tag:theconversation.com,2011:/id/topics/europa-14808/articlesEuropa – The Conversation2024-03-28T12:50:48Ztag:theconversation.com,2011:article/2257712024-03-28T12:50:48Z2024-03-28T12:50:48ZNASA’s mission to an ice-covered moon will contain a message between water worlds<figure><img src="https://images.theconversation.com/files/584594/original/file-20240326-30-7p4fl7.jpg?ixlib=rb-1.1.0&rect=7%2C8%2C1191%2C1212&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An illustration of the Europa Clipper spacecraft, which will head to Jupiter's moon Europa. </span> <span class="attribution"><a class="source" href="https://europa.nasa.gov/resources/173/europa-clipper-journey-to-an-ocean-world-poster/">NASA/JPL-Caltech</a></span></figcaption></figure><p>NASA’s <a href="https://europa.nasa.gov/">Europa Clipper</a> spacecraft, <a href="https://theconversation.com/jupiters-moons-hide-giant-subsurface-oceans-two-missions-are-sending-spacecraft-to-see-if-these-moons-could-support-life-203207">headed to Jupiter’s ice-covered moon</a> Europa in October 2024, will carry <a href="https://europa.nasa.gov/spacecraft/vault-plate/">a laser-etched message</a> that celebrates humanity’s connection to water. The message pays homage to past NASA missions that carried similar messages. </p>
<p>As <a href="https://meti.org/en/board/douglas-vakoch">the president</a> of <a href="https://meti.org/mission">Messaging Extraterrestrial Intelligence, or METI, International</a>, I helped design the message on Clipper with two fellow members of our board of directors: linguists <a href="https://meti.org/en/board/sheri-wells-jensen">Sheri Wells-Jensen</a> and <a href="https://longnow.org/people/laura/">Laura Buszard-Welcher</a>. METI International is a scientific organization dedicated to transmitting powerful radio messages to extraterrestrial life.</p>
<p>We collected audio recordings in 103 languages, and we decided how to <a href="https://europa.nasa.gov/spacecraft/vault-plate/#otp_waveform_generator">convert these into waveforms</a> that show these sounds visually. Colleagues from NASA etched these waveforms into the metal plate that shields the spacecraft’s sensitive electronics from <a href="https://www.astronomy.com/science/what-is-the-source-of-jupiters-radiation/">Jupiter’s harsh radiation</a>. </p>
<p>I also designed another part of the message that visually depicts the wavelengths of water’s constituents, because water is so important to the search for intelligent life in the universe. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/8coGQ9kvBas?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">NASA’s design for the Clipper message heading to Jupiter’s moon Europa.</span></figcaption>
</figure>
<p>Etching messages into spacecraft isn’t a new practice, and Clipper’s message fits into a decades-old tradition started by <a href="https://www.britannica.com/biography/Carl-Sagan">astronomer Carl Sagan</a>.</p>
<p>In 1972 and 1973, two Pioneer spacecraft headed to Jupiter and Saturn carrying metal plaques engraved with scientific and pictorial messages. In 1977, two <a href="https://theconversation.com/what-the-voyager-space-probes-can-teach-humanity-about-immortality-and-legacy-as-they-sail-through-space-for-trillions-of-years-177513">Voyager spacecraft</a> headed to Jupiter, Saturn, Uranus and Nepture bearing <a href="https://theconversation.com/voyager-golden-records-40-years-later-real-audience-was-always-here-on-earth-79886">gold-plated copper phonograph records</a>. These records contained tutorials in mathematics and chemistry, as well as music, photos and sounds of Earth and greetings in 55 languages.</p>
<h2>Water words</h2>
<p>As water is essential for life on Earth, searching for its presence elsewhere has been key to many NASA missions. Astronomers <a href="https://science.nasa.gov/jupiter/moons/europa/">suspect that Europa</a>, where Clipper is headed, <a href="https://theconversation.com/jupiters-moons-hide-giant-subsurface-oceans-two-missions-are-sending-spacecraft-to-see-if-these-moons-could-support-life-203207">has an ocean underneath its icy surface</a>, making it a prime candidate for the search for life in the outer solar system.</p>
<p>Part of the Clipper message features the word for water in 103 languages. We started with audio files collected online, but we then needed to analyze those and find an output that could be engraved on a metal plate. I ended up going back to some of the techniques I used in some of my early psycholinguistic research, where I explored how <a href="https://doi.org/10.1121/1.408973">emotions are encoded in speech</a>.</p>
<p>The 103 spoken words we recorded represent a global snapshot of the diversity of Earth’s languages. The outward-facing side of the Clipper plate shows the words as waveforms that track the varying intensity of sound as each word is spoken. </p>
<p>Each person whom we recorded saying the word “water” for the waveform had a connection to water. For example, the lawyer who contributed the word for water in Uzbek – “suv” – organizes an annual music festival in Uzbekistan to raise awareness of the desertification of the Aral Sea. </p>
<p>The native speaker of the Catalan water word – “aigua” – hunts <a href="https://theconversation.com/nasas-tess-spacecraft-is-finding-hundreds-of-exoplanets-and-is-poised-to-find-thousands-more-122104">for exoplanets</a>, discovering potentially habitable planets that orbit other stars. </p>
<h2>The Drake Equation</h2>
<p>Clipper’s message also pays homage to <a href="https://www.seti.org/frank-drake">astronomer Frank Drake</a>, the father of SETI – <a href="https://www.seti.org/">the Search for Extraterrestrial Intelligence</a> – by bearing <a href="https://www.seti.org/drake-equation-index">the Drake Equation</a>, his namesake formula. By drawing on scientific data, as well as some best guess hunches, the Drake Equation estimates the number of extraterrestrial civilizations in the galaxy currently sending messages into the cosmos. </p>
<p>By one <a href="https://www.britannica.com/science/Drake-equation">widely quoted estimate</a>, there are a tenth as many of these extraterrestrial civilizations as one’s average lifetime in years. If civilizations survive for a million years, for example, there should be about 100,000 in the galaxy. If they last only a century on average, scientists would estimate that about 10 exist.</p>
<p>Radio astronomers study the universe by examining the radiation that chemical elements in space give off. They spend much of their time mapping the distribution of the most abundant chemical in the universe – hydrogen.</p>
<p>Hydrogen emits radiation at a certain frequency called the <a href="http://www.setileague.org/askdr/hydrogen.htm">hydrogen line</a>, which radio telescopes can detect. During <a href="https://www.seti.org/project-ozma">Project Ozma</a>, the first modern-day SETI experiment, Drake looked for artificial signals at the same frequency, because he figured scientists on other worlds might recognize hydrogen as universally significant and broadcast signals at that frequency.</p>
<h2>The water hole</h2>
<p>As our team developed our water words message, I realized that the message would only make sense if it were discovered by someone already familiar with the contents inscribed on the plate. The Drake Equation would only make sense if someone already knew what each of the terms in the equation stood for. </p>
<p>The Europa Clipper will crash into Jupiter or one of its other moons, with <a href="https://www.space.com/europa-clipper-might-crash-into-ganymede">Ganymede or Callisto the leading candidates</a>. But if for some reason the mission changes and it survives that fate, then humans far in the future with a radically different cultural background and different language conventions may retrieve it millennia from now as an ancient artifact.</p>
<p>To ensure we had at least one part of the message that a distant future scientist might be able to understand, I also designed a pictorial representation of the same frequency that Drake used for Project Ozma: the hydrogen line. We engraved this on the Clipper plate, along with a frequency called the hydroxyl line.</p>
