cannot tell how an individual planet or brown dwarf formed. In the case of GJ3512b, the likely formation method is more like that of a star than that of a planet.</p>
<p>So the picture is even more confused than it was before, and may only be solved by future discoveries. Increasing the census of planetary systems will ultimately show which formation mechanisms are most common.</p><img src="https://counter.theconversation.com/content/124150/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Andrew Norton has previously received funding from the Science & Technology Facilities Council (STFC). </span></em></p>The discovery of a huge planet orbiting a small star challenges our understanding of planet formation.Andrew Norton, Professor of Astrophysics Education, The Open UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1223682019-08-26T16:59:21Z2019-08-26T16:59:21ZAn exoplanet within arm’s reach: the Earth<figure><img src="https://images.theconversation.com/files/289322/original/file-20190825-170906-oypk77.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C7360%2C4737&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Landscape in the Var area of France with fossilised Permian pelites (Permian Middle, 270 Ma) and "muddle cracks".</span> <span class="attribution"><span class="license">Author provided</span></span></figcaption></figure><p><a href="https://www.ncbi.nlm.nih.gov/books/NBK217840/">Exobiology</a> is an exciting discipline. It is based simultaneously on the latest data from astrophysics, planetary geology and the origins of life on Earth, all of which are evolving as we continue to study them. It could be said that exobiology is essentially Earth-oriented, as it’s based primarily on knowledge learned here that we try to apply to other possible or observed situations.</p>
<p>As revealed through the study of geology, the biology of evolution allows us to understand how life forms came to populate our planet, and also to anticipate its future (an aspect that is unfortunately underdeveloped at present). Indeed, these disciplines are based on the assumption that the physicochemical and biological rules that are exerted on the Earth since it was formed are essentially the same elsewhere in the universe (all this in the absence of proof – yet – that life exists elsewhere).</p>
<h2>Reading the future from the past</h2>
<p>The study of the fossil record often upsets our preconceptions and constantly raises questions, almost as if we are regularly discovering a “new” planet. Indeed, whether it is at the beginning of the birth of life on Earth or in the great episodes of the evolution of the <a href="https://en.wikipedia.org/wiki/Paleozoic">Paleozoic</a> (the Primary Era) and the <a href="https://en.wikipedia.org/wiki/Mesozoic">Mesozoic</a> (the Secondary Era), many forms of life very different from those we know today emerged, developed and had their time of glory. </p>
<p>Alongside these successes are many extinct communities and lineages – trial runs, as it were. Some were present at the origin of life as we know it, others are known only by fossils. It’s as if each great stratum of life corresponded to different planetary conditions, with their particular procession of living creatures. How many more of these <a href="https://theconversation.com/are-the-paleozoic-eras-giant-dragonflies-still-among-us-102384">“exotic” forms of life</a> are waiting for us to be discovered in the Earth’s archives?</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/226785/original/file-20180709-122262-17iht74.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/226785/original/file-20180709-122262-17iht74.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/226785/original/file-20180709-122262-17iht74.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/226785/original/file-20180709-122262-17iht74.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/226785/original/file-20180709-122262-17iht74.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/226785/original/file-20180709-122262-17iht74.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/226785/original/file-20180709-122262-17iht74.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A paleontology laboratory in California.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:George_C._Page_Museum_Paleontology_Lab_04.jpg#/media/File:George_C._Page_Museum_Paleontology_Lab_04.jpg">Joe Mabel/Wikimedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>The <a href="https://en.wikipedia.org/wiki/Ediacaran_biota">Ediacaran fauna</a> in Australia (-575 Ma), the <a href="https://en.wikipedia.org/wiki/Burgess_Shale">Burgess faunas</a> in Canada (-625 Ma) and <a href="https://en.wikipedia.org/wiki/Maotianshan_Shales">Chengjiang fauna</a> (-530 Ma) in China testify to the complex lifeforms that arose early in the history of our planet that are now extinct. Recently the beautiful discovery of an <a href="https://en.wikipedia.org/wiki/Francevillian_biota">enigmatic fossil</a> in Gabon has pushed the beginnings of multicellular life to more than 2 billion years.</p>
<p>Much closer to us in time is amber, from the middle of the Cretaceous (99 million years), tree resin in which <a href="http://www.eartharchives.org/articles/trapped-in-time-the-top-10-amber-fossils/">plants, insects and even small animals</a> became trapped and that subsequently fossilised. They’re an extraordinary record of life on earth, including a fragment of <a href="https://www.cell.com/current-biology/fulltext/S0960-9822(16)31193-9">tail of a dinosaur</a> – with feathers.</p>
<p>For scientists, these previously unknown families, orders and forms suggest that the territories in which they developed were isolated, almost like planets themselves – ancient islands with unique fauna, the evolutionary hotspots of the past…</p>
<h2>What does the sci-fi say?</h2>
<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/226789/original/file-20180709-122247-1o30df7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/226789/original/file-20180709-122247-1o30df7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=848&fit=crop&dpr=1 600w, https://images.theconversation.com/files/226789/original/file-20180709-122247-1o30df7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=848&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/226789/original/file-20180709-122247-1o30df7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=848&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/226789/original/file-20180709-122247-1o30df7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1066&fit=crop&dpr=1 754w, https://images.theconversation.com/files/226789/original/file-20180709-122247-1o30df7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1066&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/226789/original/file-20180709-122247-1o30df7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1066&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The series <em>Terra Nova</em>.</span>
<span class="attribution"><span class="source">dvdbash.com</span></span>
</figcaption>
</figure>
<p>Science fiction tends to look at the fate of humanity in the future, or of time travellers as they search for resources on a long-ago Earth. They may seek to escape from the destruction of our planet (as in the series <a href="https://www.youtube.com/watch?v=8lGS0YyLU7E"><em>Terra Nova</em></a>) or be caught up in unearthly mysteries (<a href="https://www.youtube.com/watch?v=29bSzbqZ3xE"><em>Fringe</em></a>.</p>
<p>Indeed if the search for a habitable exoplanet could serve humanity (something central to the series <a href="https://www.youtube.com/watch?v=27JmggM5GGQ"><em>The Expanse</em></a>), reaching back to our planet’s “origins” is logical… if we could solve the problem of travel time and its associated paradoxes. If we change the past, what will be the impact on the “future” in which we now live? Fiction has extensively looked at <a href="https://en.wikipedia.org/wiki/Multiverse">multiverse hypotheses</a>, including <em>Men in Black</em> and <em>The Man in the High Castle</em>.</p>
<p>In the same way that we need to fully understand the Earth’s current biodiversity, the paleodiversity of our planet is full of information on the processes of evolution and functioning our planet, and even the discovery of new resources and, in a sense, “lost worlds” – <a href="https://en.wikipedia.org/wiki/Lake_Vostok">Lake Vostok</a> under the Antarctic ice sheet, the glacial valleys of Greenland revealed by melting ice…</p>
<h2>Preserve the archives of the Earth</h2>
<p>While understanding the past functioning of our planet is crucial, paleosciences aren’t yet in the spotlight in the academic world. The only exception is when they concern the “near” past and allow us to understand better the <a href="http://theconversation.com/co-levels-and-climate-change-is-there-really-a-controversy-119268">variations of the climate</a> and the development and lives of the first humans.</p>
<p>There is currently a lack of will to preserve the fossil record of our ancient rocks and sediments that is the Earth’s archives. Every day and everywhere on our planet, unpublished information is destroyed, crushed, ground, paved over, polluted, damaged. How many unique fossil biota have been yet destroyed ?. As with archaeology, we can’t keep everything from the past, but “preventive paleontology” is essential if we are to understand the origin of our planet and the life forms that have lived here.</p>
