tag:theconversation.com,2011:/fr/topics/habitable-planets-39124/articlesHabitable planets – The Conversation2023-12-06T19:39:11Ztag:theconversation.com,2011:article/2191952023-12-06T19:39:11Z2023-12-06T19:39:11ZEarth may have had all the elements needed for life within it all along − contrary to theories that these elements came from meteorites<figure><img src="https://images.theconversation.com/files/563960/original/file-20231206-27-mh7rrg.jpg?ixlib=rb-1.1.0&rect=5%2C11%2C1994%2C1485&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Scientists still debate the origins of Earth's life-sustaining elements.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/hot-sunrise-in-space-royalty-free-image/160306742?phrase=Tobias+Roetsch+Future+Publishing+earth&adppopup=true">BlackJack3D/E+ via Getty Images</a></span></figcaption></figure><p>For many years, scientists have predicted that many of the <a href="https://www.khanacademy.org/science/ap-biology/chemistry-of-life/elements-of-life/a/matter-elements-atoms-article">elements that are crucial ingredients for life</a>, like sulfur and nitrogen, first came to Earth when asteroid-type objects carrying them crashed into our planet’s surface. </p>
<p>But new research <a href="https://doi.org/10.1126/sciadv.adh0670">published by our team</a> in Science Advances suggests that many of these elements, called volatiles, may have existed in the Earth from the beginning, while it formed into a planet.</p>
<p>Volatiles evaporate more readily than other elements. Common examples include carbon, hydrogen and nitrogen, though our research focused on a <a href="https://www.sciencedirect.com/topics/chemistry/chalcogen">group called chalcogens</a>. Sulfur, selenium and tellurium are all chalcogens.</p>
<p>Understanding how these volatile elements made it to Earth helps <a href="https://scholar.google.com/citations?user=DpHUpCwAAAAJ&hl=en">planetary scientists</a> <a href="https://scholar.google.com/citations?user=h0uFkzgAAAAJ&hl=zh-CN">like us</a> better understand Earth’s geologic history, and it could teach us more about the habitability of terrestrial planets beyond Earth. </p>
<h2>Why it matters</h2>
<p>The popular “late veneer” theory predicts that Earth first formed from <a href="https://www.ox.ac.uk/news/2017-09-27-volatile-processes-shaped-earth">materials that are low in volatiles</a>. After the formation of the Earth’s core, the theory says, the <a href="https://doi.org/10.1126/science.1186239">planet got volatiles</a> when volatile-rich bodies from the outer solar system hit the surface. </p>
<p>These objects brought <a href="https://doi.org/10.1007/978-3-642-11274-4_870">around a half a percent of Earth’s mass</a>. If the late veneer theory is right, then most elements that make up life arrived on Earth sometime <a href="https://physicsworld.com/a/how-the-earths-core-was-formed/">after the Earth’s core had formed</a>.</p>
<p>But our new research suggests that Earth had all its life-essential volatile elements from the very beginning, during the planet’s formation. These results challenge the late veneer theory and are consistent with another study <a href="https://newsroom.ucla.edu/releases/earth-like-planets-may-be-an-inevitability">tracing the origin of water on Earth</a>. </p>
<h2>How we did our work</h2>
<p>To study the origin of volatiles in the Earth, we used a computational technique called <a href="https://www.jeol.com/words/emterms/20121023.055758.php#gsc.tab=0">first-principles calculation</a>. This technique describes the <a href="https://www.ducksters.com/science/chemistry/radiation_and_radioactivity.php">behaviors of isotopes</a>, which are atoms of an element that have varying numbers of neutrons. You can think of an element as a family – every atom has the same number of protons, but <a href="https://theconversation.com/hunting-for-rare-isotopes-the-mysterious-radioactive-atomic-nuclei-that-will-be-in-tomorrows-technology-86177">different isotope cousins</a> have different numbers of neutrons.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/42gUZNYco0c?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Isotopes have a host of useful applications, from archaeology and medicine to planetary science.</span></figcaption>
</figure>
<p>Different isotopes behaved slightly differently during each stage of Earth’s formation. And the isotopes left behind a signature after each formation stage that scientists can use as a kind of fingerprint to track where they were throughout Earth’s formation. </p>
<p>First-principles calculation allowed us to calculate what isotope signatures we’d expect to see for different chalcogens, depending on how the Earth formed. We ran a few models and compared our isotope predictions for each model with the actual measurements of chalcogen isotopes on Earth.</p>
<p><a href="https://doi.org/10.1126/sciadv.adh0670">We found that</a> while many volatiles evaporated during Earth’s formation, when it was hot and glowing, many more are still left over today. Our findings suggest that most of the volatiles on Earth now are likely left over from the early stage of Earth’s formation.</p>
<h2>What’s next</h2>
<p>While chalcogens are interesting to study, future research should look at other critical-for-life volatiles, like nitrogen. And more research into how these volatiles behave <a href="https://education.nationalgeographic.org/resource/core/">under extreme conditions</a> could help us know more about how isotopes were behaving during each of the growth stages of Earth’s formation. </p>
<p>We also hope to use this approach to see <a href="https://theconversation.com/nasas-tess-spacecraft-is-finding-hundreds-of-exoplanets-and-is-poised-to-find-thousands-more-122104">whether some exoplanets</a> – planets beyond our solar system – could be <a href="https://theconversation.com/distant-star-toi-700-has-two-potentially-habitable-planets-orbiting-it-making-it-an-excellent-candidate-in-the-search-for-life-198274">habitable to life</a>.</p>
<p><em>The <a href="https://theconversation.com/us/topics/research-brief-83231">Research Brief</a> is a short take about interesting academic work.</em></p><img src="https://counter.theconversation.com/content/219195/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Shichun Huang is funded by National Science Foundation, and UTK Gerald D. Sisk Endowed Professorship.</span></em></p><p class="fine-print"><em><span>Wenzhong Wang receives funding from the National Natural Science Foundation of China. </span></em></p>Scientists analyzing isotope ratios have found that many of the elements that make up life could be left over from Earth’s formation.Shichun Huang, Associate Professor of Earth and Planetary Sciences, University of TennesseeWenzhong Wang, Professor of Planetary Science, University of Science and Technology of ChinaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2016222023-03-16T12:36:48Z2023-03-16T12:36:48ZWater in space – a ‘Goldilocks’ star reveals previously hidden step in how water gets to planets like Earth<figure><img src="https://images.theconversation.com/files/515568/original/file-20230315-1821-gn9l6v.jpg?ixlib=rb-1.1.0&rect=28%2C45%2C1249%2C1038&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The star system V883 Orionis contains a rare star surrounded by a disk of gas, ice and dust.</span> <span class="attribution"><a class="source" href="http://www.eso.org/public/images/eso1626a/">A. Angelich (NRAO/AUI/NSF)/ALMA (ESO/NAOJ/NRAO)</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>Without water, life on Earth could not exist as it does today. Understanding the history of water in the universe is critical to understanding how planets like Earth come to be.</p>
<p>Astronomers typically refer to the journey water takes from its formation as individual molecules in space to its resting place on the surfaces of planets as “the water trail.” The trail starts in the interstellar medium with hydrogen and oxygen gas and ends with oceans and ice caps on planets, with icy moons orbiting gas giants and icy comets and asteroids that orbit stars. The beginnings and ends of this trail are easy to see, but the middle has remained a mystery.</p>
<p><a href="https://www.cv.nrao.edu/%7Ejtobin/">I am an astronomer</a> who studies the formation of stars and planets using observations from radio and infrared telescopes. In a new paper, my colleagues and I describe the <a href="https://www.nature.com/articles/s41586-022-05676-z">first measurements ever made</a> of this previously hidden middle part of the water trail and what these findings mean for the water found on planets like Earth.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/515526/original/file-20230315-18-7eqg1b.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="The progression of a star system from a cloud of dust and gas into a mature star with orbiting planets." src="https://images.theconversation.com/files/515526/original/file-20230315-18-7eqg1b.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/515526/original/file-20230315-18-7eqg1b.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/515526/original/file-20230315-18-7eqg1b.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/515526/original/file-20230315-18-7eqg1b.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/515526/original/file-20230315-18-7eqg1b.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/515526/original/file-20230315-18-7eqg1b.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/515526/original/file-20230315-18-7eqg1b.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Star and planet formation is an intertwined process that starts with a cloud of molecules in space.</span>
<span class="attribution"><a class="source" href="https://www.nrao.edu/pr/2012/clumpcores/">Bill Saxton, NRAO/AUI/NSF</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>How planets are formed</h2>
<p>The formation of stars and planets is intertwined. The so-called “emptiness of space” – or the interstellar medium – in fact contains <a href="https://doi.org/10.1146/annurev.aa.32.090194.001203">large amounts of gaseous hydrogen</a>, smaller amounts of other gasses and <a href="https://doi.org/10.1086/162480">grains of dust</a>. Due to gravity, some pockets of the interstellar medium will become <a href="https://doi.org/10.1086/311687">more dense as particles attract each other</a> and form clouds. As the density of these clouds increases, atoms begin to collide more frequently and <a href="https://doi.org/10.1086/381775">form larger molecules</a>, including water that forms <a href="https://doi.org/10.1080/0144235X.2015.1046679">on dust grains and coats the dust in ice</a>.</p>
<p>Stars begin to form when parts of the collapsing cloud reach a certain density and heat up enough to start fusing hydrogen atoms together. Since only a small fraction of the gas initially collapses into the newborn protostar, the rest of the gas and dust <a href="https://doi.org/10.48550/arXiv.1001.1404">forms a flattened disk of material</a> circling around the spinning, newborn star. Astronomers call this a proto-planetary disk.</p>
<p>As icy dust particles collide with each other inside a proto-planetary disk, <a href="https://doi.org/10.1051/0004-6361/200811158">they begin to clump together</a>. The process continues and eventually forms the familiar objects of space like asteroids, comets, rocky planets like Earth and gas giants like Jupiter or Saturn.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/515633/original/file-20230315-3008-q4peeq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A cloudy filament against a backdrop of stars." src="https://images.theconversation.com/files/515633/original/file-20230315-3008-q4peeq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/515633/original/file-20230315-3008-q4peeq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=679&fit=crop&dpr=1 600w, https://images.theconversation.com/files/515633/original/file-20230315-3008-q4peeq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=679&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/515633/original/file-20230315-3008-q4peeq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=679&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/515633/original/file-20230315-3008-q4peeq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=854&fit=crop&dpr=1 754w, https://images.theconversation.com/files/515633/original/file-20230315-3008-q4peeq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=854&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/515633/original/file-20230315-3008-q4peeq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=854&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Gas and dust can condense into clouds, like the Taurus Molecular Cloud, where collisions between hydrogen and oxygen can form water.</span>
<span class="attribution"><a class="source" href="http://www.eso.org/public/images/eso1209a/">ESO/APEX (MPIfR/ESO/OSO)/A. Hacar et al./Digitized Sky Survey 2</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Two theories for the source of water</h2>
<p>There are two potential pathways that water in our solar system could have taken. The first, called <a href="https://doi.org/10.1051/0004-6361/200810846">chemical inheritance</a>, is when the water molecules originally formed in the interstellar medium are delivered to proto-planetary disks and all the bodies they create without going through any changes. </p>