<p>When hydrogen (H+) and <a href="https://www.sciencedirect.com/topics/chemistry/hydroxyl">hydroxyl (OH-)</a> combine, they form water. Scientists call the range of frequencies between these lines the “<a href="http://www.setileague.org/general/waterhol.htm">water hole</a>.” The water hole represents the part of the radio spectrum where astronomers conducted the first SETI experiments.</p>
<p>We displayed the hydrogen and hydroxyl lines using their wavelengths in the Clipper message. The metal plate also has diagrams showing what hydrogen and hydroxyl look like at the atomic level. </p>
<p>We’re hoping that future chemists would recognize these chemical components as the ingredients of water. If they do, we will have succeeded in communicating at least a few core scientific concepts across time, space and language. </p>
<p>Waveforms let our team tie the messages on the two sides of the Clipper plate together. On the water words side, over a hundred words are depicted by their waveforms. On the other side, the wavelengths of hydrogen and hydroxyl – the constituents of water – are etched into the plate.</p>
<p>METI International funded the collection and curation of the water words, as well as my design of the hydrogen and hydroxyl lines, providing these to NASA at no cost.</p>
<p>While designing the message for the Europa Clipper, we got to reflect on the importance of water on Earth, and think about why astronomers feel so compelled to search for it beneath the icy crust of Jupiter’s moon Europa. The spacecraft is scheduled to enter Jupiter’s orbit in April 2030.</p><img src="https://counter.theconversation.com/content/225771/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Douglas Vakoch 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>Europa Clipper will contain a plaque that celebrates humanity’s relationship with water and a decades-old tradition of searching for life outside Earth.Douglas Vakoch, President, METI International; Professor Emeritus, California Institute of Integral StudiesLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2250022024-03-04T16:15:33Z2024-03-04T16:15:33ZJupiter’s moon Europa produces less oxygen than we thought – it may affect our chances of finding life there<figure><img src="https://images.theconversation.com/files/579561/original/file-20240304-24-hmeyeg.jpeg?ixlib=rb-1.1.0&rect=20%2C0%2C1976%2C1000&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Europa seen in true colour (left) and false colour (right).</span> <span class="attribution"><span class="source">NASA</span></span></figcaption></figure><p>Jupiter’s icy moon Europa has long been thought of as one of the most habitable worlds in the Solar System. Now the Juno mission to Jupiter has directly sampled its atmosphere in detail for the first time. The results, <a href="https://www.nature.com/articles/s41550-024-02206-x">published in Nature Astronomy</a>, show that Europa’s icy surface produces less oxygen than we thought.</p>
<p>There are plenty of reasons to be excited about the possibility of finding microbial life on Europa. Evidence from the Galileo mission has shown that the moon <a href="https://pubmed.ncbi.nlm.nih.gov/9450749/">has an ocean</a> below its icy surface containing about twice the amount of water as Earth’s oceans. Also, models derived from Europa data show that its ocean floor is in contact with rock, enabling chemical water-rock interactions that <a href="https://theconversation.com/nasa-considers-sending-swimming-robots-to-habitable-ocean-worlds-of-the-solar-system-186228">produce energy</a>, making it the prime candidate for life.</p>
<p>Telescope observations, meanwhile, reveal a weak, <a href="https://europa.nasa.gov/news/18/hubble-finds-oxygen-atmosphere-on-jupiters-moon-europa/">oxygen-rich atmosphere</a>. It also looks as though <a href="https://www.nasa.gov/news-release/nasas-hubble-spots-possible-water-plumes-erupting-on-jupiters-moon-europa/">plumes of water erupt</a> intermittently from the ocean. And there is some evidence of the presence of <a href="https://europa.nasa.gov/why-europa/ingredients-for-life/#:%7E:text=NASA%2FJPL%2DCaltech-,Europa's%20surface%20is%20blasted%20by%20radiation%20from%20Jupiter.,in%20Europa's%20extremely%20tenuous%20atmosphere.">basic chemical elements</a> on the surface – including carbon, hydrogen, nitrogen, oxygen, phosphorus and sulphur – used by life on Earth. Some of these could seep down into the water from the atmosphere and surface.</p>
<p>The heating of Europa and its ocean is partly thanks to the moon’s orbit around Jupiter, which produces tidal forces to heat an otherwise frigid environment. </p>
<p>Although Europa boasts three basic ingredients for life – water, the right chemical elements and a source of heat – we don’t yet know if there has been enough time for life to develop.</p>
<figure class="align-center ">
<img alt="Plumes seen on Europa." src="https://images.theconversation.com/files/579569/original/file-20240304-16-u47ybe.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/579569/original/file-20240304-16-u47ybe.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=506&fit=crop&dpr=1 600w, https://images.theconversation.com/files/579569/original/file-20240304-16-u47ybe.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=506&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/579569/original/file-20240304-16-u47ybe.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=506&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/579569/original/file-20240304-16-u47ybe.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=636&fit=crop&dpr=1 754w, https://images.theconversation.com/files/579569/original/file-20240304-16-u47ybe.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=636&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/579569/original/file-20240304-16-u47ybe.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=636&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Plumes seen on Europa.</span>
<span class="attribution"><span class="source">Nasa</span></span>
</figcaption>
</figure>
<p>The other prime candidate in our solar system is Mars, the Rosalind Franklin rover’s target in 2028. Life <a href="https://theconversation.com/perseverance-mars-rover-how-to-prove-whether-theres-life-on-the-red-planet-154982">might have started on Mars</a> at the same time as it did on Earth, but then probably stopped due to climate change. </p>
<p>A third candidate is Saturn’s moon Enceladus where the Cassini-Huygens mission discovered plumes of water from a sub-surface salty ocean, <a href="https://www.nature.com/articles/s41586-023-05987-9">also in contact with rock</a> at the ocean’s floor. </p>
<p>Titan is the closest runner up in fourth place, <a href="https://iopscience.iop.org/article/10.3847/2041-8213/aa7851">with its thick atmosphere</a> of organic compounds including hydrocarbon and tholins, born in the high atmosphere. These then float down to the surface coating it with ingredients for life.</p>
<h2>Losing oxygen</h2>
<p>The Juno mission boasts <a href="https://ui.adsabs.harvard.edu/abs/2017SSRv..213..547M/abstract">the best charged particle instruments</a> sent to Jupiter so far. It can measure the energy, direction and composition of charged particles on the surface. Similar instruments at Saturn and Titan <a href="https://uwaterloo.ca/chem13-news-magazine/february-2017/chemistry/what-earth-are-tholins">found tholins</a> (a type of organic substance) there. But they also measured particles that suggested atmospheres at Saturn’s moons Rhea and Dione, in addition to those at Titan and Enceladus.</p>
<p>These particles are known as <a href="https://www.sciencedirect.com/topics/physics-and-astronomy/pickup-ions">pickup ions</a>. Planetary atmospheres consist of neutral particles, but the top of an atmosphere becomes “ionised” (meaning it loses electrons) in sunlight and via collisions with other particles, forming ions (charged atoms that have lost electrons) and free electrons. </p>
<p>When a plasma – a charged gas making up the fourth state of matter beyond solid, liquid and gas – flows past an atmosphere with newly formed ions, it disturbs the atmosphere with electric fields which can accelerate the new ions – the first part of an ion pickup process. </p>