<p>Thankfully, there is an enthusiasm among the general public for these sciences of the past, from museum expositions to local initiatives. Investments in research and the preservation of our paleontological heritage can even be a source of geotourism. A leading example is South Africa, which as palaeontology a <a href="https://www.forbes.com/sites/shaenamontanari/2016/08/17/inside-the-dinosaur-paleontology-renaissance-in-south-africa/#249480e726d1">national cause</a> or public enthusiasm in Argentina (https://palaeo-electronica.org/content/2014/1003-comment-paleontology-in-argentina) and provides substantial resources. Compensating for the lack sufficient resources in the paleosciences, the work of <a href="https://en.wikipedia.org/wiki/Citizen_science">citizen scientists</a> also helps us to reach back into the Earth’s archives – and allow us to better understand its future.</p><img src="https://counter.theconversation.com/content/122368/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Romain Garrouste has received funding from MNHN, CNRS, Sorbonne University, Labex BIODiv, ANR and National Geographic.</span></em></p>The geological and biological archives of the Earth shed light on both the distant past of our planet and allow us to imagine its future.Romain Garrouste, Chercheur à l’Institut de systématique, évolution, biodiversité (UMR 7205 MNHN-CNRS-UPMC-EPHE-Univ. Antilles), Muséum national d’histoire naturelle (MNHN)Licensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1068622018-11-14T19:02:07Z2018-11-14T19:02:07ZA super-Earth found in our stellar back yard<figure><img src="https://images.theconversation.com/files/245246/original/file-20181113-194513-10nb2c1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An artist’s impression of the surface of the planet orbiting Barnard's Star.</span> <span class="attribution"><span class="source">ESO - M. Kornmesser</span></span></figcaption></figure><p>The potential discovery of a planet orbiting Barnard’s Star – the second closest stellar system to the Sun – was announced by researchers <a href="https://www.nature.com/articles/s41586-018-0677-y">today in Nature</a>.</p>
<p>This discovery pushes the bounds of what we can do with our best <a href="https://astrobites.org/2017/04/04/planet-or-noise/">current astronomical instrumentation</a>, so the authors are understandably cautious in claiming a “planet candidate”, rather than a confirmed discovery. </p>
<p>The new exoplanet (if it exists) is an icy world just over three times the mass of Earth, and has only been uncovered as a result of an exhaustive search by teams across the globe.</p>
<p>So what does this find mean, and why is it important?</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-are-there-living-things-on-different-galaxies-98562">Curious Kids: Are there living things on different galaxies?</a>
</strong>
</em>
</p>
<hr>
<h2>Barnard’s Star – an ancient cosmic tearaway</h2>
<p>Shining 16 times too faintly to see with the unaided eye, Barnard’s Star is an ancient <a href="https://www.youtube.com/watch?v=LS-VPyLaJFM">red dwarf</a> – significantly older than the Sun. Aside from the <a href="https://www.youtube.com/watch?v=8ESpLYWb9SQ">Alpha Centauri system</a>, it is the closest star to the Solar system. </p>
<p>Barnard’s Star’s biggest claim to fame is the rate at which it is tearing across the night sky. It moves so rapidly <a href="https://www.youtube.com/watch?v=bZfFdCknTQc">against the background stars</a> that it would cross the <a href="https://www.skyandtelescope.com/astronomy-blogs/on-the-move-with-barnards-star-and-61-cygni06032105/">diameter of the full Moon in a little over 100 years</a>.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/CJGn-2taacc?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Barnard’s Star is the fastest moving star in our night sky. Astronomer’s call such movement ‘proper motion’.</span></figcaption>
</figure>
<p>In the middle of the last century, astronomer Peter van de Kamp <a href="http://www.armaghplanet.com/blog/barnards-star-and-its-phantom-planets.html">was convinced Barnard’s star was accompanied by two Jupiter-mass planets</a>. Over several decades, starting in the late 1930s, he studied the star, taking myriad images, and observing it moving against the background stars. </p>
<p>Rather than moving in a straight line, his observations suggested Barnard’s Star was wobbling as it moved, <a href="https://www.youtube.com/watch?v=l46-8PvT44Y">rocking back and forth</a> as though pulled by unseen companions. His data invoked the presence of two planets tugging the star around as it moved through space.</p>
<p>But despite their best efforts, astronomers elsewhere could find no evidence of van de Kamp’s worlds. Where his observations showed a wobbling star, theirs showed no such wobble – just a linear motion through space.</p>
<p>What was going on? van de Kamp’s observations were made using a <a href="https://www.youtube.com/watch?v=_v1RWyzQAng">large refracting telescope</a>, and astronomers eventually realised that the telescope’s main objective lens had been cleaned and modified several times during the decades of his study. These changes caused the apparent position of the Barnard’s Star to shift back and forth relative to the bluer background stars.</p>
<p>The Jupiter-mass planets around Barnard’s star were no more.</p>
<p>Successive surveys ruled out ever smaller planets. Astronomers are now confident no planet larger than ten Earth masses exists in the system. Which brings us to our new find.</p>
<h2>The new discovery</h2>
<p>The new candidate planet, Barnard’s Star b, is thought to have a mass between those of Earth and Neptune in the Solar system. While no such planet exists in our backyard, the <a href="https://theconversation.com/keplers-findings-are-out-of-this-world-and-the-best-is-yet-to-come-5249">Kepler spacecraft</a> revealed that such planets are common in the cosmos.</p>
<p>Barnard’s Star b orbits its host at a distance of 60 million kilometres. That might suggest a warm, temperate world – but Barnard’s Star is a dim object, far less luminous than the Sun. As a result, Barnard’s Star b lies beyond what is known as the ice line, so far from the star that water would freeze harder than rock. This means it must be a frigid world.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/245247/original/file-20181113-194503-1c4awkb.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/245247/original/file-20181113-194503-1c4awkb.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/245247/original/file-20181113-194503-1c4awkb.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/245247/original/file-20181113-194503-1c4awkb.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/245247/original/file-20181113-194503-1c4awkb.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/245247/original/file-20181113-194503-1c4awkb.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/245247/original/file-20181113-194503-1c4awkb.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/245247/original/file-20181113-194503-1c4awkb.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">Artist’s impression of Barnard’s Star b under the orange-tinted light from its red dwarf host.</span>
<span class="attribution"><span class="source">IEEC/Science-Wave - Guillem Ramisa</span></span>
</figcaption>
</figure>
<p>But that icy orbit adds to our confidence that the planet could really be there. Planets form over millions of year in discs of material around young stars. Grains of dust (and ice) collide slowly, growing ever larger worlds. Eventually, the disc of gas and dust is blown away, leaving behind any planets it formed. </p>
<p>This predicts that planets will form most rapidly, and grow fastest, just beyond the ice line, where the presence of water ice will greatly increase the amount of solid material available to the growing world.</p>
<p>In other words, the most massive planet in a given system should form just beyond the ice line. That is true in the Solar system (Jupiter), and also seems true for Barnard’s Star – if the planet really exists.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/5ONxjXuQQVo?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Loacting Barnard’s Star candidate planet.</span></figcaption>
</figure>
<h2>The future – a timely find</h2>
<p>If Barnard’s Star b exists, its discovery could not have come at a more opportune time. As it orbits one of the Solar system’s closest neighbours, it presents a perfect target for future observations.</p>
<p>There are a few ways the planet’s existence could be verified. In the near future, the answer might come from the <a href="https://www.youtube.com/watch?v=Jdy09y0A4t0">GAIA spacecraft</a>, which has spent the past few years measuring the <a href="https://www.cosmos.esa.int/web/gaia/data-release-2">precise locations and distances of some two billion stars in the night sky</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/245248/original/file-20181113-194491-ixreuz.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/245248/original/file-20181113-194491-ixreuz.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/245248/original/file-20181113-194491-ixreuz.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=341&fit=crop&dpr=1 600w, https://images.theconversation.com/files/245248/original/file-20181113-194491-ixreuz.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=341&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/245248/original/file-20181113-194491-ixreuz.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=341&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/245248/original/file-20181113-194491-ixreuz.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=428&fit=crop&dpr=1 754w, https://images.theconversation.com/files/245248/original/file-20181113-194491-ixreuz.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=428&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/245248/original/file-20181113-194491-ixreuz.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=428&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Graphic representation of the relative distances to the nearest stars from the Sun.</span>
<span class="attribution"><span class="source">IEEC/Science-Wave - Guillem Ramisa</span></span>
</figcaption>
</figure>
<p>Every time GAIA observes Barnard’s Star, it measures its location with a precision far greater than any previous observatory could manage. If there is a planet orbiting the star, three times the mass of Earth, the same technique espoused by van de Kamp should reveal its presence. </p>
<p>In the coming decade, the <a href="https://www.youtube.com/watch?v=qwOE0y3K6Ew">next generation of astronomical observatory</a> will revolutionise our ability to peer into the space close to the nearest stars, looking for the dim glow of their planets, reflecting the light of their host stars.</p>