<p>The second theory is called <a href="https://doi.org/10.1051/0004-6361/201628509">chemical reset</a>. In this process, the heat from the formation of the proto-planetary disk and newborn star breaks apart water molecules, which then reform once the proto-planetary disk cools.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/515531/original/file-20230315-26-gk368.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Models of protium and deuterium." src="https://images.theconversation.com/files/515531/original/file-20230315-26-gk368.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/515531/original/file-20230315-26-gk368.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=448&fit=crop&dpr=1 600w, https://images.theconversation.com/files/515531/original/file-20230315-26-gk368.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=448&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/515531/original/file-20230315-26-gk368.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=448&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/515531/original/file-20230315-26-gk368.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=563&fit=crop&dpr=1 754w, https://images.theconversation.com/files/515531/original/file-20230315-26-gk368.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=563&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/515531/original/file-20230315-26-gk368.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=563&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Normal hydrogen, or protium, does not contain a neutron in its nucleus, while deuterium contains one neutron, making it heavier.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Hydrogen_Deuterium_Tritium_Nuclei_Schmatic-en.svg">Dirk Hünniger/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>To test these theories, astronomers like me look at the ratio between normal water and a special kind of water called semi-heavy water. Water is normally made of two hydrogen atoms and one oxygen atom. Semi-heavy water is made of one oxygen atom, one hydrogen atom and one atom of deuterium – a heavier isotope of hydrogen with an extra neutron in its nucleus. </p>
<p>The ratio of semi-heavy to normal water is a guiding light on the water trail – measuring the ratio can tell astronomers a lot about the source of water. <a href="https://doi.org/10.1051/0004-6361/202039084">Chemical models</a> and <a href="https://doi.org/10.1086/591506">experiments</a> have shown that about 1,000 times more semi-heavy water will be produced in the cold interstellar medium <a href="https://doi.org/10.1126/science.1258055">than in the conditions of a protoplanetary disk</a>. </p>
<p>This difference means that by measuring the ratio of semi-heavy to normal water in a place, astronomers can tell whether that water went through the chemical inheritance or chemical reset pathway.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/515533/original/file-20230315-1689-gn9l6v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A star surrounded by a ring of gas and dust." src="https://images.theconversation.com/files/515533/original/file-20230315-1689-gn9l6v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/515533/original/file-20230315-1689-gn9l6v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=337&fit=crop&dpr=1 600w, https://images.theconversation.com/files/515533/original/file-20230315-1689-gn9l6v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=337&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/515533/original/file-20230315-1689-gn9l6v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=337&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/515533/original/file-20230315-1689-gn9l6v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/515533/original/file-20230315-1689-gn9l6v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/515533/original/file-20230315-1689-gn9l6v.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">V883 Orionis is a young star system with a rare star at its center that makes measuring water in the proto-planetary cloud, shown in the cutaway, possible.</span>
<span class="attribution"><a class="source" href="https://public.nrao.edu/news/water-v883-orionis/">ALMA (ESO/NAOJ/NRAO), B. Saxton (NRAO/AUI/NSF)</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Measuring water during the formation of a planet</h2>
<p>Comets have a ratio of semi-heavy to normal water almost perfectly in line with <a href="https://doi.org/10.2458/azu_uapress_9780816531240-ch037">chemical inheritance</a>, meaning the water hasn’t undergone a major chemical change since it was first created in space. Earth’s ratio sits somewhere in between the inheritance and reset ratio, making it unclear where the water came from.</p>
<p>To truly determine where the water on planets comes from, astronomers needed to find a goldilocks proto-planetary disk – one that is just the right temperature and size to allow observations of water. Doing so has <a href="https://doi.org/10.1051/0004-6361/201935994">proved to be incredibly difficult</a>. It is possible to detect semi-heavy and normal water when water is a gas; unfortunately for astronomers, the vast majority of proto-plantary disks are very cold and <a href="https://doi.org/10.1126/science.1239560">contain mostly ice</a>, and it is nearly <a href="https://doi.org/10.1051/0004-6361:20031277">impossible to measure water ratios</a> from ice at interstellar distances. </p>
<p>A breakthrough came in 2016, when my colleagues and I were studying proto-planetary disks around a rare type of young star called FU Orionis stars. Most young stars consume matter from the proto-planetary disks around them. FU Orionis stars are unique because they consume matter about 100 times faster than typical young stars and, as a result, <a href="https://doi.org/10.1146/annurev-astro-081915-023347">emit hundreds of times more energy</a>. Due to this higher energy output, the proto-planetary disks around FU Orionis stars are heated to much higher temperatures, turning ice into water vapor out to large distances from the star.</p>
<p>Using the <a href="https://public.nrao.edu/telescopes/alma/">Atacama Large Millimeter/submillimeter Array</a>, a powerful radio telescope in northern Chile, <a href="https://ui.adsabs.harvard.edu/abs/2016Natur.535..258C/abstract">we discovered</a> a large, warm proto-planetary disk around the Sunlike young star V883 Ori, about 1,300 light years from Earth in the constellation Orion.</p>
<p>V883 Ori emits 200 times more energy than the Sun, and my colleagues and I recognized that it was an ideal candidate to observe the semi-heavy to normal water ratio. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/515565/original/file-20230315-14-dfl7h6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A radio image of the disk around V883 Ori." src="https://images.theconversation.com/files/515565/original/file-20230315-14-dfl7h6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/515565/original/file-20230315-14-dfl7h6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=672&fit=crop&dpr=1 600w, https://images.theconversation.com/files/515565/original/file-20230315-14-dfl7h6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=672&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/515565/original/file-20230315-14-dfl7h6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=672&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/515565/original/file-20230315-14-dfl7h6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=844&fit=crop&dpr=1 754w, https://images.theconversation.com/files/515565/original/file-20230315-14-dfl7h6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=844&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/515565/original/file-20230315-14-dfl7h6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=844&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 proto-planetary disk around V883 Ori contains gaseous water, shown in the orange layer, allowing astronomers to measure the ratio of semi-heavy to normal water.</span>
<span class="attribution"><a class="source" href="https://public.nrao.edu/news/water-v883-orionis/#PRimage2">ALMA (ESO/NAOJ/NRAO), J. Tobin, B. Saxton (NRAO/AUI/NSF)</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Completing the water trail</h2>
<p>In 2021, the Atacama Large Millimeter/submillimeter Array took measurements of V883 Ori for six hours. The data revealed a <a href="https://doi.org/10.1038/s41586-022-05676-z">strong signature of semi-heavy and normal water</a> coming from V883 Ori’s proto-planetary disk. We measured the ratio of semi-heavy to normal water and found that the ratio was very <a href="https://doi.org/10.1051/0004-6361/202039084">similar to ratios found in comets</a> as well as the ratios found <a href="https://doi.org/10.1051/0004-6361/201322845">in younger protostar systems</a>.</p>
<p>These results fill in the gap of the water trail forging a direct link between water in the interstellar medium, protostars, proto-planetary disks and planets like Earth through the process of inheritance, not chemical reset.</p>
<p>The new results show definitively that a substantial portion of the water on Earth most likely formed billions of years ago, before the Sun had even ignited. Confirming this missing piece of water’s path through the universe offers clues to origins of water on Earth. Scientists have previously suggested that most water on Earth <a href="https://doi.org/10.1051/0004-6361/201935554">came from comets impacting the planet</a>. The fact that Earth has less semi-heavy water than comets and V883 Ori, but more than chemical reset theory would produce, means that water on Earth likely came from more than one source.</p><img src="https://counter.theconversation.com/content/201622/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>John Tobin receives funding from NASA, </span></em></p>Astronomers have long known where water is first formed in the universe and how it ends up on planets, asteroids and comets. A recent discovery has finally answered what happens in between.John Tobin, Scientist, National Radio Astronomy ObservatoryLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2008292023-03-05T19:19:56Z2023-03-05T19:19:56ZWhat are the best conditions for life? Exploring the multiverse can help us find out<figure><img src="https://images.theconversation.com/files/513318/original/file-20230303-18-ugje3l.jpeg?ixlib=rb-1.1.0&rect=12%2C0%2C4013%2C3024&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Israel Pina / Unsplash</span></span></figcaption></figure><p>Is our universe all there is, or could there be more? Is our universe just one of a countless multitude, all together in an all-encompassing multiverse? </p>
<p>And if there are other universes, what would they be like? Could they be habitable?</p>
<p>This might feel like speculation heaped upon speculation, but it’s not as crazy as you might think. </p>
<p>My colleagues and I have been exploring what other parts of the multiverse might be like – and what these hypothetical neighbouring universes can tell us about the conditions that make life possible, and how they arise.</p>
<h2>What-if universes</h2>
<p>Some physicists <a href="https://www.space.com/25100-multiverse-cosmic-inflation-gravitational-waves.html">contend</a> that a burst of rapid expansion at the cosmic dawn known as inflation makes some form of multiverse inevitable. Our universe would really just be one of many. </p>
<p>In this theory, each new universe crystallises out of the seething background of inflation, imprinted with its own unique mix of physical laws.</p>
<p>If physical laws similar to ours govern these other universes, then we can come to grips with them. Well, at least in theory. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/513319/original/file-20230303-14-sdad7i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/513319/original/file-20230303-14-sdad7i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/513319/original/file-20230303-14-sdad7i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=396&fit=crop&dpr=1 600w, https://images.theconversation.com/files/513319/original/file-20230303-14-sdad7i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=396&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/513319/original/file-20230303-14-sdad7i.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=396&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/513319/original/file-20230303-14-sdad7i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=498&fit=crop&dpr=1 754w, https://images.theconversation.com/files/513319/original/file-20230303-14-sdad7i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=498&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/513319/original/file-20230303-14-sdad7i.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">The history of our universe. Other universes with slightly different laws of physics may also have crystallised from the early period of inflation.</span>
<span class="attribution"><a class="source" href="http://map.gsfc.nasa.gov/media/060915/index.html">NASA</a></span>
</figcaption>
</figure>
<p>Within our universe, physics is governed by rules that tell us how things should interact with each other, and constants of nature, such as the speed of light, that dictate the strengths of these interactions. So, we can imagine hypothetical “what-if” universes where we change these properties and explore the consequences within mathematical equations.</p>
<p>This might sound simple, but the rules we tinker with are the fundamental makeup of the universe. If we imagine a universe where, say, the electron is a hundred times heavier than in our universe, then what would its consequences be for stars, planets and even life?</p>