<p>These pickup ions then spiral around the planet’s magnetic field and are usually lost from the atmosphere, while some hit the surface and are absorbed. The pickup process has rid the Martian atmosphere of particles after the red planet’s magnetic field was lost 3.8 billion years ago.</p>
<p>Europa also has a pickup process. The new measurements show the telltale signs of pickup molecular oxygen and hydrogen ions from the surface and atmosphere. Some of these escape from Europa, whereas some hit the icy surface enhancing the amount of oxygen at and under the surface. </p>
<p>This confirms that oxygen and hydrogen are indeed the main constituents of Europa’s atmosphere – in agreement with remote observations. However, the measurements imply that the amount of oxygen being produced – released by the surface to the atmosphere – is only about 12kg per second, at the lower end of earlier estimates from about 5kg to 1,100 kg per second. </p>
<p>This would indicate that the surface suffers very little erosion. The measurements indicate that this may amount to only 1.5cm of Europa’s surface per million years, which is less than we had thought. So Europa is constantly losing oxygen due to pickup processes, with only a small amount of additional oxygen being released from the surface to replenish it and ending up back on the surface.</p>
<p>So what does that mean for its chances of hosting life? Some of the oxygen trapped in the surface may find its way to the subsurface ocean to nourish any life there. But based on the study’s estimate of the overall loss of oxygen, this should be less than the 0.3kg-300kg per second estimated earlier. </p>
<p>It remains to be seen whether this rate, recorded on 29, September 2022, is usual. Perhaps it is not representative of the overall oxygen on the moon. It may be that the eruption of plumes, orbital position and upstream conditions increase and decrease the rate at certain times, respectively.</p>
<p>Nasa’s <a href="https://www.jpl.nasa.gov/missions/europa-clipper">Europa Clipper mission</a>, to be launched later this year, and the Juice mission which will make two flybys of Europa on its way to orbit Ganymede, will be able to follow up these measurements, and provide much more information on Europa’s habitability.</p><img src="https://counter.theconversation.com/content/225002/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Andrew Coates receives funding from STFC and UKSA (UK). </span></em></p>Only about 12kg of oxygen is produced per second on Europa, which is on the lower side of previous estimates from about 5kg to 1,100 kg per second.Andrew Coates, Professor of Physics, Deputy Director (Solar System) at the Mullard Space Science Laboratory, UCLLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2194402023-12-29T11:39:42Z2023-12-29T11:39:42ZSix space missions to look forward to in 2024<figure><img src="https://images.theconversation.com/files/565441/original/file-20231213-29-hd06pq.png?ixlib=rb-1.1.0&rect=27%2C21%2C1367%2C1253&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Nasa</span></span></figcaption></figure><p>It’s going to be a bumper time for space missions in 2024 – especially to the Moon, our nearest neighbour. And that’s following on from an already epic 2023. </p>
<p>I’m a laboratory scientist, so I always like to have a “proper” sample to analyse. Rather than peering through telescopes to look at the stars, I prefer to see them in a vial in my lab. My technique of choice is to burn the material to ashes while measuring the organic compounds and other species that are liberated in the process. </p>
<p>So it was a great delight to see the safe return of <a href="https://theconversation.com/osiris-rex-nasa-reveals-evidence-of-water-and-carbon-in-sample-delivered-to-earth-from-an-asteroid-215484">Nasa’s Osiris-Rex</a> mission from asteroid (101955) Bennu in September 2023. It was an even greater pleasure to receive a few precious crumbs of Bennu to study. </p>
<h2>CLPS missions</h2>
<p>Nasa’s series of <a href="https://www.nasa.gov/commercial-lunar-payload-services/">Commercial Lunar Payload Service (CLPS) missions</a>, many of which will launch in 2024, are set to bring a variety of instruments to the Moon. These missions are built and launched by different private companies under contract from Nasa. </p>
<p>The CLPS programme is part of Nasa’s <a href="https://theconversation.com/artemis-why-it-may-be-the-last-mission-for-nasa-astronauts-195065">Artemis initiative</a> to continue human exploration of the Moon. One of the main aims of the programme is to investigate the possibilities of using lunar resources as fuel – hence, some of the instruments on CLPS-1, aka <a href="https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=PEREGRN-1">Peregrine</a>, are designed to assess the amount of hydrogen on the lunar surface. In fact, my colleagues at the Open University have <a href="https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/PITMS_a_mini_mass_spectrometer_for_the_Moon">built an instrument</a> for doing so.</p>
<p>CLPS-2 is timetabled to launch in early January 2024, and there are four other CLPS missions planned for launch throughout the year. That is the good thing about the Moon – it’s so close that there aren’t many worries about launch windows (no complicated orbits to compute) or distance to travel.</p>
<p>Indeed, it is hoped that human exploration of the Moon will take a small step forward, possibly as early as November 2024, when <a href="https://www.nasa.gov/mission/artemis-ii/">Artemis II</a> orbits the Moon for several days. One of the astronauts on-board will be female – definitely a giant leap in what has, until now, been a solely masculine exploration of our nearest neighbour.</p>
<h2>Trailblazer</h2>
<p>Continuing the lunar theme, Nasa’s <a href="https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=L-TRLBLZR">Trailblazer mission</a> travels to the Moon to understand where any water is situated. Is it locked inside rock as part of the mineral structure, or is it deposited as ice on the rocky surface? </p>
<p>Trailblazer is currently scheduled for launch in the first quarter of 2024. However, no precise date has been confirmed. It’s a small mission, part of the <a href="https://www.nasa.gov/specials/artemis/">Artemis</a> human lunar exploration programme.</p>
<h2>Chang'e 6</h2>
<p>The launch of <a href="https://en.wikipedia.org/wiki/Chang%27e_6">Chang’e 6</a>, the latest Chinese mission to the Moon, is planned for May 2024 and is intended to bring material back to Earth. This is particularly significant because the spacecraft will collect material from the lunar farside – the South Pole Aitkin Basin. </p>
<p>This is a region where it is believed there is abundant frozen water. We do not have any samples of material from this part of the Moon – and although any ice will be long gone by the time the samples are back on Earth, it is anticipated we will learn a lot about this unexplored region and its potential as a source of water for human visitors. </p>
<h2>Hera</h2>
<p>In September 2022, Nasa’s <a href="https://science.nasa.gov/mission/dart/">Dart mission</a> encountered a system consisting of two asteroids called Didymos and Dimorphos, and crashed into Dimorphos (the junior partner). The impact had a purpose: to see if such a collision could divert the asteroid in its path – a necessary goal if ever Earth were to be the target of a direct hit by an incoming asteroid. </p>
<figure class="align-center ">
<img alt="Artist's impression of Hera mission." src="https://images.theconversation.com/files/564917/original/file-20231211-27-3yuer.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/564917/original/file-20231211-27-3yuer.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=337&fit=crop&dpr=1 600w, https://images.theconversation.com/files/564917/original/file-20231211-27-3yuer.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=337&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/564917/original/file-20231211-27-3yuer.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=337&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/564917/original/file-20231211-27-3yuer.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/564917/original/file-20231211-27-3yuer.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/564917/original/file-20231211-27-3yuer.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Artist’s impression of Hera mission.</span>