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Read more:
<a href="https://theconversation.com/a-goblin-could-guide-us-to-a-mystery-planet-thought-to-exist-in-the-solar-system-104325">A Goblin could guide us to a mystery planet thought to exist in the Solar system</a>
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<p>Because Barnard’s star is so close, the separation between the planet and star in the sky will be relatively large. If the planet is really there, we will likely get our first direct images confirming its existence within the next ten years.</p>
<p>Beyond that? Who knows. One thing we have learned through the exoplanet era is that, where one planet lurks, more are sure to follow. If the existence of Barnard’s Star b is confirmed, it may indicate there are other, smaller worlds orbiting this ancient star.</p><img src="https://counter.theconversation.com/content/106862/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jake Clark is supported by an Australian Government Research Training Program (RTP) Scholarship.</span></em></p><p class="fine-print"><em><span>Jonti Horner does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The new planet is believed to be orbiting Barnard’s Star, a red dwarf that’s not visible to the naked eye but one of the closest stars to our Solar System.Jonti Horner, Professor (Astrophysics), University of Southern QueenslandJake Clark, PhD Candidate, University of Southern QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/890242017-12-15T06:38:43Z2017-12-15T06:38:43ZGoogle’s artificial intelligence finds two new exoplanets missed by human eyes<figure><img src="https://images.theconversation.com/files/199386/original/file-20171215-17878-rik7zz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Artist impression of Kepler-90i, the eighth planet discovered orbiting around Kepler-90.</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/press-release/artificial-intelligence-nasa-data-used-to-discover-eighth-planet-circling-distant-star">NASA</a></span></figcaption></figure><p>Two new exoplanets have been discovered thanks to NASA’s collaboration with Google’s artificial intelligence (AI). One of those in <a href="https://arxiv.org/abs/1712.05044">today’s announcement</a> is an eighth planet – Kepler-90i – found orbiting the Sun-like star Kepler-90. This makes it the first system discovered with an equal number of planets to our own Solar system. </p>
<p>A mere road trip away, at 2,545 light-years from Earth, Kepler-90i orbits its host star every 14.4 Earth days, with a sizzling surface temperature similar to Venus of 426°C.</p>
<p>The new exoplanets are added to the growing list of known worlds found orbiting other stars. </p>
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<figcaption>
<span class="caption">The Kepler-90 planets have a similar configuration to our solar system with small planets found orbiting close to their star, and the larger planets found farther away.</span>
<span class="attribution"><span class="source">NASA/Ames Research Center/Wendy Stenzel</span></span>
</figcaption>
</figure>
<p>This new Solar system rival provides evidence that a similar process occurred within Kepler-90 that formed our very own planetary neighbourhood: small terrestrial worlds close to the host star, and larger gassy planets further away. But to say the system is a twin of our own Solar system is a stretch. </p>
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Read more:
<a href="https://theconversation.com/exoplanet-discovery-by-an-amateur-astronomer-shows-the-power-of-citizen-science-75912">Exoplanet discovery by an amateur astronomer shows the power of citizen science</a>
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<p>The entire Kepler-90 system of eight planets would easily fit within Earth’s orbit of the Sun. All eight planets, bar Kepler-90h, would be too hostile for life, lying outside the so-called <a href="https://arxiv.org/pdf/1708.01363.pdf">habitable zone</a>.</p>
<p>Evidence also suggests that planets within the Kepler-90 system started out farther apart, much like our own Solar system. Some form of migration occurred, dragging this system inwards, producing the orbits we see in Kepler-90 today. </p>
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<a href="https://images.theconversation.com/files/199346/original/file-20171215-26031-1637tt1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/199346/original/file-20171215-26031-1637tt1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/199346/original/file-20171215-26031-1637tt1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/199346/original/file-20171215-26031-1637tt1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/199346/original/file-20171215-26031-1637tt1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/199346/original/file-20171215-26031-1637tt1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/199346/original/file-20171215-26031-1637tt1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/199346/original/file-20171215-26031-1637tt1.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>
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<span class="caption">Kepler-90 is a Sun-like star, but all of its eight planets are scrunched into the equivalent distance of Earth to the Sun.</span>
<span class="attribution"><span class="source">NASA/Ames Research Center/Wendy Stenzel</span></span>
</figcaption>
</figure>
<p>Google’s collaboration with NASA’s space telescope Kepler mission has now opened up new and exciting opportunities into AI helping with scientific discoveries.</p>
<p>So how exactly did Google’s AI discover these planets? And what sort of future discoveries can this technology provide?</p>
<h2>Training AI for exoplanet discoveries</h2>
<p>Traditionally, software developers program computers to perform a particular task, from playing your favourite cat video, to determining exoplanetary signals from space based telescopes such as NASA’s Kepler Mission. </p>
<p>These programs are executed to serve a single purpose. Using code intended for cat videos to hunt exoplanets in <a href="https://youtu.be/BFi4HBUdWkk">light curves</a> would lead to some very interesting, yet false, results. </p>
<p>Googles’s AI is programmed rather differently, using machine learning. In machine learning, AI is trained through artificial neural networks – somewhat replicating our brain’s biological neural networks – to perform tasks like reading this article. It then learns from its mistakes, becoming more efficient at its particular task.</p>
<p>Google’s DeepMind AI, AlphaGo, was trained previously to play Go, an extremely complex yet elegant Chinese board game. Last year, <a href="https://theconversation.com/googles-go-victory-shows-ai-thinking-can-be-unpredictable-and-thats-a-concern-56209">AlphaGo defeated Lee Sedol</a>, the world’s best Go player, by four games to one. It simply trained itself by watching thousands of previously played games, then competing against itself.</p>
<p>In our exoplantary case, AI was trained to identify transiting exoplanets, sifting through 15,000 signals from the Kepler exoplanet catalogue. It learned what was and wasn’t a signal caused by an exoplanet eclipsing its host star. These 15,000 signals were previously vetted by NASA scientists prior to the AI’s training, guiding it to a 96% efficiency of detecting known exoplanets. </p>
<p>Researchers then directed their AI network to search in multiplanetary systems for weaker signals. This research culminated in <a href="https://www.nasa.gov/press-release/artificial-intelligence-nasa-data-used-to-discover-eighth-planet-circling-distant-star">today’s announcement</a> of both Kepler-90i and another Earth-sized exoplanet, Kepler-80g, in a separate planetary system.</p>
<h2>Hunting for more exoplanets using AI</h2>
<p>Google’s AI has analysed only 10% of the 150,000 stars NASA’s Kepler Mission has been eyeing off across the Milky Way galaxy. </p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/S_HRh0ZynjE?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">How AI helps in the hunt for other exoplanets.</span></figcaption>
</figure>
<p>There’s potential then for sifting through Kepler’s entire catalogue and finding other exoplanetary worlds that have either been skimmed by scientist or haven’t been checked yet, due to Kepler’s rich data set. And that’s exactly what Google’s researchers are planning to do.</p>
<p>Machine learning neural networks have been assisting astronomers for a few years now. But the potential for AI to assist in exoplanetary discoveries will only increase within the next decade. </p>
<h2>Beyond Kepler</h2>
<p>The Kepler mission has been running since 2009, with observations slowly coming to an end. Within the next 12 months, all of its on-board fuel will be fully depleted, ending what has been, one of the greatest scientific endeavours in modern times.</p>
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<span class="caption">NASA’s new TESS mission will inundate astronomers with 20,000 exoplanetary candidates in the next two years.</span>
<span class="attribution"><span class="source">Chet Beals/MIT Lincoln Lab</span></span>
</figcaption>
</figure>
<p>Kepler’s successor, the Transiting Exoplanet Survey Satellite (<a href="https://tess.gsfc.nasa.gov/">TESS</a>) will be launching this coming March. </p>
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Read more:
<a href="https://theconversation.com/a-machine-astronomer-could-help-us-find-the-unknowns-in-the-universe-68347">A machine astronomer could help us find the unknowns in the universe</a>
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<p>TESS is predicted to find 20,000 exoplanet candidates during its two-year mission. To put that into perspective, in the past 25 years, we’ve managed to discover just over 3,500. </p>
<p>This unprecedented inundation of exoplanetary data needs to either be confirmed by other transiting observations or other methods such as ground-based radial velocity measurements.</p>