<h2>What does life need?</h2>
<p>We recently tackled this question in a series of papers where we considered habitability across the multiverse. Of course, habitability is a complex concept, but we think life requires a few choice ingredients to get going.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/the-multiverse-is-huge-in-pop-culture-right-now-but-what-is-it-and-does-it-really-exist-181781">The multiverse is huge in pop culture right now – but what is it, and does it really exist?</a>
</strong>
</em>
</p>
<hr>
<p>Complexity is one of those ingredients. For life on Earth, that complexity comes from the elements of the periodic table, which can be mixed and arranged into a myriad of different molecules. We are living molecular machines. </p>
<p>But a stable environment and a steady flow of energy are also essential. It is no surprise that Earthly life began on the surface of a rocky planet, with an abundance of chemical elements, bathed in the light of a long-lived stable star.</p>
<h2>Tweaking the fundamental forces</h2>
<p>Do similar environments exist across the extent of the multiverse? We started our theoretical exploration by considering the <a href="https://www.mdpi.com/2218-1997/8/12/651">abundance of chemical elements</a>. </p>
<p>In our universe, other than primordial hydrogen and helium that were formed in the Big Bang, all elements arise through the lives of stars. They are either generated through the nuclear reactions in stellar cores, or in the supreme violence of supernovae, when a massive star tears itself apart at the end of its life.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/we-are-lucky-to-live-in-a-universe-made-for-us-46988">We are lucky to live in a universe made for us</a>
</strong>
</em>
</p>
<hr>
<p>All these processes are governed by the four fundamental forces in the universe. Gravity squeezes the stellar core, driving it to immense temperatures and densities. Electromagnetism tries to force atomic nuclei apart, but if they can get close enough, the strong nuclear force can bind them into a new element. Even the weak nuclear force, which can flip a proton into a neutron, plays an important role in the ignition of the stellar furnace.</p>
<p>The masses of the fundamental particles, such as electrons and quarks, can also play a pivotal role. </p>
<p>So, to explore these hypothetical universes, we have many dials we can adjust. The changes to the fundamental universe flow through to the rest of physics.</p>
<h2>The carbon–oxygen balance</h2>
<p>To tackle the immense complexity of this problem, we chopped the various pieces of physics into manageable chunks: <a href="https://www.mdpi.com/2218-1997/9/1/4">stars and atmospheres</a>, <a href="https://www.mdpi.com/2218-1997/9/1/2">planets and plate tectonics</a>, the <a href="https://www.mdpi.com/2218-1997/9/1/42">origins of life</a>, and more. And then we pinned the chunks together to tell an overall story about habitability across the multiverse.</p>
<p>A complex picture emerges. Some factors can strongly influence the habitability of a universe. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/does-a-planet-need-plate-tectonics-to-develop-life-61303">Does a planet need plate tectonics to develop life?</a>
</strong>
</em>
</p>
<hr>
<p>For example, the ratio of carbon to oxygen, something set by a particular chain of nuclear reactions in the heart of a star, appears to be particularly important. </p>
<p>Straying too far from the value in our universe, where there are roughly equal amounts of the two elements, results in environments where it would be extremely difficult for life to emerge and thrive. </p>
<p>But the abundance of other elements appears to be less important. As long as they are stable, which does depend on the balance of the fundamental forces, they can play a pivotal role in the building blocks of life.</p>
<h2>More complexity to explore</h2>
<p>We have only been able to take a broad-brush approach to unravel habitability across the multiverse, sampling the space of possibilities in very discrete steps. </p>
<p>Furthermore, to make the problem manageable, we had to take several theoretical shortcuts and approximations. So we are only at the first stage of understanding the conditions for life across the multiverse.</p>
<p>In the next steps, the full complexity of alternative physics of other universes needs to be considered. We will need to understand the influence of the fundamental forces at the small scale and extrapolate it to the large scale, onto the formation of stars and eventually planets. </p>
<h2>A word of caution</h2>
<p>The notion of a multiverse is still only a hypothesis, an idea that has yet to be tested. In truth, we don’t yet know if it is an idea that <em>can</em> be tested. </p>
<p>And we don’t know if the physical laws could be different across the multiverse and, if they are, just how different they could be. </p>
<p>We may be at the start of a journey that will reveal our ultimate place within infinity – or we may be heading for a scientific dead end.</p><img src="https://counter.theconversation.com/content/200829/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Geraint Lewis receives funding from Australian Research Council. </span></em></p>Some physicists think we live in a multiverse, surrounded by universes not quite like our own. What does that mean for life?Geraint Lewis, Professor of Astrophysics, University of SydneyLicensed as Creative Commons – attribution, no derivatives.tag: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">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>Are there any planets outside of our solar system? - Eli W., age 8, Baton Rouge, Louisiana</strong></p>
</blockquote>
<hr>
<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>
<figure class="align-center ">
<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">
<figcaption>
<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>
</figcaption>
</figure>
<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>
<figure class="align-center ">
<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">
<figcaption>
<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>
</figcaption>
</figure>
<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>
<figure>
<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>
</figure>
<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>
<figure>
<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>
</figure>
<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>
<figure>
<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>
</figure>
<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>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>.
Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/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/1030532018-11-06T11:41:10Z2018-11-06T11:41:10ZColonizing Mars means contaminating Mars – and never knowing for sure if it had its own native life<figure><img src="https://images.theconversation.com/files/242763/original/file-20181029-76411-ioau9b.jpg?ixlib=rb-1.1.0&rect=814%2C0%2C3775%2C2574&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Once people get there, Mars will be contaminated with Earth life.</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/multimedia/imagegallery/image_feature_261.html">NASA/Pat Rawlings, SAIC</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>The closest place in the universe where extraterrestrial life might exist is Mars, and human beings are poised to attempt to colonize this planetary neighbor within the next decade. Before that happens, we need to recognize that a very real possibility exists that the first human steps on the Martian surface will lead to a collision between terrestrial life and biota native to Mars.</p>
<p>If the red planet is sterile, a human presence there would create no moral or ethical dilemmas on this front. But if life does exist on Mars, human explorers could easily lead to the extinction of Martian life. <a href="https://scholar.google.com/citations?user=KOrEwdkAAAAJ&hl=en&oi=ao">As an astronomer</a> who explores these questions in my book “<a href="https://press.princeton.edu/titles/11233.html">Life on Mars: What to Know Before We Go</a>,” I contend that we Earthlings need to understand this scenario and debate the possible outcomes of colonizing our neighboring planet in advance. Maybe missions that would carry humans to Mars need a timeout.</p>
<h2>Where life could be</h2>
<p>Life, scientists suggest, has some basic requirements. It could exist anywhere in the universe that has liquid water, a source of heat and energy, and copious amounts of a few essential elements, such as carbon, hydrogen, oxygen, nitrogen and potassium.</p>
<p>Mars qualifies, as do at least two other places in our solar system. Both <a href="https://solarsystem.nasa.gov/moons/jupiter-moons/europa/in-depth/">Europa</a>, one of Jupiter’s large moons, and <a href="https://solarsystem.nasa.gov/moons/saturn-moons/enceladus/in-depth/">Enceladus</a>, one of Saturn’s large moons, appear to possess these prerequisites for hosting native biology.</p>
<p>I suggest that how scientists planned the exploratory missions to these two moons provides valuable background when considering how to explore Mars without risk of contamination.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/242558/original/file-20181026-7050-3k87rh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/242558/original/file-20181026-7050-3k87rh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/242558/original/file-20181026-7050-3k87rh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=685&fit=crop&dpr=1 600w, https://images.theconversation.com/files/242558/original/file-20181026-7050-3k87rh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=685&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/242558/original/file-20181026-7050-3k87rh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=685&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/242558/original/file-20181026-7050-3k87rh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=860&fit=crop&dpr=1 754w, https://images.theconversation.com/files/242558/original/file-20181026-7050-3k87rh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=860&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/242558/original/file-20181026-7050-3k87rh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=860&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Cassini shot this false-color image of jets erupting from the southern hemisphere of Enceladus on Nov. 27, 2005.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/mission_pages/cassini/media/saturn_sponge.html">NASA/JPL/Space Science Institute</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Below their thick layers of surface ice, both Europa and Enceladus have global oceans in which 4.5 billion years of churning of the primordial soup may have enabled life to develop and take root. NASA spacecraft have even imaged spectacular geysers ejecting plumes of water out into space from these subsurface oceans.</p>
<p>To find out if either moon has life, planetary scientists are actively developing the <a href="https://europa.nasa.gov/">Europa Clipper mission</a> for a 2020s launch. They also hope to plan future missions that will target Enceladus.</p>
<h2>Taking care to not contaminate</h2>
<p>Since the start of the space age, scientists have taken the threat of biological contamination of other worlds seriously. As early as 1959, NASA held meetings <a href="https://www.nasa.gov/connect/ebooks/when_biospheres_collide_detail.html">to debate the necessity of sterilizing spacecraft</a> that might be sent to other worlds. Since then, all planetary exploration missions have adhered to sterilization standards that balance their scientific goals with limitations of not damaging sensitive equipment, which could potentially lead to mission failures. Today, NASA protocols exist for the <a href="https://sma.nasa.gov/sma-disciplines/planetary-protection">protection of all solar system bodies</a>, including Mars.</p>
<p>Since avoiding the biological contamination of Europa and Enceladus is an extremely well-understood, high-priority requirement of all missions to the Jovian and Saturnian environments, their moons remain uncontaminated.</p>
<p>NASA’s <a href="https://solarsystem.nasa.gov/missions/galileo/overview/">Galileo mission explored Jupiter</a> and its moons from 1995 until 2003. Given Galileo’s orbit, the possibility existed that the spacecraft, once out of rocket propellant and subject to the whims of gravitational tugs from Jupiter and its many moons, could someday crash into and thereby contaminate Europa. </p>
<p>Such a collision might not occur until many millions of years from now. Nevertheless, though the risk was small, it was also real. NASA paid close attention to guidance from the <a href="https://www.nap.edu/initiative/committee-on-planetary-and-lunar-exploration">National Academies’ Committee on Planetary and Lunar Exploration</a>, which noted serious national and international objections to the possible accidental disposal of the Galileo spacecraft on Europa.</p>
<p>To completely eliminate any such risk, on Sept. 21, 2003, NASA used the last bit of fuel on the spacecraft to send it plunging into Jupiter’s atmosphere. At a speed of 30 miles per second, <a href="https://www.nasa.gov/vision/universe/solarsystem/galileo_final.html">Galileo vaporized within seconds</a>.</p>