<span class="attribution"><span class="source">Esa/wikipedia</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Two years later, the European Space Agency’s <a href="https://www.esa.int/Space_Safety/Hera">Hera</a> mission will launch to visit the same pair of asteroids. It is not designed to hit either body, but to measure the effect of Dart’s earlier impact. At the time of the collision, the orbit of Dimorphos around Didymos got faster by 33 minutes – a significant movement that showed the path of an asteroid could be deflected. </p>
<p>But what we don’t know (and won’t until Hera arrives in 2026) is how effective the impact was. Has Dimorphos remained in its new orbit, bounced back into its old orbit, or continued to speed up? Hera will investigate in detail – and its results will help to define Earth’s planetary defence protocol. Assuming, that is, <a href="https://theconversation.com/dont-look-up-several-asteroids-are-heading-towards-earth-heres-how-we-deal-with-threats-in-real-life-174512">we take notice</a>.</p>
<h2>Europa Clipper</h2>
<p>Launching almost at the same time as Hera is a Nasa flagship mission: the <a href="https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=EUROPA-CL">Europa Clipper</a> to Jupiter’s icy moon, Europa.</p>
<p>This mission has been long-awaited, ever since the Galileo mission first showed us views of Europa’s icy surface in the late 1990s. Since then, we have learnt about the ocean that lurks beneath the icy shell. Excitingly, Europa <a href="https://theconversation.com/europa-there-may-be-life-on-jupiters-moon-and-two-new-missions-will-pave-the-way-for-finding-it-122551">may host life</a> in the form of a substantial fauna analogous to the animals that live on the deep ocean floor around hydrothermal vents. </p>
<figure class="align-center ">
<img alt="Artist's impression of Europa Clipper." src="https://images.theconversation.com/files/564913/original/file-20231211-27-kjjpd2.jpg?ixlib=rb-1.1.0&rect=9%2C9%2C1573%2C1360&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/564913/original/file-20231211-27-kjjpd2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=528&fit=crop&dpr=1 600w, https://images.theconversation.com/files/564913/original/file-20231211-27-kjjpd2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=528&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/564913/original/file-20231211-27-kjjpd2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=528&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/564913/original/file-20231211-27-kjjpd2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=664&fit=crop&dpr=1 754w, https://images.theconversation.com/files/564913/original/file-20231211-27-kjjpd2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=664&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/564913/original/file-20231211-27-kjjpd2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=664&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Artist’s impression of Europa Clipper.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech</span></span>
</figcaption>
</figure>
<p>Europa Clipper will fly past Europa between 40 and 50 times, taking detailed images of the surface, monitoring the satellite for icy plumes – and, most importantly, looking to see whether this moon has the conditions suitable to support life. The mission will also investigate whether Europa’s ocean is salty, and whether the essential building blocks of life (carbon, nitrogen and sulphur) are present.</p>
<p>Sadly though, it is not until 2030 that any of these observations will be transmitted back to us, so we will have to wait patiently until then. The investigation will be complemented by observations from Esa’s Juice mission, which is currently on its way to Jupiter.</p>
<h2>MMX</h2>
<p>I began this article with mention of my delight at the return of material from Bennu. I will finish it with my anticipation of further delights to come. I know I have mentioned return of material from the Moon – but in fact, I am much more excited by the prospect of material returning from another moon. The moon in question is Phobos, one of the satellites of Mars. </p>
<p>The launch of the Japanese Space Agency’s <a href="https://theconversation.com/the-longstanding-mystery-of-mars-moons-and-the-mission-that-could-solve-it-219161">Martian Moon Exploration (MMX)</a> mission to Phobos is currently scheduled for September 2024, and designed to return material to Earth in 2029.</p>
<p>I’ll be 70 by the time the material comes back – but, I hope, not too decrepit to take pleasure in analysis of a unique sample from an enigmatic body.</p><img src="https://counter.theconversation.com/content/219440/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Monica Grady works for The Open University. She receives funding from The UKRI-Science and Technology Facilities Council. She is a Senior Research Fellow at the Natural History Museum, London and Chancellor of Liverpool Hope University. She tweets (X's?) as @MonicaGrady</span></em></p>Moons and asteroids will be visited by spacecraft from Earth next year.Monica Grady, Professor of Planetary and Space Sciences, The Open UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2180002023-12-26T19:41:32Z2023-12-26T19:41:32ZFrom the Moon’s south pole to an ice-covered ocean world, several exciting space missions are slated for launch in 2024<figure><img src="https://images.theconversation.com/files/565859/original/file-20231214-25-glo8i8.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C4498%2C3003&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">NASA isn't the only space agency with exciting missions to watch for in 2024. </span> <span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/d5633dd767384229af78233cd6dccb06?ext=true">AP Photo/John Raoux</a></span></figcaption></figure><p>The year 2023 proved to be an important one for space missions, with NASA’s OSIRIS-REx mission <a href="https://www.pbs.org/newshour/science/watch-live-ancient-asteroid-sample-lands-on-earth-in-last-leg-of-nasa-osiris-rex-mission">returning a sample from an asteroid</a> and India’s Chandrayaan-3 mission <a href="https://www.space.com/chandrayaan-3-moon-temperature-lunar-south-pole-first-time">exploring the lunar south pole</a>, and 2024 is shaping up to be another exciting year for space exploration.</p>
<p>Several new missions under NASA’s <a href="https://www.nasa.gov/specials/artemis/">Artemis plan</a> and <a href="https://www.nasa.gov/commercial-lunar-payload-services/">Commercial Lunar Payload Services initiative</a> will target the Moon.</p>
<p>The latter half of the year will feature several exciting launches, with the launch of the Martian Moons eXploration mission in September, Europa Clipper and Hera in October and Artemis II and VIPER to the Moon in November – if everything goes as planned.</p>
<p><a href="https://www.eaps.purdue.edu/people/profile/bramsona.html">I’m a planetary scientist</a>, and here are six of the space missions I’m most excited to follow in 2024.</p>
<h2>1. Europa Clipper</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/563177/original/file-20231204-15-5dr2r5.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A spacecraft with two large rectangular panels coming off a small cylinder flies above a brown and white moon, with a brown striped planet in the background." src="https://images.theconversation.com/files/563177/original/file-20231204-15-5dr2r5.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/563177/original/file-20231204-15-5dr2r5.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/563177/original/file-20231204-15-5dr2r5.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/563177/original/file-20231204-15-5dr2r5.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/563177/original/file-20231204-15-5dr2r5.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/563177/original/file-20231204-15-5dr2r5.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/563177/original/file-20231204-15-5dr2r5.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Illustration of what the Europa Clipper spacecraft will look like flying by Europa, a moon of Jupiter.</span>
