tag:theconversation.com,2011:/africa/topics/kepler-mission-101/articlesKepler Mission – The Conversation2021-07-19T12:06:44Ztag:theconversation.com,2011:article/1640622021-07-19T12:06:44Z2021-07-19T12:06:44ZAre there any planets outside of our solar system?<figure><img src="https://images.theconversation.com/files/410219/original/file-20210707-25-2zom23.jpg?ixlib=rb-1.1.0&rect=31%2C15%2C5161%2C2903&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Artist illustration of an exoplanet.
</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/beautiful-exoplanet-with-exo-moons-orbiting-an-royalty-free-image/873145010?adppopup=true">dottedhippo/iStock via Getty Images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
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<p><strong>Are there any planets outside of our solar system? - Eli W., age 8, Baton Rouge, Louisiana</strong></p>
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<p>This is a question that human beings have wondered about for thousands of years. </p>
<p>Here’s how the ancient Greek mathematician <a href="https://en.wikipedia.org/wiki/Metrodorus_of_Chios">Metrodorus</a> (400-350 B.C.) put it: A universe where Earth is “the only world,” he said, is about as believable as a “large field containing a single stalk.” </p>
<p>About 2,000 years later, in the 16th century, the Italian philosopher <a href="https://www.britannica.com/biography/Giordano-Bruno">Giordano Bruno</a> suggested something similar. </p>
<p>“Countless suns and countless earths” existed elsewhere, he said, all rotating “round their suns in exactly the same way as the planets of our system.” </p>
<p>Scientists now know that both Metrodorus and Bruno were essentially correct. Today, <a href="https://scholar.google.com/citations?hl=en&user=VRJuiHUAAAAJ">astronomers like me</a> are still exploring this question, using new tools. </p>
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<img alt="An exoplanet orbiting a red dwarf star." src="https://images.theconversation.com/files/410231/original/file-20210707-6685-1pr3hko.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/410231/original/file-20210707-6685-1pr3hko.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=350&fit=crop&dpr=1 600w, https://images.theconversation.com/files/410231/original/file-20210707-6685-1pr3hko.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=350&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/410231/original/file-20210707-6685-1pr3hko.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=350&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/410231/original/file-20210707-6685-1pr3hko.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=439&fit=crop&dpr=1 754w, https://images.theconversation.com/files/410231/original/file-20210707-6685-1pr3hko.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=439&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/410231/original/file-20210707-6685-1pr3hko.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=439&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">An exoplanet orbiting a red dwarf, a star that is dimmer than our Sun and about half the size.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/artwork-of-gliese-887-b-and-c-royalty-free-illustration/1271698835">Mark Garlick/Science Photo Library via Getty Images</a></span>
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<h2>The exoplanets</h2>
<p>There is now evidence that demonstrates the existence of “exoplanets” – that is, planets orbiting stars other than our Sun. </p>
<p>That evidence is based on the discoveries made by the <a href="https://kidsdiscover.com/spotlight/kepler/">Kepler space telescope</a>, launched by NASA in 2009.</p>
<p>For four years, the telescope stared continuously at a single region of space within the <a href="https://kids.kiddle.co/Cygnus_(constellation)">constellation Cygnus</a>.</p>
<p>Looking from Earth, it’s an area that takes up less than 1% of your view of the sky. </p>
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<img alt="An illustration shows the Kepler telescope in space, next to a star and its planet." src="https://images.theconversation.com/files/410236/original/file-20210707-25-1fxhfsx.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/410236/original/file-20210707-25-1fxhfsx.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=350&fit=crop&dpr=1 600w, https://images.theconversation.com/files/410236/original/file-20210707-25-1fxhfsx.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=350&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/410236/original/file-20210707-25-1fxhfsx.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=350&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/410236/original/file-20210707-25-1fxhfsx.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=440&fit=crop&dpr=1 754w, https://images.theconversation.com/files/410236/original/file-20210707-25-1fxhfsx.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=440&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/410236/original/file-20210707-25-1fxhfsx.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=440&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Artist illustration of NASA’s Kepler space telescope.</span>
<span class="attribution"><a class="source" href="https://exoplanets.nasa.gov/news/1526/latest-on-the-kepler-spacecraft/">NASA Images</a></span>
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<h2>How the telescope worked</h2>
<p>Kepler had 42 cameras on board, similar to the kind of smartphone camera that you use to take pictures. In that one region, the telescope detected more than 150,000 stars. </p>
<p>About every half-hour it observed the amount of light radiating from each star. Back here on Earth, a team of Kepler scientists analyzed the data.</p>
<p>For most stars, the amount of light stayed pretty much the same. </p>
<p>But for about 3,000 stars, the amount of light repeatedly decreased, by small amounts and for several hours. These drops in brightness happened at regular intervals, like clockwork. </p>
<p>The drops, astronomers concluded, were caused by a planet orbiting its star, periodically blocking some of the light that Kepler’s cameras would otherwise detect. </p>
<p>This event – when a planet passes between a star and its observer – is known as a <a href="https://exoplanets.nasa.gov/faq/31/whats-a-transit/">transit</a>.</p>
<p>And that means that in that one speck of space the Kepler telescope found 3,000 planets.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/BFi4HBUdWkk?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">NASA Video: Animation of a exoplanet transiting its star.</span></figcaption>
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<h2>That’s only the beginning</h2>
<p>Although 3,000 planets sounds like a lot, it’s certain many others within that area remain undetected. </p>
<p>That’s because their orbits never blocked the light as seen by Kepler. After all, planetary orbits aren’t all the same; they’re randomly oriented. </p>
<p>But because of the number of transits observed by Kepler, and astronomers’ knowledge of geometry, we can make a good guess on the total number of exoplanets out there.</p>
<p>And after making those calculations, scientists now think, on average, <a href="https://www.popsci.com/science/article/2012-01/new-exoplanet-analysis-determines-planets-are-more-common-stars-milky-way/">that every star has at least one planet</a>. </p>
<p>This discovery has revolutionized astronomy and our view of the universe. </p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/4IXYp9Fse44?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">NASA Video: Weird and Wondrous Worlds.</span></figcaption>
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<h2>100 billion stars, 100 billion planets</h2>
<p>For instance, our Milky Way galaxy has at least 100 billion stars; that means it has at least 100 billion planets too.</p>
<p>But remember: The universe holds up to 2 trillion galaxies. That’s 2,000,000,000,000! And each galaxy contains tens or even hundreds of billions of stars. </p>
<p>So the number of planets in the universe is truly astronomical, roughly equivalent to the <a href="https://www.universetoday.com/106725/are-there-more-grains-of-sand-than-stars/">number of grains of dry sand</a> on every beach on Earth. </p>
<p>Some of those planets are gas giants, like <a href="https://spaceplace.nasa.gov/all-about-jupiter/en/">Jupiter</a> in our solar system. Others are boiling hot, like <a href="https://spaceplace.nasa.gov/all-about-venus/en/">Venus</a>. Others may be <a href="https://www.nasa.gov/specials/ocean-worlds/">water worlds</a> or <a href="https://spaceplace.nasa.gov/ice-on-other-planets/en/">ice planets</a>. And some are Earth-like.</p>
<p>In fact, the Kepler team calculated the abundance of Earth-like planets in the “habitable zone,” a sector of space around each star where a world might have moderate temperatures and liquid water. </p>
<p>They found approximately <a href="https://www.nasa.gov/feature/ames/kepler-occurrence-rate">50% of Sun-like stars in the Milky Way</a> host an Earth-like planet in the habitable zone. </p>
<p>That adds up to <a href="https://www.space.com/habitable-planets-common-sunlike-stars-milky-way">billions of potentially habitable worlds</a> just in our galaxy.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/J04YN9azln8?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">NASA/JPL-Caltech Video: What is the “Habitable Zone”?</span></figcaption>
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<h2>Could life exist elsewhere?</h2>
<p>Although scientists haven’t found proof yet, many – <a href="https://seti.ucla.edu/jlm/">including me</a> – now think it’s unlikely that Earth is the only planet where life evolved. That would be as surprising as a large field containing a single stalk.</p>
<p>When will humans detect life elsewhere? Will it be intelligent life? Will people ever receive a message from another civilization?</p>
<p>Today, hundreds of scientists around the world are trying to answer those questions.</p>
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<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>.
Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/164062/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jean-Luc Margot receives funding from the National Aeronautics and Space Administration, the National Science Foundation, and philanthropists.</span></em></p>Billions of galaxies are in the universe, with billions of stars in every galaxy. Could billions of planets be out there too?Jean-Luc Margot, Professor of Earth, Planetary, and Space Sciences, University of California, Los AngelesLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1535242021-03-24T17:02:11Z2021-03-24T17:02:11ZPreviously thought to be science fiction, a planet in a triple-star system has been discovered<figure><img src="https://images.theconversation.com/files/391059/original/file-20210323-23-pvr9g2.jpg?ixlib=rb-1.1.0&rect=38%2C0%2C12941%2C4000&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A planet in a triple-star system has been discovered.</span> <span class="attribution"><span class="source">(Shutterstock)</span></span></figcaption></figure><p>KOI-5Ab is a <a href="https://www.caltech.edu/about/news/a-tale-of-planetary-resurrection">newly discovered planet</a> in a triple-star system. It is a great example of the kind of astonishing discoveries that result from co-operation between large teams of astronomers using different types of telescopes and observation techniques. </p>
<p>There is a stereotype that “lone genius” scientists make discoveries without any help from others. This is propagated by the prestigious Nobel Prize, which is awarded to at most two or three scientists at a time. </p>
<p>But major discoveries, particularly in the fields of astronomy and physics, are increasingly achieved by teams of dozens or even hundreds of scientists combining data from multiple experiments and observation techniques. </p>
<h2>How to find an exoplanet</h2>
<p>One of the fastest-growing areas of astronomy research is the study of planets in other solar systems, called exoplanets. As of this writing, <a href="https://exoplanetarchive.ipac.caltech.edu/">4,367 exoplanets have been discovered</a>. Trying to observe an exoplanet orbiting around a distant star is a bit like trying to see a firefly crawling on a searchlight, so the vast majority of exoplanets have been discovered using a variety of clever indirect techniques.</p>
<p>One of these is the radial velocity technique, which has been used to discover 833 exoplanets so far. This technique measures <a href="https://www.nasa.gov/kepler/overview/planetdetectionmethods">tiny shifts in the colour of light</a> from the star as it is gently tugged by its orbiting exoplanet. </p>
<p>Most of the early exoplanet discoveries were made using this technique. The first tentative detection of an exoplanet was by a <a href="http://doi.org/10.1086/166608">Canadian team in 1988</a> using radial velocity. The first <a href="https://doi.org/10.1038/378355a0">definite discovery of an exoplanet</a> in 1995 earned the discoverers the <a href="https://www.nobelprize.org/prizes/physics/2019/summary/">2019 Nobel Prize in Physics</a>.</p>
<p>Radial velocity was first, but now more than three-quarters of the known exoplanets have been discovered using the transit technique. This technique works by measuring a star’s brightness over time, watching for regularly repeated drops in brightness, which could be caused by a planet passing in front of a star during its orbit. </p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/-pNLWQT4yG0?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The transit method measures fluctuations in a star’s brightness.</span></figcaption>
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<h2>Thousands of planets</h2>
<p>The <a href="https://www.nasa.gov/mission_pages/kepler/overview/index.html">Kepler Mission</a> carefully measured the brightness of 180,000 stars every one to 30 minutes for four years using a <a href="https://www.jpl.nasa.gov/missions/kepler">space-based telescope</a>. Almost 2,400 exoplanets were discovered (and over 400 more in the follow-up <a href="https://www.nasa.gov/mission_pages/kepler/main/index.html">K2 mission</a>). The Kepler Mission Team <a href="https://exoplanets.nasa.gov/news/1529/meet-the-kepler-mission-team/">officially</a> includes <a href="https://directory.eoportal.org/web/eoportal/satellite-missions/k/kepler">dozens of astronomers and support scientists</a>, and dozens more were able to analyze the <a href="https://exoplanetarchive.ipac.caltech.edu/docs/KeplerMission.html">publicly available data</a> for additional planetary discoveries.</p>
<p>The Kepler Mission measured its last exoplanet in 2018, and now the <a href="https://www.nasa.gov/tess-transiting-exoplanet-survey-satellite">Transiting Exoplanet Survey Satellite (TESS)</a> is following in its footsteps. Instead of focusing on a single patch of sky, TESS <a href="https://www.youtube.com/watch?v=evHF_mnIdj4&feature=emb_logo">monitors several patches of sky</a>. </p>
<p>The downside to the simple transit technique is that there are other astrophysical effects that can cause the same periodic drop in brightness, like background stars that <a href="https://www.aavso.org/variables-what-are-they-why-observe-them">vary in brightness</a>, or starspots (like <a href="https://www.swpc.noaa.gov/phenomena/sunspotssolar-cycle">sunspots</a>). Because of this, when interesting signals are first discovered by transit surveys, they are dispassionately numbered as “objects of interest” until they are validated as real exoplanets by another exoplanet detection technique, often radial velocity. </p>
<p>Right now, the TESS mission has more than two thousand objects of interest and over 100 <a href="https://exoplanetarchive.ipac.caltech.edu/cgi-bin/TblView/nph-tblView?app=ExoTbls&config=planets&constraint=pl_facility+like+%27%25TESS%25%27">confirmed exoplanets</a>. The validation process is where many of the really surprising, fascinating exoplanetary systems are teased apart by impressive feats of scientific collaboration and cooperation, and the TESS and Kepler teams <a href="https://exofop.ipac.caltech.edu/">maintain a coordination centre</a> to plan and share follow-up data. </p>
<h2>Amazing exoplanet systems</h2>
<p>Some of the really remarkable exoplanet discoveries to date include planets that orbit around a <a href="https://exoplanets.nasa.gov/news/1430/earth-sized-tatooine-planets-could-be-habitable/">pair of stars</a> (yes, like <a href="https://www.starwars.com/databank/tatooine">Tatooine in Star Wars</a>), <a href="https://exoplanets.nasa.gov/trappist1/">seven</a> <a href="https://www.system-sounds.com/trappist-sounds/">exoplanets</a> in the same system all closer to their star than Mercury is to our sun, <a href="https://www.theatlantic.com/science/archive/2020/01/stars-eating-exoplanets/604462/">evaporating planets</a> and a <a href="https://arxiv.org/pdf/1609.08485">brown dwarf with rings</a> that <a href="https://www.rochester.edu/newscenter/gigantic-ring-system-around-j1407b/">puts Saturn’s to shame</a>.</p>
<p>All of these discoveries required a lot of additional modelling and data collection in order to understand the systems, but one of the most complicated exoplanet systems yet was <a href="https://www.nasa.gov/feature/ames/planetary-sleuthing-finds-triple-star-world">announced in January 2020</a>. </p>
<p>Kepler Object of Interest 5 (KOI-5) was one of the first batch of possible exoplanets sent down by the Kepler space telescope in 2009. But the first follow-up data quickly showed the system was complicated by an additional star and weird follow-up observations. Mission astronomers were gleefully (and perhaps slightly frantically) wading through possible exoplanet discoveries, so it was put aside and the data was left in the public archive. The same system was flagged again a decade later by TESS as a TESS Object of Interest (TOI-1241).</p>
<p>High-resolution imaging by one team of astronomers was combined with longer time baseline radial velocity data from another team and the story began to emerge: KOI-5 was a triple-star system with an exoplanet orbiting one of the stars. This discovery was <a href="https://aas.org/sites/default/files/2021-01/AAS237_Mon2_Ciardi.pdf">presented</a> at the <a href="https://aas.org/meetings/aas237">January 2021 American Astronomical Society meeting</a>, and a peer-reviewed paper is forthcoming. </p>
<p>I have been a user of various public data archives for exoplanet systems in my <a href="https://academic.oup.com/mnras/article/444/3/2665/1067501">research</a> and <a href="https://iopscience.iop.org/article/10.1088/0004-637X/752/1/53">work</a>, and I fully appreciate how open data policies maximize the scientific research output that can be accomplished with each dataset.</p>
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<a href="https://images.theconversation.com/files/382044/original/file-20210202-23-1paidd4.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="an illustration showing the triple-star system" src="https://images.theconversation.com/files/382044/original/file-20210202-23-1paidd4.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/382044/original/file-20210202-23-1paidd4.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/382044/original/file-20210202-23-1paidd4.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/382044/original/file-20210202-23-1paidd4.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/382044/original/file-20210202-23-1paidd4.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/382044/original/file-20210202-23-1paidd4.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/382044/original/file-20210202-23-1paidd4.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The KOI-5 triple-star system with its newly discovered exoplanet.</span>
<span class="attribution"><span class="source">(Caltech/R. Hurt, Infrared Processing and Analysis Center)</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>Complex orbits</h2>
<p>Two sun-sized stars, designated A and B, orbit each other every 29 years in the middle of the system, while a third, smaller star orbits the two central stars every 400 years. The discovered planet is called KOI-5Ab, because it orbits star A, on an orbit that is tilted wildly away from the plane of the stars’ orbits.</p>
<p>Data from Kepler and TESS, which required the effort of dozens of astronomers working together, has revealed the size of KOI-5Ab: seven times the radius of the Earth. Another team of astronomers used radial velocity data to measure the mass of KOI-5Ab: 57 times the mass of the Earth. Combining these numbers gives the density, and tells us this planet is a <a href="https://exoplanets.nasa.gov/what-is-an-exoplanet/planet-types/gas-giant/">gas giant planet</a>, a bit smaller and denser than Saturn.</p>
<p>As someone who became an astronomer because I’ve always loved reading science fiction stories, I like thinking about what it would be like to visit an exoplanet like this. Being a gas planet, we couldn’t actually stand on the surface, but if we could hover on the edge of its atmosphere with our spaceship, what would we see? </p>
<p>A few exoplanets have been <a href="https://iopscience.iop.org/article/10.1086/683797">measured to be very dark</a>, so imagine looking down to see dark brown and grey clouds swirling in turbulent stripes driven by <a href="https://www.mcgill.ca/newsroom/channels/news/hot-jupiter-unusual-winds-284028">ferocious winds</a>. In the sky, you would see one sun, 17 times larger than our sun. There would also be another much smaller sun, only half a per cent as bright as our sun (which would still be a thousand times brighter than the Earth’s full moon). This smaller sun would complete an orbit through the constellations in the sky every thirty years. The third star in the system would move much more slowly relative to the background stars, and despite its large distance, would still appear much brighter than the full moon in our sky.</p>
<p>Even in orbit over this planet, full darkness would only be available for brief snatches every couple hundred years when all three stars wandered into the same portion of the celestial sphere. This exoplanet system sounds like a <a href="https://us.macmillan.com/books/9780765382030">science fiction story</a>, but astronomers have been able to conclusively prove its existence.</p>
<h2>Collaborative discovery</h2>
<p>Astronomy is one of the better sciences for sharing data. We have the <a href="https://arxiv.org/archive/astro-ph">arXiv</a> repository of freely accessible peer-reviewed papers, and standard practice is for telescope data to be publicly accessible in <a href="https://www.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/en/">various</a> <a href="https://archive.stsci.edu/">databases</a> after a short (usually one year) proprietary period. </p>
<p>The co-operation between astronomers using many different observation techniques has led to incredible discoveries like the KOI-5Ab system, and as long as <a href="https://www.technologyreview.com/2020/09/02/1007938/satellite-mega-constellations-risk-ruining-astronomy-forever/">satellites</a> do not <a href="https://theconversation.com/spacexs-starlink-satellites-are-about-to-ruin-stargazing-for-everyone-149516">ruin ground-based astronomy</a>, large team efforts and collaborations between telescope facilities will continue to produce astronomical discoveries remarkable enough to surpass science fiction.</p><img src="https://counter.theconversation.com/content/153524/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Samantha Lawler receives funding from the Natural Sciences and Engineering Research Council of Canada. </span></em></p>Publicly available data and collaborations between scientists have led to the discovery of a planet in a triple-star system.Samantha Lawler, Assistant professor of astronomy, University of ReginaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1564272021-03-11T13:51:37Z2021-03-11T13:51:37ZHow can some planets be hotter than stars? We’ve started to unravel the mystery<figure><img src="https://images.theconversation.com/files/388811/original/file-20210310-13-13fmyhj.jpg?ixlib=rb-1.1.0&rect=31%2C0%2C6888%2C4882&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Artist impression of KELT-9 b, the orange blob orbiting a blue star.</span> <span class="attribution"><span class="source">Léa Changeat</span>, <span class="license">Author provided</span></span></figcaption></figure><p>Until the early 2000s, the only known planets were located in our own neighbourhood, the Solar System. They broadly form two categories: the small rocky planets in the inner Solar System and the cold gaseous planets located in the outer part. With the discovery of exoplanets, planets orbiting stars other than the Sun, additional classes of planets were discovered and <a href="https://theconversation.com/more-than-1-000-new-exoplanets-discovered-but-still-no-earth-twin-59274">a new picture started to emerge</a>. Our Solar System is by no means typical. </p>