<p>There just isn’t enough people-power to sift through all of this data. That’s why these machine learning networks are needed, so they can aid astronomers in sifting through big data sets, ultimately assisting in more exoplanetary discoveries. Which begs the question, who exactly gets credit for such a discovery?</p><img src="https://counter.theconversation.com/content/89024/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jake Clark is supported by an Australian Government Research Training Program (RTP) Scholarship.</span></em></p>Google’s artificial intelligence has been taught to look for planets around other stars. It’s already making new discoveries that scientists have missed.Jake Clark, PhD Student, University of Southern QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/870112017-11-15T19:19:36Z2017-11-15T19:19:36ZWe’ve found an exo-planet with an extraordinarily eccentric orbit<figure><img src="https://images.theconversation.com/files/193903/original/file-20171109-14221-1d2ramr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An artist's impression of the exoplanet in close orbit to a star.</span> <span class="attribution"><a class="source" href="http://www.spacetelescope.org/images/heic0807a/">ESA, NASA, G. Tinetti (University College London, UK & ESA) and M. Kornmesser (ESA/Hubble)</a></span></figcaption></figure><p>The discovery of a planet with a highly elliptical orbit around an ancient star could help us understand more about how planetary systems form and evolve over time.</p>
<p>The new planet, HD76920b, is four times the mass of Jupiter, and can be found some 587 light years away in the southern constellation Volans, the Flying Fish. At its closest it skims the surface of its host star, HD76920. At its furthest, it orbits almost twice as far from its star as Earth does from the Sun.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/193771/original/file-20171108-27001-la83tj.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/193771/original/file-20171108-27001-la83tj.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/193771/original/file-20171108-27001-la83tj.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=481&fit=crop&dpr=1 600w, https://images.theconversation.com/files/193771/original/file-20171108-27001-la83tj.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=481&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/193771/original/file-20171108-27001-la83tj.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=481&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/193771/original/file-20171108-27001-la83tj.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=604&fit=crop&dpr=1 754w, https://images.theconversation.com/files/193771/original/file-20171108-27001-la83tj.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=604&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/193771/original/file-20171108-27001-la83tj.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=604&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Superimposing HD76920b’s orbit on the Solar system shows how peculiar it is. Its orbit is more like that of the asteroid Phaethon than any of the Solar system’s planets.</span>
<span class="attribution"><span class="source">Jake Clark</span></span>
</figcaption>
</figure>
<p>Details of the planet and its discovery are <a href="http://arxiv.org/abs/1711.05378">published today</a>. So how does this fit into the planet formation narrative, and are planets like it common in the cosmos?</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/a-fleeting-visit-an-asteroid-from-another-planetary-system-just-shot-past-earth-86482">A fleeting visit: an asteroid from another planetary system just shot past Earth</a>
</strong>
</em>
</p>
<hr>
<h2>The Solar system</h2>
<p>Before the first exoplanet discovery, our understanding of how planetary systems formed came from the only example we had at the time: <a href="https://solarsystem.nasa.gov/planets/">our Solar system</a>.</p>
<p>Close to the Sun orbit four rocky planets – Mercury, Venus, Earth and Mars. Further out are four giants – Jupiter, Saturn, Uranus and Neptune. </p>
<p>Scattered in their midst we have debris – <a href="http://cometography.com/">comets</a>, <a href="https://solarsystem.nasa.gov/planets/asteroids">asteroids</a> and the <a href="https://theconversation.com/planet-or-dwarf-planet-all-worlds-are-worth-investigating-74682">dwarf planets</a>.</p>
<p>The eight planets move in almost circular orbits, close to the same plane. The bulk of the debris also lies close to that plane, although on orbits that are somewhat more eccentric and inclined.</p>
<p>How did this system form? The idea was that it coalesced from a disk of material surrounding the embyronic Sun. The colder outer reaches were rich in ices, while the hotter inner regions contained just dust and gas.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/194299/original/file-20171113-27579-1t07ti9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/194299/original/file-20171113-27579-1t07ti9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/194299/original/file-20171113-27579-1t07ti9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=375&fit=crop&dpr=1 600w, https://images.theconversation.com/files/194299/original/file-20171113-27579-1t07ti9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=375&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/194299/original/file-20171113-27579-1t07ti9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=375&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/194299/original/file-20171113-27579-1t07ti9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=471&fit=crop&dpr=1 754w, https://images.theconversation.com/files/194299/original/file-20171113-27579-1t07ti9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=471&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/194299/original/file-20171113-27579-1t07ti9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=471&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Solar system formed from a protoplanetary disk, surrounding the young Sun.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech</span></span>
</figcaption>
</figure>
<p>Over millions of years, the tiny particles of dust and ice collided with one another, slowly building ever larger objects. In the icy depths of space, the giant planets grew rapidly. In the hot, rocky interior, growth was slower. </p>
<p>Eventually, the Sun blew away the gas and dust leaving a (relatively) orderly system – roughly co-planar planets, moving on near-circular orbits.</p>
<h2>The exoplanet era</h2>
<p>The first exoplanets, discovered in the 1990s, shattered this simple model of planet formation. We quickly learned that they are <a href="https://www.nasa.gov/feature/jpl/20-intriguing-exoplanets">far more diverse</a> than we could have possibly imagined.</p>
<p>Some systems feature giant planets, larger than Jupiter, <a href="https://theconversation.com/its-all-in-the-rotation-exploring-planets-orbiting-distant-stars-59593">orbiting incredibly close to their star</a>. Others host eccentric, solitary worlds, with no companions to call their own. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/193775/original/file-20171108-26968-fbdoei.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/193775/original/file-20171108-26968-fbdoei.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/193775/original/file-20171108-26968-fbdoei.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=857&fit=crop&dpr=1 600w, https://images.theconversation.com/files/193775/original/file-20171108-26968-fbdoei.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=857&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/193775/original/file-20171108-26968-fbdoei.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=857&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/193775/original/file-20171108-26968-fbdoei.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1078&fit=crop&dpr=1 754w, https://images.theconversation.com/files/193775/original/file-20171108-26968-fbdoei.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1078&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/193775/original/file-20171108-26968-fbdoei.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1078&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Artist’s impression of the Hot Jupiter HD209458b - a planet so close to its star that its atmosphere is evaporating to space.</span>
<span class="attribution"><span class="source">European Space Agency, A.Vidal-Madjar (Institut d'Astrophysique de Paris, CNRS, France) and NASA</span></span>
</figcaption>
</figure>
<p>This wealth of data reveals one thing – planet formation and evolution is <a href="https://theconversation.com/from-dust-clouds-to-wobbly-orbits-for-new-planets-29704">more complicated and diverse than we ever imagined</a>.</p>
<h2>Core accretion vs dynamical instability</h2>
<p>As a result of these discoveries, astronomers developed two competing models for planet formation. </p>
<p>The first is <a href="https://blog.planethunters.org/tag/core-accretion/">core accretion</a>, where planets form gradually, through collisions between grains of dust and ice. The theory has grown out of our old models of Solar system formation. </p>
<p>The competing theory is dynamical instability. Once again, the story begins with a disk of material around a youthful star. But that disk is more massive, and becomes unstable under its own self-gravity, causing clumps to grow. These clumps rapidly form planets, in thousands of years.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/lqrXSsoXpRs?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Massive protoplanetary disks can become unstable, rapidly giving birth to giant planets.</span></figcaption>
</figure>
<p>Both models can explain some, but not all, of the newly discovered planets. Depending on the initial conditions around the star, it seems that both processes can occur. </p>
<p>Each theory offers potential to explain eccentric worlds in somewhat different ways.</p>
<h2>How do you get an eccentric planet?</h2>
<p>In the dynamical instability model you can easily get several clumps forming and interacting, slinging one another around until their orbits are both tilted and eccentric. </p>