<span class="attribution"><a class="source" href="https://www.jpl.nasa.gov/images/pia24321-europa-clipper-spacecraft-illustration">NASA/JPL-Caltech</a></span>
</figcaption>
</figure>
<p>NASA will launch <a href="https://europa.nasa.gov/">Europa Clipper</a>, which will explore <a href="https://science.nasa.gov/jupiter/moons/europa/">one of Jupiter’s largest moons, Europa</a>. Europa is slightly smaller than Earth’s Moon, with a surface made of ice. Beneath its icy shell, Europa likely harbors a saltwater ocean, which scientists expect contains over twice as much water as all the <a href="https://europa.nasa.gov/why-europa/ingredients-for-life">oceans here on Earth combined</a>.</p>
<p>With Europa Clipper, scientists want to investigate whether Europa’s ocean could be <a href="https://europa.nasa.gov/mission/about/#pre-project-planning-pre-phase-a">a suitable habitat for extraterrestrial life</a>.</p>
<p>The mission plans to do this by flying past Europa <a href="https://www.astronomy.com/science/ask-astro-why-will-europa-clipper-orbit-jupiter-instead-of-europa/">nearly 50 times</a> to study the moon’s icy shell, its surface’s geology <a href="https://doi.org/10.1038/s41467-020-15160-9">and its subsurface ocean</a>. The mission will also look for <a href="https://europa.nasa.gov/news/40/are-water-plumes-spraying-from-europa-nasas-europa-clipper-is-on-the-case/">active geysers</a> spewing out from Europa.</p>
<p>This mission will change the game for <a href="https://theconversation.com/jupiters-moons-hide-giant-subsurface-oceans-two-missions-are-sending-spacecraft-to-see-if-these-moons-could-support-life-203207">scientists hoping to understand ocean worlds</a> like Europa. </p>
<p>The launch window – the period when the mission could launch and achieve its planned route – <a href="https://europa.nasa.gov/mission/timeline/">opens Oct. 10, 2024</a>, and lasts 21 days. The spacecraft will <a href="https://www.nasa.gov/news-release/nasa-awards-launch-services-contract-for-europa-clipper-mission/">launch on a SpaceX Falcon Heavy rocket</a> and arrive at the Jupiter system in 2030.</p>
<h2>2. Artemis II launch</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/563207/original/file-20231204-17-459f6.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Four people in orange spacesuits stand in a small white room." src="https://images.theconversation.com/files/563207/original/file-20231204-17-459f6.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/563207/original/file-20231204-17-459f6.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/563207/original/file-20231204-17-459f6.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/563207/original/file-20231204-17-459f6.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/563207/original/file-20231204-17-459f6.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/563207/original/file-20231204-17-459f6.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/563207/original/file-20231204-17-459f6.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Artemis II astronauts at the launchpad during a ground systems test in September 2023 at Kennedy Space Center.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/general/first-artemis-crew-trains-for-mission-around-moon/">NASA</a></span>
</figcaption>
</figure>
<p>The Artemis program, <a href="https://theconversation.com/who-is-artemis-nasas-latest-mission-to-the-moon-is-named-after-an-ancient-lunar-goddess-turned-feminist-icon-189504">named after Apollo’s twin sister</a> in Greek mythology, is <a href="https://www.nasa.gov/humans-in-space/artemis/">NASA’s plan to go back to the Moon</a>. It will send humans to the Moon for the first time since 1972, including the <a href="https://www.nasa.gov/general/what-is-artemis/">first woman and the first person of color</a>. Artemis also includes plans for <a href="https://www.space.com/rebooting-moon-nasa-artemis-sustainability">a longer-term, sustained presence in space</a> that will prepare NASA for eventually sending people even farther – <a href="https://www.nasa.gov/news-release/new-program-office-leads-nasas-path-forward-for-moon-mars/">to Mars</a>.</p>
<p>Artemis II is the first crewed step in this plan, with <a href="https://theconversation.com/meet-the-next-four-people-headed-to-the-moon-how-the-diverse-crew-of-artemis-ii-shows-nasas-plan-for-the-future-of-space-exploration-203214">four astronauts</a> planned to be on board during the 10-day mission.</p>
<p>The mission builds upon <a href="https://www.nasa.gov/mission/artemis-i/">Artemis I</a>, which sent an uncrewed <a href="https://www.nasa.gov/humans-in-space/orion-spacecraft/">capsule</a> into orbit around the Moon in late 2022.</p>
<p>Artemis II will put the astronauts into orbit around the Moon before returning them home. It is currently planned for <a href="https://phys.org/news/2023-03-nasa-artemis-mission-moon-november.html">launch as early as November 2024</a>. But there is a chance it will get pushed back to 2025, depending on whether all the necessary gear, such as spacesuits and oxygen equipment, <a href="https://www.space.com/artemis-2-humans-moon-orbit">is ready</a>.</p>
<h2>3. VIPER to search for water on the Moon</h2>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/S9Y6n1G5hhc?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The VIPER rover to survey water at the south pole of the Moon.</span></figcaption>
</figure>
<p><a href="https://science.nasa.gov/mission/viper/">VIPER</a>, which stands for Volatiles Investigating Polar Exploration Rover, is a robot the size of a golf cart that NASA will use to explore the Moon’s <a href="https://www.nasa.gov/news-release/nasas-artemis-rover-to-land-near-nobile-region-of-moons-south-pole/">south pole</a> in late 2024. </p>
<p><a href="https://www.nasa.gov/solar-system/nasa-replans-clps-delivery-of-viper-to-2024-to-reduce-risk-2/">Originally scheduled for launch in 2023</a>, NASA pushed the mission back to complete more tests on the lander system, which <a href="https://www.astrobotic.com/">Astrobotic</a>, a private company, developed as part of the <a href="https://www.nasa.gov/commercial-lunar-payload-services/">Commercial Lunar Payload Services</a> program.</p>
<p>This robotic mission is designed to search for <a href="https://www.planetary.org/space-missions/viper">volatiles</a>, which are molecules that easily vaporize, like water and carbon dioxide, at lunar temperatures. These materials could provide resources for <a href="https://theconversation.com/scientists-suspect-theres-ice-hiding-on-the-moon-and-a-host-of-missions-from-the-us-and-beyond-are-searching-for-it-216060">future human exploration</a> on the Moon.</p>
<p>The VIPER robot will rely on batteries, heat pipes and radiators throughout its <a href="https://science.nasa.gov/mission/viper/in-depth/">100-day mission</a>, as it navigates everything from the extreme heat of lunar daylight – when temperatures can reach 224 degrees Fahrenheit (107 degrees Celsius) – to the Moon’s <a href="https://www.smithsonianmag.com/science-nature/five-things-to-know-about-nasas-lunar-rover-viper-180978787/">frigid shadowed regions</a> that can reach a mind-boggling -400 F (-240 C).</p>
<p>VIPER’s launch and delivery to the lunar surface is scheduled for <a href="https://www.nasa.gov/solar-system/nasa-replans-clps-delivery-of-viper-to-2024-to-reduce-risk-2/">November 2024</a>.</p>
<h2>4. Lunar Trailblazer and PRIME-1 missions</h2>
<p>NASA has recently invested in a class of small, low-cost planetary missions called <a href="https://soma.larc.nasa.gov/simplex/">SIMPLEx</a>, which stands for Small, Innovative Missions for PLanetary Exploration. These missions save costs by tagging along on other launches as what is called a rideshare, or secondary payload. </p>
<p>One example is the <a href="https://www.planetary.org/space-missions/lunar-trailblazer">Lunar Trailblazer</a>. Like VIPER, Lunar Trailblazer will look for water on the Moon. </p>