<p>For example, data from the <a href="https://www.nasa.gov/mission_pages/kepler/overview/index.html">Kepler mission</a> has shown that large, gaseous exoplanets can orbit very close to their star – rather than far away from it, as is the case in our Solar System, causing them to reach temperatures exceeding 1,000K (727°C). These have been dubbed “hot” or “ultra-hot” Jupiters. And while most other exoplanets are smaller, between the size of Neptune and Earth, we don’t know much about their composition.</p>
<p>But how can hot, gaseous planets form and exist so close to their star? What kind of extreme physical processes happen here? Answers to those questions have large implications in our understanding of exoplanets and solar system planets. In our recent study, <a href="https://iopscience.iop.org/article/10.3847/2041-8213/abd84f/meta">published in The Astrophysical Journal Letters</a>, we have added another piece to the puzzle of planet formation and evolution.</p>
<h2>Kelt-9 b</h2>
<p>The hottest exoplanet known so far is <a href="https://www.forbes.com/sites/jamiecartereurope/2020/07/03/nasa-uncovers-kelt-9b-a-big-boiling-and-bizarre-planet-with-four-seasons-and-a-36-hour-year/">Kelt-9 b</a>, which was discovered in 2016. Kelt-9 b orbits a star that is twice as hot as our Sun, at a distance ten times closer than Mercury orbits our star. It is a large gaseous exoplanet, with a radius 1.8 times that of Jupiter and temperatures reaching 5,000K. For comparison, this is hotter than 80% of all the stars in the universe and a similar temperature to our Sun.</p>
<p>In essence, hot Jupiters are a window into <a href="https://theconversation.com/the-seven-most-extreme-planets-ever-discovered-78959">extreme physical and chemical processes</a>. They offer an incredible opportunity to study physics in environmental conditions that are near impossible to reproduce on Earth. Studying them enhances our understanding of chemical and thermal processes, atmospheric dynamics and cloud formation. Understanding their origins can also help us improve planetary formation and evolution models. </p>
<p>We are still struggling to explain how planets form and how elements, such as water, were delivered to our own Solar System. To find out, we need to learn more about exoplanet compositions by observing their atmospheres.</p>
<h2>Observing atmospheres</h2>
<p>There are two <a href="https://theconversation.com/explainer-how-do-you-find-exoplanets-24153">main methods</a> to study exoplanet atmospheres. In the transit method, we can pick up stellar light that is filtered through the exoplanet’s atmosphere when it passes in front of its star, revealing the fingerprints of any chemical elements that exist there. </p>
<p>The other method to investigate a planet is during an “eclipse”, when it passes behind its host star. Planets also emit and reflect a small fraction of light, so by comparing the small changes in the total light when the planet is hidden and visible, we can extract the light coming from the planet. </p>
<p>Both types of observations are performed at different wavelengths, or colours, and since chemical elements and compounds absorb and emit at very specific wavelengths, a spectrum (light broken down by wavelength) can be produced for the planet to infer the composition of its atmosphere. </p>
<h2>The secrets of Kelt-9 b</h2>
<p>In our study, we used publicly available data, taken by the <a href="https://theconversation.com/hubbles-deep-field-images-of-the-early-universe-are-postcards-from-billions-of-years-ago-40519">Hubble Space Telescope</a>, to obtain the eclipse spectrum of this planet. </p>
<p>We then used open-source software to extract the presence of molecules and found there were plenty of metals (made from molecules). This discovery is interesting as it was previously thought that these molecules would not be present at such extreme temperatures – they would be broken apart into smaller compounds.</p>
<p>Subject to the strong gravitational pull from its host star, Kelt-9 b is “tidally locked”, which means that the same face of the planet permanently faces the star. This results in a strong temperature difference between the planet’s day and night sides. As the eclipse observations probe the hotter day-side, we suggested that the observed molecules could in fact be dragged by dynamic processes from the cooler regions, such as the night-side or from deeper in the interior of the planet. These observations suggest that the atmospheres of these extreme worlds are ruled by complex processes that are poorly understood.</p>
<figure class="align-center ">
<img alt="Artist''s impression of Kelt b orbiting its parent star." src="https://images.theconversation.com/files/388813/original/file-20210310-14-iabbyr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/388813/original/file-20210310-14-iabbyr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/388813/original/file-20210310-14-iabbyr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/388813/original/file-20210310-14-iabbyr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/388813/original/file-20210310-14-iabbyr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/388813/original/file-20210310-14-iabbyr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/388813/original/file-20210310-14-iabbyr.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">Artist’s impression of Kelt-9 b orbiting its parent star.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech</span></span>
</figcaption>
</figure>
<p>Kelt-9 b is interesting because of its inclined orbit of about 80 degrees. This suggests a violent past, with possible collisions, which in fact is also seen for many other planets of this class. It is most likely that this planet formed away from its parent star and that the collisions happened as it migrated inwards toward the star. This supports the theory that large planets tend to form away from their host star in proto-stellar disks – which give rise to solar systems – capturing gaseous and solid materials as they migrate toward their star. </p>
<p>But we don’t know the details of how this happens. So it is crucial to characterise many of these worlds to confirm various scenarios and better understand their history as a whole.</p>
<h2>Future missions</h2>
<p>Observatories, such as the <a href="https://theconversation.com/hubbles-deep-field-images-of-the-early-universe-are-postcards-from-billions-of-years-ago-40519">Hubble Space Telescope</a>, were not designed to study exoplanet atmospheres. The next generation of space telescopes, such as 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> and the <a href="https://arielmission.space/">Ariel mission</a>, will have much better capabilities and instruments specifically tailored for the rigorous observation of exoplanet atmospheres. They will allow us to answer many of the fundamental questions raised by the extremely hot-Jupiter planet class, but they will not stop there.</p>
<p>This new generation of telescopes will also probe the atmosphere of small worlds, a category that current instruments struggle to reach. In particular, Ariel, which is expected to launch in 2029, will observe about 1,000 exoplanets to tackle some of the most fundamental questions in exoplanet science.</p>
<p>Ariel will also be the first space mission to look in details at the atmosphere of these worlds. It should finally tell us what these exoplanets are made of and how they formed and evolved. This will be a true revolution.</p><img src="https://counter.theconversation.com/content/156427/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Quentin Changeat has received funding from the European Research Council under the European Union’s Horizon 2020 research and innovation programme, and from the Science and Technology Funding Council (STFC).</span></em></p><p class="fine-print"><em><span>Billy Edwards has received funding from the European Research Council under the European Union’s Horizon 2020 research and innovation programme, and from the Science and Technology Funding Council (STFC).</span></em></p>The hottest exoplanet known so far has metals in its atmosphere – something scientists thought would be impossible.Quentin Changeat, Postdoctoral Research Fellow in Astronomy, UCLBilly Edwards, Project Scientist of the Twinkle Space Mission, Research Fellow of Astronomy, UCLLicensed 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/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/942912018-04-19T01:36:48Z2018-04-19T01:36:48ZNASA’s planet-hunting spacecraft TESS is now on its mission to search for new worlds<figure><img src="https://images.theconversation.com/files/215506/original/file-20180419-163971-16jb1ut.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">NASA’s Transiting Exoplanet Survey Satellite (TESS) successfully launched on a SpaceX Falcon 9.</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/image-feature/spacex-falcon-9-rocket-engines-roar-to-life">NASA Television</a></span></figcaption></figure><p>The latest of <a href="https://www.nasa.gov/">NASA</a>’s incredible planet-hunting space telescopes was launched today from <a href="https://www.kennedyspacecenter.com/">Cape Canaveral Air Force Station</a> in Florida. </p>
<p>Known as the <a href="https://www.nasa.gov/tess-transiting-exoplanet-survey-satellite">Transiting Exoplanet Survey Satellite</a> (or <a href="https://tess.gsfc.nasa.gov/">TESS</a> to its friends), this exciting new mission promises to provide the next great leap forward in our understanding of our place in the universe. </p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"986742455050653696"}"></div></p>
<p>Over the next two years, TESS is likely to find thousands of new exoplanets – planets orbiting distant stars – and will help to reveal the degree to which our Solar system is unique in the cosmos. </p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/googles-artificial-intelligence-finds-two-new-exoplanets-missed-by-human-eyes-89024">Google's artificial intelligence finds two new exoplanets missed by human eyes</a>
</strong>
</em>
</p>
<hr>
<p>In doing so, it will build on the fascinating results of the past few decades, cementing our place in the “Exoplanet Era”.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/215494/original/file-20180418-163995-106pj74.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/215494/original/file-20180418-163995-106pj74.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/215494/original/file-20180418-163995-106pj74.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/215494/original/file-20180418-163995-106pj74.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/215494/original/file-20180418-163995-106pj74.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/215494/original/file-20180418-163995-106pj74.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/215494/original/file-20180418-163995-106pj74.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/215494/original/file-20180418-163995-106pj74.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">Illustration of NASA’s Transiting Exoplanet Survey Satellite (TESS) in front of a lava planet orbiting its host star.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/image-feature/goddard/2018/tess-illustration-1">NASA's Goddard Space Flight Center</a></span>
</figcaption>
</figure>
<h2>The Kepler revolution</h2>
<p>At the end of 2008, the year before NASA’s earlier planet-hunting telescope <a href="https://www.nasa.gov/mission_pages/kepler/overview/index.html">Kepler</a> launched, about 300 exoplanets had been discovered. Today, the number is an order of magnitude larger: <a href="https://exoplanetarchive.ipac.caltech.edu/">more than 3,700</a>. </p>
<p><a href="https://www.nasa.gov/kepler/discoveries/">Kepler discovered</a> more than 2,300 exoplanets, with a further 2,200 or so “candidate” planets still awaiting followup. This incredible haul is the result of the spacecraft staring, unblinking, at the night sky, <a href="https://theconversation.com/explainer-how-to-find-an-exoplanet-part-1-56682">watching for the tiny flickers that reveal planets passing between us and their host stars</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/214974/original/file-20180416-105522-1dkx9aj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/214974/original/file-20180416-105522-1dkx9aj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/214974/original/file-20180416-105522-1dkx9aj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=350&fit=crop&dpr=1 600w, https://images.theconversation.com/files/214974/original/file-20180416-105522-1dkx9aj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=350&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/214974/original/file-20180416-105522-1dkx9aj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=350&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/214974/original/file-20180416-105522-1dkx9aj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=440&fit=crop&dpr=1 754w, https://images.theconversation.com/files/214974/original/file-20180416-105522-1dkx9aj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=440&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/214974/original/file-20180416-105522-1dkx9aj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=440&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 illustration of NASA’s Kepler spacecraft that carried out the first great census of the Exoplanet Era.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/ames/kepler/nasas-planet-hunting-kepler-and-k2-missions-take-your-questions-on-reddit">NASA Ames/ W Stenzel</a></span>
</figcaption>
</figure>
<p>In essence, Kepler carried out the <a href="https://theconversation.com/kepler-finds-more-earth-like-planets-but-are-they-really-like-earth-59252">first great census of the Exoplanet Era</a>. It taught us that planets are ubiquitous – a standard and natural byproduct of the formation of stars.</p>
<p>But the vast majority of the stars around which Kepler found planets were very faint and very distant. This makes it a great challenge for observers on the ground to follow up on those discoveries and learn more about the planets the spacecraft revealed.</p>
<h2>Along comes TESS</h2>
<p>Whereas <a href="https://www.nasa.gov/mission_pages/kepler/multimedia/images/kepler-field-of-view-photo.html">Kepler focused for four years on just one small patch of the northern sky</a>, TESS will target stars across almost the whole night sky. In doing so, it will survey some of the brightest stars in the sky – making the task of following up on its myriad discoveries far easier.</p>
<p>TESS consists of four cameras, configured to give it an observation sector that covers an area slightly larger than a 90° arc on the sky.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/214957/original/file-20180416-577-21qevo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/214957/original/file-20180416-577-21qevo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/214957/original/file-20180416-577-21qevo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/214957/original/file-20180416-577-21qevo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/214957/original/file-20180416-577-21qevo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/214957/original/file-20180416-577-21qevo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=565&fit=crop&dpr=1 754w, https://images.theconversation.com/files/214957/original/file-20180416-577-21qevo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=565&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/214957/original/file-20180416-577-21qevo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=565&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Image showing how TESS’ four cameras will be used to survey the night sky, sector by sector.</span>
<span class="attribution"><a class="source" href="https://heasarc.gsfc.nasa.gov/docs/tess/operations.html">NASA</a></span>
</figcaption>
</figure>
<p>TESS will watch that observation sector continually for just over 27 days, never blinking. The spacecraft will then pivot around, swinging to target its next sector. </p>
<p>In this manner, over the course of a year, the spacecraft will target almost the entirety of one hemisphere of the sky. After that, it will flip over, and spend the next year watching the other hemisphere.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/evHF_mnIdj4?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">TESS will cover much more than Kepler in its hunt for exoplanets.</span></figcaption>
</figure>
<p>For the first year TESS will be gazing to the south, scouring skies that are best seen from the southern hemisphere, finding planets orbiting the very stars you see when you step outside and look up at the night sky, right here in Australia.</p>
<h2>Many stars, many planets?</h2>
<p>TESS’s main mission will involve it observing a <a href="https://tess.gsfc.nasa.gov/overview.html">total of 200,000 stars</a>, measuring their brightness every single minute that they fall within its field of view. To do this, it will process images before sending them back to Earth, extracting just the data on those stars to send back to the Earth. </p>
<p>TESS will also provide full-frame images (a picture of the spacecraft’s full field of view) every half an hour, yielding a trove of tens of millions of objects observed.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/214969/original/file-20180416-47416-10tr3qb.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/214969/original/file-20180416-47416-10tr3qb.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/214969/original/file-20180416-47416-10tr3qb.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=383&fit=crop&dpr=1 600w, https://images.theconversation.com/files/214969/original/file-20180416-47416-10tr3qb.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=383&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/214969/original/file-20180416-47416-10tr3qb.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=383&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/214969/original/file-20180416-47416-10tr3qb.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=481&fit=crop&dpr=1 754w, https://images.theconversation.com/files/214969/original/file-20180416-47416-10tr3qb.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=481&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/214969/original/file-20180416-47416-10tr3qb.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=481&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">TESS will process data on board the spacecraft, to make the amount sent back to Earth manageable.</span>
<span class="attribution"><a class="source" href="https://heasarc.gsfc.nasa.gov/docs/tess/operations.html">NASA</a></span>
</figcaption>
</figure>
<p>Put all that together, and the expected planet yield should be enormous. Based on the statistics of planet discoveries to date, it is likely that TESS will find <a href="https://tess.gsfc.nasa.gov/overview.html">at least a couple of thousand potential planets</a> around its main target stars, while those in the full-frame images might yield tens of thousands of additional candidates.</p>
<p>These numbers are incredible, and TESS will revolutionise our understanding of our place in the universe. But such amazing results bring with them a unique problem – and one that we, in Australia, are ideally placed to help solve.</p>
<h2>Too many planets, too little time</h2>
<p>The reason that only half of the Kepler mission’s candidate planets have been confirmed is that doing so <a href="http://www.skyandtelescope.com/astronomy-news/a-tidal-wave-of-exoplanet-candidates/">requires extensive follow-up work from the ground</a>.</p>
<p>Astronomers have to rule out other effects that could cause the behaviour seen in the potential planet’s host star before we can be certain that we’re really seeing evidence of a new planet.</p>
<p>Most of the stars observed by Kepler are simply too faint for that kind of work to be carried out from the ground – except, perhaps, <a href="https://www.space.com/14075-10-biggest-telescopes-earth-comparison.html">with the largest telescopes on the planet</a>. Getting time on those telescopes is challenging – all of the world’s other astronomers covet that time too, for their own projects. </p>
<p>Quite simply, it is a case of too many planets, too little time.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/214975/original/file-20180416-540-1py5ym6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/214975/original/file-20180416-540-1py5ym6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/214975/original/file-20180416-540-1py5ym6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=396&fit=crop&dpr=1 600w, https://images.theconversation.com/files/214975/original/file-20180416-540-1py5ym6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=396&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/214975/original/file-20180416-540-1py5ym6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=396&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/214975/original/file-20180416-540-1py5ym6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=498&fit=crop&dpr=1 754w, https://images.theconversation.com/files/214975/original/file-20180416-540-1py5ym6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=498&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/214975/original/file-20180416-540-1py5ym6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=498&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Too many potential exoplanets, too little time.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/multimedia/imagegallery/image_feature_2233.html">NASA, ESA, and M. Kornmesser (ESO)</a></span>
</figcaption>
</figure>
<p>The problem is only going to get worse with TESS. When the first few planets were found, in the late 20th century, the discoveries came in a trickle. Those discoveries were easy for scientists to drink in and follow up, and all was good.</p>
<p>With Kepler, the discovery rate went through the roof. From a trickle, it was like someone had turned on a tap – a continual stream of new potential planets to study.</p>
<p>If Kepler was a tap, then TESS will be a fire hose, and there are simply too few telescopes available for us to use to study all of the planets TESS finds at once. </p>
<p>That is where the Australian connection comes to the fore – in the form of a dedicated new facility being built on the Darling Downs, in southeast Queensland.</p>
<h2>The Australian connection - MINERVA-Australis</h2>
<p>At the University of Southern Queensland, we are <a href="http://www.abc.net.au/news/2016-08-17/astronomers-search-for-earth-like-planets-usq/7746654">constructing MINERVA-Australis</a> – a collection of six telescopes dedicated to nothing but the search for and characterisation of planets around other stars.</p>
<p>When TESS turns on the fire hose, finding thousands of planets in the southern sky, we stand ready. Every clear night, we will be observing those stars that TESS suggests could host planets, doing our utmost to confirm whether those planets really exist.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/weve-found-an-exo-planet-with-an-extraordinarily-eccentric-orbit-87011">We've found an exo-planet with an extraordinarily eccentric orbit</a>
</strong>
</em>
</p>
<hr>