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<figcaption><span class="caption">Cassini’s ‘Grand Finale’ ended with the spacecraft burning up in Saturn’s atmosphere.</span></figcaption>
</figure>
<p>Fourteen years later, NASA repeated this protect-the-moon scenario. The <a href="https://solarsystem.nasa.gov/missions/cassini/overview/">Cassini mission orbited and studied Saturn</a> and its moons from 2004 until 2017. On Sept. 15, 2017, when fuel had run low, on instructions from NASA Cassini’s operators deliberately <a href="https://saturn.jpl.nasa.gov/mission/about-the-mission/summary/">plunged the spacecraft into Saturn’s atmosphere</a>, where it disintegrated.</p>
<h2>But what about Mars?</h2>
<p>Mars is the target of <a href="https://mars.nasa.gov/#missions">seven active missions</a>, including two rovers, <a href="https://mars.nasa.gov/programmissions/missions/present/2003/">Opportunity</a> and <a href="https://mars.nasa.gov/msl/mission/mars-rover-curiosity-mission-updates/">Curiosity</a>. In addition, on Nov. 26 NASA’s <a href="https://mars.nasa.gov/insight/">InSight mission</a> is scheduled to land on Mars, where it will make measurements of Mars’ interior structure. Next, with planned 2020 launches, both ESA’s <a href="http://exploration.esa.int/mars/48088-mission-overview/">ExoMars rover</a> and NASA’s <a href="https://mars.nasa.gov/mars2020/">Mars 2020 rover</a> are designed to search for evidence of life on Mars.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/242772/original/file-20181029-76413-otea1r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/242772/original/file-20181029-76413-otea1r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/242772/original/file-20181029-76413-otea1r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=430&fit=crop&dpr=1 600w, https://images.theconversation.com/files/242772/original/file-20181029-76413-otea1r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=430&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/242772/original/file-20181029-76413-otea1r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=430&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/242772/original/file-20181029-76413-otea1r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=540&fit=crop&dpr=1 754w, https://images.theconversation.com/files/242772/original/file-20181029-76413-otea1r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=540&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/242772/original/file-20181029-76413-otea1r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=540&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Curiosity rover was tested under clean conditions on Earth before launch to prevent microbial stowaways.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/mission_pages/msl/msl20100913.html">NASA/JPL-Caltech</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
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<p>The good news is that robotic rovers pose little risk of contamination to Mars, since all spacecraft designed to land on Mars are subject to <a href="https://www.nasa.gov/missions/solarsystem/mer_clean.html">strict sterilization procedures before launch</a>. This has been the case since NASA imposed “rigorous sterilization procedures” for the <a href="https://mars.nasa.gov/programmissions/missions/past/viking/">Viking Lander Capsules</a> in the 1970s, since they would directly contact the Martian surface. These rovers likely have an extremely low number of microbial stowaways.</p>
<p>Any terrestrial biota that do manage to hitch rides on the outside of those rovers would have a very hard time surviving the half-year journey from Earth to Mars. The vacuum of space combined with exposure to harsh X-rays, ultraviolet light and cosmic rays would <a href="https://www.nasa.gov/connect/ebooks/when_biospheres_collide_detail.html">almost certainly sterilize the outsides of any spacecraft</a> sent to Mars.</p>
<p>Any bacteria that sneaked rides inside one of the rovers might arrive at Mars alive. But if any escaped, the <a href="https://www.space.com/16903-mars-atmosphere-climate-weather.html">thin Martian atmosphere</a> would offer virtually no protection from high energy, sterilizing radiation from space. Those bacteria would likely be killed immediately. Because of this harsh environment, life on Mars, if it currently exists, almost certainly must be hiding beneath the planet’s surface. Since no rovers have explored caves or dug deep holes, we have not yet had the opportunity to come face-to-drill-bit with any possible Martian microbes.</p>
<p>Given that the exploration of Mars has so far been limited to unmanned vehicles, the planet likely remains free from terrestrial contamination.</p>
<p>But when Earth sends astronauts to Mars, they’ll travel with life support and energy supply systems, habitats, 3D printers, food and tools. None of these materials can be sterilized in the same ways systems associated with robotic spacecraft can. Human colonists will produce waste, try to grow food and use machines to extract water from the ground and atmosphere. Simply by living on Mars, human colonists will contaminate Mars.</p>
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<h2>Can’t turn back the clock after contamination</h2>
<p>Space researchers have developed a careful approach to robotic exploration of Mars and a hands-off attitude toward Europa and Enceladus. Why, then, are we collectively willing to overlook the risk to Martian life of human exploration and colonization of the red planet?</p>
<p>Contaminating Mars isn’t an unforeseen consequence. A quarter century ago, a National Research Council report entitled <a href="https://doi.org/10.17226/12305">“Biological Contamination of Mars: Issues and Recommendations”</a> asserted that missions carrying humans to Mars will inevitably contaminate the planet. </p>
<p>I believe it’s critical that every attempt be made to obtain evidence of any past or present life on Mars well in advance of future missions to Mars that include humans. What we discover could influence our collective decision whether to send colonists there at all.</p>
<p>Even if we ignore or don’t care about the risks a human presence would pose to Martian life, the issue of bringing Martian life back to Earth has serious societal, legal and international implications that deserve discussion before it’s too late. What risks might Martian life pose to our environment or our health? And does any one country or group have the right to risk back contamination if those Martian lifeforms could attack the DNA molecule and thereby put all of life on Earth at risk?</p>
<p>But players both public – NASA, United Arab Emirates’ <a href="https://government.ae/en/more/uae-future/2030-2117">Mars 2117 project</a> – and private – <a href="https://www.spacex.com/mars">SpaceX</a>, <a href="https://www.mars-one.com">Mars One</a>, <a href="https://www.blueorigin.com">Blue Origin</a> – already plan to transport colonists to build cities on Mars. And these missions will contaminate Mars. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/242775/original/file-20181029-76399-1ozr59w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/242775/original/file-20181029-76399-1ozr59w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/242775/original/file-20181029-76399-1ozr59w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=312&fit=crop&dpr=1 600w, https://images.theconversation.com/files/242775/original/file-20181029-76399-1ozr59w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=312&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/242775/original/file-20181029-76399-1ozr59w.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=312&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/242775/original/file-20181029-76399-1ozr59w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=392&fit=crop&dpr=1 754w, https://images.theconversation.com/files/242775/original/file-20181029-76399-1ozr59w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=392&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/242775/original/file-20181029-76399-1ozr59w.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=392&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 hypothesize that dark narrow streaks were formed by briny liquid water – necessary for life – flowing down the walls of a crater on Mars.</span>
<span class="attribution"><a class="source" href="https://mars.nasa.gov/resources/7488/dark-recurring-streaks-on-walls-of-garni-crater/">NASA/JPL-Caltech/Univ. of Arizona</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p><a href="https://doi.org/10.1126/science.1165243">Some scientists believe they</a> <a href="https://doi.org/10.1126/science.aaq0131">have already uncovered</a> <a href="https://www.nasa.gov/press-release/nasa-finds-ancient-organic-material-mysterious-methane-on-mars">strong evidence for life on Mars</a>, both past and present. If life already exists on Mars, then Mars, for now at least, belongs to the Martians. Mars is their planet, and Martian life would be threatened by a human presence there.</p>
<p>Does humanity have an inalienable right to colonize Mars simply because we will soon be able to do so? We have the technology to use robots to determine whether Mars is inhabited. Do ethics demand that we use those tools to answer definitively whether Mars is inhabited or sterile before we put human footprints on the Martian surface?</p><img src="https://counter.theconversation.com/content/103053/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Weintraub 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>NASA’s InSight Mars lander touches down Nov. 26, part of a careful robotic approach to exploring the red planet. But human exploration of Mars will inevitably introduce Earth life. Are you OK with that?David Weintraub, Professor of Astronomy, Vanderbilt UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/988782018-06-27T08:49:36Z2018-06-27T08:49:36ZEight ethical questions about exploring outer space that need answers<figure><img src="https://images.theconversation.com/files/224917/original/file-20180626-112604-ieul2t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Blast off. </span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/space-exploration-background-mixed-media-519472267?src=Wf2opYG55d1aspAIUgTwwA-1-1">Sergey Nivens</a></span></figcaption></figure><p>Metallic shrapnel flying faster than bullets; the Space Shuttle smashed to pieces; astronauts killed or ejected into space. The culprit? Space debris – remnants of a Russian satellite blown up by a Russian missile. The one survivor, Ryan Stone, has to find her way back to Earth with oxygen supplies failing and the nearest viable spacecraft hundreds of miles away. </p>
<p>Over on Mars, 20 years in the future, an exploration mission from Earth is going wrong. An epic dust storm forces the crew to abandon the planet, leaving behind an astronaut, Mark Watney, who is presumed dead. He has to figure out how to grow food while awaiting rescue.</p>
<p>Hollywood knows how to terrify and inspire us about outer space. Movies like <a href="https://www.imdb.com/title/tt1454468/">Gravity</a> (2013) and <a href="https://www.imdb.com/title/tt3659388/">The Martian</a> (2015), present space as hostile and unpredictable – spelling danger for any intrepid human who dares to venture outside Earth’s hospitable confines.</p>
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<a href="https://images.theconversation.com/files/224919/original/file-20180626-112641-pvqd9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/224919/original/file-20180626-112641-pvqd9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/224919/original/file-20180626-112641-pvqd9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/224919/original/file-20180626-112641-pvqd9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/224919/original/file-20180626-112641-pvqd9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/224919/original/file-20180626-112641-pvqd9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/224919/original/file-20180626-112641-pvqd9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/224919/original/file-20180626-112641-pvqd9.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>
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<span class="caption">Matt Damon is …</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/san-francisco-november-4-2017-martian-748233988?src=0VXU797DRwWxNbcR53RzEg-1-24">Pe3k</a></span>
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<p>This is only part of the story, however – the bit with people centre stage. Sure, no one wants to see astronauts killed or stranded in space. And we all want to enjoy the fruits of successful planetary science, like determining <a href="https://theconversation.com/explainer-how-do-you-find-exoplanets-24153">which planets</a> could host human life or simply whether we’re alone in the universe. </p>
<h2>Valuing space</h2>
<p>But should we care about the universe beyond how it affects us as humans? That is the big question – call it question #1 of extraterrestrial environmental ethics, a field too many people have ignored for too long. I’m one of a <a href="http://ceppa.wp.st-andrews.ac.uk/research-projects/exoplanet-ethics/">group of researchers</a> at the University of St Andrews trying to change that. How we ought to value the universe depends on two other intriguing philosophical questions:</p>