<p>But while VIPER will land on the Moon’s surface, studying a specific area near the south pole in detail, Lunar Trailblazer will orbit the Moon, measuring the temperature of the surface and <a href="https://trailblazer.caltech.edu/objectives.html">mapping out the locations of water molecules</a> across the globe. </p>
<p>Currently, Lunar Trailblazer is on track <a href="https://trailblazer.caltech.edu/index.html">to be ready by early 2024</a>.</p>
<p>However, because it is a secondary payload, Lunar Trailblazer’s launch timing depends on the primary payload’s launch readiness. The <a href="https://www.nasa.gov/mission/polar-resources-ice-mining-experiment-1-prime-1">PRIME-1</a> mission, <a href="https://nextspaceflight.com/launches/details/6828">scheduled for a mid-2024 launch</a>, is Lunar Trailblazer’s ride.</p>
<p>PRIME-1 will drill into the Moon – it’s a test run for the kind of drill <a href="https://www.nasa.gov/centers-and-facilities/kennedy/apollo-to-artemis-drilling-on-the-moon/">that VIPER will use</a>. But its launch date will likely depend on whether earlier launches go on time. </p>
<p>An earlier Commercial Lunar Payload Services mission with the <a href="https://www.space.com/intuitive-machines">same landing partner</a> was <a href="https://www.intuitivemachines.com/post/intuitive-machines-im-1-lunar-mission-launch-update">pushed back to February 2024 at the earliest</a>, and further delays could push back PRIME-1 and Lunar Trailblazer.</p>
<h2>5. JAXA’s Martian Moon eXploration mission</h2>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/yiS6NdpEL2A?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The JAXA MMX mission concept to study Phobos and Deimos, Mars’ moons.</span></figcaption>
</figure>
<p>While Earth’s Moon has many visitors – big and small, robotic and crewed – planned for 2024, Mars’ moons Phobos and Deimos will soon be getting a visitor as well. The Japanese Aerospace Exploration Agency, or JAXA, has a robotic mission in development called the <a href="https://www.mmx.jaxa.jp/en/">Martian Moon eXploration, or MMX,</a> planned for launch around September 2024. </p>
<p>The mission’s main science objective is to determine the origin of Mars’ moons. Scientists aren’t sure whether Phobos and Deimos are <a href="https://doi.org/10.1126/science.199.4324.64">former asteroids that Mars captured into orbit with its gravity</a> or if they <a href="https://doi.org/10.1007/s00159-011-0044-6">formed out of debris</a> that was already in orbit around Mars.</p>
<p>The spacecraft will spend three years around Mars conducting <a href="https://doi.org/10.1186/s40623-021-01546-6">science operations</a> to observe Phobos and Deimos. MMX will also land on Phobos’ surface and <a href="https://doi.org/10.1186/s40623-021-01545-7">collect a sample</a> before returning to Earth. </p>
<h2>6. ESA’s Hera mission</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/565308/original/file-20231212-25-dpf9ef.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An illustration of two gray asteroids, next to a gold box with two large rectangular panels on either side, and two smaller crafts." src="https://images.theconversation.com/files/565308/original/file-20231212-25-dpf9ef.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/565308/original/file-20231212-25-dpf9ef.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=337&fit=crop&dpr=1 600w, https://images.theconversation.com/files/565308/original/file-20231212-25-dpf9ef.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=337&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/565308/original/file-20231212-25-dpf9ef.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=337&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/565308/original/file-20231212-25-dpf9ef.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/565308/original/file-20231212-25-dpf9ef.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/565308/original/file-20231212-25-dpf9ef.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">An artist’s conception of the Hera mission to literally measure the impact of NASA’s DART mission in 2022.</span>
<span class="attribution"><a class="source" href="https://www.heramission.space/press-room">ESA</a></span>
</figcaption>
</figure>
<p><a href="https://www.heramission.space/">Hera</a> is a mission by the European Space Agency to return to the Didymos-Dimorphos asteroid system that NASA’s <a href="https://science.nasa.gov/mission/dart/">DART mission</a> visited in 2022.</p>
<p>But DART didn’t just visit these asteroids, <a href="https://theconversation.com/in-a-world-first-nasas-dart-mission-is-about-to-smash-into-an-asteroid-what-will-we-learn-189391">it collided with one of them</a> to test a <a href="https://www.space.com/planetary-defense-explained">planetary defense</a> technique called “kinetic impact.” DART hit Dimorphos with such force that <a href="https://www.nasa.gov/news-release/nasa-confirms-dart-mission-impact-changed-asteroids-motion-in-space/">it actually changed its orbit</a>.</p>
<p>The kinetic impact technique smashes something into an object in order to alter its path. This could prove useful if humanity ever finds a <a href="https://www.livescience.com/what-are-potentially-hazardous-asteroids">potentially hazardous object</a> on a collision course with Earth and needs to redirect it.</p>
<p>Hera will launch in <a href="https://www.esa.int/Space_Safety/Hera">October 2024</a>, making its way in late 2026 to Didymos and Dimorphos, where it will study <a href="https://doi.org/10.3847/PSJ/ac6f52">physical properties of the asteroids</a>.</p><img src="https://counter.theconversation.com/content/218000/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ali M. Bramson receives funding from NASA. </span></em></p>Expect lots of space missions to launch this coming year, with exciting new science to follow.Ali M. Bramson, Assistant Professor of Earth, Atmospheric, and Planetary Sciences, Purdue UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2114672023-09-18T21:55:08Z2023-09-18T21:55:08ZDiscovering the universe from our own backyards<figure><img src="https://images.theconversation.com/files/542371/original/file-20230809-19-r1poh9.jpg?ixlib=rb-1.1.0&rect=5%2C4%2C988%2C661&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Is there life beyond our world?</span> <span class="attribution"><span class="source">(Shutterstock)</span></span></figcaption></figure><p>When I was a college student, I worked at the Charlevoix Astronomical Observatory in Québec. </p>
<p>It was a pretty decent summer job, as I got to observe celestial bodies until the dead of night, talk to astronomy buffs about space exploration and watch children be amazed by Saturn’s rings. </p>
<p>Over the dozens of astronomy nights I’ve hosted, one question has consistently come up:</p>
<p>“Does life exist anywhere else?”</p>
<p>Answering this fundamental question, articulated by the first philosophers, which has transcended time and eras and <a href="https://theconversation.com/are-we-alone-in-the-universe-4-essential-reads-on-potential-contact-with-aliens-210955">still remains at the heart of our rational thinking</a>, was a big assignment for me as a CEGEP student at the time. </p>
<p>I merely offered a simple “most likely,” before adding a surprising “and if that’s the case, the answer lies here, on Earth, in places called ‘planetary analogues.’”</p>
<p>Planetary analogues are locations on Earth that replicate one or more extreme conditions found on another celestial body. For example, temperature, pressure and solar radiation.</p>
<p>Both for technical and financial reasons, carrying out several space missions per year, manned or unmanned, is simply not realistic, especially as these missions take several years to complete.</p>
<p>Yet the Earth, our magnificent blue planet where life thrives, has some extreme, dangerous and cruel places. These places can reproduce certain conditions found in the arid deserts of Mars or the suffocating atmosphere of Venus. </p>
<p>What if these places were, in fact, habitats where life has developed?</p>
<h2>Lakes under ice</h2>
<p>For example, consider Europa, one of the moons of Jupiter, which, along with Mars, is one of the top contenders in our quest for extraterrestrial life. Its surface is covered in a dense layer of ice about ten kilometres thick, beneath which lies… an ocean. An ocean <a href="https://doi.org/10.1038/34857">of… liquid water</a>! </p>