<p>Once we confirm TESS’s new discoveries, we will be able to use our facility to study the newly found worlds in more detail. By observing the planet’s transits, we can measure its physical size, <a href="https://theconversation.com/its-all-in-the-rotation-exploring-planets-orbiting-distant-stars-59593">by seeing how much of the light from its host the planet blocks</a>.</p>
<p>In addition, we will be examining the light we receive from the star, measuring the telltale wobbles caused by the planet as it orbits its host. With those measurements, <a href="https://theconversation.com/its-all-in-the-rotation-exploring-planets-orbiting-distant-stars-59593">we will be able to calculate the planet’s mass</a>.</p>
<p>Put the mass and the size together, and we can really begin to work out the planet’s true nature. Is it rocky (like the Earth), or gaseous, like Jupiter and Saturn? </p>
<p>Over the coming years, TESS will push the Exoplanet Era through its next great revolution – finding thousands or tens of thousands of new exoplanets. Here in southeast Queensland, we will be at the forefront of that journey of discovery, helping to reveal the true nature of those alien worlds.</p>
<p>I don’t know about you, but I can’t wait to see what we’ll learn next!</p><img src="https://counter.theconversation.com/content/94291/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jonti Horner is part of a team of researchers at the University of Southern Queensland who received funding from the Australian Research Council to build MINERVA-Australis - an astronomical observatory dedicated to following up and characterising the myriad exoplanets that will be discovered by TESS</span></em></p>The new planet-hunting telescope TESS was successfully launched today by NASA, and Australia will play a key role in checking out any new worlds it discovers.Jonti Horner, Professor (Astrophysics), University of Southern QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/936882018-04-09T10:33:24Z2018-04-09T10:33:24ZGoodbye Kepler, hello TESS: Passing the baton in the search for distant planets<figure><img src="https://images.theconversation.com/files/213635/original/file-20180406-5578-h4ba8e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Imagined view from Kepler-10b, a planet that orbits one of the 150,000 stars that the Kepler spacecraft is monitoring.</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/mission_pages/kepler/multimedia/images/kepler10_5.html">NASA/Kepler Mission/Dana Berry</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>For centuries, human beings have wondered about the possibility of other Earths orbiting distant stars. Perhaps some of these alien worlds would harbor strange forms of life or have unique and telling histories or futures. But it was only in 1995 that astronomers spotted the first planets orbiting sunlike stars outside of our solar system. </p>
<p>In the last decade, in particular, the number of planets known to orbit distant stars grew from under 100 to well over 2,000, with another 2,000 likely planets awaiting confirmation. Most of these new discoveries are due to a single endeavor — <a href="https://www.nasa.gov/mission_pages/kepler/overview/index.html">NASA’s Kepler mission</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/213631/original/file-20180406-5572-1e5h7cx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/213631/original/file-20180406-5572-1e5h7cx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/213631/original/file-20180406-5572-1e5h7cx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/213631/original/file-20180406-5572-1e5h7cx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/213631/original/file-20180406-5572-1e5h7cx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/213631/original/file-20180406-5572-1e5h7cx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/213631/original/file-20180406-5572-1e5h7cx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/213631/original/file-20180406-5572-1e5h7cx.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">Number of confirmed exoplanets continues to grow.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/image-feature/ames/planetary-systems-by-number-of-known-planets">NASA/Ames Research Center/Wendy Stenzel and The University of Texas at Austin/Andrew Vanderburg</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/213633/original/file-20180406-5597-1xrglfy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/213633/original/file-20180406-5597-1xrglfy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/213633/original/file-20180406-5597-1xrglfy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=255&fit=crop&dpr=1 600w, https://images.theconversation.com/files/213633/original/file-20180406-5597-1xrglfy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=255&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/213633/original/file-20180406-5597-1xrglfy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=255&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/213633/original/file-20180406-5597-1xrglfy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=321&fit=crop&dpr=1 754w, https://images.theconversation.com/files/213633/original/file-20180406-5597-1xrglfy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=321&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/213633/original/file-20180406-5597-1xrglfy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=321&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Scientists can determine the size or radius of a planet by measuring the depth of the dip in brightness and knowing the size of the star.</span>
<span class="attribution"><span class="source">NASA Ames</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Kepler is a spacecraft housing a 1-meter telescope that illuminates a 95 megapixel digital camera the size of a cookie sheet. The instrument detected tiny variations in the brightness of 150,000 distant stars, looking for the telltale sign of a planet blocking a portion of the starlight as it transits across the telescope’s line of sight. It’s so sensitive that it could detect a fly buzzing around a single streetlight in Chicago from an orbit above the Earth. It can see stars shake and vibrate; it can see starspots and flares; and, in favorable situations, it can see planets as small as the moon.</p>
<p>Kepler’s thousands of discoveries revolutionized our understanding of planets and planetary systems. Now, however, the spacecraft has run out of its hydrazine fuel and officially entered retirement. Luckily for planet hunters, NASA’s TESS mission launched in April and will take over the exoplanet search.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/213634/original/file-20180406-5581-17gqrvc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/213634/original/file-20180406-5581-17gqrvc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/213634/original/file-20180406-5581-17gqrvc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=402&fit=crop&dpr=1 600w, https://images.theconversation.com/files/213634/original/file-20180406-5581-17gqrvc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=402&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/213634/original/file-20180406-5581-17gqrvc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=402&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/213634/original/file-20180406-5581-17gqrvc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=505&fit=crop&dpr=1 754w, https://images.theconversation.com/files/213634/original/file-20180406-5581-17gqrvc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=505&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/213634/original/file-20180406-5581-17gqrvc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=505&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Prepping the Kepler spacecraft pre-launch in 2009.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/mission_pages/kepler/multimedia/09-02-03.html">NASA/Tim Jacobs</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Kepler’s history</h2>
<p>The Kepler mission was conceived in the early 1980s by NASA scientist <a href="https://www.nasa.gov/mission_pages/kepler/team/william_borucki.html">Bill Borucki</a>, with later help from <a href="https://www.nasa.gov/mission_pages/kepler/team/David_Koch.html">David Koch</a>. At the time, there were no known planets outside of the solar system. Kepler was eventually assembled in the 2000s and launched in March of 2009. <a href="https://scholar.google.com/citations?user=pyXWfSgAAAAJ&hl=en&oi=ao">I joined</a> the Kepler Science Team in 2008 (as a wide-eyed rookie), eventually co-chairing the group studying the motions of the planets with <a href="https://www.nasa.gov/centers/ames/research/2007/lissauer.html">Jack Lissauer</a>.</p>
<p>Originally, the mission was planned to last for three and a half years with possible extensions for as long as the fuel, or the camera, or the spacecraft lasted. As time passed, portions of the camera began to fail but the mission has persisted. However, in 2013 <a href="https://www.nature.com/news/the-wheels-come-off-kepler-1.13032">when two of its four stabilizing gyros</a> (technically “reaction wheels”) stopped, the original Kepler mission effectively ended.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/213632/original/file-20180406-5600-hmzwbd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/213632/original/file-20180406-5600-hmzwbd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/213632/original/file-20180406-5600-hmzwbd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=541&fit=crop&dpr=1 600w, https://images.theconversation.com/files/213632/original/file-20180406-5600-hmzwbd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=541&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/213632/original/file-20180406-5600-hmzwbd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=541&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/213632/original/file-20180406-5600-hmzwbd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=679&fit=crop&dpr=1 754w, https://images.theconversation.com/files/213632/original/file-20180406-5600-hmzwbd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=679&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/213632/original/file-20180406-5600-hmzwbd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=679&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">NASA scientists figured out how to use solar pressure to stabilize Kepler.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/kepler/keplers-second-light-how-k2-will-work">NASA Ames/W Stenzel</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Even then, with some ingenuity, NASA was able to use <a href="https://www.nasa.gov/kepler/keplers-second-light-how-k2-will-work">reflected light from the Sun to help steer the spacecraft</a>. The mission was rechristened as K2 and continued finding planets for another half decade. Now, with the fuel gauge near empty, the business of planet hunting is winding down and the spacecraft will be left adrift in the solar system. The final catalog of planet candidates from the original mission was completed late last year and the last observations of K2 are wrapping up.</p>
<h2>Kepler’s science</h2>
<p>Squeezing what knowledge we can from those data will continue for years to come, but what we’ve seen thus far has amazed scientists across the globe.</p>
<p>We have seen some planets that orbit their host stars in only a few hours and are so hot that the surface rock <a href="https://www.nasa.gov/content/disintegrating-super-mercury-size-planet">vaporizes and trails behind the planet</a> like a comet tail. Other systems have <a href="http://www.washington.edu/news/2012/06/21/astronomers-spy-two-planets-in-tight-quarters-as-they-orbit-a-distant-star/">planets so close together</a> that if you were to stand on the surface of one, the second planet would appear larger than 10 full moons. One system is so packed with planets that <a href="https://www.nasa.gov/image-feature/ames/kepler-90-planets-orbit-close-to-their-star">eight of them are closer to their star</a> than the Earth is to the Sun. <a href="https://www.nasa.gov/ames/kepler/nasa-keplers-hall-of-fame-small-habitable-zone-exoplanets">Many have planets</a>, and sometimes multiple planets, orbiting within the <a href="https://www.nasa.gov/ames/kepler/habitable-zones-of-different-stars">habitable zone</a> of their host star, where liquid water may exist on their surfaces.</p>
<p>As with any mission, the Kepler package came with trade-offs. It needed to stare at a single part of the sky, blinking every 30 minutes, for four straight years. In order to study enough stars to make its measurements, the stars had to be quite distant – just as when you stand in the middle of a forest, there are more trees farther from you than right next to you. Distant stars are dim, and their planets are hard to study. Indeed, one challenge for astronomers who want to study the properties of Kepler planets is that Kepler itself is often the best instrument to use. High quality data from ground-based telescopes requires long observations on the largest telescopes – precious resources that limit the number of planets that can be observed.</p>
<p>We now know that there are at least as many planets in the galaxy as there are stars, and many of those planets are quite unlike what we have here in the solar system. Learning the characteristics and personalities of the wide variety of planets requires that astronomers investigate the ones orbiting brighter and closer stars where more instruments and more telescopes can be brought to bear.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/213636/original/file-20180406-5603-e2bdy9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/213636/original/file-20180406-5603-e2bdy9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/213636/original/file-20180406-5603-e2bdy9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=357&fit=crop&dpr=1 600w, https://images.theconversation.com/files/213636/original/file-20180406-5603-e2bdy9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=357&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/213636/original/file-20180406-5603-e2bdy9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=357&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/213636/original/file-20180406-5603-e2bdy9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=449&fit=crop&dpr=1 754w, https://images.theconversation.com/files/213636/original/file-20180406-5603-e2bdy9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=449&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/213636/original/file-20180406-5603-e2bdy9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=449&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Once launched, TESS will identify exoplanets orbiting the brightest stars just outside our solar system.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/image-feature/goddard/2016/tess-artist-concept">NASA's Goddard Space Flight Center</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Enter TESS</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/213679/original/file-20180407-5569-5e4hvm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/213679/original/file-20180407-5569-5e4hvm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/213679/original/file-20180407-5569-5e4hvm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=548&fit=crop&dpr=1 600w, https://images.theconversation.com/files/213679/original/file-20180407-5569-5e4hvm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=548&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/213679/original/file-20180407-5569-5e4hvm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=548&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/213679/original/file-20180407-5569-5e4hvm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=689&fit=crop&dpr=1 754w, https://images.theconversation.com/files/213679/original/file-20180407-5569-5e4hvm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=689&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/213679/original/file-20180407-5569-5e4hvm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=689&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Duration of TESS’ observations on the celestial sphere, taking into account the overlap between sectors.</span>
<span class="attribution"><a class="source" href="https://tess.gsfc.nasa.gov/science.html">NASA</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p><a href="https://tess.gsfc.nasa.gov">NASA’s Transiting Exoplanet Survey Satellite mission</a>, led by MIT’s <a href="https://tess.gsfc.nasa.gov/dr-george-ricker-bio.html">George Ricker</a>, is searching for planets using the same detection technique that Kepler used. TESS’ orbit, rather than being around the Sun, has a close relationship with the Moon: TESS orbits the Earth twice for each lunar orbit. TESS’ observing pattern, rather than staring at a single part of the sky, will scan nearly the entire sky with overlapping fields of view (much like the petals on a flower).</p>
<p>Given what we learned from Kepler, astronomers expect TESS to find thousands more planetary systems. By surveying the whole sky, we will find systems that orbit stars 10 times closer and 100 times brighter than those found by Kepler – opening up new possibilities for measuring planet masses and densities, studying their atmospheres, characterizing their host stars, and establishing the full nature of the systems in which the planets reside. This information, in turn, will tell us more about our own planet’s history, how life may have started, what fates we avoided and what other paths we could have followed.</p>
<p>The quest to find our place in the universe continues as Kepler finishes its leg of the journey and TESS takes the baton.</p><img src="https://counter.theconversation.com/content/93688/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jason Steffen receives funding from NASA. </span></em></p>When NASA first started planning the Kepler mission, no one knew if the universe held any planets outside our solar system. Thousands of exoplanets later, the search enters a new phase as Kepler retires.Jason Steffen, Assistant Professor of Physics and Astronomy, University of Nevada, Las VegasLicensed 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>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/199331/original/file-20171214-27568-gwz0lp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/199331/original/file-20171214-27568-gwz0lp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/199331/original/file-20171214-27568-gwz0lp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/199331/original/file-20171214-27568-gwz0lp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/199331/original/file-20171214-27568-gwz0lp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/199331/original/file-20171214-27568-gwz0lp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/199331/original/file-20171214-27568-gwz0lp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/199331/original/file-20171214-27568-gwz0lp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Kepler-90 planets have a similar configuration to our solar system with small planets found orbiting close to their star, and the larger planets found farther away.</span>
<span class="attribution"><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>
<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>
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</em>
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<hr>
<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>
<figure class="align-center zoomable">
<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>
<figcaption>
<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>
<figure>
<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>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/199360/original/file-20171215-26009-gw0pyk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/199360/original/file-20171215-26009-gw0pyk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/199360/original/file-20171215-26009-gw0pyk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=478&fit=crop&dpr=1 600w, https://images.theconversation.com/files/199360/original/file-20171215-26009-gw0pyk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=478&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/199360/original/file-20171215-26009-gw0pyk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=478&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/199360/original/file-20171215-26009-gw0pyk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=600&fit=crop&dpr=1 754w, https://images.theconversation.com/files/199360/original/file-20171215-26009-gw0pyk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=600&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/199360/original/file-20171215-26009-gw0pyk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=600&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<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>
<hr>
<p>
<em>
<strong>
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>
</strong>
</em>
</p>
<hr>
<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/602432016-06-05T20:10:50Z2016-06-05T20:10:50ZRIP E.T. – alien life on most exoplanets dies young<figure><img src="https://images.theconversation.com/files/124713/original/image-20160601-1946-13gj6ik.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Artist's rendition of one of the billions of rocky exoplanets in our galaxy.
Did life once exist on its surface?</span> <span class="attribution"><span class="source">NASA/JPL-Caltech</span></span></figcaption></figure><p>Astronomers have found a <a href="http://exoplanetarchive.ipac.caltech.edu/">plethora of planets</a> around nearby stars. And it appears that Earth-sized planets in habitable zones are <a href="http://theconversation.com/alien-worlds-most-stars-have-planets-in-the-habitable-zone-38964">probably common</a>.</p>
<p>So, with tens or even hundreds of <a href="https://www.washingtonpost.com/news/speaking-of-science/wp/2015/07/24/nasa-estimates-1-billion-earths-in-our-galaxy-alone/">billions</a> of potentially habitable planets within our galaxy, the question becomes: are we alone?</p>
<p>Indeed, the <a href="http://astrobiology.nasa.gov/our-research/astrobiology-at-nasa/astrobiology-strategy/">search for alien life</a> has become the holy grail for the next generation of telescopes and space missions to Mars and beyond. But could our search for E.T. be naively optimistic?</p>
<p>Many scientists and commentators equate “<a href="https://exoplanets.jpl.nasa.gov/news/1346/">more planets</a>” with “more E.T.s”. However, the violence and instability of the early formation and evolution of rocky planets suggests that most aliens will be extinct fossil microbes.</p>
<p>Just as dead dinosaurs don’t walk, talk or breathe, microbes that have been fossilised for billions of years are not easy to detect by the remote sampling of exoplanetary atmospheres.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/124904/original/image-20160602-1951-k4ymfi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/124904/original/image-20160602-1951-k4ymfi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=480&fit=crop&dpr=1 600w, https://images.theconversation.com/files/124904/original/image-20160602-1951-k4ymfi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=480&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/124904/original/image-20160602-1951-k4ymfi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=480&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/124904/original/image-20160602-1951-k4ymfi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=603&fit=crop&dpr=1 754w, https://images.theconversation.com/files/124904/original/image-20160602-1951-k4ymfi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=603&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/124904/original/image-20160602-1951-k4ymfi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=603&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Conservative estimates suggest that there are more than a billion Earth-like planets within our.