<p>Question #2: the <a href="https://theconversation.com/if-we-are-to-find-life-beyond-earth-we-need-to-be-explorers-not-hunters-45001">kind of life</a> we are <a href="https://theconversation.com/the-hunt-for-life-on-mars-new-findings-on-rock-chimneys-could-hold-key-to-success-97998">most likely</a> to discover elsewhere is <a href="https://theconversation.com/our-rover-could-discover-life-on-mars-heres-what-it-would-take-to-prove-it-89625">microbial</a> – so how should we view this lifeform? Most people would accept that all humans have intrinsic value, and matter not only in relation to their usefulness to someone else. Accept this and it follows that ethics places limits on how we may treat them and their living spaces. </p>
<p>People are <a href="https://www.thoughtco.com/historical-timeline-of-animal-rights-movement-127594">starting to</a> accept that the same is true of mammals, birds and other animals. So what about microbial beings? Some philosophers like Albert Schweitzer and Paul Taylor <a href="https://study.com/academy/lesson/biocentrism-in-environmental-ethics.html">have previously argued</a> that all living things have a value in themselves, which would obviously include microbes. Philosophy as a whole has not reached a consensus, however, on whether it agrees with this so-called biocentrism. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/224920/original/file-20180626-112604-o8mju1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/224920/original/file-20180626-112604-o8mju1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/224920/original/file-20180626-112604-o8mju1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/224920/original/file-20180626-112604-o8mju1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/224920/original/file-20180626-112604-o8mju1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/224920/original/file-20180626-112604-o8mju1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/224920/original/file-20180626-112604-o8mju1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/224920/original/file-20180626-112604-o8mju1.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">‘What do we want, rights for microbes …’</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/abstract-background-germs-microorganism-cells-under-678600079?src=bXyBmuHE2IFDaxJmHHuiGw-1-72">Who is Danny</a></span>
</figcaption>
</figure>
<p>Question #3: for planets and other places not hospitable to life, what value should we place on their environment? Arguably we care about our environment on Earth primarily because it supports the species that live here. If so, we might extend the same thinking to other planets and moons that can support life. </p>
<p>But this doesn’t work for “dead” planets. Some <a href="https://www.sdcity.edu/Portals/0/CollegeServices/StudentSupportResources/learning-communities/Philosophical%20Problems%20for%20Environmentalism.pdf">have proposed</a> an idea called aesthetic value, that certain things should be treasured not because they are useful but because they are aesthetically wonderful. They have applied this not only to great artistic works like Leonardo da Vinci’s Mona Lisa and Beethoven’s Fifth, but also to parts of the Earth’s environment, such as the Grand Canyon. Could that apply to other planets?</p>
<h2>Alien environments</h2>
<p>Supposing we could answer these theoretical questions, we could proceed to four important practical questions about space exploration:</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/224918/original/file-20180626-112598-wvw5he.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/224918/original/file-20180626-112598-wvw5he.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/224918/original/file-20180626-112598-wvw5he.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=900&fit=crop&dpr=1 600w, https://images.theconversation.com/files/224918/original/file-20180626-112598-wvw5he.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=900&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/224918/original/file-20180626-112598-wvw5he.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=900&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/224918/original/file-20180626-112598-wvw5he.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1130&fit=crop&dpr=1 754w, https://images.theconversation.com/files/224918/original/file-20180626-112598-wvw5he.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1130&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/224918/original/file-20180626-112598-wvw5he.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1130&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Yip yip.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/airchinapilot/2976214346/in/photolist-5wZSQs-qwJXQw-jYhDZD-cUYaNo-9QLmcN-7Vp7gb-23rEPi6-pQsDne-e3jsXd-VVYcwy-HcbizT-aoyaja-aJfUvX-66F8Tb-4dFQWN-dfXGfd-dp8Q91-qLiH9e-7r8xkd-SBMDFe-aqYtky-88ydwt-u9PMJ9-qPiace-7Hdepi-pqa8Zf-71HcCo-8AReey-dPDrfQ-6RJSzV-TARcNo-5uuE5g-7BSzXq-9t292n-7FT2fV-bxxLKZ-suCumU-qvowFh-hE8nH3-dWCUsD-4MHChw-e6PhBG-65VZtc-Wk4V1N-23FUTEF-a6RkqQ-26t2Xsa-5QwbXY-tk4yk4-aJfVjp">Keith Loh</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Question #4: is there a duty to protect the environment on other planets? When it comes to sending astronauts, instruments or robots to other worlds, there are clearly important scientific reasons for <a href="https://theconversation.com/mars-contamination-planetary-protection-and-the-search-for-life-48363">making sure</a> they don’t take terrestrial organisms with them and wind up depositing them there. </p>
<p>Otherwise, if we discovered life, we wouldn’t know whether it was indigenous – not to mention the risk of wiping it out entirely. But is scientific clarity all that matters, or do we need to start thinking about galactic environmental protection?</p>
<p>Question #5: what, besides biological contamination, would count as violating such an obligation to treat that planet’s environment with respect? Drilling for core samples, perhaps, or leaving instruments behind, or putting tyre tracks in the dirt? </p>
<p>Question #6: what about asteroids? The race is well underway to develop technology to harvest the untold trillions of pounds of mineral wealth presumed to exist on asteroids, as <a href="https://theconversation.com/mining-asteroids-could-unlock-untold-wealth-heres-how-to-get-started-95675">already reported</a> in The Conversation. It helps that no one seems to think of asteroids as environments we need to protect. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/224922/original/file-20180626-112598-duxifc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/224922/original/file-20180626-112598-duxifc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/224922/original/file-20180626-112598-duxifc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=334&fit=crop&dpr=1 600w, https://images.theconversation.com/files/224922/original/file-20180626-112598-duxifc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=334&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/224922/original/file-20180626-112598-duxifc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=334&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/224922/original/file-20180626-112598-duxifc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=419&fit=crop&dpr=1 754w, https://images.theconversation.com/files/224922/original/file-20180626-112598-duxifc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=419&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/224922/original/file-20180626-112598-duxifc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=419&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Gold in them craters.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/asteroidal-landscape-strewn-rubble-starfield-horizon-3139158?src=wdDSfgAAOu05zbhRux2QBg-1-98">Jan Kaliciak</a></span>
</figcaption>
</figure>
<p>The same goes for empty space. The movie Gravity gave us some human-centred reasons to be worried about the buildup of <a href="https://theconversation.com/how-to-clean-up-space-debris-using-game-theory-50347">debris in space</a>, but might there be other reasons to object? If so, would our obligation be to merely create less debris, or something stronger – like not producing any new debris or even cleaning up what we’ve left already?</p>
<hr>
<p><em><strong>Read more: <a href="https://theconversation.com/the-seven-most-extreme-planets-ever-discovered-78959">The seven most extreme planets ever discovered</a></strong></em> </p>
<hr>
<p>Question #7: what considerations might offset arguments in favour of behaving ethically in space? Of the various reasons for going there – intellectual/scientific, utilitarian, profit-driven – are any strong enough to override our obligations? </p>
<p>We also need to factor in the inevitable risks and uncertainties here. We can’t know what benefits space missions will have. We can’t be certain of not biologically contaminating the planets we visit. What risk/reward trade-offs should we be willing to undertake?</p>
<h2>Terra-ism</h2>
<p>Discussions about outer space have the advantage that we have very little attachment to anything out there. These ethical questions might therefore be some of the only ones humans can address with a large measure of emotional distance. For this reason, answering them might help us to make progress with Earth-bound issues like global warming, mass extinction and nuclear waste disposal. </p>
<p>Space exploration also directly raises questions about our relationship to Earth – once we overcome the technological puzzles preventing <a href="https://www.universetoday.com/113346/how-do-we-terraform-mars/">the terraforming</a> of a planet like Mars, or find ways of reaching habitable exoplanets. I’ll leave you with one extremely important one for the future: </p>
<p>Question #8: given that the Earth is not the only potential home for human beings, what reasons for protecting its environment would remain once we can realistically go somewhere else?</p><img src="https://counter.theconversation.com/content/98878/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Benjamin Sachs receives funding from the Royal Society of Edinburgh.</span></em></p>Nearly 50 years since the first man walked on the moon, our morals are still stranded on Earth.Benjamin Sachs-Cobbe, Senior Lecturer in Philosophy, University of St AndrewsLicensed 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/867192017-11-01T14:52:36Z2017-11-01T14:52:36ZWhat evolutionary theory can teach us about the appearance of aliens<figure><img src="https://images.theconversation.com/files/192834/original/file-20171101-19850-1xw0u3e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Andrii Vodolazhskyi/Shutterstock</span></span></figcaption></figure><p>Aliens could be everywhere. There are at least 100 billion planets in our galaxy alone, and at least 20% of them <a href="https://theconversation.com/the-five-most-earth-like-exoplanets-so-far-50669">could be habitable</a>. Even if a tiny fraction of those planets – less than one percent of one percent – evolved life, there would still be tens of thousands of planets with aliens in our vicinity. But if we want to figure out where to start looking for these neighbours, we need to understand what they might be like and where they might thrive. </p>
<p>Ultimately, we want to understand as much as possible about an extraterrestrial species <a href="https://theconversation.com/how-to-tell-the-world-youve-discovered-an-alien-civilisation-60014">before we encounter it</a>. And yet, making predictions about aliens is hard. The reason is simple: we have only one example – life on Earth – <a href="https://theconversation.com/what-do-aliens-look-like-the-clue-is-in-evolution-63899">to extrapolate from</a>. Just because eyes and limbs have evolved many times on Earth doesn’t mean they’ll appear even once elsewhere. Just because we are made of carbon and coded by DNA doesn’t mean aliens will be – they could be silicon based and coded by “XNA”.</p>
<p>However, as my colleagues and I argue in our new study, <a href="https://doi.org/10.1017/S1473550417000362">published in the International Journal of Astrobiology</a>, there is another approach to making predictions about aliens that gets around this problem. That is to use evolutionary theory as a guiding principle. The theory of natural selection allows us to make predictions that don’t depend on the details of Earth, and so will hold even for eyeless, nitrogen-breathing aliens.</p>
<p>Darwin formulated his <a href="https://theconversation.com/the-five-most-common-misunderstandings-about-evolution-54845">theory of natural selection</a> long before we knew what DNA was, how mutations appeared, or even how traits were passed on. It is remarkably simple, and requires just a few ingredients to work: variation (some giraffes have longer necks than others), heritability of that variation (long-necked giraffes have long-necked babies) and differential success linked to the variation (long-necked giraffes eat more leaves and have more babies).</p>
<h2>Darwin’s aliens</h2>