<p>Under the core accretion model things are a bit harder, as this method naturally creates co-planar, ordered planetary systems. But over time those systems can become unstable.</p>
<p>One possible outcome is for one planet to eject the others through a series of chaotic encounters. That would naturally leave it as a solitary body, following a highly elongated orbit.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/194290/original/file-20171113-27573-s6akrq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/194290/original/file-20171113-27573-s6akrq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/194290/original/file-20171113-27573-s6akrq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/194290/original/file-20171113-27573-s6akrq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/194290/original/file-20171113-27573-s6akrq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/194290/original/file-20171113-27573-s6akrq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/194290/original/file-20171113-27573-s6akrq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/194290/original/file-20171113-27573-s6akrq.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">Chaotic planetary systems can eject planets entirely, leading to lonely rouge planets.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech</span></span>
</figcaption>
</figure>
<p>But there is another option. <a href="http://www.atnf.csiro.au/outreach/education/senior/astrophysics/binary_intro.htmlhttp://www.atnf.csiro.au/outreach/education/senior/astrophysics/binary_intro.html">Many stars in our galaxy are binary</a> – they have stellar companions. The interactions between a planet and its host star’s sibling could readily stir it up and eventually eject it, or place it on an extreme orbit.</p>
<h2>An eccentric planet</h2>
<p>This brings us to our newly discovered world, HD76920b. A handful of similarly eccentric worlds have been found before, but HD76920b is unique. It orbits an ancient star, more than two billion years older than the Sun.</p>
<p>The orbit HD76920b is following is not tenable in the long-term. As it swings close to its host star, it will experience dramatic tides. </p>
<p>A gaseous planet, HD76920b will change shape as it swings past its star, stretched by its enormous gravity. Those tides will be far greater than any we experience on Earth.</p>
<p>That tidal interaction will act over time to circularise the planet’s orbit. The point of closest approach to the star will remain unchanged, but the most distant point will gradually be dragged closer in, driving the orbit towards circularity.</p>
<p>All of this suggests that HD76920b cannot have occupied its current orbit since its birth. If that were the case, the orbit would have circularised aeons ago.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/194298/original/file-20171113-27573-1dmbb6a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/194298/original/file-20171113-27573-1dmbb6a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/194298/original/file-20171113-27573-1dmbb6a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/194298/original/file-20171113-27573-1dmbb6a.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/194298/original/file-20171113-27573-1dmbb6a.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/194298/original/file-20171113-27573-1dmbb6a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/194298/original/file-20171113-27573-1dmbb6a.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/194298/original/file-20171113-27573-1dmbb6a.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">Extremely eccentric planets have been discovered before, but this is the first around such an ancient star.</span>
<span class="attribution"><span class="source">Goddard Space Flight Center/NASA</span></span>
</figcaption>
</figure>
<p>Perhaps what we’re seeing is evidence of a planetary system gone rogue. A system that once contained several planets on circular (or near circular) orbits. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/exoplanet-discovery-by-an-amateur-astronomer-shows-the-power-of-citizen-science-75912">Exoplanet discovery by an amateur astronomer shows the power of citizen science</a>
</strong>
</em>
</p>
<hr>
<p>Over time, those planets nudged one another around, eventually hitting a chaotic architecture as their star evolved. The result – chaos – with most planets scattered and flung to the depths of space leaving just one – HD76920b.</p>
<p>The truth is, we just don’t know – yet. As is always the case in astronomy, more observations are needed to truly understand the life story of this peculiar planet.</p>
<p>One thing we do know is the story is coming to a fiery end. In the next few million years, the star will swell, devouring its final planet. Then, HD76920b will be no more.</p><img src="https://counter.theconversation.com/content/87011/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jonti Horner receives funding from the Australian Research Council. </span></em></p><p class="fine-print"><em><span>Jake Clark is supported by an Australian Government Research Training Program (RTP) Scholarship.</span></em></p><p class="fine-print"><em><span>Rob Wittenmyer receives funding from the Australian Research Council.</span></em></p><p class="fine-print"><em><span>Stephen Kane receives funding from NASA.</span></em></p>A solitary planet in an eccentric orbit around an ancient star may help astronomers understand exactly how such planetary systems are formed.Jonti Horner, Vice Chancellor's Senior Research Fellow, University of Southern QueenslandJake Clark, PhD Student, University of Southern QueenslandRob Wittenmyer, Associate Professor (Astrophysics), University of Southern QueenslandStephen Kane, Associate Professor, University of California, RiversideLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/733522017-02-22T19:18:43Z2017-02-22T19:18:43ZSeven Earth-sized planets discovered orbiting a nearby star<figure><img src="https://images.theconversation.com/files/157806/original/image-20170222-20297-13i0lwk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An artist's concept of what it could look like on the surface of one of the exoplanets of TRAPPIST-1. </span> <span class="attribution"><span class="source">NASA/JPL-Caltech</span></span></figcaption></figure><p>An international team of astronomers has found that a nearby star is accompanied by a swarm of at least seven small, rocky worlds. </p>
<p>One of the eyecatching claims in the work, <a href="http://nature.com/articles/doi:10.1038/nature21360">published today in Nature</a>, is that in the appropriate circumstances, there is a chance that any (or all) the planets could host the right conditions for liquid water to exist on their surface.</p>
<p>The orbits of several of the planets also appear locked in a delicate dance that could explain how such planetary systems form.</p>
<p>The host of this newly uncovered planetary system is a dim little object called <a href="http://www.trappist.one/">TRAPPIST-1</a>, which lies almost 40 light years from our Sun. </p>
<p>TRAPPIST-1 is so tiny that it only barely counts as a star. It has just 8% of the mass of the Sun and lies <a href="http://www.slate.com/blogs/bad_astronomy/2014/06/11/the_brown_dwarf_limit_astronomers_have_found_the_smallest_star_known.html">right on the boundary between normal stars and brown dwarfs</a>.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/157819/original/image-20170222-20310-vh6bnu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/157819/original/image-20170222-20310-vh6bnu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=420&fit=crop&dpr=1 600w, https://images.theconversation.com/files/157819/original/image-20170222-20310-vh6bnu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=420&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/157819/original/image-20170222-20310-vh6bnu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=420&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/157819/original/image-20170222-20310-vh6bnu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=528&fit=crop&dpr=1 754w, https://images.theconversation.com/files/157819/original/image-20170222-20310-vh6bnu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=528&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/157819/original/image-20170222-20310-vh6bnu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=528&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">TRAPPIST-1 is a tiny ultracool red dwarf, far smaller than the Sun.</span>
<span class="attribution"><a class="source" href="http://www.eso.org/public/images/eso1615e/">ESO</a></span>
</figcaption>
</figure>
<p>Were this tiny star slightly less massive, it would be too lightweight to fire nuclear fusion in its core, and it would be a <a href="http://coolcosmos.ipac.caltech.edu/cosmic_classroom/cosmic_reference/brown_dwarfs.html">failed star</a>. </p>
<p>If TRAPPIST-1 was dropped into our Solar System in the place of the Sun, it would shine in our sky only marginally more brightly than the full Moon. It would be deep red in colour, with a surface temperature of just over 2,200°C.</p>
<p>In this hypothetical scenario, the Solar System would be a lifeless place. Earth’s oceans would freeze, and then our atmosphere would do the same.</p>
<p>To be warm enough to potentially host liquid water, any planets around this dimly glowing ember would have to <a href="https://theconversation.com/for-life-to-form-on-a-planet-it-needs-to-orbit-the-right-kind-of-star-33477">huddle close and tight</a>. </p>
<h2>Three little worlds</h2>