own galaxy. On how many of them has life been able to persist for billions of years?</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech</span></span>
</figcaption>
</figure>
<h2>Gaian Bottleneck</h2>
<p>In research <a href="http://bit.ly/gaianbottleneck">published</a> in the journal Astrobiology, we argue that early extinction could be the cosmic default for life in the universe. This is because the earliest habitable conditions may be unstable. </p>
<p>In our “Gaian Bottleneck” model, planets need to be inhabited in order to remain habitable. So even if the emergence of life is common, its persistence may be rare.</p>
<p>Mars, Venus and Earth were more similar to each other in their first billion years than they are today. Even if only one of the planets saw the emergence of life, this era coincided with heavy bombardment from asteroids, which could have spread life between the planets. </p>
<p>But about 1.5 billion years after formation, Venus started to experience runaway heating and Mars experienced runaway cooling. If Mars and Venus once harboured life, that life quickly went extinct. </p>
<p>Even if wet rocky Earth-like planets are in the “<a href="http://www.abc.net.au/news/2016-02-22/goldilocks-zones-habitable-zone-astrobiology-exoplanets/6907836">Goldilocks Zone</a>” of their host stars, it seems that runaway freezing or heating may be their default fate. </p>
<p>Large impactors and huge variation in the amounts of water and greenhouse gases can induce positive feedbacks cycles that push planets away from habitable conditions.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/125136/original/image-20160603-11593-6frd5l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/125136/original/image-20160603-11593-6frd5l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/125136/original/image-20160603-11593-6frd5l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=271&fit=crop&dpr=1 600w, https://images.theconversation.com/files/125136/original/image-20160603-11593-6frd5l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=271&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/125136/original/image-20160603-11593-6frd5l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=271&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/125136/original/image-20160603-11593-6frd5l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=340&fit=crop&dpr=1 754w, https://images.theconversation.com/files/125136/original/image-20160603-11593-6frd5l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=340&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/125136/original/image-20160603-11593-6frd5l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=340&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">How did Earth manage to remain habitable for almost 4 billion years while one sibling turned into a hot hell-house and the other a frozen ice-box?</span>
<span class="attribution"><span class="source">JAXA/NASA/ESA</span></span>
</figcaption>
</figure>
<p>The <a href="https://en.wikipedia.org/wiki/Carbonate%E2%80%93silicate_cycle">carbonate-silicate weathering cycle</a>, which provides the major negative feedback to stabilise Earth’s climate today, was probably inoperative, or at least inefficient, until about 3 billion years ago. </p>
<p>However, life on Earth may have had the fortuitous ability to create stability by suppressing the positive runaway feedback loops and enhancing the negative feedback loops.</p>
<p>We should probably thank the unpredictable evolution of microbial communities our planet hosted early in its history for saving us from runaway conditions that would make Earth too hot or too cold for us to live. </p>
<p>As soon as life became widespread on Earth, the earliest metabolisms began to modulate the greenhouse gas composition of the atmosphere. It is no coincidence that methane, carbon dioxide, hydrogen and water are all potent greenhouse gases and also the reactants and products of metabolic reactions of the earliest microbial mats and biofilms.</p>
<p>The emergence of life’s ability to regulate initially non-biological feedback mechanisms (what we call “Gaian regulation”) could be the most significant factor responsible for life’s persistence on Earth.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/124717/original/image-20160601-2812-11y3z2j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/124717/original/image-20160601-2812-11y3z2j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/124717/original/image-20160601-2812-11y3z2j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=220&fit=crop&dpr=1 600w, https://images.theconversation.com/files/124717/original/image-20160601-2812-11y3z2j.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=220&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/124717/original/image-20160601-2812-11y3z2j.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=220&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/124717/original/image-20160601-2812-11y3z2j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=276&fit=crop&dpr=1 754w, https://images.theconversation.com/files/124717/original/image-20160601-2812-11y3z2j.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=276&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/124717/original/image-20160601-2812-11y3z2j.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=276&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">We postulate a habitable zone (yellow) that is unstable and lasts only from ~0.5 to ~1 billion years after the planet forms. Then, in the next ~0.5 billion years, surface temperatures drift or run away from habitability.</span>
<span class="attribution"><span class="source">Chopra & Lineweaver (2016)</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>Abiotic habitable zones are transient</h2>
<p>The Earth is not the only planet in our galaxy with liquid water on its surface and energy sources and nutrients to enable life to form.</p>
<p>Although the universe is <a href="http://www.annualreviews.org/eprint/snrJJ6k6fsvCkb3e4dmz/full/10.1146/annurev-earth-042711-105531">filled with stars and planets conducive to life</a>, the absence of any evidence for alien life suggests that even if the emergence of life is easy, its persistence may be difficult.</p>
<p>Our work challenges conventional views that physics-based habitable zones provide stable conditions for life for many billions of years. </p>
<p>Although, the cottage industry of habitable zone modellers can turn various knobs that control atmospheric and geophysical properties to stabilise planets over short-timescales, they have <a href="https://arxiv.org/abs/1603.00950">mostly ignored</a> the <a href="http://www.astrobio.net/news-exclusive/life-went-global/">role of biology</a> in keeping planets habitable over billions of years. </p>
<p>This is in part because the complexities of interactions between microbial communities that keep ecosystems stable are not sufficiently understood.</p>
<p>We hypothesise that even if life does emerge on a planet, it rarely evolves quickly enough to regulate greenhouse gases, and thereby keep surface temperatures compatible with liquid water and habitability. </p>
<p>Maintaining life on an initially wet rocky planet in the habitable zone may be like trying to ride a wild bull. Most riders falls off. So inhabited planets may be rare in the universe, not because emergent life is rare, but because habitable environments are difficult to maintain during the first billion years.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/124719/original/image-20160601-1964-aj0vfr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/124719/original/image-20160601-1964-aj0vfr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/124719/original/image-20160601-1964-aj0vfr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=316&fit=crop&dpr=1 600w, https://images.theconversation.com/files/124719/original/image-20160601-1964-aj0vfr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=316&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/124719/original/image-20160601-1964-aj0vfr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=316&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/124719/original/image-20160601-1964-aj0vfr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=398&fit=crop&dpr=1 754w, https://images.theconversation.com/files/124719/original/image-20160601-1964-aj0vfr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=398&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/124719/original/image-20160601-1964-aj0vfr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=398&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Astronaut Mark Watney did not find Martians to keep him company while he farmed potatoes. Why not? Perhaps life on Mars went extinct billions of years ago – a fate common to most life in the universe.</span>
<span class="attribution"><span class="source">20th Century Fox</span></span>
</figcaption>
</figure>
<h2>Most life dies young</h2>
<p>Our suggestion that the universe is filled with dead aliens might disappoint some, but the universe is under no obligation to prevent disappointment. </p>
<p>We should not expect technological or spacefaring civilisations because there is <a href="http://tedxtalks.ted.com/video/Science-humility-and-the-fallac">no evidence</a> that biological evolution converges to human-like intelligence. And subjective philosophical notions of life in the universe should not inform our estimates of the probability of life beyond Earth. </p>
<p>Superficially, these ideas seem to undermine the motivation for <a href="https://theconversation.com/au/topics/seti">SETI</a> and the recently announced <a href="https://theconversation.com/au/topics/breakthrough-listen">Breakthrough Listen</a> project. </p>
<p>Nevertheless, we support <a href="https://theconversation.com/what-is-the-search-for-extraterrestrial-intelligence-actually-looking-for-44977">SETI</a> because when we explore new regions of parameter space, we often find the <a href="https://theconversation.com/its-not-all-about-aliens-listening-project-may-unveil-other-secrets-of-the-universe-45031">unexpected</a>.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/124908/original/image-20160602-1951-o4g2rn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/124908/original/image-20160602-1951-o4g2rn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=408&fit=crop&dpr=1 600w, https://images.theconversation.com/files/124908/original/image-20160602-1951-o4g2rn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=408&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/124908/original/image-20160602-1951-o4g2rn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=408&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/124908/original/image-20160602-1951-o4g2rn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=513&fit=crop&dpr=1 754w, https://images.theconversation.com/files/124908/original/image-20160602-1951-o4g2rn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=513&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/124908/original/image-20160602-1951-o4g2rn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=513&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Our search for extant extraterrestrial life may be thwarted by planetary instability snuffing out incipient life.</span>
<span class="attribution"><span class="source">Author provided</span></span>
</figcaption>
</figure>
<p>In his book <a href="http://www.planetary.org/explore/space-topics/earth/pale-blue-dot.html">Pale Blue Dot</a>, Carl Sagan reminded us that “in our obscurity, in all this vastness, there is no hint that help will come from elsewhere to save us from ourselves”. </p>
<p>In the two decades since it was published, we’ve learnt that our cosmic backyard is littered with pale dots, probably in many colours of the rainbow. As we embark on the adventure of exploring our galactic neighbourhood with bigger and better <a href="https://www.sciencenews.org/article/new-telescopes-will-search-signs-life-distant-planets">telescopes</a>, we may find only spooky planets haunted by long dead microbial E.T.s.</p><img src="https://counter.theconversation.com/content/60243/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Complex life may be rare in the universe because most planets become either too hot or too cold before life has a chance to get a foothold. This might explain why we have yet to bump into E.T.Aditya Chopra, Post-doctoral Research Fellow, Australian National UniversityCharley Lineweaver, Researcher at Research School of Astronomy and Astrophysics and the Research School of Earth Sciences, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/570922016-04-14T10:06:14Z2016-04-14T10:06:14ZHow could we build an invisibility cloak to hide Earth from an alien civilization?<figure><img src="https://images.theconversation.com/files/118208/original/image-20160411-21965-h6pv1u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A laser could hide – or broadcast – our existence.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/esoastronomy/8497613660">European Southern Observatory</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>What would it take to hide an entire planet? It sounds more like a question posed in an episode of “Star Trek” than in academic discourse, but sometimes the bleeding edge of science blurs with themes found in science fiction.</p>
<p>Of course we’ve been leaking our own position to distant stars via radio and television signals for six decades now, largely ignorant of the cosmic implications. But several notable scientists, <a href="http://www.hawking.org.uk/life-in-the-universe.html">such as Stephen Hawking</a>, have <a href="http://setiathome.berkeley.edu/meti_statement_0.html">publicly voiced concerns</a> about revealing our presence to other civilizations. These concerns largely draw from the darker chapters of our own history, when a more advanced civilization would subjugate and displace a less advanced one.</p>
<p>It might be too late for us to withdraw back into invisibility, but maybe not for other intelligent alien civilizations out there. A far-off planet’s inhabitants might prefer to hide from the likes of us. In 2016, my graduate student <a href="http://www.coolworlds.nyc">Alex Teachey and I</a> published a paper that <a href="http://doi.org/10.1093/mnras/stw672">proposes a way to cloak planets</a>, as well as a way to broadcast a civilization’s existence. Even if we’re not manipulating our own signal in this way, it doesn’t mean other planets out there aren’t. It’s possible what we see as we scan the universe for other habitable planets has been engineered to disguise or highlight the existence of other civilizations.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/118197/original/image-20160411-21959-10r7w7l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/118197/original/image-20160411-21959-10r7w7l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/118197/original/image-20160411-21959-10r7w7l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=255&fit=crop&dpr=1 600w, https://images.theconversation.com/files/118197/original/image-20160411-21959-10r7w7l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=255&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/118197/original/image-20160411-21959-10r7w7l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=255&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/118197/original/image-20160411-21959-10r7w7l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=321&fit=crop&dpr=1 754w, https://images.theconversation.com/files/118197/original/image-20160411-21959-10r7w7l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=321&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/118197/original/image-20160411-21959-10r7w7l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=321&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">When a planet passes between us and its star, the star’s light seems to dim.</span>
<span class="attribution"><a class="source" href="http://www.nasa.gov/mission_pages/kepler/multimedia/images/transit-light-curve.html">NASA Ames</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Tracking transits to find other planets</h2>
<p>Before we talk about how to hide a planet from distant voyeurs, consider the best way we’ve figured out to find one.</p>
<p>Humanity’s most successful technique for detecting other planets is the transit method. A transit occurs when a planet appears to pass in front of its parent sun, blocking out some of its starlight for a few hours. So if we have our telescopes trained at one part of the universe and a star seems to fade out for part of a day, that tells us that a planet has temporarily come between us as it goes about its orbit.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/118219/original/image-20160411-21963-76ym4b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/118219/original/image-20160411-21963-76ym4b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/118219/original/image-20160411-21963-76ym4b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/118219/original/image-20160411-21963-76ym4b.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/118219/original/image-20160411-21963-76ym4b.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/118219/original/image-20160411-21963-76ym4b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=565&fit=crop&dpr=1 754w, https://images.theconversation.com/files/118219/original/image-20160411-21963-76ym4b.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=565&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/118219/original/image-20160411-21963-76ym4b.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=565&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Kepler Mission identified 4,696 planet candidates by July 2015.</span>
<span class="attribution"><a class="source" href="http://www.nasa.gov/ames/kepler/kepler-planet-candidates-july-2015">NASA Ames/W. Stenzel</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Using this technique, <a href="http://www.nasa.gov/mission_pages/kepler/overview/index.html">NASA’s Kepler Mission</a> has <a href="http://kepler.nasa.gov/Mission/discoveries/">discovered several thousand planets</a>.</p>
<p>It seems likely that any advanced civilization would be aware of this simple method. Each time a planet transits its star, its existence is essentially being advertised to all points lying along the same plane as the planet and star.</p>
<p>An advanced civilization might be okay having its planet’s location, size and even <a href="http://www.exoclimes.com/topics/transmission-spectroscopy/">atmospheric chemistry</a> advertised across the cosmos. Or it might wish to conceal its presence. If the latter, it might choose to build a cloak.</p>
<h2>A planetary invisibility cloak</h2>
<p>It turns out that hiding planets from the transit method would be surprisingly easy, so easy that we earthlings could do it right now, if we chose. Since transits appear as a brightness decrease of a distant star, our hypothetical cloak simply produces the opposite brightness increase.</p>
<p>Lasers provide an efficient means of countering that dip in brightness. All a laser’s power is contained in a relatively narrow beam, as opposed to spreading out in all directions like starlight does. Due to the way light spreads as it travels – called diffraction – the laser beam would spread to encompass entire solar systems after journeying many light years across space, bathing that distant planetary system within the cloaking beam. No dip in brightness makes it look like there’s no planet there at all.</p>
<p>A laser cloak capable of hiding the Earth from an alien version of NASA’s Kepler Mission would require 30 megawatts of power at peak intensity, approximately equivalent to 10 wind turbines worth of power output.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/z1Pqqf_6J9w?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Alex Teachey describes how a cloaking system would work.</span></figcaption>
</figure>
<p>While Kepler sees light in only one color, advanced civilizations might use more sophisticated detectors capable of collecting light at all wavelengths. Here too, our current technology could cloak us using <a href="https://www.rp-photonics.com/supercontinuum_generation.html">modern tunable lasers</a>, for a cost of about 10 times more power overall. More advanced civilizations might be able to detect other fine details of the light’s properties, betraying the cloak. But here too there’s no reason why with a little bit of work we couldn’t engineer solutions, leading to a near perfect cloak which could be targeted at distant stars where we suspect someone might be home.</p>
<h2>Why choose to hide</h2>
<p>So yes, it sounds like science fiction, but even current technology could do a fine job of cloaking the Earth’s transit signature.</p>
<p>Forget the Earth though; we never really thought of this as something humanity should or should not do. Instead, we posit that if our rudimentary human technology can build such an effective transit cloak at relatively little economic cost, then more advanced civilizations may be able to hide from us with respect to all detection techniques. The universe might not be all that it seems.</p>
<p>Why might a civilization choose to wrap itself in invisibility? It could be a sort of insurance policy: find the nearby planets with potential for supporting life and turn on a targeted cloak – just in case a civilization ever emerges. Such a policy effectively buys them time to reveal their presence when they see fit.</p>
<p>Given how cheap such a cloak would be, an insurance policy for your home planet is perhaps not as strange as it seems. It’s certainly not implausible a civilization might want to bide its time – surveilling the neighbors for a while before rolling out the intergalactic welcome mat. But there’s a flip side to this technology that could turn it from an invisibility cloak into more of a we-are-here spotlight.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/118216/original/image-20160411-21965-1l0nhwy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/118216/original/image-20160411-21965-1l0nhwy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/118216/original/image-20160411-21965-1l0nhwy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/118216/original/image-20160411-21965-1l0nhwy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/118216/original/image-20160411-21965-1l0nhwy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/118216/original/image-20160411-21965-1l0nhwy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/118216/original/image-20160411-21965-1l0nhwy.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">We think we know what it means when we see certain transit signals….</span>
<span class="attribution"><a class="source" href="http://www.spacetelescope.org/images/opo1354a/">NASA Goddard Space Flight Center</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>The reverse: flick on the beacon</h2>
<p>Perhaps not all civilizations are xenophobic – some might want to talk. If you wanted to reveal your presence to other civilizations as cheaply and unambiguously as possible, how might you do it?</p>
<p>Imagine looking at some data of a distant planet – which has become a somewhat normal enterprise for astronomers – and noticing something weird. The signature of the planet has a strange shape – in fact, none of your models are able to explain it. It looks like someone has imprinted a series of spikes into the data, following the prime number series. Nothing in nature can do this – you have just detected another civilization’s beacon. Alternative use of the cloaking system’s laser could be to make a planet’s signal look highly artificial, instead of hidden. Now they don’t care about building the perfect cloak; they want to be found!</p>
<p>Could such signals be lurking in our existing measurements? Perhaps so. No one has ever looked, and we hope our work sparks efforts on that front. It may be a long shot, since to even get to this point we need to try to imagine how aliens might think – but given the scientific prize on offer it’s also worth it. If we identify a strange transit, it may well contain information encoded via laser light pulses. Huge volumes of information could be hidden within the transit signatures of other planets.</p>
<p>For us, this was an exercise in intellectual curiosity. We simply calculated how much energy it would take to either cloak or broadcast a planet’s existence. Whether we should seriously consider wrapping Earth in a protective cloak of invisibility – or conversely, getting serious about trumpeting our existence – via laser manipulations is something we should all decide together.</p><img src="https://counter.theconversation.com/content/57092/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Kipping does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>There are technological ways to hide a planet from intergalactic detection – as well as ways to signal that we’re just sitting here, eager for contact.David Kipping, Assistant Professor of Astronomy, Columbia UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/493322015-10-21T10:24:38Z2015-10-21T10:24:38ZThe astronomer and the witch – how Kepler saved his mother from the stake<figure><img src="https://images.theconversation.com/files/99168/original/image-20151021-15410-1uf5rfc.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Great Comet of 1577, which Kepler witnessed as a child.</span> </figcaption></figure><p>Johannes Kepler (1571-1630) is one of the world’s most famous astronomers. He defended Copernicus’s sun-centred universe and discovered that planets move in ellipses. A planet, NASA mission and planet-hunting spacecraft are named after him. </p>