<p>It turns out that in Antarctica, almost 400 lakes exist in similar conditions, that is to say that they lie below a permanent ice blanket, protected from everything that happens on the surface. These are known as “subglacial” lakes.</p>
<p>Such is the case of <a href="https://doi.org/10.1038/414603a">Lake Vostok</a>, the largest and deepest lake in Antarctica. It was in the 1960s that scientists first suspected the presence of a lake beneath a four-kilometre thick layer of ice. </p>
<p>This icy barrier deprives the lake of gaseous exchanges with the atmosphere or exposure to solar radiation, making it a permanently dark place that is poor in nutrients and subject to enormous pressure — not very hospitable.</p>
<p>However, the water at the surface of the lake is concentrated in oxygen, the key chemical element for living metabolism. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/542010/original/file-20230809-24-a15igl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/542010/original/file-20230809-24-a15igl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/542010/original/file-20230809-24-a15igl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=1067&fit=crop&dpr=1 600w, https://images.theconversation.com/files/542010/original/file-20230809-24-a15igl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=1067&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/542010/original/file-20230809-24-a15igl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=1067&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/542010/original/file-20230809-24-a15igl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1340&fit=crop&dpr=1 754w, https://images.theconversation.com/files/542010/original/file-20230809-24-a15igl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1340&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/542010/original/file-20230809-24-a15igl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1340&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Lake Vostok (Antarctica) lies under four kilometres of ice.</span>
<span class="attribution"><span class="source">Wikimedia</span></span>
</figcaption>
</figure>
<h2>A love for extreme conditions</h2>
<p>In 2008, <a href="https://doi.org/10.1126/science.286.5447.2144">analyses of the ice covering Lake Vostok</a> revealed the presence of micro-organisms! This essentially means that life can indeed adapt to hostile environments that would otherwise be fatal for most organisms. These super-organisms, or “extremophile,” are able to tolerate these extreme conditions. </p>
<p>As a result, the waters of Lake Vostok, isolated from the Earth’s surface for millions of years, could well contain life too — an ideal planetary analogue.</p>
<p>Studying Lake Vostok, and its possible extremophile life forms, is almost like being on Jupiter’s moon Europa. And it’s almost like studying its ocean. Were Lake Vostok able to develop life, why not the ocean on Europa as well?</p>
<p>Subglacial lakes such as Vostok are just one example of the dozens of planetary analogue sites that have been identified. For example, in order to study certain Martian craters, the <a href="https://doi.org/10.1017/S1473550413000396">Earth’s deserts are the perfect playgrounds</a>. Scientists are exploring the Mojave (United States), <a href="https://doi.org/10.1038/s41467-023-36172-1">Atacama (Chile)</a> and Namib (Africa) deserts, which are dry and arid. Their soil also contains extremophiles, the study of which tells us about the development of life in hot environments where water is limited.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/542017/original/file-20230809-17-hzx8dz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Mojave desert" src="https://images.theconversation.com/files/542017/original/file-20230809-17-hzx8dz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/542017/original/file-20230809-17-hzx8dz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=382&fit=crop&dpr=1 600w, https://images.theconversation.com/files/542017/original/file-20230809-17-hzx8dz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=382&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/542017/original/file-20230809-17-hzx8dz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=382&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/542017/original/file-20230809-17-hzx8dz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=480&fit=crop&dpr=1 754w, https://images.theconversation.com/files/542017/original/file-20230809-17-hzx8dz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=480&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/542017/original/file-20230809-17-hzx8dz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=480&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 soil of the Mojave Desert contains extremophilic organisms.</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
</figcaption>
</figure>
<h2>Preparing for space missions on Earth</h2>
<p>As well as providing a better understanding of life and its emergence, investigating planetary analogues has another advantage: preparing and simulating space missions.</p>
<p>Just think — if we’re developing a new technology to sample a rock on Mars, it would be wise to try it out first, wouldn’t it? And not just inside NASA studios, where the parameters are controlled. We must step out and go to remote, uncomfortable regions. </p>
<p>That’s what the <a href="https://doi.org/10.1130/SPE483">Apollo astronauts of the 50s and 60s</a> did (those who aimed for the moon). They went to meteorite impact craters, volcanoes, deserts, all over the Earth, for months on end. All so they could practice their techniques with a variety of adapted tools, all slowed down by their space suits. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/542009/original/file-20230809-27-z4e7sr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/542009/original/file-20230809-27-z4e7sr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/542009/original/file-20230809-27-z4e7sr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/542009/original/file-20230809-27-z4e7sr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/542009/original/file-20230809-27-z4e7sr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/542009/original/file-20230809-27-z4e7sr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/542009/original/file-20230809-27-z4e7sr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/542009/original/file-20230809-27-z4e7sr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Astronauts Dave Scott (left) and Jim Irwin (right) sample rocks for a possible mission to the moon in 1971.</span>
<span class="attribution"><span class="source">(Analogs for Planetary Exploration [2011])</span></span>
</figcaption>
</figure>
<h2>It all begins on Earth</h2>
<p>Space exploration and the understanding of our solar system begin on Earth. At first glance, this idea may seem counter-intuitive, but it actually makes a lot of sense when you consider the remote, almost inaccessible and extreme environments our planet contains. </p>
<p>Astrochemistry and astrobiology have emerged in this same way, as multidisciplinary fields that equip us for our research into the evolution of Earth and life.</p>
<p>Now, if I were asked the question — “Does life exist anywhere else?” — I, still naive, but starting my PhD in the chemistry of extreme polar environments, would answer:</p>
<blockquote>
<p>Ask me again in five years!</p>
</blockquote>
<p>Joking aside, analogues have their limitations in that the conditions can never be recreated in their entirety. As a result, scientists need to be cautious in their approach and avoid jumping to hasty conclusions. </p>