<p>In May last year, a team of astronomers using the TRansiting Planets and PlanetesImals Small Telescope (<a href="http://www.trappist.ulg.ac.be/cms/c_3300885/en/trappist-portail">TRAPPIST</a>) announced their <a href="http://www.nature.com/nature/journal/v533/n7602/full/nature17448.html">first exoplanet discovery</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/157810/original/image-20170222-20302-1f8vw6d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/157810/original/image-20170222-20302-1f8vw6d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/157810/original/image-20170222-20302-1f8vw6d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=420&fit=crop&dpr=1 600w, https://images.theconversation.com/files/157810/original/image-20170222-20302-1f8vw6d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=420&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/157810/original/image-20170222-20302-1f8vw6d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=420&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/157810/original/image-20170222-20302-1f8vw6d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=528&fit=crop&dpr=1 754w, https://images.theconversation.com/files/157810/original/image-20170222-20302-1f8vw6d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=528&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/157810/original/image-20170222-20302-1f8vw6d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=528&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">An artist’s impression of the three planets discovered orbiting TRAPPIST-1 in May 2016.</span>
<span class="attribution"><span class="source">ESO/M Kornmesser/N Risinger (skysurvey.org)</span></span>
</figcaption>
</figure>
<p>That team had found striking evidence that a dim, ultracool dwarf star was host to <a href="https://theconversation.com/ultracool-dwarf-star-hosts-three-potentially-habitable-earth-sized-planets-just-40-light-years-away-58695">at least three small rocky planets</a>. Over a period of a 62 days, the star was observed to wink periodically, dimming slightly, then returning to its normal brightness. </p>
<p>These winks were the <a href="https://theconversation.com/explainer-how-to-find-an-exoplanet-part-1-56682">telltale sign of planetary companions</a>. </p>
<p>As this was the telescope’s first discovery, the star was named TRAPPIST-1, and the planets TRAPPIST-1b, c and d.</p>
<p>The inner two planets were found to orbit the star every 1.5 and 2.4 days, respectively. They were small, only very slightly larger than Earth. </p>
<p>Because they huddled in so close to the star (within 2 million km) they would be warm. Most likely, they would be too warm to host liquid water on their surface. But if conditions were just right, then there might, just might, be an outside chance that they could be both warm and wet.</p>
<h2>The seven new ‘Earths’</h2>
<p>With today’s announcement, the TRAPPIST-1 system has suddenly became much more interesting. The same team has invested a huge amount of time following up on their discovery, using telescopes across the planet. </p>
<figure>
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</figure>
<p>Those observations have borne great fruit, with the capture of a large sample of transits. The result is the confirmation of the three previously known planets and the discovery of four more. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/157805/original/image-20170222-20326-145bgyw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/157805/original/image-20170222-20326-145bgyw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/157805/original/image-20170222-20326-145bgyw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=300&fit=crop&dpr=1 600w, https://images.theconversation.com/files/157805/original/image-20170222-20326-145bgyw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=300&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/157805/original/image-20170222-20326-145bgyw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=300&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/157805/original/image-20170222-20326-145bgyw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=377&fit=crop&dpr=1 754w, https://images.theconversation.com/files/157805/original/image-20170222-20326-145bgyw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=377&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/157805/original/image-20170222-20326-145bgyw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=377&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">An artist’s conception shows what the TRAPPIST-1 planetary system may look like.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech</span></span>
</figcaption>
</figure>
<iframe src="https://datawrapper.dwcdn.net/lk2KO/1/" frameborder="0" allowtransparency="true" allowfullscreen="allowfullscreen" webkitallowfullscreen="webkitallowfullscreen" mozallowfullscreen="mozallowfullscreen" oallowfullscreen="oallowfullscreen" msallowfullscreen="msallowfullscreen" width="100%" height="450"></iframe>
<p>The TRAPPIST-1 planetary system is amazingly compact, with all the planets orbiting within 10 million km of their host star. To put that into perspective, Earth orbits almost 150 million km from the Sun.</p>
<p>So the scale of the TRAPPIST-1 system is dramatically different to that of our Solar system. But a better analogue lies close at hand – the satellites of <a href="http://solarsystem.nasa.gov/planets/jupiter">Jupiter</a>.</p>
<h2>A Galilean solar system?</h2>
<p>The scale of the TRAPPIST-1 system is strikingly similar to that of the Jovian system. Jupiter’s four most massive moons – Io, Europa, Ganymede and Callisto – all cluster within 2 million km of the giant planet. Known as the <a href="http://lasp.colorado.edu/education/outerplanets/moons_galilean.php">Galilean satellites</a>, their orbital periods span the same relative range as TRAPPIST-1’s planets.</p>
<p>The inner three Galilean satellites are trapped in what is known as a Laplace resonance, with Io completing four laps of Jupiter in the time it takes Europa to complete two, and Ganymede to complete one.</p>
<p>Their tightly packed nature and orbital resonance gives an important clue as to their formation. The idea is that those moons formed further from Jupiter than their current orbits, and migrated inwards, becoming trapped in the resonance as they went. </p>
<p>Which brings us back to TRAPPIST-1’s planetary system. Where three of Jupiter’s moons lie trapped in mutual resonance, the TRAPPIST-1 system takes things to a whole new level. The six inner planets all lie in near-resonance, with periods in the ratio 24:15:9:6:4:3. </p>
<p>This is the first time such a long near-resonant chain of orbits has ever been found. It remains possible that, when more data are available for the outermost planet, it will add to the chain.</p>
<p>This striking similarity to the Galilean satellites suggests a similar formation process. It hints that the planets orbiting TRAPPIST-1 may have begun their formation further from the star, before migrating inwards to their current orbits. </p>
<h2>Could there be water?</h2>
<p>Based on their distances from TRAPPIST-1, the authors make a first rough attempt to calculate whether the planets could host liquid water. </p>
<p>The innermost should be too warm (unless it is highly reflective, absorbing little of the light that falls upon it). The outermost should be too cold (unless it has a thick, insulating atmosphere). </p>
<p>For the others, things seem a little more promising. In terms of the amount of energy they receive from their star, planets c, d and f seem strikingly similar to Venus, Earth and Mars.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/157807/original/image-20170222-20343-sxdwzg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/157807/original/image-20170222-20343-sxdwzg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/157807/original/image-20170222-20343-sxdwzg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/157807/original/image-20170222-20343-sxdwzg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/157807/original/image-20170222-20343-sxdwzg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/157807/original/image-20170222-20343-sxdwzg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/157807/original/image-20170222-20343-sxdwzg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/157807/original/image-20170222-20343-sxdwzg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The seven planets of TRAPPIST-1 with their orbital periods, distances from their star, radii and masses as compared to those of Earth. The bottom row shows data about Mercury, Venus, Earth and Mars.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech</span></span>
</figcaption>
</figure>
<p>In the Solar system, it seems likely that Venus <a href="https://climate.nasa.gov/news/2475/nasa-climate-modeling-suggests-venus-may-have-been-habitable/">was once warm and wet</a>, before a runaway greenhouse led to the ocean’s boiling and the planet becoming inhospitable. </p>
<p>Mars was once <a href="https://theconversation.com/the-lost-ocean-of-mars-38739">warm and wet</a> before its atmosphere bled to space and was chemically drawn down into the surface, causing the planet to become frigid and barren.</p>
<p>The idea that TRAPPIST-1’s planets might have migrated from further out in the system could add weight to the possibility of their having water. </p>
<p>Farther from TRAPPIST-1, temperatures are colder, which would mean that in the <a href="https://theconversation.com/giant-impacts-planet-formation-and-the-search-for-life-elsewhere-33478">nebula from which the planets formed</a>, there should have been plenty of water ice for the planets to acquire as they accreted, giving the possibility that these are wet worlds.</p>
<p>But there’s a great difference between “maybe” and “yes”. As it stands, we have no evidence that these planets are wet. They could just as easily be <a href="http://geosci.uchicago.edu/%7Ekite/doc/Catling2009.pdf">barren, airless worlds, stripped of their atmospheres</a> by TRAPPIST-1’s youthful exuberance. </p>
<p>Or, given their resonant nature, they could be volcanic hellholes, just like Jupiter’s Io, with <a href="http://www.geology.sdsu.edu/how_volcanoes_work/io.html">continual and fiery volcanic activity</a>, <a href="https://www.nasa.gov/topics/solarsystem/features/io-volcanoes-displaced.html">driven by tidal interactions</a> with one another. We simply don’t know. But that could change in the coming years with new and better observations.</p>