<p>Yet in recent years Kepler and his family have appeared as dubious, even murderous people. In 2004 for example, a team of American journalists <a href="http://www.publishersweekly.com/978-0-385-50844-5">alleged</a> that Kepler systematically poisoned the man he succeeded at the court of Rudolf II in Prague: Tycho Brahe. He may well be the scientist with the worst reputation.</p>
<p>But the majority of slurs concern the astronomer’s mother, Katharina. Arthur Koestler’s famous history of astronomy, <a href="https://www.nytimes.com/books/00/01/02/specials/koestler-sleepwalkers.html">The Sleepwalkers</a>, where Katharina features as a “hideous little woman” whose evil tongue and “suspect background” predestined her as victim of the witchcraze. </p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/98888/original/image-20151019-23249-1c9mqjc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/98888/original/image-20151019-23249-1c9mqjc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/98888/original/image-20151019-23249-1c9mqjc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=824&fit=crop&dpr=1 600w, https://images.theconversation.com/files/98888/original/image-20151019-23249-1c9mqjc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=824&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/98888/original/image-20151019-23249-1c9mqjc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=824&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/98888/original/image-20151019-23249-1c9mqjc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1035&fit=crop&dpr=1 754w, https://images.theconversation.com/files/98888/original/image-20151019-23249-1c9mqjc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1035&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/98888/original/image-20151019-23249-1c9mqjc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1035&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Kepler, 1610.</span>
</figcaption>
</figure>
<p>Then there’s John Banville’s prize-winning historical novel <a href="http://www.nytimes.com/1983/05/29/books/he-remodeled-the-cosmos.html">Kepler</a>, which vividly portrays Katharina as a crude old woman who makes a dangerous business of healing by boiling potions in a black pot. She meets with old hags in a kitchen infested with cat smells. Outside in her garden lies a dead rat. Kepler desperately tries to hide his mother’s magical arts from his wife as they visit and Katharina searches for a bag filled with bat-wings. This horrendous mother is scary, disgusting, and probably a witch.</p>
<p>There is something behind these hints: the portrayals stem to the astonishing fact that 400 years ago, when her son was at the very height of his scientific career, Katharina Kepler was accused of witchcraft. It is because of this that it has become commonplace in Anglo-American writing to depict Kepler’s mother as a difficult, bizarre and half-crazed old crone.</p>
<p>But what is the real story? Kepler certainly must rank as one of the most influential scientists to come from a disadvantaged background. Whereas Galileo’s father was a noted scholar of music, Kepler’s was a soldier who kept running away from the family. His parents argued and the only brother close to him in age suffered from epilepsy. This made it difficult for the brother to attend school or learn a trade. </p>
<p>Johannes Kepler, by contrast, soon emerged as an extremely talented boy. He was picked up by one of the most advanced Lutheran scholarship systems in Germany at the time and lived in boarding schools. He once fought against a boy who insulted his father, and was in his teens when the father disappeared for good.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/99163/original/image-20151021-15440-1t7pfx3.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/99163/original/image-20151021-15440-1t7pfx3.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=660&fit=crop&dpr=1 600w, https://images.theconversation.com/files/99163/original/image-20151021-15440-1t7pfx3.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=660&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/99163/original/image-20151021-15440-1t7pfx3.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=660&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/99163/original/image-20151021-15440-1t7pfx3.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=829&fit=crop&dpr=1 754w, https://images.theconversation.com/files/99163/original/image-20151021-15440-1t7pfx3.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=829&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/99163/original/image-20151021-15440-1t7pfx3.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=829&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Kepler’s model of the solar system.</span>
</figcaption>
</figure>
<p>Kepler wrote bleak little characterisations of his parents and paternal family around the time that he finished university. He also wrote about himself as a flawed young man, obsessively interested in fame, worried about money, unable to communicate his ideas in a straightforward way. These pieces of writing have principally served as evidence who want to depict Kepler and his family as horrendous, even murderous.</p>
<p>Yet these writings need to be put into context. Kepler wrote them very early in his life, and he did so in order to analyse his horoscopes. The whole convention of astrology was to point to character problems, rather than to laud lovely people. Kepler was a deeply Christian man, and one of his most impressive characteristics is how optimistic he soon began to feel about the world he lived in, against his odds and despite looming war. He built his own family and deeply cared about his wife and children. Kepler was confident about the importance of his discoveries and productive, even though he was never offered a university position.</p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/99164/original/image-20151021-15424-a5nct0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/99164/original/image-20151021-15424-a5nct0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/99164/original/image-20151021-15424-a5nct0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/99164/original/image-20151021-15424-a5nct0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/99164/original/image-20151021-15424-a5nct0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/99164/original/image-20151021-15424-a5nct0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/99164/original/image-20151021-15424-a5nct0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1005&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Statue of Katharina Kepler in Eltingen.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Katharina_Kepler_Eltingen.jpg">Harke</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Then came the accusation against his mother. The proceedings which led to a criminal trial lasted six years. The Imperial mathematician formally took over his mother’s legal defence. No other public intellectual figure would have ever involved themselves in a similar role, but Kepler put his whole existence on hold, stored up his books, papers and instruments in boxes, moved his family to southern Germany and spent nearly a year trying to get his mother out of prison.</p>
<p>Local records for the small town in which Katharina Kepler lived are abundant. There is no evidence that she was brought up by an aunt who was burnt for witchcraft – this was one of the charges which her enemies invented. There is no evidence either that she made a living from healing – she simply mixed herbal drinks for herself and sometimes offered her help to others, like anyone else. A woman in her late 70s, Katharina Kepler withstood a trial and final imprisonment, during which she was chained to the floor for more than a year. </p>
<p>Kepler’s defence was a rhetorical masterpiece. He was able to dismantle the inconsistencies in the prosecution case, and show that the “magical” illnesses for which they blamed his mother could be explained using medical knowledge and common sense. In the autumn of 1621, Katharina was finally set free.</p>
<p>Johannes Kepler and his mother lived through one of the most epic tragedies in the age of the witch-craze. It’s high time to re-evaluate what kind of man Kepler was: he does not deserve to be the scientist with the worst reputation. And nor does his mother deserve to be portrayed as a witch.</p>
<hr>
<p><em><a href="http://ukcatalogue.oup.com/product/9780198736776.do">The Astronomer And The Witch</a> by Ulinka Rublack was published by Oxford University Press on October 22. A talk by the author will be part of the <a href="http://www.festivalofideas.cam.ac.uk/events">Cambridge Festival of Ideas</a>.</em></p><img src="https://counter.theconversation.com/content/49332/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ulinka Rublack 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>When Kepler was at the very height of his scientific career, his mother was accused of witchcraft.Ulinka Rublack, Professor of Early Modern European History, University of CambridgeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/492902015-10-17T11:59:05Z2015-10-17T11:59:05ZWhatever the strangest star in the galaxy is, it’s sure to be amazing<figure><img src="https://images.theconversation.com/files/98618/original/image-20151016-25123-sk5ke8.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Is this what we're seeing around KIC 8462852 - a colossal megastructure built by alien intelligence? Probably not. The reality might be even more interesting.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/kevinmgill/21983905140/">Kevin Gill/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>For the past few days, the <a href="http://www.theatlantic.com/science/archive/2015/10/the-most-interesting-star-in-our-galaxy/410023/">media has been abuzz</a> with one of the most peculiar astronomical observations for many years. As described in a <a href="http://arxiv.org/pdf/1509.03622v1.pdf">recent paper on the arXiv</a> preprint service, a faint star in the northern constellation Cygnus has been seen acting incredibly strangely. </p>
<p>The star, KIC 8462852 – somewhat hotter, younger and more luminous than our sun – was observed by the <a href="http://kepler.nasa.gov/">Kepler spacecraft</a> for over four years, 24 hours per day, 365 days a year, along with more than 100,000 other stars in the same patch of sky.</p>
<p>Kepler was designed to monitor the brightness of those stars with exquisite precision, looking for tell-tale tiny “winks” that would indicate that they were orbited by planets. </p>
<p>And Kepler has found planets in abundance; more than 1,000 to date, with more being confirmed all the time. </p>
<p>But in the case of this faint star in Cygnus, it has found something else. Something unexpected. And we still have no idea what it is. </p>
<p><a href="http://www.slate.com/blogs/bad_astronomy/2015/10/14/weird_star_strange_dips_in_brightness_are_a_bit_baffling.html">Some commentators</a> have even suggested that the observations <em>might</em> represent the discovery of advanced alien life!</p>
<p>That might be something of a stretch, but it is certainly true to say that the current observations have astronomers baffled. But that isn’t a bad thing. </p>
<h2>The unexpected through astronomical history</h2>
<p>Many of the greatest and most exciting discoveries in astronomical history were unexpected and serendipitous, and ended up greatly revolutionising our understanding of the universe. Usually, such discoveries were made as new or improved technology allowed astronomers to study the sky in new ways, or in more detail. </p>
<p>That’s exactly what’s happened here, with KIC 8462852. It’s purely because of the unique ability of Kepler to study hundreds of thousands of stars continually for years at a time that the unusual behaviour was found. </p>
<p>Here are just three examples of how serendipity has driven astronomical understanding:</p>
<h2>The solar system’s first ‘new’ planet</h2>
<p>In 1781, using a homemade telescope Sir William Herschel discovered Uranus while scouring the sky looking for double stars. In one fell swoop, Herschel’s discovery doubled the radial scale of our solar system, and gave birth to the search for other planets. The chance find eventually led to the discovery of Neptune, through its gravitational pull on Uranus.</p>
<p>The idea that there could be more planets in our solar system also led to the scouring of the sky that found the first asteroids in the early 1800s. The first asteroid found (Ceres) was another serendipitous discovery! </p>
<p>Although some astronomers were searching for objects between the orbits of Mars and Jupiter, Giuseppe Piazzi was instead constructing a new catalogue of stars. As he scoured the sky, he stumbled on the faint moving asteroid, purely by chance. </p>
<p>From those humble beginnings, we now know of hundreds of thousands of asteroids orbiting between Mars and Jupiter. We have also found tens of thousands of similar small bodies further from the sun (the planetary Trojans, and the trans-Neptunian objects). </p>
<p>Our knowledge of these objects, their distribution and their sizes, has been an incredible boon to scientists trying to disentangle the story of our solar system’s formation and evolution.</p>
<h2>Bird poop in our telescope or the Big Bang?</h2>
<p>In the early 1960s, there was great debate over the origin of the universe. The two leading theories – the <a href="http://physics.about.com/od/astronomy/f/BigBang.htm">Big Bang</a> and <a href="http://physics.about.com/od/physicsqtot/g/SteadyStateTheory.htm">Steady State</a> models – had been developed in response to the observed expansion of the universe (another serendipitous discovery, in the early part of the 20th century, by Vesto Slipher and others).</p>
<p>Theorists studying the two models were striving to make predictions of what we might observe in each case. A number of scientists had pointed out that if the universe had been created in a Big Bang, and was once smaller, denser and hotter than it is today, then a relic of that heat should be observable to the current day. </p>
<p>As a result, astronomers at Princeton University were in the process of preparing a survey to search for that “relic radiation”. At the same time, just down the road, Arno Penzias and Robert Wilson were testing a new 6m horn antenna radio telescope. </p>
<p>That telescope was highly sensitive, and Penzias and Wilson were attempting to characterise its performance, and to remove known sources of interference so that it could be used to maximum effect.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/98616/original/image-20151016-25138-nnkscv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/98616/original/image-20151016-25138-nnkscv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/98616/original/image-20151016-25138-nnkscv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/98616/original/image-20151016-25138-nnkscv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/98616/original/image-20151016-25138-nnkscv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/98616/original/image-20151016-25138-nnkscv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/98616/original/image-20151016-25138-nnkscv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/98616/original/image-20151016-25138-nnkscv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Holmdel Horn Antenna used to discover the cosmic microwave background radiation.</span>
<span class="attribution"><span class="source">Fabioj/Wikimedia</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>They first cooled their detector, using liquid helium, to just four degrees above absolute zero. They then processed their data, removing all traces of known interference. </p>
<p>But one signal remained: a persistent background noise that was present no matter where in the sky the looked, or whether they were observing at night or during the day.</p>
<p>They considered a variety of different sources of noise that could cause the signal. They even, famously, cleaned the horn of guano deposited by pigeons nesting in the antenna. But none of this got rid of the signal. The only conclusion that remained was that it was extra-terrestrial, but the two were still flummoxed. </p>
<p>As it turned out, they had accidentally discovered what is now known as the microwave background – the thermal radiation left behind by the Big Bang. Their accidental discovery netted them a Nobel Prize, in 1978, and in many ways gave birth to modern observational cosmology!</p>
<h2>‘Little Green Man 1’</h2>
<p>In July 1967, a talented young PhD student at Cambridge University was carrying out observations using a new radio telescope, the <a href="https://en.wikipedia.org/wiki/Interplanetary_Scintillation_Array">Interplanetary Scintillation Array</a>. <a href="http://www.britannica.com/biography/Jocelyn-Bell-Burnell">Jocelyn Bell</a> (now Dame Jocelyn Bell Burnell) was undertaking a painstaking analysis, by eye, of vast reams of data traced out by the telescope as it scanned the sky. </p>
<p>As she scanned through her data, she spotted an incredibly regular pulsating signal that was tracking with the background stars across the sky. Like the observations of KIC 8462852, the signal initially defied all explanation. </p>
<p>Such regular radio pulses, originating from a single point in the night sky, were totally unexpected. The “clock” was ticking once every 1.33730208831 seconds, more regularly than clockwork.</p>
<p>As they tried to understand the nature of the signal, Jocelyn and her PhD supervisor, Anthony Hewish (who was eventually awarded the Nobel Prize for his part in the discovery), considered several possible origins, including speculative thoughts that it just might be an extra-terrestrial signal (though they thought that unlikely).</p>
<p>Once their observations were published, theoreticians elsewhere quickly realised that the best explanation for the unexpected signal was in fact purely natural. The source was not “little green men”. Instead, it was something almost more fantastical: the dead core of a star more massive than the sun, left behind by an ancient supernova explosion. </p>
<p>That object, a <a href="https://theconversation.com/explainer-what-is-a-neutron-star-29341">neutron star</a>, was smaller than a city, and the pulses were the result of hot spots on its surface, flicking across our view each time the star completed a single revolution on its axis. The object was a pulsar, and a new branch of astronomy was born.</p>
<h2>The odd behaviour of KIC 8462852</h2>
<p>All of this brings us back to our latest big news story. Over the past few years since it was first observed by Kepler, KIC 8462852 has exhibited occasional, short lived, dips in brightness. So far, that’s how every Kepler story starts.</p>
<p>But with KIC 8462852, the dips are different. When a star is transited by a planet, a tiny fraction of that star’s light is blocked, and we see a dip in its brightness. The bigger the planet, the bigger the dip in brightness, and the easier it is to spot. </p>
<p>But where a planet like Jupiter, the solar system’s largest planet, would cause the sun to dim by just ~1% as it passed between us and our star, the dips seen for KIC 8462852 are huge: the largest being 15% and 22% of the star’s light, fading out, then brightening again.</p>
<p>That, in itself, is weird. But there’s more. For a planet, the winks generated would be periodic: one orbit, one wink. </p>
<p>Here, and by contrast, the dips in KIC 8462852’s brightness are not periodic. The two largest occurred roughly 730 days apart, but smaller dips have also been seen. And the most recent large drop (22% of the stars light) was followed by two other, smaller dips over the month that followed.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/98620/original/image-20151016-25146-1y1tvg1.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/98620/original/image-20151016-25146-1y1tvg1.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/98620/original/image-20151016-25146-1y1tvg1.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=412&fit=crop&dpr=1 600w, https://images.theconversation.com/files/98620/original/image-20151016-25146-1y1tvg1.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=412&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/98620/original/image-20151016-25146-1y1tvg1.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=412&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/98620/original/image-20151016-25146-1y1tvg1.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=518&fit=crop&dpr=1 754w, https://images.theconversation.com/files/98620/original/image-20151016-25146-1y1tvg1.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=518&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/98620/original/image-20151016-25146-1y1tvg1.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=518&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Kepler data showing huge dips in brightness of KIC 8462852, up to 22 percent in the star.</span>
<span class="attribution"><a class="source" href="http://arxiv.org/pdf/1509.03622v1.pdf">Boyajian et al, 2015</a></span>
</figcaption>
</figure>
<p>Added together, it is clear something very strange is happening. No star has ever been observed behaving like this before. And so speculation has run rife as people attempt to explain this new and unexpected behaviour.</p>
<h2>So what could be behind KIC 8462852’s odd behaviour?</h2>
<p>The short answer here is: we don’t know. At least, not yet. The authors of the paper on arXiv suggest the most likely explanation could be a cloud of comets, disintegrating as they orbit the star. </p>
<p>Such events are known to occur around the sun, so this idea isn’t entirely outlandish. </p>
<p>The Kreutz family of sun-grazing comets, which include some of the most spectacular comets in recorded history, have a long fragmentation history, and may be linked to a parent that was over 100km across, just a few thousand years ago.</p>
<p>The Taurid debris stream is all that remains of another giant comet, thought to have fragmented tens of thousands of years back. It delivers upwards of 50% of all the dust falling on Earth, and includes the famous comet 2P/Encke. It is so vast that it is encountered by all the terrestrial planets, and Earth spends almost six months of every year traversing it.</p>
<p>So comet fragmentation can occur. But even with a colossal cometary collapse, it is hard to imagine how fully 20% of a stars light would be obscured. Add to that that such a collapse should produce a vast quantity of dust, which will make the star shine brightly at infrared wavelengths, which is something we simply do not see.</p>
<p>So what else could it be? </p>
<p>Perhaps it is a young planetary system, and two of the planets just collided? That would create a huge amount of dust, which again could obscure the light from the star. </p>
<p>But once again, we come back to the problem of infrared light. So much dust would give the star a huge infrared excess, absorbing its visible radiation, getting hot, and re-radiating it beyond the visible. That simply isn’t seen.</p>
<p>So we come to the most speculative suggestion, and the reason that this faint star has attracted so much attention over the past week or so. What if the dips in brightness aren’t natural? Maybe they’re caused by a giant mega-structure built, or under construction, by intelligent advanced aliens. </p>
<p>Could the dips be explained by something like a partial <a href="http://earthsky.org/space/what-is-a-dyson-sphere">Dyson sphere</a>? Giant structures like this pervade science fiction and are the signature of species with technology immeasurably beyond our own. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/ECLvFLkvY7Y?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>Well, it’s certainly possible, but I wouldn’t place bets on it just yet! Extraordinary claims like this require extraordinary evidence, and astronomers will be studying KIC 8462852 for years to come, trying to disentangle the mystery.</p>
<p>Personally, my money would be on this being something akin to the discovery of the first pulsar: unexpected, and unexplained as of yet, and opening a door to a new process or kind of object previously unknown. Not life, but something almost as interesting: new science!</p><img src="https://counter.theconversation.com/content/49290/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>There’s a lot of speculation about a star behaving strangely in our galaxy. But even if it’s not evidence of alien intelligence, it’s sure to be an amazing discovery.Jonti Horner, Vice Chancellor's Senior Research Fellow, University of Southern QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/451442015-07-23T22:32:51Z2015-07-23T22:32:51ZExoplanet Kepler-452b offers a glimpse into the future fate of our Earth<figure><img src="https://images.theconversation.com/files/89569/original/image-20150723-22821-gcthfn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Mirror image?</span> <span class="attribution"><span class="source">NASA</span></span></figcaption></figure><p>NASA has announced the discovery <a href="http://www.nasa.gov/press-release/nasa-kepler-mission-discovers-bigger-older-cousin-to-earth">of the most Earth-like exoplanet</a> to date. The new planet – named Kepler-452b – orbits a sun-like star and lies in the star’s <a href="https://theconversation.com/if-we-are-to-find-life-beyond-earth-we-need-to-be-explorers-not-hunters-45001">habitable zone</a>, an area which is neither too hot nor too cold for orbiting planets to support liquid water on the surface. </p>