<p>In our paper, we use evolutionary theory to make a number of predictions about aliens. First, we argue that aliens will undergo natural selection. This is something often either taken for granted or assumed to be an unknown. We show that there are firm theoretical grounds for believing that aliens will undergo (or have undergone) natural selection. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/192830/original/file-20171101-19853-1w5dzxj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/192830/original/file-20171101-19853-1w5dzxj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=444&fit=crop&dpr=1 600w, https://images.theconversation.com/files/192830/original/file-20171101-19853-1w5dzxj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=444&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/192830/original/file-20171101-19853-1w5dzxj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=444&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/192830/original/file-20171101-19853-1w5dzxj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=558&fit=crop&dpr=1 754w, https://images.theconversation.com/files/192830/original/file-20171101-19853-1w5dzxj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=558&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/192830/original/file-20171101-19853-1w5dzxj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=558&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Illustration of levels of complexity. A) A simple replicating molecule. B) Cell-like entity. C) An alien.</span>
<span class="attribution"><span class="source">Helen S. Cooper</span></span>
</figcaption>
</figure>
<p>This is because “apparent design” is what sets life apart from non-life – such as a single celled organism from inert rocks. Living things have many intricate parts fine tuned for the common purpose of replicating the organism. The only way to achieve this apparent design, or adaptedness, the only way to get life, is through natural selection.</p>
<p>So as aliens are highly likely to undergo natural selection, we can make some predictions about what they will be like. In particular, our predictions are about complex aliens. By complexity, we mean anything more complex than, say, a virus. </p>
<p>Even a bacterial cell has intricate parts that work together to achieve goals, like moving and eating. In other words, most “aliens” we would be interested in finding, or even able to find, are complex. That’s because the only things so simple that they could have arisen without natural selection would be molecules, which are both physically hard to detect and hard to distinguish from the background of inert molecules. They’d also be transient – without natural selection making them fitter they’d disappear. Even if we did find them, we probably wouldn’t even classify them as life.</p>
<p>Complexity on Earth has arisen through a handful of something called “major transitions in individuality”. These occur when independent organisms come together to form a new type of individual. On Earth, genes came together to form genomes, single celled organisms formed multi-cellular organisms, like us. In some rare cases, multi-cellular organisms, like insects, have formed societies that act as “super organisms” themselves. These events are rare, and require extreme evolutionary conditions to occur. </p>
<p>We argue that complex aliens will, too, have undergone major transitions, as this is likely the only way to advance beyond a simple replicating molecule. Because the conditions for major transitions to occur are rare, and because they are quite well understood from an evolutionary perspective, this allows us to say something about the makeup of aliens.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/192831/original/file-20171101-19853-o8a3qu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/192831/original/file-20171101-19853-o8a3qu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=448&fit=crop&dpr=1 600w, https://images.theconversation.com/files/192831/original/file-20171101-19853-o8a3qu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=448&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/192831/original/file-20171101-19853-o8a3qu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=448&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/192831/original/file-20171101-19853-o8a3qu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=563&fit=crop&dpr=1 754w, https://images.theconversation.com/files/192831/original/file-20171101-19853-o8a3qu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=563&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/192831/original/file-20171101-19853-o8a3qu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=563&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Illustration of a complex alien that comprises a hierarchy of entities, where each lower level collection of entities has aligned evolutionary interests.</span>
<span class="attribution"><span class="source">Helen S. Cooper</span></span>
</figcaption>
</figure>
<p>In particular, just as you and I are made up of cells which are made up of nuclei and mitochondria (the breathing engine of the cell) which are made up of genes, aliens will be a similar nested hierarchy of units. Aliens might not be made of “cells” as we think of them, but they will be made up of parts which were once free living, and those parts in turn will be too – all the way down to the aliens’ hereditary material (whatever it is). Our parts have mechanisms in place that keep all the parts working together to make an organism. </p>
<p>For example, our cells all <a href="https://en.wikipedia.org/wiki/Zygote">start as one single cell</a> (the “zygote”), and this means all our cells are clones, which is why they cooperate to make us. Aliens will have similar ways of enforcing cooperation between their internal parts, at each level of units.</p>
<p>Aliens may not have two legs, or any legs at all, but their structure, from an evolutionary standpoint, will be much more familiar than we might have thought. By familiar, I don’t mean superficially familiar. They may look, on the surface, wildly different from anything on Earth. But they will be similar on a more fundamental level: their bodies will be constructed in the same way (formerly free-living parts within formerly free-living parts), and they will have undergone a similar evolutionary history (independent organisms cooperating to form new, higher level organisms).</p>
<p>There is much more work to be done to understand what aliens might be like and where we might find them. And the tantalising question – “Are we alone?” – remains unanswered. But, as we have shown, if we’re not alone, perhaps we understand more about the makeup of our neighbours than science fiction would have us believe.</p><img src="https://counter.theconversation.com/content/86719/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Samuel Levin receives funding from NERC, Hertford College, and The Clarendon Fund. </span></em></p>Aliens are highly likely to undergo natural selection, shows new research.Samuel Levin, PhD candidate in Zoology, University of OxfordLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/847422017-09-29T02:35:41Z2017-09-29T02:35:41ZWorries about spreading Earth microbes shouldn’t slow search for life on Mars<figure><img src="https://images.theconversation.com/files/188019/original/file-20170928-2939-1iwisqx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Viking landers in the 1970s were the last to look directly for life on Mars.</span> <span class="attribution"><a class="source" href="https://images.nasa.gov/#/details-PIA00382.html">NASA/JPL</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>There may be no bigger question than whether we are alone in our solar system. As our spacecraft find new clues about the presence of liquid water now or in the past on Mars, the possibility of some kind of life there looks more likely. On Earth, water means life, and that’s why the exploration of Mars is guided by the idea of following the water.</p>
<p>But the search for life on Mars is paired with plenty of strong warnings about how we must sterilize our spacecraft to avoid contaminating our neighbor planet. How will we know what’s native Martian if we unintentionally seed the place with Earth organisms? A popular analogy points out that Europeans unknowingly brought smallpox to the New World, and they took home syphilis. Similarly, it is argued, our robotic explorations could contaminate Mars with terrestrial microorganisms.</p>
<p>As an astrobiologist who researches the environments of early Mars, I suggest these arguments are misleading. The current danger of contamination via unmanned robots is actually quite low. But contamination <a href="https://doi.org/10.1089/ast.2017.1703">will become unavoidable once astronauts get there</a>. <a href="https://www.nasa.gov/content/journey-to-mars-overview">NASA</a>, other agencies and the <a href="http://www.spacex.com/mars">private sector</a> hope to send <a href="https://www.nytimes.com/2017/09/28/science/elon-musk-mars.html">human missions to Mars by the 2030s</a>.</p>
<p>Space agencies have long prioritized preventing contamination over our hunt for life on Mars. Now is the time to reassess and update this strategy – before human beings get there and inevitably introduce Earth organisms despite our best efforts.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/188026/original/file-20170928-1449-h7tdl9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/188026/original/file-20170928-1449-h7tdl9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/188026/original/file-20170928-1449-h7tdl9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=449&fit=crop&dpr=1 600w, https://images.theconversation.com/files/188026/original/file-20170928-1449-h7tdl9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=449&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/188026/original/file-20170928-1449-h7tdl9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=449&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/188026/original/file-20170928-1449-h7tdl9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=564&fit=crop&dpr=1 754w, https://images.theconversation.com/files/188026/original/file-20170928-1449-h7tdl9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=564&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/188026/original/file-20170928-1449-h7tdl9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=564&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Microbiologists frequently collect swab samples from the floor of clean rooms during spacecraft assembly.</span>
<span class="attribution"><a class="source" href="https://images.nasa.gov/#/details-PIA17368.html">NASA/JPL-Caltech</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>What planetary protection protocols do</h2>
<p>Arguments calling for extra caution have permeated Mars exploration strategies and led to the creation of specific guiding policies, known as <a href="https://planetaryprotection.nasa.gov/">planetary protection</a> protocols. </p>
<p>Strict cleaning procedures are required on our spacecraft before they’re allowed to sample regions on Mars which could be a habitat for microorganisms, either native to Mars or brought there from Earth. These areas are labeled by the planetary protection offices as “<a href="https://www.nap.edu/catalog/21816/review-of-the-mepag-report-on-mars-special-regions">Special Regions</a>.”</p>
<p>The worry is that, otherwise, terrestrial invaders could jeopardize potential Mars life. They also could confound future researchers trying to distinguish between any indigenous Martian life forms and life that arrived as contamination from Earth via today’s spacecraft. </p>
<p>The sad consequence of these policies is that the multi-billion-dollar Mars spacecraft programs run by <a href="https://mars.nasa.gov/programmissions/overview/">space</a> <a href="http://exploration.esa.int/mars/44997-the-red-planet/">agencies</a> in the West have not proactively looked for life on the planet since the late 1970s.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/188014/original/file-20170928-1438-4xut2s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/188014/original/file-20170928-1438-4xut2s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/188014/original/file-20170928-1438-4xut2s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=403&fit=crop&dpr=1 600w, https://images.theconversation.com/files/188014/original/file-20170928-1438-4xut2s.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=403&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/188014/original/file-20170928-1438-4xut2s.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=403&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/188014/original/file-20170928-1438-4xut2s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=506&fit=crop&dpr=1 754w, https://images.theconversation.com/files/188014/original/file-20170928-1438-4xut2s.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=506&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/188014/original/file-20170928-1438-4xut2s.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=506&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Dr. Carl Sagan poses with a model of the Viking lander in Death Valley, California.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/sites/default/files/images/151106main_image_feature_599_ys_full.jpg">NASA</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>That’s when NASA’s Viking landers made the only attempt ever to find life on Mars (or on any planet outside Earth, for that matter). They carried out specific biological experiments looking for evidence of microbial life. Since then, that incipient biological exploration has shifted to less ambitious geological surveys that try to demonstrate only that Mars was “<a href="https://mars.nasa.gov/msl/mission/science/objectives/">habitable</a>” in the past, meaning it had conditions that could likely support life.</p>