<p>Until then, we can only speculate on what the planets around this ultracool, dim ember might be like.</p><img src="https://counter.theconversation.com/content/73352/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jonti Horner does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Several of the newly-discovered exoplanets orbiting a small star appear to be locked in an intricate dance that hints at how such planetary systems can form.Jonti Horner, Vice Chancellor's Senior Research Fellow, University of Southern QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/733942017-02-22T18:02:53Z2017-02-22T18:02:53ZSolar system with seven Earth-like planets found around nearby star – here’s what they could be like<figure><img src="https://images.theconversation.com/files/157841/original/image-20170222-1364-hr3hcv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Artist's impression of what the view might be like from the surface of the exoplanet TRAPPIST-1f. </span> <span class="attribution"><span class="source">NASA/JPL-Caltech</span></span></figcaption></figure><p>There have been many discoveries of potentially habitable planets orbiting stars other than our own over the last few years. Now things are getting even more exciting. Scientists <a href="http://nature.com/articles/doi:10.1038/nature21360">have documented</a> a star surrounded by no fewer than seven Earth-like planets – several or all of which could be at the right temperature for liquid water, and potentially life, to exist.</p>
<p>But is it possible to know anything about what these planets are like beyond simple measures such as temperature and mass? There are indeed several factors that can give us a clue. So let’s take a look at what planetary processes we might expect to find there – and ultimately whether life could exist.</p>
<p>The seven planets orbit an “<a href="https://astronomynow.com/tag/ultra-cool-dwarf-stars/">ultracool dwarf</a>” about 39 light years away. But don’t think this star is wearing shades. With a mass of only 8% of the sun’s and shining less than 0.1% as brightly, it is at the small, faint end of the “<a href="http://www.space.com/23772-red-dwarf-stars.html">red dwarf</a>” star type, barely able to power itself by nuclear fusion. Proxima, the nearest star beyond the solar system (4.24 light years away), where <a href="https://theconversation.com/possibly-habitable-planet-found-around-our-nearest-neighbour-star-64321">recently a single planet was discovered</a>, has 12% of the sun’s mass and is an ordinary (not ultracool) red dwarf.</p>
<h2>Telling transits</h2>
<p>In 2010, a group of scientists began monitoring the closest dwarf stars using a robotic telescope in Chile called <a href="http://www.trappist.ulg.ac.be/cms/c_3300885/en/trappist-portail">TRAPPIST (the Transiting Planets and Planetesimals Small Telescope)</a>. They were hoping to find periodic dips in brightness caused by a planet passing in front of the star’s disc, cutting out part of its light (a transit). In 2016, they found their first candidate: an ultracool dwarf.</p>
<p>They named this star TRAPPIST-1 and began to study it with more powerful telescopes, including <a href="http://www.spitzer.caltech.edu/">NASA’s Spitzer space telescope</a>. This fuller survey has now revealed a total of seven transiting exoplanets there (see video). </p>
<figure>
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<figcaption><span class="caption">How Spitzer made the discovery.</span></figcaption>
</figure>
<p>The amount of light blocked out by each exoplanet during a transit reveals its size. The repeat frequency reveals each exoplanet’s orbital period, from which the laws of gravity allow us to deduce its distance from the star. These exoplanets have no names, but by convention are designated as TRAPPIST-1b (the innermost) to TRAPPIST-1h (the outermost).</p>
<p>Amazingly, the planets of TRAPPIST-1 span only a narrow range of sizes, not much different to Earth. They huddle round their star almost as closely as Jupiter’s major moons to Jupiter, and are all much closer to their star than the Earth is to the sun. However, TRAPPIST-1 is so faint that even its innermost planet may be just about cool enough for liquid water to exist on its surface, while its outermost planet may be just warm enough to avoid global freezing. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/157716/original/image-20170221-18643-5tcqc1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/157716/original/image-20170221-18643-5tcqc1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/157716/original/image-20170221-18643-5tcqc1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/157716/original/image-20170221-18643-5tcqc1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/157716/original/image-20170221-18643-5tcqc1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/157716/original/image-20170221-18643-5tcqc1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/157716/original/image-20170221-18643-5tcqc1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">This artist’s conception shows what the seven planets of TRAPPIST-1 may look like, based on available data about their sizes, masses and distances from the star.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech</span></span>
</figcaption>
</figure>
<p>Transits reveal exoplanets’ sizes rather than their masses, but mass can be deduced when, as in the TRAPPIST-1 system, there are slight irregularities in transit timings attributable to neighbouring exoplanets perturbing each others’ orbits. This suggests that most of the family are Earth-like in their density and not just their size. There is no way to be sure yet how much water most of them have, if any. Similarly, it’s hard to know whether any resemblance to Earth extends as far as having <a href="https://theconversation.com/does-a-planet-need-plate-tectonics-to-develop-life-61303">plate tectonics</a> and a distinction between oceanic and continental crust (like Earth) or a more globally homogeneous crust (like Mars and Venus).</p>
<p>The exception is TRAPPIST-1f which seems to be notably less dense, implying a lot more water and less rock and iron. If this planet has a deep global ocean we can imagine it as one with many hot springs or even volcanoes on its floor. This is because the planets b through g have “resonant orbits” (their periods are simple multiples of each other) leading to a tidal pull that distorts their interiors and adds heat in addition to the heat generated internally by decay of radioactive elements contained within the rock.</p>
<h2>Seeds of life?</h2>
<p>With most or maybe even all of its seven known planets in the not-too-hot, not-too-cold “<a href="https://theconversation.com/exo-earths-and-the-search-for-life-elsewhere-a-brief-history-33096">Goldilocks zone</a>” around the star, TRAPPIST-1 offers the intriguing prospect of several Earth-like planets capable of hosting Earth-like life around the same star.</p>
<p>TRAPPIST-1 is young as ultracool dwarfs go, maybe only half a billion years old. But thanks to the frugal rate at which it uses its nuclear fuel it has a further 10 trillion years left to run (a thousand times longer then the sun). On Earth, it took two billion years to go from microbes to multi-cellular organisms, and another billion years for intelligence to emerge. So while we may not expect advanced civilisations to exist on the TRAPPIST-1 planets, some simple lifeforms may be in the works or already exist.</p>
<p>We don’t yet know how easy it is for life to get started even when conditions are right. But were life to exist or suddenly begin on <em>any</em> of TRAPPIST-1’s planets it is very likely that it would spread to its neighbours, <a href="https://theconversation.com/twin-civilisations-how-life-on-an-exoplanet-could-spread-to-its-neighbour-51638">as shown in a recent study</a>.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/157717/original/image-20170221-18643-fpx70g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/157717/original/image-20170221-18643-fpx70g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=750&fit=crop&dpr=1 600w, https://images.theconversation.com/files/157717/original/image-20170221-18643-fpx70g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=750&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/157717/original/image-20170221-18643-fpx70g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=750&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/157717/original/image-20170221-18643-fpx70g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=943&fit=crop&dpr=1 754w, https://images.theconversation.com/files/157717/original/image-20170221-18643-fpx70g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=943&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/157717/original/image-20170221-18643-fpx70g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=943&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">TRAPPIST-1 and its seven planets. Orbits drawn to scale, but the sizes of planets exaggerated.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech</span></span>
</figcaption>
</figure>
<p>Dwarf stars are more common than sun-like stars, and now we know they can have numerous Earth-like planets. It is beginning to look as if stars like our sun, a fast-burning “main sequence star”, may be less important as hosts for life-bearing planets than their stunted cousins.</p>