<p>An international team of scientists, led by Jon Jenkins from NASA <a href="http://www.nasa.gov/centers/ames/home/index.html">Ames Research Centre in California</a>, discovered the planet alongside 11 other planets in habitable zones using a <a href="https://www.google.co.uk/search?q=kepler+exoplanet+mission&ie=utf-8&oe=utf-8&gws_rd=cr&ei=EV6xVY3TL8ny7AaunZjwAQ">space-based telescope called Kepler</a>. They made the discovery by monitoring the brightness of stars. A planet transiting in front of a star will create a temporary dip in its brightness as it blocks out a little of its light. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/89576/original/image-20150723-22830-mxg4zz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/89576/original/image-20150723-22830-mxg4zz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=424&fit=crop&dpr=1 600w, https://images.theconversation.com/files/89576/original/image-20150723-22830-mxg4zz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=424&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/89576/original/image-20150723-22830-mxg4zz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=424&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/89576/original/image-20150723-22830-mxg4zz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=532&fit=crop&dpr=1 754w, https://images.theconversation.com/files/89576/original/image-20150723-22830-mxg4zz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=532&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/89576/original/image-20150723-22830-mxg4zz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=532&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">How do we compare?</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>The new planet, which has a 385-day orbit, is possibly a rocky body, <a href="http://www.nasa.gov/sites/default/files/atoms/files/ms-r1b.pdf">a little larger than the Earth</a> with a radius of 1.63 times that of the Earth and twice as much surface gravity. The <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/starlog/staspe.html">G2-type star</a> it orbits lies 1400 light years away from Earth. </p>
<p>The exoplanet is only 5% further away from its host star than the Earth is from our sun. Jenkins and his team think the planet has always been in the habitable zone and will remain there for <a href="http://www.nasa.gov/sites/default/files/atoms/files/ms-r1b.pdf">another 3 billion years</a>. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/89570/original/image-20150723-22826-1kapntq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/89570/original/image-20150723-22826-1kapntq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=449&fit=crop&dpr=1 600w, https://images.theconversation.com/files/89570/original/image-20150723-22826-1kapntq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=449&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/89570/original/image-20150723-22826-1kapntq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=449&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/89570/original/image-20150723-22826-1kapntq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=565&fit=crop&dpr=1 754w, https://images.theconversation.com/files/89570/original/image-20150723-22826-1kapntq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=565&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/89570/original/image-20150723-22826-1kapntq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=565&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Endless probabilities as there are 4,696 planet candidates now known.</span>
</figcaption>
</figure>
<p>The study of exoplanets <a href="http://www.bbc.co.uk/science/space/universe/key_places/51_pegasi">began in earnest only 20 years</a> ago with the discovery of larger planets called “hot Jupiters” around distant stars. The latest release of data from the Kepler project has increased the number of new exoplanet candidates by 521 since 2013, meaning there are now nearly 4700 candidates. However further analysis is needed to confirm that they really are planets.</p>
<p>Today, <a href="http://www.bbc.co.uk/science/space/universe/sights/extrasolar_planets">nearly 2,000 planets have been confirmed</a>. Nine planets with a radius less than twice that of Earth was found in the past 4 years’ worth of Kepler data. </p>
<p>The star which the planet orbits has the same temperature and is 20% brighter than our sun. It is also slightly larger than our sun and is 1.5 billion years older. So while Kepler-452b is the closest analogue to our Earth-Sun system yet discovered by Kepler, it may be further along in its evolution. This gives us a glimpse into the future fate of our Earth as the Sun uses up its fuel, expanding and evolving into a <a href="http://abyss.uoregon.edu/%7Ejs/ast122/lectures/lec16.html">red giant</a>. </p>
<p>These fascinating observations of a distant world offer scientists hope that many more Earth-Sun systems may be discovered in the future, helping to quantify how rare our own environment is and offering the possibility to look for signs of life far outside our own Solar System.</p>
<p>The authors speculate that there could have been an ancient civilisation on Kepler-452b or the moon orbiting it. This may even have moved to an outer planet that we are yet to discover to escape the the loss of water as the increasing energy from its aging sun could be warming up the surface. This may yet offer hope to those engaged in <a href="https://theconversation.com/its-not-all-about-aliens-listening-project-may-unveil-other-secrets-of-the-universe-45031">searching for technological civilisations on distant planets</a>.</p><img src="https://counter.theconversation.com/content/45144/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Carole Mundell receives funding from the Science and Technology Facilities Council, the Royal Society and the Wolfson Foundation. However, the views expressed here are her own and not those of the research council.</span></em></p>A new exoplanet has been discovered that is a lot like Earth.Carole Mundell, Head of Astrophysics, University of BathLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/196842013-10-31T01:51:21Z2013-10-31T01:51:21ZAlmost Earth – another step on the road to habitable worlds<figure><img src="https://images.theconversation.com/files/34091/original/n7kynmjy-1383108477.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Kepler 78b is a lot like Earth...if Earth was on fire.</span> <span class="attribution"><span class="source">TORLEY/Flickr</span></span></figcaption></figure><p><a href="http://www.nature.com/nature/journal/vaop/ncurrent/full/nature12767.html">Two</a> <a href="http://www.nature.com/nature/journal/vaop/ncurrent/full/nature12768.html">papers</a> were published today in Nature, each independently revealing that a planet discovered by the <a href="http://kepler.nasa.gov/">Kepler mission</a> is the closest thing we’ve found yet to another Earth. But don’t pack your bags just yet — this new “Earth” is certainly not the <a href="http://en.wikipedia.org/wiki/Planetary_habitability">habitable world</a> we’ve all been waiting for.</p>
<h2>A brief history of exoplanets</h2>
<p>The search for planets around other stars is one of the most exciting fields of modern research, and cuts to the core of one of the oldest questions known to humanity — “<a href="http://www.ted.com/playlists/82/are_we_alone_in_the_universe.html">are we alone?</a>”. </p>
<p>The first planets discovered orbiting sun-like stars, in the mid 1990s, led to an immediate revolution in our understanding of planetary science and planetary formation. Before the discovery of <a href="http://en.wikipedia.org/wiki/51_Pegasi_b">51 Pegasi b</a>, in 1995, <a href="http://en.wikipedia.org/wiki/Nebular_hypothesis">models of planet formation</a> predicted that planets we found around other stars would be much like our own. </p>
<p>There would be <a href="http://en.wikipedia.org/wiki/Terrestrial_planet">rocky worlds</a>, huddled close around the heat of their host star (like <a href="http://tinyurl.com/z266n">Mercury</a>, <a href="http://en.wikipedia.org/wiki/Venus">Venus</a>, <a href="http://en.wikipedia.org/wiki/Earth">Earth</a> and <a href="http://en.wikipedia.org/wiki/Mars">Mars</a>), and <a href="http://en.wikipedia.org/wiki/Gas_giant">giant planets</a> further out (<a href="http://en.wikipedia.org/wiki/Jupiter">Jupiter</a>, <a href="http://en.wikipedia.org/wiki/Saturn">Saturn</a>, <a href="http://en.wikipedia.org/wiki/Uranus">Uranus</a> and <a href="http://en.wikipedia.org/wiki/Neptune">Neptune</a>). </p>
<p>It was a shock, then, when the first exoplanets, such as 51 Pegasi b, turned out to be “<a href="http://en.wikipedia.org/wiki/Hot_Jupiter">Hot Jupiters</a>”, giant planets orbiting their stars at a tiny fraction of the distance from Earth to the sun.</p>
<p>Those first discoveries revolutionised our understanding of planet formation, and of the variety of planetary systems we expect to find elsewhere. The surprises have kept coming ever since — from <a href="https://theconversation.com/star-wars-planet-with-two-suns-a-step-towards-luke-skywalkers-tatooine-3379">planets with two suns</a> to <a href="https://theconversation.com/diamond-planets-climate-change-and-the-scientific-method-3329">diamond planets</a>, and many, many more.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/34123/original/jd5m8rdf-1383170777.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/34123/original/jd5m8rdf-1383170777.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/34123/original/jd5m8rdf-1383170777.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=441&fit=crop&dpr=1 600w, https://images.theconversation.com/files/34123/original/jd5m8rdf-1383170777.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=441&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/34123/original/jd5m8rdf-1383170777.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=441&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/34123/original/jd5m8rdf-1383170777.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=554&fit=crop&dpr=1 754w, https://images.theconversation.com/files/34123/original/jd5m8rdf-1383170777.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=554&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/34123/original/jd5m8rdf-1383170777.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=554&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Hot Jupiters: the first exoplanets around sunlike stars.</span>
<span class="attribution"><span class="source"> Kevin M. Gill</span></span>
</figcaption>
</figure>
<h2>Ever smaller, ever colder</h2>
<p>As time has passed, we have become <a href="http://en.wikipedia.org/wiki/Discoveries_of_extrasolar_planets">ever more proficient at finding exoplanets</a>. We have found planets at ever greater distances from their host stars. And we have found ever-smaller planets, which are significantly harder to detect. </p>
<p>The methods we use to look for planets are biased toward finding larger ones. The <a href="http://astro.unl.edu/classaction/animations/extrasolarplanets/radialvelocitysimulator.html">radial velocity method</a> measures the wobble of a given star along our line of sight as it rocks back and forth in response to the gravitational pull of its unseen planetary companion. This tells us the planet’s mass. The closer the planet to its host, or the more massive the planet compared to its host, the larger the wobble will be. </p>
<p>The <a href="http://kepler.nasa.gov/multimedia/animations/?ImageID=38">transit method</a> (used by the <a href="https://theconversation.com/keplers-findings-are-out-of-this-world-and-the-best-is-yet-to-come-5249">Kepler mission</a>, records how much light a planet blocks from its star and tells us the physical size of the planet relative to its host. </p>
<p>The bigger the planet, the more of its host star’s light it will block as it passes between us and that star. The shorter the planet’s orbital period, the more frequently it will pass between us and the star, and so the more data we will be able to obtain to show that the planet is there.</p>
<p>The <a href="https://theconversation.com/keplers-findings-are-out-of-this-world-and-the-best-is-yet-to-come-5249">Kepler mission</a> has helped to push us remarkably close to the goal of finding truly Earth-like planets, and it is almost certain that such planets lurk amongst the <a href="http://kepler.nasa.gov/">3602 candidate planets</a> awaiting confirmation. </p>
<p>Today’s discovery takes us one step further down the road towards the first true exo-Earth.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/34124/original/kmwrwbw2-1383171832.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/34124/original/kmwrwbw2-1383171832.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/34124/original/kmwrwbw2-1383171832.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/34124/original/kmwrwbw2-1383171832.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/34124/original/kmwrwbw2-1383171832.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/34124/original/kmwrwbw2-1383171832.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/34124/original/kmwrwbw2-1383171832.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/34124/original/kmwrwbw2-1383171832.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">What a lot of candidates…</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<h2>Kepler 78b - delving into the nature of a tiny transiting planet</h2>
<p>The discovery of an Earth-sized planet on a very short period orbit around the star Kepler 78 was announced a <a href="http://kepler.nasa.gov/news/nasakeplernews/index.cfm?Fuse">couple of months ago</a>. The size of the planet made it a fascinating target for further study, and two groups of astronomers began independent programs of radial velocity observations of the planet’s host star. The results of those studies are published today. </p>
<p>The two disparate measurement methods — transit and radial velocity — can each tell us something about the planet in question, but they are insufficient to give us the full picture. But if it possible to observe a given planet using both techniques, then suddenly things become far more exciting. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/-BuwWtMygxU?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">How to find an exoplanet.</span></figcaption>
</figure>
<p>Once you have both the size of the planet and its mass, you can calculate its density — and at that point, you can tell whether it is gaseous, rocky, metallic. </p>
<p>This is the game that the astronomers have played with the planet orbiting the star Kepler 78. We now know that Kepler 78b is slightly bigger than Earth — one of the two papers gives its radius as 1.20 times that of Earth (something like 8080 km); the other gives a radius of 1.173 times that of Earth (approximately 7470 km).</p>
<p>The uncertainties on these measurements are relatively small, but they are mutually consistent (the uncertainties overlap) — so we can say with some certainty that Kepler 78b is a planet that is only slightly larger than our Earth.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/34089/original/xms7rkzv-1383108019.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/34089/original/xms7rkzv-1383108019.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/34089/original/xms7rkzv-1383108019.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/34089/original/xms7rkzv-1383108019.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/34089/original/xms7rkzv-1383108019.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/34089/original/xms7rkzv-1383108019.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/34089/original/xms7rkzv-1383108019.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 mass of known exoplanets, relative to the mass of Jupiter, as a function of their year of discovery. Figure plotted using http://exoplanets.org/plots . Aside from the extremely unusual planets discovered around pulsars in the early 1990s, the ongoing trend to discover ever smaller planets is clear. For comparison, the mass of the Earth is 1/317.8th that of Jupiter - i.e. 0.00315 Jupiter masses.</span>
<span class="attribution"><span class="source">http://exoplanets.org/plots</span></span>
</figcaption>
</figure>
<h2>A remarkably Earth-like world</h2>
<p>The two groups whose work is published today carried out intensive radial velocity observations of the star Kepler 78 using the <a href="https://plone.unige.ch/HARPS-N/">HARPS-N instrument</a> (on La Palma, in the Canary Islands) and the <a href="https://www2.keck.hawaii.edu/inst/hires/">HIRES spectrometer</a> on the 10 metre <a href="http://www.keckobservatory.org/">Keck-I Telescope</a> (which sits on top of the Hawaiian island of <a href="http://www.ifa.hawaii.edu/info/vis/visiting-mauna-kea/visiting-the-summit.html">Mauna Kaea</a>). The use of the world’s best facilities have allowed the authors to measure the tiny radial velocity variations in the light from Kepler 78, allowing them to precisely determine the mass of the Kepler 78b. </p>
<p>Again, the two papers offer slightly different values for the planet’s mass — 1.69 or 1.86 times that of the Earth. Again, given the size of the uncertainties in these measurements, they are entirely consistent with one another — and they reveal that Kepler 78b is not significantly more massive than our Earth. A super-Earth it is, but one not too dissimilar to our own planet — at least in terms of its mass and its size.</p>
<p>The similarities between the two planets go deeper. Based on the masses and radii determined in these works, they both calculate the density of the planet. Again, their final values differ slightly — with values of 5.3 and 5.57 grams per cubic centimetre. Remarkably, these values are essentially the same as the density of the Earth — 5.52 grams per cubic centimetre. </p>
<p>Because Kepler 78b is more massive than the Earth, you might expect the gravitational pull at its surface to be stronger than that we experience here on Earth. However, because the planet is also larger than our Earth, it turns out that the acceleration due to gravity at its surface is startlingly similar to that we experience here. One of the two papers calculates that, on the planet’s surface, you would experience an acceleration of around 11.4 metres per second squared (just 1.16 times greater than that at Earth’s surface).</p>
<h2>Earth-like, if Earth was on fire</h2>
<p>Physically, then, Kepler 78b seems remarkably similar to our Earth — it is slightly more massive, slightly larger, and the gravitational pull on its surface is only slightly stronger than that we experience here. There, unfortunately, the similarities end.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/34131/original/yz7yt6gs-1383175802.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/34131/original/yz7yt6gs-1383175802.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/34131/original/yz7yt6gs-1383175802.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=910&fit=crop&dpr=1 600w, https://images.theconversation.com/files/34131/original/yz7yt6gs-1383175802.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=910&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/34131/original/yz7yt6gs-1383175802.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=910&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/34131/original/yz7yt6gs-1383175802.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1144&fit=crop&dpr=1 754w, https://images.theconversation.com/files/34131/original/yz7yt6gs-1383175802.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1144&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/34131/original/yz7yt6gs-1383175802.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1144&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">You don’t need a blowtorch to melt gold on Kepler 78b.</span>
<span class="attribution"><span class="source">World Bank Photos</span></span>
</figcaption>
</figure>
<p>The Earth takes just over 365 days to orbit the Sun, at a distance of roughly 150 million kilometres. By contrast, Kepler 78b takes just eight and a half hours to orbit its host, at a separation of less than one and a half million kilometers. </p>
<p>Kepler 78b orbits less than a million kilometers above the <a href="http://en.wikipedia.org/wiki/Photosphere">photosphere</a> of its star. As a result, the surface temperature of our Earth-like planet is estimated in one of the two new papers to lie in the range 1500 - 3000 K (~1230 - 2730 degree Celsius). </p>
<p>To put this intense heat in perspective, one only has to look at the temperatures at which given elements <a href="http://en.wikipedia.org/wiki/List_of_elements_by_melting_point">melt and boil</a>. </p>
<p>Astronomers often discuss how the Venutian surface would be <a href="http://science1.nasa.gov/science-news/science-at-nasa/2001/ast20feb_1/">hot enough to melt lead</a>. On Kepler 78b, even the “coldest” estimate of the temperature would be sufficient to melt gold, silver, and copper. At the high end of the temperature range, copper and silver would boil, and gold wouldn’t be far off.</p>
<p>Kepler 78b orbits so close to its host star that it is almost certainly locked in what astronomers call a “1:1 spin-orbit resonance”. In other words, the planet almost certainly keeps one face pointed towards the star, the other facing away. From one side of Kepler 78b (if one exists), its parent star will sit stationary, spanning a 40 degree swathe of the sky. From the other, the star will never rise.</p>
<h2>A watershed moment</h2>
<p>So Kepler 78b isn’t the exo-Earth we’ve been looking for, the twin of our own planet so dear to science fiction. But it is a vital step on the way. It is by far the most Earth-like planet found to date — almost the right size, and with almost the right composition, but located on an orbit which ensures it is about as hellish as possible. </p>
<p>In fact, aside from its orbit, the similarities with the Earth are striking — and to find a planet like this so soon as astronomers plough through the reams of data provided by Kepler is a hugely promising sign. </p>
<p>Generations have dreamt of discovering other Earths around distant stars — and these observations of Kepler 78b show us that dream is tantalisingly close to being realised.</p><img src="https://counter.theconversation.com/content/19684/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>Two papers were published today in Nature, each independently revealing that a planet discovered by the Kepler mission is the closest thing we’ve found yet to another Earth. But don’t pack your bags just…Jonti Horner, Post Doctoral Research Fellow, UNSW SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/159532013-07-11T03:49:23Z2013-07-11T03:49:23ZThe end of Kepler? That would be universally bad<figure><img src="https://images.theconversation.com/files/27276/original/b3rp9fdy-1373507714.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Two of Kepler's four reaction wheels have stopped working, which may mean the end for the spacecraft.</span> <span class="attribution"><span class="source">NASA/Kepler mission/Wendy Stenzel</span></span></figcaption></figure><p>As I write this, engineers at NASA and <a href="http://www.ballaerospace.com/">Ball Aerospace & Technologies</a> have their fingers crossed they’ll be able to restart the stricken <a href="http://kepler.nasa.gov/">Kepler</a> space observatory, which has been in <a href="http://www.nasa.gov/mission_pages/kepler/news/keplerm-20130515.html#.Ud4R5T5Nt90">hibernation mode</a> since May 15. If they can’t, the telescope’s haul of planet candidates – 3,277 at <a href="http://www.nasa.gov/content/kepler-mission-manager-update-preparing-for-recovery/#.Ud4L-T5Nt90">the last count</a> and including many Earth-like systems – might have come to an end. </p>
<p>Kepler has been idling roughly 64 million kilometres from Earth since the failure of one of its reaction wheel 4 – one of four mechanisms used to orient the spacecraft and stabilise its gaze. The plan, by no means assured of success, is to try to re-engage either the stalled-out wheel 4, or another that failed shortly after launch in 2009.</p>
<p>If this doesn’t work, the loss will be huge.</p>
<h2>A once-in-a-lifetime mission</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/27273/original/kb3hcpwm-1373506921.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/27273/original/kb3hcpwm-1373506921.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/27273/original/kb3hcpwm-1373506921.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=780&fit=crop&dpr=1 600w, https://images.theconversation.com/files/27273/original/kb3hcpwm-1373506921.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=780&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/27273/original/kb3hcpwm-1373506921.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=780&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/27273/original/kb3hcpwm-1373506921.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=981&fit=crop&dpr=1 754w, https://images.theconversation.com/files/27273/original/kb3hcpwm-1373506921.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=981&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/27273/original/kb3hcpwm-1373506921.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=981&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 section of Milky Way that includes the Kepler field of view.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>Kepler has been <a href="https://theconversation.com/exoplanets-how-the-search-for-life-became-sexy-43">the most revolutionary facility</a> the science of astronomy has seen in more than two decades. It’s hard to get across to other astronomers - let alone the general reader - just how exquisitely Kepler <a href="http://kepler.nasa.gov/Mission/faq/#a2">measures the amount of light</a> coming from its target stars as it searches for the tiny repeating dips in that light that reveal the presence of an otherwise unseen planet.</p>