<p>Even worse, if a dedicated life-seeking spacecraft ever does get to Mars, planetary protection policies will allow it to search for life everywhere on the Martian surface, except in the very places we suspect life may exist: the Special Regions. The concern is that exploration could contaminate them with terrestrial microorganisms.</p>
<h2>Can Earth life make it on Mars?</h2>
<p>Consider again the Europeans who first journeyed to the New World and back. Yes, smallpox and syphilis traveled with them, between human populations, living inside warm bodies in temperate latitudes. But that situation is irrelevant to Mars exploration. Any analogy addressing possible biological exchange between Earth and Mars must consider the absolute contrast in the planets’ environments.</p>
<p>A more accurate analogy would be bringing 12 Asian tropical parrots to the Venezuelan rainforest. In 10 years we may very likely have an invasion of Asian parrots in South America. But if we bring the same 12 Asian parrots to Antarctica, in 10 hours we’ll have 12 dead parrots.</p>
<p>We’d assume that any indigenous life on Mars should be much better adapted to Martian stresses than Earth life is, and therefore would outcompete any possible terrestrial newcomers. Microorganisms on Earth have evolved to thrive in challenging environments like salt crusts in the Atacama desert or hydrothermal vents on the deep ocean floor. In the same way, we can imagine any potential Martian biosphere would have experienced enormous evolutionary pressure during billions of years to become expert in inhabiting <a href="http://online.liebertpub.com/doi/abs/10.1089/ast.2015.1380">Mars’ today environments</a>. The microorganisms hitchhiking on our spacecraft wouldn’t stand much of a chance against super-specialized Martians in their own territory.</p>
<p>So if Earth life cannot survive and, most importantly, reproduce on Mars, concerns going forward about our spacecraft contaminating Mars with terrestrial organisms are unwarranted. This would be the parrots-in-Antarctica scenario.</p>
<p>On the other hand, perhaps Earth microorganisms can, in fact, survive and create active microbial ecosystems on present-day Mars – the parrots-in-South America scenario. We can then presume that terrestrial microorganisms are already there, carried by any one of the dozens of spacecraft sent from Earth in the last decades, or by the natural exchange of rocks pulled out from one planet by a meteoritic impact and transported to the other. </p>
<p>In this case, protection protocols are overly cautious since contamination is already a fact.</p>
<h2>Technological reasons the protocols don’t make sense</h2>
<p>Another argument to soften planetary protection protocols hinges on the fact that current sterilization methods don’t actually “sterilize” our spacecraft, a feat engineers still don’t know how to accomplish definitively.</p>
<p>The cleaning procedures we use on our robots rely on pretty much the same stresses prevailing on the Martian surface: oxidizing chemicals and radiation. They end up killing only those microorganisms with no chance of surviving on Mars anyway. So current cleaning protocols are essentially conducting an artificial selection experiment, with the result that we carry to Mars only the most hardy microorganisms. This should put into question the whole cleaning procedure.</p>
<p>Further, technology has advanced enough that distinguishing between Earthlings and Martians is no longer a problem. If Martian life is biochemically similar to Earth life, we could sequence genomes of any organisms located. If they don’t match anything we know is on Earth, we can surmise it’s native to Mars. Then we could add Mars’ creatures to the tree of DNA-based life we already know, probably somewhere on its lower branches. And if it is different, we would be able to identify such differences based on its building blocks.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/188023/original/file-20170928-22252-1wes7l6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/188023/original/file-20170928-22252-1wes7l6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/188023/original/file-20170928-22252-1wes7l6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=473&fit=crop&dpr=1 600w, https://images.theconversation.com/files/188023/original/file-20170928-22252-1wes7l6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=473&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/188023/original/file-20170928-22252-1wes7l6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=473&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/188023/original/file-20170928-22252-1wes7l6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=594&fit=crop&dpr=1 754w, https://images.theconversation.com/files/188023/original/file-20170928-22252-1wes7l6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=594&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/188023/original/file-20170928-22252-1wes7l6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=594&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Bacterial species <em>Tersicoccus phoenicis</em> is found in only two places: clean rooms in Florida and South America where spacecraft are assembled for launch.</span>
<span class="attribution"><a class="source" href="https://images.nasa.gov/#/details-PIA17369.html">NASA/JPL-Caltech</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Mars explorers have yet another technique to help differentiate between Earth and Mars life. The microbes <a href="https://doi.org/10.1089/ast.2012.0906">we know persist in clean spacecraft assembly rooms</a> provide an excellent control with which to monitor potential contamination. Any microorganism found in a Martian sample identical or highly similar to those present in the clean rooms would very likely indicate contamination – not indigenous life on Mars.</p>
<h2>The window is closing</h2>
<p>On top of all these reasons, it’s pointless to split hairs about current planetary protection guidelines as applied to today’s unmanned robots since human explorers are on the horizon. <a href="https://doi.org/10.1016/j.actaastro.2009.08.015">People would inevitably bring microbial hitchhikers with them</a>, because we cannot sterilize humans. Contamination risks between robotic and manned missions are simply not comparable. </p>
<p>Whether the microbes that fly with humans will be able to last on Mars is a separate question – though their survival is probably assured if they stay within a spacesuit or a human habitat engineered to preserve life. But no matter what, they’ll definitely be introduced to the Martian environment. Continuing to delay the astrobiological exploration of Mars now because we don’t want to contaminate the planet with microorganisms hiding in our spacecrafts isn’t logical considering astronauts (and their microbial stowaways) may arrive within two or three decades.</p>
<p>Prior to landing humans on Mars or bringing samples back to Earth, it makes sense to determine whether there is indigenous Martian life. What might robots or astronauts encounter there – and import to Earth? More knowledge now will increase the safety of Earth’s biosphere. After all, we still don’t know if returning samples could endanger humanity and the terrestrial biosphere. Perhaps reverse contamination should be our big concern.</p>
<p>The main goal of Mars exploration should be to try to find life on Mars and address the question of whether it is a separate genesis or shares a common ancestor with life on Earth. In the end, if Mars is lifeless, maybe we are alone in the universe; but if there is or was life on Mars, then there’s a zoo out there.</p><img src="https://counter.theconversation.com/content/84742/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Alberto G. Fairén receives funding from the European Research Council.</span></em></p>Planetary protection protocols try to make sure we don’t seed places like Mars with life from our planet. An astrobiologist argues they’re misguided – especially with human astronauts on the horizon.Alberto G. Fairén, Research Scientist at Centro de Astrobiología, Spain, and Visiting Scientist in Astronomy, Cornell UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/796972017-06-26T08:10:35Z2017-06-26T08:10:35ZHelp us find out what our possibly habitable exoplanet neighbour is actually like<figure><img src="https://images.theconversation.com/files/174676/original/file-20170620-24868-k3gv2a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Artist's impression of Proxima Centauri b.</span> <span class="attribution"><span class="source">ESO/M. Kornmesser</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>There was a lot of excitement when <a href="https://theconversation.com/possibly-habitable-planet-found-around-our-nearest-neighbour-star-64321?sr=1">Proxima b was discovered</a> – a potentially habitable exoplanet around our nearest neighbour star, Proxima Centauri. Located a mere 4.24 light years away, we may actually be able to send <a href="https://theconversation.com/why-sailing-to-the-stars-has-suddenly-become-a-realistic-goal-57762">tiny robots there in the next few decades</a>. And now you can help lead the way.</p>
<p>While a lot of work has been done to try to figure out what this world might be like, the follow up campaign of observations is only now getting under way. Excitingly, you can be a part of it.</p>
<p>The original discovery of Proxima b in 2016 came from a campaign led by my colleagues, called Pale Red Dot. This used the <a href="http://www.eso.org/sci/facilities/lasilla/instruments/harps.html">High Accuracy Radial velocity Planet Searcher (HARPS)</a>, an instrument on the European Southern Observatory’s 3.6-metre <a href="http://www.eso.org/public/unitedkingdom/teles-instr/lasilla/">La Silla telescope</a>, for 60 days in early 2016. This measured the “spectrum” of light (the breakdown of light by colour or equivalently frequency) emitted from Proxima Centauri, allowing astronomers to look for small changes in the frequencies of its features due to the star’s motion. An oscillation in that star’s motion can reveal the gravitational tug of an orbiting planet on its star.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/135140/original/image-20160823-30238-13grujs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/135140/original/image-20160823-30238-13grujs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=636&fit=crop&dpr=1 600w, https://images.theconversation.com/files/135140/original/image-20160823-30238-13grujs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=636&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/135140/original/image-20160823-30238-13grujs.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=636&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/135140/original/image-20160823-30238-13grujs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=799&fit=crop&dpr=1 754w, https://images.theconversation.com/files/135140/original/image-20160823-30238-13grujs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=799&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/135140/original/image-20160823-30238-13grujs.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=799&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A view of the southern skies with images of the stars Proxima Centauri (lower-right) and the double star Alpha Centauri AB (lower-left) from the NASA/ESA Hubble Space Telescope.</span>
<span class="attribution"><span class="source">Y. Beletsky (LCO)/ESO/ESA/NASA/M. Zamani</span></span>
</figcaption>
</figure>
<p>The new campaign, <a href="https://reddots.space/">called Red Dots</a>, will take 90 more days of data from Proxima Centauri and two other nearby stars: <a href="http://www.solstation.com/stars/barnards.htm">Barnard’s Star</a> and <a href="https://en.wikipedia.org/wiki/Ross_154">Ross 154</a>. By gathering more data the team hope to find out more about Proxima b, greatly improving the accuracy of our measurements so far. While we know it lies in the star’s habitable zone, where liquid water could be present on the planet’s surface (and hence life could exist), we don’t know very much about the shape of the planet’s orbit, for instance. </p>
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<p>All we can say at the moment is that it could be anywhere between being perfectly circular to as elliptical as Pluto’s journey around the sun. This small detail may have great consequences for whether the planet is “tidally locked” to the star – meaning one side always facing the star in perpetual day and the other in unending darkness. This obviously has a huge impact on surface temperatures. These details will be especially important if there is an atmosphere and oceans. However, it will take space telescopes, such as the planned <a href="https://theconversation.com/how-hubbles-successor-will-give-us-a-glimpse-into-the-very-first-galaxies-45970?sr=2">James Webb Space Telescope</a>, or much larger ground-based telescopes, like the upcoming instruments on the <a href="http://www.eso.org/public/unitedkingdom/teles-instr/paranal-observatory/vlt/">Very Large Telescope</a>, to answer these questions with actual observations. </p>
<h2>More neighbours?</h2>
<p>The new campaign may also find brother or sister planets to Proxima b. This isn’t just a pipe dream, the data collected so far shows some evidence towards at least another planet possibly being present. Indeed, the calculations suggest we can’t rule out several additional Earth-like planets or planets that are similar to Earth but bigger, as these wouldn’t destabilise Proxima b’s orbit.</p>