<p>TRAPPIST-1 and its planets are sure to be among the prime targets for the <a href="https://theconversation.com/how-hubbles-successor-will-give-us-a-glimpse-into-the-very-first-galaxies-45970">James Webb Space Telescope</a>, likely to begin operations in 2019. This should be able to detect the presence of any atmosphere about a planet while it is in transit across the star and maybe even reveal whether atmospheric composition seems to have been modified by living processes.</p><img src="https://counter.theconversation.com/content/73394/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Rothery is author of Planet Mercury - from Pale Pink Dot to Dynamic World (Springer, 2015), Moons: A Very Short Introduction (Oxford University Press, 2015) and Planets: A Very Short Introduction (Oxford University Press, 2010). He receives funding from the UK Space Agency and the Science & Technology Facilities Council for work related to Mercury and the European Space Agency's Mercury orbiter BepiColombo. He is Educator on the Open University/FutureLearn Moons MOOC <a href="https://www.futurelearn.com/courses/moons">https://www.futurelearn.com/courses/moons</a></span></em></p>If there’s life on one of the Earth’s seven sisters, chances are it has spread to all of them.David Rothery, Professor of Planetary Geosciences, The Open UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/724252017-02-08T07:39:05Z2017-02-08T07:39:05ZUntil we get better tools, excited reports of ‘habitable planets’ need to come back down to Earth<p>In 1950, physicist <a href="https://commons.wikimedia.org/wiki/File:%22Where_is_Everybody%3F%22_An_Account_of_Fermi%27s_Question.pdf">Enrico Fermi famously asked</a>, “Where are they?” as a kind of lament about the lack of observational evidence for alien intelligence in our universe. Today, the question is still asked in the context of the always-hoped-for discovery of other worlds like our own, with the thought that maybe, just maybe, we will finally find those aliens.</p>
<p>Against this backdrop, advances that have occurred in the past 20 years in the field of exoplanet discovery have excited the imaginations of scientists and enthusiasts alike.</p>
<p>When, the question goes, will we finally discover a planet that can sustain life? When will we discover Earth 2.0?</p>
<p>The impatience associated with this question has led many in the media and even some in the scientific community to <a href="http://gizmodo.com/this-is-the-most-earth-like-planet-ever-discovered-1719724534">make premature declarations</a> that an “Earth analogue” has been discovered. But when exoplanets are discovered, claims that they are similar to Earth are based on, at best, optimistic modelling and, at worst, sensationalism.</p>
<p>Many such claims have been made <a href="http://www.nature.com/articles/s41550-017-0042">on the basis of invented ranking systems</a> that use the observed properties of exoplanets to extrapolate how Earth-like a planet might be. Unfortunately, these systems must make extremely simple – and almost certainly incorrect – assumptions about the characteristics of the planets they are trying to describe. </p>
<h2>Ranking habitability: not so easy</h2>
<p>Before any exoplanets had been discovered at all, certain astrophysicists proposed that each star had an associated zone around it that came to be known as the “<a href="http://www.as.utexas.edu/astronomy/education/spring02/scalo/kasting.pdf">habitable zone</a>”. This zone is at a distance from every star where a hypothetical Earth twin would have an average surface temperature between the freezing and boiling point of water. Too close and you exceed 100°C; too far and you drop below 0°C. </p>
<p>But if a planet has an atmospheric composition different from Earth’s, its true surface temperature is likely to be completely different. </p>
<p>Gaseous planets do not even have a well-defined surface to consider. And, for rocky planets, a thinner atmosphere can make them much colder (especially at night) while a thicker atmosphere can make them much hotter. </p>
<p>One of the most dramatic examples of this problem is Venus. Owing to its thick atmosphere and <a href="http://www.esa.int/Our_Activities/Space_Science/Venus_Express/Greenhouse_effects_also_on_other_planets">a runaway greenhouse effect</a>, the planet has a temperature of a whopping 450°C — far higher than than the 25°C you would calculate given an Earth-like atmosphere. Although Venus lies within our Sun’s nominal habitable zone, it is surely not accurate to call it habitable.</p>
<p>The two most fruitful methods for discovering exoplanets (the “<a href="http://www.planetary.org/explore/space-topics/exoplanets/transit-photometry.html">transit method</a>” and the “<a href="https://lco.global/spacebook/radial-velocity-method/">radial velocity method</a>”) both give a <a href="http://www.calctool.org/CALC/phys/astronomy/planet_orbit">straightforward way to determine the distance between a star and an exoplanet</a>. That, together with our knowledge of how much heat is given off by the star, lets us calculate whether the planet is in the star’s habitable zone. But, as we have seen, that is not the same thing as discovering a habitable planet.</p>
<p>Nevertheless, discoveries of planets in the habitable zones of other stars have been identified in the media and even in press releases of scientific institutions as <a href="https://www.nasa.gov/ames/kepler/nasas-kepler-discovers-first-earth-size-planet-in-the-habitable-zone-of-another-star">discoveries of second Earths</a>. Since we do not know the surface temperatures of any exoplanet, whether they are actual Earth analogues can only be guessed at using other lines of evidence. </p>
<h2>Learning more about exoplanets</h2>
<p>Our best understanding to date is that surface temperatures are strongly dependent on atmospheric composition and planet density. The density of a planet is dependent on both its mass and volume, but the two detection methods only allow for one or the other of the two complementary characteristics to be directly measured. </p>
<p>The transit method detects the shadow a planet casts on the star it is orbiting, allowing the planet’s area (and, <a href="https://www.scientificamerican.com/article/why-are-planets-round/">because planets are spheres</a>, its volume) to be measured. What is not directly discoverable from this method, however, is the planet’s mass. </p>
<p>Alternatively, the radial velocity method detects a planet via a wobble in the star’s motion that can be used to infer a minimum possible planetary mass tugging on the star with its gravity. In many cases, the tug is being done at an angle so <a href="http://spiff.rit.edu/classes/phys301/lectures/mass_ii/mass_ii.html">we see a reduced effect</a>, which makes us infer a mass that is smaller than the actual mass of planet. Aside from this potential confusion, there is no way via the radial velocity method alone to determine a planet’s volume.</p>
<p>Astrophysicists who model planet formation and composition have proposed a <a href="https://www.cfa.harvard.edu/%7Elzeng/planetmodels.html">variety of models</a> that offer possible relationships between the volumes and masses of planets depending on planet compositions. </p>
<p>The smallest planets in our own solar system are rocky and the largest planets are gaseous, but we see a number of exoplanets whose sizes lie between the smallest gaseous planet (Neptune) and the largest rocky planet (Earth). We have models that can accommodate “<a href="http://www.universetoday.com/108452/what-is-a-super-earth/">super-Earths</a>” that are rocky or “<a href="http://www.space.com/23079-alien-planets-super-earth-mini-neptune.html">mini-Neptunes</a>” that are gaseous and <a href="http://www.nature.com/articles/s41550-017-0043">all manner of hybrids in between</a>. </p>
<p>These varied models can accommodate a range of atmospheres, and the exoplanets will have very different surface temperatures depending on all of this. It is therefore of some importance that we learn more about exoplanet atmospheres directly using better telescopes and more sensitive techniques. </p>
<p><a href="http://iopscience.iop.org/article/10.1088/0004-637X/814/2/91/pdf">Some astronomers have proposed a scheme</a> to decide which exoplanets are most likely to have their atmospheres directly detected – the obvious next step in working towards determining a planet’s surface temperature and ultimately whether it is habitable.</p>
<h2>Jumping the gun</h2>
<p>A regrettable tendency right now is to jump the gun. Planets have been discovered in the habitable zones of other stars with <a href="https://www.eso.org/public/chile/news/eso0019/">radial-velocity-measured minimum masses that are similar to Earth’s</a> and <a href="https://www.nasa.gov/ames/kepler/a-keplers-dozen-small-habitable-zone-planets">transit-measured surface areas that are not much larger than Earth’s</a>. </p>
<p>Crucially, none of these “analogues” has yet been measured in both ways. But almost every time such planets are discovered, <a href="http://thetechnews.com/2017/01/21/could-wolf-1061c-be-the-next-earth/">breathless</a> <a href="https://phys.org/news/2016-08-earth-like-planet-proxima-centauri.html">reports</a> <a href="http://www.bbc.com/news/science-environment-33641648">of</a> <a href="https://www.thesun.co.uk/news/2295568/astronomers-spot-mysterious-second-earth-and-its-got-perfect-conditions-for-alien-life/">their</a> <a href="https://www.inverse.com/article/26715-wolf-1061-planet-sustain-life">possible</a> <a href="http://nypost.com/2017/01/21/scientists-searching-for-life-on-nearby-super-earth/">import</a> <a href="http://fox13now.com/2016/08/24/new-earth-like-planet-found-that-could-potentially-support-life/">are</a> <a href="http://www.space.com/30030-earth-cousin-kepler-452b-exoplanet-details-infographic.html">generated</a>. </p>
<p>While discoveries of exoplanets are exciting, it is definitely premature to try to decide how Earth-like any planet is or is not on the basis of the scant data we are now able to gather. The best we can hope to do at this time is collate a list of possible targets for future observation.</p>
<p>Someday, we may discover definitive proof that another Earth is out there. But that day has not yet arrived – despite the excited headlines.</p><img src="https://counter.theconversation.com/content/72425/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Joshua Tan receives funding from the Chilean government's Comisión Nacional de Investigación Científica y Tecnológica under a grant from the Fondo Nacional de Desarrollo Científico y Tecnológico; Project Number 3150484.</span></em></p>Over the last 20 years, advances in the field of exoplanet discovery have excited the imaginations of scientists and enthusiasts alike. But we’re in position to know yet whether a planet is habitable.Joshua Tan, Astronomer at the Instituto de Astrofísica, Universidad Católica de ChileLicensed as Creative Commons – attribution, no derivatives.