<p>Most astronomers who study the distant universe tend to think they’ve done pretty well if they measure the brightness of an object to a precision of 10%. Those who study stars in our galaxy (or in nearby galaxies) think they’ve done pretty well if they measure a brightness to a precision of 1%. And anyone who routinely measures a brightness to 0.1% can justifiably think of themselves as a “god” of the science of <a href="http://www.britannica.com/EBchecked/topic/458013/photometry">photometry</a>.</p>
<p>But Kepler leaves the rest of us in the dust. It measures its target stars at precisions of ten parts-per-million or better. That’s 0.001%, or 100 times better than the mere “gods” of ground-based photometry can do.</p>
<p>And Kepler must reach those levels of precision if it’s to achieve its <a href="http://kepler.nasa.gov/Mission/QuickGuide/">primary mission goal</a> - detecting Earth-like planets orbiting sun-like stars.</p>
<p>Earth-like planets, you see, are very, very small. And stars are very, very big. So the amount of star light blocked by an Earth-sized planet is just a tiny (and not entirely coincidental) 10 parts per million, which has allowed Kepler to give us our first, albeit indirect, glimpses of other “Earths”.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/27231/original/snvqgqs7-1373436367.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/27231/original/snvqgqs7-1373436367.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/27231/original/snvqgqs7-1373436367.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=480&fit=crop&dpr=1 600w, https://images.theconversation.com/files/27231/original/snvqgqs7-1373436367.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=480&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/27231/original/snvqgqs7-1373436367.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=480&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/27231/original/snvqgqs7-1373436367.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=603&fit=crop&dpr=1 754w, https://images.theconversation.com/files/27231/original/snvqgqs7-1373436367.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=603&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/27231/original/snvqgqs7-1373436367.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=603&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Kepler 22’s planetary system compared to the Earth.</span>
<span class="attribution"><span class="source">NASA/Kepler mission</span></span>
</figcaption>
</figure>
<h2>Keeping watch</h2>
<p>One of Kepler’s key strategies for success has been to carry out its observations in as “differential” a fashion as possible - that is, the satellite looks at a set of stars hour-after-hour, day-after-day, week-after-week, for periods of up to three months. </p>
<p>In that time it tries to keep absolutely everything about the satellite the same, so the only thing that varies is the brightness of the stars.</p>
<p>And that requires keeping the telescope pointed at the same patch of the sky to a very high level of precision. This is done with the aid of its “reaction wheels”, two of which are shown in the picture below. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/27278/original/gr3pvkc3-1373508104.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/27278/original/gr3pvkc3-1373508104.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/27278/original/gr3pvkc3-1373508104.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/27278/original/gr3pvkc3-1373508104.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/27278/original/gr3pvkc3-1373508104.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/27278/original/gr3pvkc3-1373508104.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/27278/original/gr3pvkc3-1373508104.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/27278/original/gr3pvkc3-1373508104.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Schematic of Kepler showing two of the four reaction wheels used to control the craft.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>If you or I want to turn around, we can plant our foot on the ground, which gives us something to push against. In space, Kepler has nothing to push against, so it relies on a physical effect called the “<a href="https://en.wikipedia.org/wiki/Angular_momentum">conservation of angular momentum</a>”. </p>
<p>By having a small wheel spin rapidly in one direction, the balancing nature of angular momentum will slowly spin the rest of the satellite in the opposite direction. By using three of these wheels in combination, it can turn itself in any direction or, more critically, make small adjustments to stay accurately pointed at the same part of the sky without moving. </p>
<p>But the trick is, it needs three functional wheels. Two just doesn’t cut it - and sadly two is what it has right now.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/rANmbeh_L1k?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<h2>One last chance</h2>
<p>NASA (having some experience with hurling widgets into space) wisely designed Kepler with an additional, redundant reaction wheel - wise because, soon after launch in 2009, one of those four wheels failed. </p>
<p>The Kepler mission was originally designed to be five years long, but has been so successful it was extended last year to a total mission of seven years. So for the past four years everyone concerned has held their breath, hoping nothing untoward happened to the other wheels for at least another three years.</p>
<p>Sadly, as we now know, a second wheel failed in May. As a result, NASA placed the satellite into what’s known as <a href="http://www.nasa.gov/mission_pages/kepler/news/keplerm-20130515.html#.Ud4R5T5Nt90">Point Rest State</a> – a state that minimises fuel usage. Then a lot of engineers sat down to have a really good think about what to do next. </p>
<p>John Troeltzsch of Ball Aerospace & Technologies was <a href="http://www.denverpost.com/breakingnews/ci_23621067/nasa-ball-aiming-give-kepler-another-shot-at">quoted this week</a> as saying:</p>
<blockquote>
<p>We are just going to try to move the wheels in the opposite direction from where they were going when they stopped working. If we can get it moving freely, we can spin it for a while and let it coast to a stop. Then we can understand the level of friction.</p>
</blockquote>
<p>Having the wheels operate in the way they did before the stall was unlikely, Troeltzsch added, before pointing out the obvious, that: </p>
<blockquote>
<p>We can’t send a repair man out.</p>
</blockquote>
<p>Astronomers acknowledge successfully restarting the wheels will <a href="http://www.sciencenews.org/view/generic/id/350625/description/Gone_perhaps_but_Kepler_wont_soon_be_forgotten">be a long shot</a>, but there really aren’t any other options. </p>
<p>Kepler’s current four-year mission is the absolute minimum needed to detect small planets in roughly one-year-long orbits. Extending that mission to seven years is critical to shrinking the large range of potential planet frequencies allowed by the current data, and nailing down just how common Earth-like planets really are.</p>
<p>So please – like the engineers – do all keep your fingers crossed.</p><img src="https://counter.theconversation.com/content/15953/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Tinney receives receives, or has received, funding from the Australian Research Council, the United Kingdom's Particle Physics & Astronomy Research Council and the University of New South Wales. He is currently an employee of the University of New South Wales. </span></em></p>As I write this, engineers at NASA and Ball Aerospace & Technologies have their fingers crossed they’ll be able to restart the stricken Kepler space observatory, which has been in hibernation mode…Chris Tinney, Professor and Associate Dean (Research), UNSW SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/52492012-03-02T02:54:04Z2012-03-02T02:54:04ZKepler’s findings are out of this world (and the best is yet to come)<figure><img src="https://images.theconversation.com/files/8279/original/838cm77w-1330652421.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Many exoplanets have been found, but there's plenty left to uncover.</span> <span class="attribution"><span class="source">Dallas1200am</span></span></figcaption></figure><p>Over the past few months, NASA’s <a href="http://kepler.nasa.gov/">Kepler mission</a> has repeatedly made headlines with announcements of new and unusual planetary systems around other stars. To name a few, we’ve had the <a href="http://www.space.com/10748-tour-kepler11-planet-system.html">most densely packed planetary system</a> known; a <a href="https://theconversation.com/star-wars-planet-with-two-suns-a-step-towards-luke-skywalkers-tatooine-3379">planet with two suns</a>; <a href="https://theconversation.com/kepler-mission-finds-two-sizzling-but-earth-sized-planets-4859">roasting, Earth-like planets</a>; and a <a href="https://theconversation.com/dont-pack-your-bags-yet-kepler-22b-probably-isnt-the-next-earth-4606">giant that might be habitable</a>.</p>
<p>But these headline results have only scratched the surface – there’s far, far more to come. </p>
<h2>Birth of a satellite</h2>
<p>The Kepler satellite was launched on March 7, 2009, starting a three-and-a-half year mission to search for planets around distant stars. </p>
<p>The telescope is pointed at an area of the northern sky, between the constellations of <a href="http://www.astro.wisc.edu/%7Edolan/constellations/constellations/Cygnus.html">Cygnus</a> and <a href="http://www.astro.wisc.edu/%7Edolan/constellations/constellations/Lyra.html">Lyra</a>, almost in the plane of our galaxy. It stares at that field, continually monitoring the brightness of more than 100,000 stars, sending the data it obtains back to Earth, to be pored over by interested scientists. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/8183/original/fvzr7fn4-1330475150.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/8183/original/fvzr7fn4-1330475150.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/8183/original/fvzr7fn4-1330475150.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=781&fit=crop&dpr=1 600w, https://images.theconversation.com/files/8183/original/fvzr7fn4-1330475150.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=781&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/8183/original/fvzr7fn4-1330475150.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=781&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/8183/original/fvzr7fn4-1330475150.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=981&fit=crop&dpr=1 754w, https://images.theconversation.com/files/8183/original/fvzr7fn4-1330475150.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=981&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/8183/original/fvzr7fn4-1330475150.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=981&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Kepler’s field of view, and the Milky Way.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>The <a href="https://theconversation.com/exoplanets-how-the-search-for-life-became-sexy-43">search for exoplanets</a> has already revealed that a significant fraction of all stars host planets. </p>
<p>That means, within the Kepler field, there will be tens of thousands of planetary systems awaiting discovery. Unfortunately, the great majority of those systems will go undetected by Kepler, which watches for the rare blinks in a field star’s brightness that occur when a planet passes between Earth and that star – an event known as a “<a href="http://en.wikipedia.org/wiki/Methods_of_detecting_extrasolar_planets#Transit_method">transit</a>”.</p>
<p>The great bulk of planets move in orbits that do not transit their host star, at least from our viewpoint. Instead, their orbits are tilted, meaning the planet passes above or below the star on the sky, rather than directly through our line of sight.</p>
<p>But if a planet’s orbit is aligned just right, it will transit across its host star once per orbit, causing the star to “wink” periodically. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/8191/original/7h48n8qn-1330478628.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/8191/original/7h48n8qn-1330478628.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/8191/original/7h48n8qn-1330478628.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/8191/original/7h48n8qn-1330478628.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/8191/original/7h48n8qn-1330478628.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/8191/original/7h48n8qn-1330478628.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/8191/original/7h48n8qn-1330478628.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/8191/original/7h48n8qn-1330478628.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">Kepler-11 is a sun-like star around which six orbiting planets have so far been discovered. At times, two or more planets pass in front of the star at once, as shown in this artist’s conception of a simultaneous transit of three planets observed by NASA’s Kepler spacecraft on August 26, 2010.</span>
<span class="attribution"><span class="source">NASA/Tim Pyle</span></span>
</figcaption>
</figure>
<h2>A single wink does not a planet make</h2>
<p>Before Kepler can claim to have found a candidate planet, it must observe at least three consecutive transit events. The first two indicate the <a href="http://en.wikipedia.org/wiki/Orbital_period">orbital period</a> of the potential planet (one transit for each orbit the planet makes around its host star), and the third confirms that the first two transits were from the same object.</p>
<p>One of the key goals of the Kepler mission is to attempt to work out how rare, or how common, Earth-like planets are. The larger the planet, the more of its host star’s light it will obscure during a transit, and so the more obvious the wink will be. </p>
<p>Thanks to its highly sensitive cameras, and the fact the satellite’s view is not obscured by the atmosphere, Kepler is more than capable of detecting planets as small as our own.</p>
<p>Around a sun-like star, a planet such as Earth (just the right distance from the star to host liquid water) would have an orbital period of around a year. So, to be sure we’ll catch three transits, we need a mission of a little bit longer than three years. </p>
<h2>Give me more</h2>
<p>Kepler has been gathering data for almost three years – and so it’s almost certain it will have observed multiple transits from Earth-like planets that lie just the right distance from their stars to be considered <a href="http://jontihorner.com/papers/Habitability.pdf">“habitable”</a>. But the vast amount of data being collected by the satellite means results from Kepler are being announced well after the data that lead to them was captured.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/8187/original/fj8ywvm6-1330477704.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/8187/original/fj8ywvm6-1330477704.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/8187/original/fj8ywvm6-1330477704.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/8187/original/fj8ywvm6-1330477704.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/8187/original/fj8ywvm6-1330477704.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/8187/original/fj8ywvm6-1330477704.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/8187/original/fj8ywvm6-1330477704.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/8187/original/fj8ywvm6-1330477704.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">Location of Kepler planet candidates.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>A significant amount of work is needed to confirm that a “candidate” planet is really what it seems to be. In fact, Kepler has discovered more than 2,300 potential planets, but only 61 of those have, to date, been <a href="http://www.nasa.gov/mission_pages/kepler/main/index.html"><em>confirmed</em> as planets</a>.</p>
<p>As things stand, we’ve really only scratched the surface of what Kepler will discover and there are tantalising hints about future results. The Kepler team has estimated that 207 of their 2,326 candidates are comparable in size to Earth, and almost 50 of those are within their star’s habitable zone.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/8221/original/w4ygqshk-1330491152.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/8221/original/w4ygqshk-1330491152.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/8221/original/w4ygqshk-1330491152.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/8221/original/w4ygqshk-1330491152.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/8221/original/w4ygqshk-1330491152.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/8221/original/w4ygqshk-1330491152.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/8221/original/w4ygqshk-1330491152.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/8221/original/w4ygqshk-1330491152.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">Kepler Mission planet candidates – a family portrait.</span>
<span class="attribution"><span class="source">Jason Rowe, NASA Ames Research Center and SETI Institute</span></span>
</figcaption>
</figure>
<p>Given these results are entirely based on the first year of Kepler data (and the satellite’s now been up there for three) it’s fair to expect those numbers to rise dramatically as more data is analysed. There will definitely be lots of exciting Kepler discoveries to come in the next few years.</p>
<p>Once the data from the main Kepler mission are analysed, we’ll no longer have to speculate as to whether the Earth is unique. We won’t know whether those planets have oceans, or life, but we will know how often planets form that are roughly the same size as ours, and in roughly the same place.</p>
<p>In addition it’ll be possible to determine the distribution of planets as a function of distance from their star for planets ranging in size from similar to Earth to bigger than Jupiter.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/8193/original/xy4kvqqn-1330479309.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/8193/original/xy4kvqqn-1330479309.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/8193/original/xy4kvqqn-1330479309.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/8193/original/xy4kvqqn-1330479309.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/8193/original/xy4kvqqn-1330479309.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/8193/original/xy4kvqqn-1330479309.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/8193/original/xy4kvqqn-1330479309.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/8193/original/xy4kvqqn-1330479309.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">Kepler’s candidate multi-planet systems.</span>
<span class="attribution"><span class="source">NASA/Tim Pyle</span></span>
</figcaption>
</figure>
<p>A huge wealth of related scientific results are also coming out of the mission. By surveying so many stars non-stop, Kepler is discovering vast numbers of eclipsing <a href="http://www.answers.com/topic/binary-star">binary stars</a>, and yielding unprecedented information about <a href="http://kepler.nasa.gov/Science/about/RelatedScience/Asteroseismology/">how stars vary and pulsate</a> – results that will trigger vast improvements in our understanding of how stars actually work. </p>
<h2>Keeping Kepler alive</h2>
<p>As things stand, funding for Kepler is scheduled to run out towards the end of this year, at the end of its originally allotted lifespan. The Kepler team would like the mission to be extended to run for at least eight years – which is technically feasible – but whether the US Congress will find the funds to support it is <a href="http://www.space.com/13857-nasa-kepler-mission-extension-alien-planets.html">still unclear</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/8198/original/mvy5m3c9-1330480122.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/8198/original/mvy5m3c9-1330480122.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/8198/original/mvy5m3c9-1330480122.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/8198/original/mvy5m3c9-1330480122.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/8198/original/mvy5m3c9-1330480122.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/8198/original/mvy5m3c9-1330480122.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/8198/original/mvy5m3c9-1330480122.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/8198/original/mvy5m3c9-1330480122.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">This artist’s concept depicts a compact planetary system. Astronomers using data from NASA’s Kepler mission and ground-based telescopes recently confirmed that the system called KOI-961 hosts the three smallest exoplanets known so far to orbit a star other than our sun.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech</span></span>
</figcaption>
</figure>
<h2>Getting involved</h2>
<p>Members of the Kepler team aren’t the only people finding planets using data sent back from the satellite. For the past 15 months or so, it’s been possible for anyone to participate in the analysis of Kepler data. </p>
<p>The <a href="http://www.planethunters.org/">Planet Hunters website</a> aims to make searching for planets in the Kepler data fun and accessible, and is using the keen eyes of volunteers to search for transits that the Kepler team and their powerful analysis tools have missed. </p>
<p>There have already been numerous success stories, such as new candidate planets being found that had previously been missed. The site has proved a remarkable success.</p>
<p>I find it truly remarkable that, less than 20 years after the discovery of the first planets orbiting sun-like stars, amateur astronomers and members of the general public are able to participate in the detection of other Earths.</p>
<p>Long may such work continue. </p><img src="https://counter.theconversation.com/content/5249/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>Over the past few months, NASA’s Kepler mission has repeatedly made headlines with announcements of new and unusual planetary systems around other stars. To name a few, we’ve had the most densely packed…Jonti Horner, Post Doctoral Research Fellow, UNSW SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/46062011-12-07T02:21:11Z2011-12-07T02:21:11ZDon’t pack your bags yet – Kepler-22b (probably) isn’t the next Earth<figure><img src="https://images.theconversation.com/files/6189/original/wnc48vg5-1323214475.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">What's so special about the latest big discovery by NASA's Kepler?</span> <span class="attribution"><span class="source">NASA/Ames/JPL-Caltech</span></span></figcaption></figure><p>On Monday, to much fanfare, astronomers working with the <a href="http://www.nasa.gov/mission_pages/kepler/main/index.html">Kepler space observatory</a> (which was launched in March 2009) <a href="http://www.nasa.gov/mission_pages/kepler/news/kepscicon-briefing.html">announced</a> their first discovery of a planet orbiting within the “<a href="http://en.wikipedia.org/wiki/Habitable_zone">habitable zone</a>” of its host star. The planet in question, <a href="http://www.nasa.gov/mission_pages/kepler/news/kepscicon-briefing.html">Kepler-22b</a>, is far from a twin to Earth (even describing it as “Earth-like” is likely pushing things a little far), but the result is still a striking one – and it’s likely to be the first of many. </p>
<h2>Searching for moths around distant candles</h2>
<p>The Kepler spacecraft searches for planets around other stars using the “<a href="http://www.planetary.org/explore/topics/extrasolar_planets/extrasolar/transit_photometry.html">Transit Method</a>”, looking for the small tell-tale <a href="http://www.nasa.gov/multimedia/videogallery/index.html?collection_id=14471">dips in a star’s brightness</a> that occur when a planet orbiting that star passes directly between Earth and its host. For such transits to occur, the orbit of the planet in question must be perfectly aligned such that the planet passes between Earth and its host. Even if the orbit is tilted by just a small amount from the planet, it will pass unseen “above” or “below” the star, as we look at it, and no transit will occur. </p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/6190/original/fktkzr8t-1323214948.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/6190/original/fktkzr8t-1323214948.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=539&fit=crop&dpr=1 600w, https://images.theconversation.com/files/6190/original/fktkzr8t-1323214948.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=539&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/6190/original/fktkzr8t-1323214948.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=539&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/6190/original/fktkzr8t-1323214948.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=677&fit=crop&dpr=1 754w, https://images.theconversation.com/files/6190/original/fktkzr8t-1323214948.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=677&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/6190/original/fktkzr8t-1323214948.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=677&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Kepler spacecraft is on the hunt.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>To put the challenge facing astronomers looking for transits into context, imagine for a moment standing outside on a perfectly clear night, far from any source of light pollution, looking up at the night sky. If you’ve allowed time for your eyes to become properly adapted to the dark, you’ll probably be able to see roughly 6,000 stars. </p>