<p>Any cousins to Proxima b around the other two stars being observed will really push our ability to detect exoplanets around such small, dim and variable stars known as <a href="https://www.space.com/23772-red-dwarf-stars.html">red dwarfs</a>. Barnard’s Star rotates very rapidly, about once every three days, and Ross 154 is much more active than Proxima Centauri. Both of these features will add to the complications of correctly identifying planets as there will be many spurious effects which could show up in the data.</p>
<p>So where do you come in? Well there are two ways you can get involved. All the data is being made available almost as soon as it comes in – so there’s the opportunity for you to try and answer some of these outstanding questions yourself. Using the toolkits provided, you can search for signals in the data corresponding to potential planets and make fits to find out their properties. Alternatively, if you operate your own telescope there’s a chance to contribute your own Proxima Centauri data throughout the campaign by proposing and taking measurements of the star and uploading them to <a href="https://reddots.space/">the Red Dots website</a>.</p>
<p>But if those sound like a bit too much effort, Red Dots will simply allow you to see the science as it happens rather than just hearing about the results at the end. Given the excitement that I got to witness behind the scenes throughout the Pale Red Dot campaign, I think it’s great that you can be a part of this new one.</p><img src="https://counter.theconversation.com/content/79697/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Martin Archer 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>You may even be able to find other planets around the star closest to our solar system.Martin Archer, Space Plasma Physicist, Queen Mary University of LondonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/783632017-05-30T12:32:56Z2017-05-30T12:32:56ZVenus has very few volcanoes – weirdly, this might be why it’s as hot as hell<figure><img src="https://images.theconversation.com/files/171352/original/file-20170529-25201-1hlmaaj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/3d-renderingvenus-resolution-best-quality-solar-580798888?src=cvbKNLlwMuWNBXqY1Qi-cg-3-90">MAX3D</a></span></figcaption></figure><p>In the quest to discover habitable planets, scientists look for qualities similar to those of Earth. We do this because Earth sustains life, of course, but it falls down when you consider Venus. Based on size, chemistry and position in the solar system, our neighbouring planet is the most Earth-like ever observed. Yet while Earth is the definition of habitable, the planet Venus is a barren, hot, hellish wasteland. </p>
<p>Geologists like myself are trying to understand why two almost identical planets became so different. This is one way we can assist the astrophysics community in the exciting hunt for habitable exoplanets. A key part of the puzzle is understanding the interplay between plate tectonics and volcanoes, since <a href="https://theconversation.com/how-the-air-we-breathe-was-created-by-earths-tectonic-plates-33278">this governs</a> the <a href="https://www.nature.com/ngeo/journal/v10/n5/full/ngeo2939.html">chemistry</a> of the air that supports life. </p>
<p>I have been part of a research collaboration to look at Venus’ volcanic history, the results of which have <a href="http://www.sciencedirect.com/science/article/pii/S0031920116301418">just been published</a> in the journal Physics of the Earth and Planetary Interiors. This study sheds some valuable light on the volcanic history of Earth’s sibling, and indirectly speaks towards how Venus became so hot in the first place. </p>
<p>The starting point to understanding Venus is the climate. The average surface temperature is 460°C – far too hot for liquid water and above the <a href="http://www.bbc.co.uk/earth/story/20160209-this-is-how-to-survive-if-you-spend-your-life-in-boilin-water">known thermal limit</a> for life, which is roughly 122°C. </p>
<p>This extreme heat is not simply because Venus is closer to the Sun, but also because it is enveloped by an über-greenhouse atmosphere. At 92 times the pressure of that on Earth, it’s enough to crush modern submarines. If you were standing on the Venusian surface it would be like swimming 1,000 metres below sea level – if the oceans were 460°C, that is. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/171350/original/file-20170529-25203-te8f7z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/171350/original/file-20170529-25203-te8f7z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/171350/original/file-20170529-25203-te8f7z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/171350/original/file-20170529-25203-te8f7z.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/171350/original/file-20170529-25203-te8f7z.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/171350/original/file-20170529-25203-te8f7z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/171350/original/file-20170529-25203-te8f7z.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/171350/original/file-20170529-25203-te8f7z.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">It ain’t half hot, mum.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/smile-crazy-scuba-diver-underwater-selfie-517820569?src=_2NAPKyoHbIWerQe60NRbw-1-85">Andrea Izzotti</a></span>
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<p>The scorching temperature of Venus’s surface has many knock-on effects. It means, for example, that there’s no Earth-like plate tectonics. Most of the crust is too soft to snap, and it “<a href="https://www.nature.com/nature/journal/v508/n7497/full/nature13072.html">heals</a>” when broken. There have recently been suggestions that the planet might either have its <a href="http://www.nature.com/ngeo/journal/v10/n5/full/ngeo2928.html">own alternative version</a> of plate tectonics, <a href="http://www.sciencedirect.com/science/article/pii/S0032063315000409">or that</a> the high surface temperature results in the Venusian crust being physically decoupled from mantle flow beneath. At any rate, where plate tectonics <a href="http://www.sciencedirect.com/science/article/pii/B9780123964533000010">is behind</a> 90% of volcanic eruptions on Earth, this is not the case on Venus. </p>
<p>Venus does have volcanoes, but they’re all of the variety we call <a href="https://www.britannica.com/science/intraplate-volcanism">intra-plate or hotspots</a>, where plumes of magma rise up from the mantle and push their way to the surface via cracks in the crust. To study them, we compared them to the ones on Earth. We only considered volcanoes situated on Earth’s oceanic crust, since it is more comparable to the Venusian crust. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/171355/original/file-20170529-25203-i4zq4o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/171355/original/file-20170529-25203-i4zq4o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/171355/original/file-20170529-25203-i4zq4o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=410&fit=crop&dpr=1 600w, https://images.theconversation.com/files/171355/original/file-20170529-25203-i4zq4o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=410&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/171355/original/file-20170529-25203-i4zq4o.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=410&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/171355/original/file-20170529-25203-i4zq4o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=516&fit=crop&dpr=1 754w, https://images.theconversation.com/files/171355/original/file-20170529-25203-i4zq4o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=516&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/171355/original/file-20170529-25203-i4zq4o.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=516&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Kilauea in Hawaii, one of Earth’s hotspot volcanoes.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Kīlauea#/media/File:Puu_Oo_cropped.jpg">Wikimedia</a></span>
</figcaption>
</figure>
<p>The oceanic crust covers 60% of Earth’s surface. It is host to more than 100,000 hotspot volcanoes that have formed in less than 100m years. Conversely, Venus’ entire surface has produced only 70,000 individual volcanoes over a period of some 700m years (give or take 300m) – roughly the age of its outer crust. In other words, the difference in the rate of intra-plate volcano production is roughly ten times. (And bear in mind this is a comparison against only a small minority of the total number of volcanoes on Earth since it was formed.) </p>
<h2>Time travelling with argon</h2>
<p>To investigate whether Venus was always so volcanically challenged over its approximately 4.6 billion-year history, we called on the services of argon (Ar). This noble gas comes in three “flavours”, each with a slightly different mass (36, 38 and 40). We know that when Venus and Earth formed, 99% of their argon-36 and argon-38 quickly ended up in the air. </p>
<p>On the other hand, the argon-40 was only able to emerge slowly from the decay of an isotope of potassium that is stored in rocks. To find its way into the air, it then needed a mechanism to transport it there – the most efficient being volcanism. Because Earth’s atmosphere nowadays contains significantly more argon-40 than Venus’s, we can therefore assume Venus has been less volcanically active for its entire existence. </p>
<p>This conclusion probably sounds counter-intuitive – you might expect a hotter planet to be more volcanically active, not less so. When we studied this using rock deformation data, we found a similar phenomenon to the one that prevents plate tectonics on Venus. Because the crust is more like Play-Doh than the toffee brittle of Earth’s crust, it is difficult for magma to move through cracks and form volcanoes. On Venus, we predict, that most magma gets stuck in the Play-Doh – as you can see from the diagram below. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/171347/original/file-20170529-25236-1yqojwt.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/171347/original/file-20170529-25236-1yqojwt.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/171347/original/file-20170529-25236-1yqojwt.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=282&fit=crop&dpr=1 600w, https://images.theconversation.com/files/171347/original/file-20170529-25236-1yqojwt.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=282&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/171347/original/file-20170529-25236-1yqojwt.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=282&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/171347/original/file-20170529-25236-1yqojwt.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=355&fit=crop&dpr=1 754w, https://images.theconversation.com/files/171347/original/file-20170529-25236-1yqojwt.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=355&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/171347/original/file-20170529-25236-1yqojwt.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=355&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
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<p>Incidentally, this lack of argon-40 in Venus’ atmosphere also probably explains why the planet has never had oceans. This is because the decaying potassium-40 that produces argon-40 exists within silicate minerals. Importantly, the crystal structure of silicate minerals also contains hydroxide anions, which is essentially water. </p>
<p>Indeed, the silicate mantles of both planets <a href="https://deepcarbon.net/feature/water-earth%E2%80%99s-transition-zone-directly-measured#.WSxiwTOZPeQ">can store</a> more than six times the mass of water present in Earth’s oceans. In other words, Earth’s volcanoes not only pumped out life-giving air, but also our oceans. </p>
<p>Furthermore, the great difference in the number of volcanoes may explain the runaway greenhouse effect on Venus. This is because fresh basalt exposed by volcanic eruptions can react with liquid water through a series of chemical reactions known as <a href="http://science.sciencemag.org/content/344/6182/373">carbonation</a> to remove carbon dioxide from the atmosphere. It is an excess of carbon dioxide that is responsible for the greenhouse effect. In short, it is no exaggeration to suggest that volcanoes may explain most of the fundamental differences between Earth and Venus. </p>
<p>For those of us at the <a href="https://www.st-andrews.ac.uk/exoplanets/index.html">St Andrews Centre for Exoplanet Science</a>, we’ll now return to the big picture. We aim to shed more light on how planets become habitable, and how to spot an Earth from a Venus at a distance so great it’s measured in light years. It’s certainly difficult doing this from Earth, but with a great set of PhD students, postdoctoral fellows and an open mind, I am confident we will get to the bottom of it.</p><img src="https://counter.theconversation.com/content/78363/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Sami Mikhail receives funding from the Natural Environment Research Council (NE/P012167/1).</span></em></p>The planet is more similar to Earth than any other – except when it comes to supporting life.Sami Mikhail, Lecturer in Earth Sciences and Environmental Sciences & the Center for Exoplanet Science, University of St AndrewsLicensed as Creative Commons – attribution, no derivatives.