<p>If every single one of those stars had a telescope pointing towards our sun, capable of detecting transits of Earth, only 30 of them would be correctly aligned, and would see transits. For the rest, the transit method would offer no evidence Earth exists. </p>
<p>In other words, if you want to find planets using the transit method, you need to survey a huge number of stars to maximise your chances that at least some of them will have transiting planets. </p>
<p>And if you want to find Earth-like planets (those that could have liquid water on their surface, and therefore potentially be habitable), you need to observe those stars continually, for a long period of time. Since Earth takes one year to orbit the sun, it would only transit once per year. </p>
<p>But one dip in a star’s brightness does not a planet make, so you really need to observe at least three transits before you can have any confidence that what you’re seeing is truly a planet. </p>
<p>That’s exactly what Kepler is doing.</p>
<h2>Investigating the habitable zone </h2>
<p>Kepler has produced a vast amount of information over the past two years, continually observing almost 150,000 stars, and the scientists working with it are trying to find particularly exciting planets to announce. This has already led to a number of astounding discoveries. </p>
<p>In February last year, Kepler announced the discovery of <a href="http://www.space.com/10748-tour-kepler11-planet-system.html">Kepler-11</a>, a planetary system with six transiting planets packed so closely together that the furthest from their host star was half the distance Earth is from the sun. And in September this year, the Kepler team announced Kepler-16(AB)b, <a href="http://theconversation.com/star-wars-planet-with-two-suns-a-step-towards-luke-skywalkers-tatooine-3379">a planet with two suns</a>. </p>
<p>On December 5th, as the centrepiece of the latest suite of Kepler announcements, the discovery of Kepler-22b, right in the “habitable zone” of its star, was announced. The “<a href="http://en.wikipedia.org/wiki/Habitable_zone">habitable zone</a>” is the range of distances from that star at which a planet’s surface would be, theoretically, just the right temperature for liquid water to exist. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/6188/original/ftzbhtwq-1323213409.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/6188/original/ftzbhtwq-1323213409.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/6188/original/ftzbhtwq-1323213409.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/6188/original/ftzbhtwq-1323213409.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/6188/original/ftzbhtwq-1323213409.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/6188/original/ftzbhtwq-1323213409.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/6188/original/ftzbhtwq-1323213409.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"></span>
<span class="attribution"><span class="source">NASA/Ames/JPL-Caltech</span></span>
</figcaption>
</figure>
<p>The above image shows the orbit of Kepler-22b and that of the four terrestrial planets in our own solar system, by way of comparison. In the solar system, Venus is too close to the sun to lie in the habitable zone. It can be seen from this diagram that Kepler-22b lies at a distance somewhere between Venus and Earth, meaning that it could have liquid water on its surface. </p>
<h2>Earth 2.0?</h2>
<p>Kepler-22b orbits a star very much like our own, albeit slightly less massive, and a little less luminous (which means that the habitable zone lies a little further in than in our own solar system). The star itself lies approximately 600 light years from Earth, making it around 150 times more distant than <a href="http://www.universetoday.com/59336/proxima-centauri/">Proxima Centauri</a>, the sun’s nearest neighbour. Astronomically speaking, although that isn’t quite in our backyard, it’s certainly in our neighbourhood. </p>
<p>The planet orbits its host star over a period of 290 days, and has only been discovered so quickly with Kepler because the first transit we could observe fell very soon after the start of the mission, meaning there has been time for the planet to complete two full orbits of its host star, and hence allow us to observe three transits. </p>
<p>Without the observation of the third transit, this planet would be just another of the 2,300+ candidates awaiting confirmation. The fact it has been found so soon is certainly a slice of good fortune.</p>
<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/6192/original/6ypyx6s4-1323217467.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/6192/original/6ypyx6s4-1323217467.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/6192/original/6ypyx6s4-1323217467.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/6192/original/6ypyx6s4-1323217467.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/6192/original/6ypyx6s4-1323217467.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/6192/original/6ypyx6s4-1323217467.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/6192/original/6ypyx6s4-1323217467.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">There could be any number of new Earths lurking in our galaxy.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech</span></span>
</figcaption>
</figure>
<p>Despite all the fanfare, Kepler-22b is certainly nothing like Earth. Transit observations don’t allow us to “weigh” a planet, but they do allow the size of the planet to be determined (a bigger planet blocks more light, causing the star’s brightness to dip by a great amount). Kepler-22b, it turns out, is around 2.4 times the radius of Earth. </p>
<p>That’s roughly half way between the size of Earth and the size of Uranus and Neptune, the solar system’s ice giants. It’s most likely, therefore, to be a “<a href="http://en.wikipedia.org/wiki/Super-Earth">super-Earth</a>”, far <a href="http://upload.wikimedia.org/wikipedia/commons/2/2c/Exoplanet_Mass-Radius_Scatter_Super-Earth.png">more massive than the Earth</a>, and probably has a thick atmosphere. It might well have a rocky crust somewhere beneath that atmosphere, but it’s hard to be sure.</p>
<p>NASA scientists have calculated that the temperature at Kepler-22b’s surface could be a balmy 22°C – which sounds remarkably clement (the average temperature of the Earth’s surface, by comparison, is around 15°C, though without the beneficial effects of the <a href="http://theconversation.com/the-greenhouse-effect-is-real-heres-why-1515">Earth’s greenhouse</a>, it would be closer to a frigid -20°C). </p>
<p>But given Kepler-22b’s mass, it may well have a significantly denser atmosphere than the Earth, which, in turn, probably means the true surface temperature will be higher than the optimistic 22°C mentioned above. Indeed, if the atmosphere of the planet is sufficiently dense, and rich in greenhouse gasses, it might well be more like Venus than the Earth, with a surface far too warm to house liquid water. </p>
<h2>A sign of things to come</h2>
<p>Given the uncertainties, it’s premature to consider Kepler-22b a habitable, Earth-like planet. But the detection of the first Kepler planet to lie comfortably within the theoretical habitable zone of its host star is still very exciting. </p>
<p>Kepler has been carrying out observations for long enough now that at least some potentially-habitable worlds will have transited their host stars the minimum of three times required for firm detection – and the longer the satellite goes on observing, the more transits by such planets will be observed. </p>
<p>In this context, the announcement of Kepler-22b isn’t actually a huge surprise – it merely shows Kepler’s observations are running on schedule. Where one planet is found, more are certain to follow, and it’s almost guaranteed that, somewhere among the 2,326 potential planets announced by the Kepler team yesterday, many more “habitable” planets have already been detected and are simply awaiting confirmation.</p><img src="https://counter.theconversation.com/content/4606/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>On Monday, to much fanfare, astronomers working with the Kepler space observatory (which was launched in March 2009) announced their first discovery of a planet orbiting within the “habitable zone” of…Jonti Horner, Post Doctoral Research Fellow, UNSW SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/33902011-09-15T04:44:51Z2011-09-15T04:44:51ZWhere is everybody? Doing the maths on extraterrestrial life<figure><img src="https://images.theconversation.com/files/3604/original/3654891414_a4a3dae010_b.jpg?ixlib=rb-1.1.0&rect=2%2C55%2C1024%2C684&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Are we getting closer to solving one of life's greatest mysteries?</span> <span class="attribution"><span class="source">jcoterhals</span></span></figcaption></figure><p>During a lunch in the summer of 1950, physicists <a href="http://www.nobelprize.org/nobel_prizes/physics/laureates/1938/fermi-bio.html">Enrico Fermi</a>, <a href="http://www.achievement.org/autodoc/page/tel0bio-1">Edward Teller</a> and <a href="http://www.telegraph.co.uk/news/obituaries/science-obituaries/5383781/Herbert-York.html">Herbert York</a> were chatting about a <a href="http://home.fnal.gov/%7Ecarrigan/pillars/New_Yorker_aliens.png">recent New Yorker cartoon</a> depicting aliens abducting trash cans in flying saucers. Suddenly, Fermi blurted out, “Where is everybody?” </p>
<p>He reasoned: “Since there are likely many other technological civilisations in the Milky Way galaxy, and since in a few tens of thousands of years at most they could have explored or even colonised many distant planets, why don’t we see any evidence of even a single extraterrestrial civilisation?”</p>
<p>This has come to be known as <a href="http://www.universetoday.com/39804/fermi-paradox/">Fermi’s Paradox</a>. </p>
<p>Clearly the question of whether other civilisations exist is one of the most important questions of modern science. Any discovery of a distant civilisation – say by analysis of microwave data – would rank as among the most far-reaching of all scientific discoveries.</p>
<h2>Drake equation</h2>
<p>At a 1960 conference regarding extraterrestrial intelligence, <a href="http://en.wikipedia.org/wiki/Frank_Drake">Frank Drake</a> (1930 —) sketched out what is now the <a href="http://en.wikipedia.org/wiki/Drake_equation">Drake equation</a>, estimating the number of civilisations in the Milky Way with which we could potentially communicate:</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/3609/original/Screen_shot_2011-09-15_at_1.59.59_PM.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/3609/original/Screen_shot_2011-09-15_at_1.59.59_PM.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=70&fit=crop&dpr=1 600w, https://images.theconversation.com/files/3609/original/Screen_shot_2011-09-15_at_1.59.59_PM.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=70&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/3609/original/Screen_shot_2011-09-15_at_1.59.59_PM.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=70&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/3609/original/Screen_shot_2011-09-15_at_1.59.59_PM.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=88&fit=crop&dpr=1 754w, https://images.theconversation.com/files/3609/original/Screen_shot_2011-09-15_at_1.59.59_PM.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=88&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/3609/original/Screen_shot_2011-09-15_at_1.59.59_PM.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=88&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p>where</p>
<p>N = number of civilisations in our galaxy that can communicate.</p>
<p>R* = average rate of star formation per year in galaxy.</p>
<p>f<sub>p</sub> = fraction of those stars that have planets.</p>
<p>n<sub>e</sub> = average number of planets that can support life, per star that has planets.</p>
<p>f<sub>l</sub> = fraction of the above that eventually develop life.</p>
<p>f<sub>i</sub> = fraction of the above that eventually develop intelligent life.</p>
<p>f<sub>c</sub> = fraction of civilisations that develop technology that signals existence into space.</p>
<p>L = length of time such civilisations release detectable signals into space.</p>
<p>The result? Drake estimated ten such civilisations were out there somewhere in the Milky Way.</p>
<p>This analysis, led to the Search for Extraterrestrial Intelligence (<a href="http://www.seti.org/">SETI</a>) project, looking for radio transmissions in a region of the electromagnetic spectrum thought best suited for interstellar communication. </p>
<p>But after 50 years of searching, using increasingly powerful equipment, nothing has been found. </p>
<p>So where is everybody?</p>
<h2>Proposed solutions to Fermi’s paradox</h2>
<p>Numerous scientists have examined Fermi’s paradox and proposed solutions. The following is a list of some of the proposed solutions, and common rejoinders:</p>
<ul>
<li>Such civilisations are here, or are observing us, but are under orders not to disclose their existence. </li>
</ul>
<p><em>Common rejoinder:</em> This explanation (known as the “zookeeper’s theory”) is preferred by some scientists including, for instance, the late <a href="http://planetary.org/about/founders/carl_sagan.html">Carl Sagan</a>. But it falls prey to the fact that it would take just one member of an extraterrestrial society to break the pact of silence – and this would seem inevitable.</p>
<ul>
<li>Such civilisations have been here and planted seeds of life, or perhaps left messages in DNA. </li>
</ul>
<p><em>Common rejoinder:</em> The notion that life began on Earth from bacterial spores or the like that originated elsewhere, known as the “<a href="http://leiwenwu.tripod.com/panspermia.htm">panspermia theory</a>”, only pushes the origin of life problem to some other star system – scientists see no evidence in DNA sequences of anything artificial.</p>
<ul>
<li>Such civilisations exist, but are too far away. </li>
</ul>
<p><em>Common rejoinder:</em> A sufficiently advanced civilisation could send probes to distant stars, which could scout out suitable planets, land and construct copies of themselves, using the latest software beamed from home. </p>
<p>So the entire Milky Way galaxy could be explored within, at most, a few million years.</p>
<ul>
<li>Such civilisations exist, but have lost interest in interstellar engagement. </li>
</ul>
<p><em>Common rejoinder:</em> As with the zookeeper theory, this would require each civilisation to forever lack interest in communication and transportation – and someone would most likely break the pact of silence.</p>
<ul>
<li>Such civilisations are calling, but we don’t recognise the signal. </li>
</ul>
<p><em>Common rejoinder:</em> This explanation doesn’t apply to signals sent with the direct purpose of communicating to nascent technological societies. Again, it is hard to see how a galactic society could enforce a global ban.</p>
<ul>
<li>Civilisations invariably self-destruct. </li>
</ul>
<p><em>Common rejoinder:</em> This contingency is already figured into the Drake equation (the L term, above). In any event, we have survived at least 100 years of technological adolescence, and have managed (until now) not to destroy ourselves in a nuclear or biological apocalypse. </p>
<p>Relatively soon we will colonise the moon and Mars, and our long-term survival will no longer rely on Earth.</p>
<ul>
<li>Earth is a unique planet in fostering long-lived ecosystems resulting in intelligent life. </li>
</ul>
<p><em>Common rejoinder:</em> Perhaps, but the latest studies, in particular the <a href="http://experimentalmath.info/blog/2011/09/where-is-everybody/">detections of extrasolar planets</a> point in the opposite direction. Environments like ours appear quite common.</p>
<ul>
<li>We are alone in the Milky Way galaxy. Some scientists further conclude we are alone in the entire observable universe. </li>
</ul>
<p><em>Common rejoinder:</em> This conclusion flies in the face of the “principle of mediocrity,” namely the presumption, popular since the time of <a href="http://plato.stanford.edu/entries/copernicus/">Copernicus</a>, that there’s nothing special about human society or environment.</p>
<p>Numerous other proposed solutions and rejoinders are given in by Stephen Webb in his 2002 book, <a href="http://books.google.com.au/books?id=Kp6g79LuKWEC&pg=PA44&lpg=PA44&dq=if+the+universe+is+teeming+with+aliens...+where+is+everybody+webb&source=bl&ots=axM0wH-Raq&sig=DXX1kvB8JcmKSeZBnzrxtbybOZM&hl=en&ei=aWBxTpaQE-GViQfMpqChBg&sa=X&oi=book_result&ct=result&resnum=2&ved=0CCAQ6AEwAQ#v=onepage&q&f=false">If the Universe Is Teeming with Aliens … Where is Everybody?</a>. </p>
<p>Two of Drake’s key terms – fp (the fraction of stars that have planets) and ne (the average number of planets that can support life, per star that has planets) are subject to measurement. </p>
<p>Scientists once thought stable planetary systems and Earth-like planets were a rarity. But <a href="http://www.washingtonpost.com/new-super-earth-is-36-light-years-distant-might-hold-water-astronomers-say/2011/09/12/gIQA4nN6MK_story.html">recent evidence</a> suggests otherwise. </p>
<p>Thanks to <a href="https://kepler-project.org/">Kepler</a> and other projects, these two terms have been found to have reasonable values, although not quite as optimistic as Drake and his colleagues first estimated.</p>
<p>With every new research finding in the area of extrasolar planets and possible extraterrestrial living organisms, the mystery of Fermi’s paradox deepens. </p>
<p>“Where is everybody?” is a question that now carries even greater resonance.</p>
<p><em>An extended version of this article first appeared at <a href="http://experimentalmath.info/blog/2011/09/where-is-everybody/">Math Drudge</a>.</em></p><img src="https://counter.theconversation.com/content/3390/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jon Borwein receives funding from ARC.</span></em></p><p class="fine-print"><em><span>David H. Bailey 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>During a lunch in the summer of 1950, physicists Enrico Fermi, Edward Teller and Herbert York were chatting about a recent New Yorker cartoon depicting aliens abducting trash cans in flying saucers. Suddenly…Jonathan Borwein (Jon), Laureate Professor of Mathematics, University of NewcastleDavid H. Bailey, PhD; Lawrence Berkeley Laboratory (retired) and Research Fellow, University of California, DavisLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/432011-04-03T20:45:35Z2011-04-03T20:45:35ZExoplanets: how the search for life became sexy<figure><img src="https://images.theconversation.com/files/39/original/extrasolar.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Hundreds of exoplanets have been discovered, but are we any closer to finding life?</span> <span class="attribution"><span class="source">AAP</span></span></figcaption></figure><p>In the late 1980s, when I was a young whipper-snapper just starting out as an astronomer, it was quite obvious some fields had an incredibly high profile and others were outré. </p>
<p>The sexy ideas at the time included <a href="http://www.youtube.com/watch?v=Kg9F5pN5tlI">cosmology at high redshift</a> and finding the next “record-breaking” distant quasar. </p>
<p>By far the most “out there” field to work in was the search for planets orbiting other stars. </p>
<h2>Unloved and unwanted</h2>
<p>The paradigm for a career in this field seemed to have been set by the Reformation-era philosopher, heretic and all-round nutcase Giordano Bruno. </p>
<p>Bruno is widely (though not very accurately) quoted as being the first person to suggest the existence of planets orbiting other stars, and was burned at the stake during the Roman Inquisition in 1600 (though for other “heretical crimes”).</p>
<p>While searching for planets as an astronomer in the 1980s didn’t mean you’d come to the same end as Bruno, it would pretty much guarantee you’d received strange glances at scientific conferences until the day you retired.</p>
<h2>Bringing sexy back</h2>
<p>A couple of decades later, things have changed. With hundreds of exoplanets discovered outside our solar system in the years since the <a href="http://owww.phys.au.dk/%7Ehans/exo/paper01.pdf">first was announced in 1995</a>, the field of “exoplanetary science” has found its groove. </p>
<p>Not only are astronomers now seriously expecting to answer questions such as, “How many habitable, Earth-like planets are there in the galaxy?”; they want to discover and observe potentially liveable planets. </p>
<h2>How do we define “liveable”?</h2>
<p>Before the discovery of exoplanets we had built up a quite complex model for the formation of our own solar system – one which reproduced the sizes, orbits and compositions of the eight planets we knew quite well. </p>
<p>Extending this model to other stars predicted (unsurprisingly) that most planetary systems would look like our own solar system. The discovery of the first hundred exoplanets, however, shattered this view.</p>
<p>Unlike our solar system, exoplanetary systems have:</p>
<ol>
<li><p>Gas-giant planets much closer to their stars than they should be able to form.</p></li>
<li><p>Planets that mostly orbit in elongated elliptical orbits (as opposed to the mostly circular orbits of our solar system).</p></li>
<li><p>Giant planets with densities ranging from that of fluffy Saturn (which is slightly less dense than liquid water), to compact Earth (as dense as silicate rock).</p></li>
</ol>
<p>Unfortunately, none of this brings us any closer to learning how common a system such as ours is in the galaxy.</p>
<h2>What are “habitable” environments? </h2>
<p>In the absence of a deeper understanding we tend to fall back on a definition of habitability that mirrors the conditions on the surface of the Earth, by requiring that a “habitable” planet must have a rocky surface that can sustain liquid water. </p>
<p>It cannot orbit too close to its parent star (or else the surface will be too hot), nor can it be too distant from that star (or else the surface be too cold).</p>
<p>“Habitable”, by this definition, is just a proxy for “Earth-like”. </p>
<p>All this is why, when asked questions such as, “Is there life out there in the universe?” most astronomers – if they are honest – answer, “I just don’t know”. </p>
<p>Unfortunately, journalists and editors hate this answer, and usually say, “go on, guess”, and those guesses are what you usually see reported.</p>
<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/38/original/kepler.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/38/original/kepler.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/38/original/kepler.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/38/original/kepler.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/38/original/kepler.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/38/original/kepler.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/38/original/kepler.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 Kepler Mission has taken great leaps forward in the search for Earth-like candidates.</span>
<span class="attribution"><span class="source">NASA Ames Research Center/Kepler Mission</span></span>
</figcaption>
</figure>
<h2>Kepler</h2>
<p>Investigating the prevalence of Earth-like planets in Earth-like orbits is the prime mission of the <a href="http://kepler.nasa.gov/" title="NASA's Kepler Mission">NASA’s Kepler Mission</a>. </p>
<p>The Kepler satellite was launched in March 2009, on a three-year mission to stare continuously at a region of sky in the northern hemisphere in the constellations of Cygnus, Lyra and Draco. </p>
<p>The mission uses a 94-megapixel camera to take an image every six seconds, recording the light output for around 100,000 stars. </p>
<p>These measurements are of exquisite quality, and they need to be, because Kepler’s aim is to detect the tiny dimming of a star as a planet passes between us and the star.</p>
<p>This is why <a href="http://kepler.nasa.gov/Mission/discoveries/">the recent announcement</a> by the Kepler Mission of some 1,235 planet candidates from their first four months of data is of “candidates” only. </p>
<h2>How do candidates graduate?</h2>
<p>We now need to wait until those blips appear again to (a) confirm the first blip was real, and (b) estimate the planet’s orbital period.</p>
<p>However it pans out, Kepler’s search will in time result in an astounding statistical database on the prevalence of small, rocky and hopefully Earth-like planets. </p>
<p>At that point we’ll finally know the answer to at least part of the puzzle of whether our type of planet is common.</p>
<p>One thing’s for sure: the search for exoplanets is where it’s at.</p><img src="https://counter.theconversation.com/content/43/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Tinney receives or has received funding from the Australian Research Council, the United Kingdom's Particle Physics & Astronomy Research Council and the University of New South Wales. He is currently an employee of the University of New South Wales.</span></em></p>In the late 1980s, when I was a young whipper-snapper just starting out as an astronomer, it was quite obvious some fields had an incredibly high profile and others were outré. The sexy ideas at the time…Chris Tinney, Professor and Associate Dean (Research), UNSW SydneyLicensed as Creative Commons – attribution, no derivatives.