<p>Life in Lake Vostok is not synonymous with life on Europa, far from it. But let’s just say that it’s an excellent first step that will guide us considerably in our future missions.</p><img src="https://counter.theconversation.com/content/211467/count.gif" alt="La Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Daniel Fillion ne travaille pas, ne conseille pas, ne possède pas de parts, ne reçoit pas de fonds d'une organisation qui pourrait tirer profit de cet article, et n'a déclaré aucune autre affiliation que son organisme de recherche.</span></em></p>Planetary analogues are sites on Earth that are so extreme that they replicate those of celestial bodies in our solar system.Daniel Fillion, Candidat au doctorat en océanographie, Université du Québec à Rimouski (UQAR)Licensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2036692023-04-13T05:40:16Z2023-04-13T05:40:16ZThe much-anticipated JUICE mission to Jupiter launches today. Here’s what it might discover<figure><img src="https://images.theconversation.com/files/520681/original/file-20230413-20-ybr84v.jpeg?ixlib=rb-1.1.0&rect=717%2C0%2C2284%2C1281&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Enhanced image by Kevin M. Gill (CC-BY) based on images provided courtesy of NASA/JPL-Caltech/SwRI/MSSS.Media</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p><strong>Editor’s note (April 14 2023):</strong> <em>The 13 April launch was postponed due to weather conditions, but the team will attempt another launch on 14 April at 10:14pm AEST. You can follow the launch live via <a href="https://www.esa.int/ESA_Multimedia/ESA_Web_TV">ESA Web TV</a>.</em> </p>
<p>The European Space Agency’s JUICE mission (Jupiter Icy Moons Explorer) <a href="https://www.esa.int/Science_Exploration/Space_Science/Juice/How_to_follow_the_Juice_launch_live">is launching today</a> at 10:15pm AEST from Europe’s spaceport in French Guiana.</p>
<p>JUICE will be targeting three water-rich worlds – Jupiter’s moons Ganymede, Europa and Callisto – to check out potential habitats and evidence of past alien life, both on and below the surface. There’s an excellent reason why these worlds in particular are the mission target – they might be habitable for life as we know it.</p>
<h2>The moons of Jupiter</h2>
<p>Although we have just one moon lighting up our night skies, <a href="https://coolcosmos.ipac.caltech.edu/ask/99-How-many-moons-does-Jupiter-have-">Jupiter has at least 92</a>. Some, including the four <a href="https://lasp.colorado.edu/outerplanets/moons_galilean.php">Galilean moons</a> (the largest Jovian moons) formed alongside Jupiter nearly 4.5 billion years ago in the early Solar System. Others have been drawn in and captured by this massive planet, adding to the collection over time.</p>
<p>These moons are made of hugely diverse materials, and some are thought to have conditions favourable for life, or could have in the past.</p>
<p>Fewer than ten interplanetary missions have ever flown past Jupiter, with only two NASA missions stopping to orbit the planet and investigate further: <a href="https://www.jpl.nasa.gov/missions/galileo">the Galileo mission</a> between 1995 and 2003, and the <a href="https://www.jpl.nasa.gov/missions/juno">current Juno mission</a>, launched in 2011. These are the only two to have also made dedicated passes of the moons, gathering valuable information for upcoming missions. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/520665/original/file-20230413-24-d6rig7.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing three missions to Jupiter" src="https://images.theconversation.com/files/520665/original/file-20230413-24-d6rig7.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/520665/original/file-20230413-24-d6rig7.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/520665/original/file-20230413-24-d6rig7.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/520665/original/file-20230413-24-d6rig7.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/520665/original/file-20230413-24-d6rig7.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/520665/original/file-20230413-24-d6rig7.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/520665/original/file-20230413-24-d6rig7.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">NASA’s Juno mission laid the groundwork for both Juice and the upcoming Europa Clipper mission.</span>
<span class="attribution"><a class="source" href="https://www.esa.int/ESA_Multimedia/Images/2022/12/A_trio_of_missions_to_Jupiter">ESA</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>Life as we know it</h2>
<p>The Galilean moons are of particular interest. The second smallest, Io, may not be habitable, but has <a href="https://theconversation.com/four-volcanic-hotspots-in-the-solar-system-202383">some of the largest active volcanoes</a> in the Solar System (with eruptions that can be seen from Earth!).</p>
<p>The other three, Ganymede, Europa and Callisto, are all thought to have large bodies of liquid water under their icy surfaces, and maybe even thin atmospheres. </p>
<p>Ganymede’s liquid iron core also <a href="https://solarsystem.nasa.gov/moons/jupiter-moons/ganymede/in-depth/">gives it a magnetic field</a>, the only known moon in the Solar System to have one. Our own magnetic field protects Earth’s atmosphere from the harsh solar winds, shielding us from solar radiation. These are factors we associate with fostering and protecting life on Earth.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/520683/original/file-20230413-24-mm3ijm.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An image of a blue circle on a black background with concentric ellipses extending to both sides" src="https://images.theconversation.com/files/520683/original/file-20230413-24-mm3ijm.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/520683/original/file-20230413-24-mm3ijm.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=367&fit=crop&dpr=1 600w, https://images.theconversation.com/files/520683/original/file-20230413-24-mm3ijm.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=367&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/520683/original/file-20230413-24-mm3ijm.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=367&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/520683/original/file-20230413-24-mm3ijm.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=461&fit=crop&dpr=1 754w, https://images.theconversation.com/files/520683/original/file-20230413-24-mm3ijm.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=461&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/520683/original/file-20230413-24-mm3ijm.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=461&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A sketch of the magnetic field lines around Ganymede, which are generated in the moon’s iron core. Hubble Space Telescope measurements of Ganymede’s aurorae, which follow magnetic field lines, suggest that a subsurface saline ocean also influences the behaviour of the moon’s auroras.</span>
<span class="attribution"><span class="source">NASA, ESA, and A. Feild (STScI)</span></span>
</figcaption>
</figure>
<p>We only know of life on Earth, so when we go looking for where life might exist (or once existed) elsewhere, we’re looking for factors we consider essential to life as we know it.</p>
<p>Watery or icy worlds are the first targets, as we know life on Earth originated in and around water. A rocky surface with warmish temperatures would be even more ideal. Jupiter itself is a complete write-off: the crushing pressures, toxic gases, freezing temperatures and lack of a stable surface would never support life as we know it. But the big, icy moons have good protection deep under the ice, potentially liquid water, and elements like carbon and oxygen.</p>
<p>JUICE will use its suite of science instruments to check out the thicknesses of the moons’ icy crusts, what they’re made of, and look for subsurface liquid water. On Europa in particular, it will look for evidence of organic molecules.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/the-search-for-life-beneath-the-ice-why-were-going-back-to-europa-43846">The search for life beneath the ice: why we're going back to Europa</a>
</strong>
</em>
</p>
<hr>
<h2>An extremely efficient journey</h2>
<p>After its launch, the solar-powered JUICE will take nearly eight years to get to Jupiter. The spacecraft will use minimal propulsion, instead using other planets to give it speed and set its course.</p>
<p>These manoeuvres are called “<a href="https://www.esa.int/Science_Exploration/Space_Science/Exploring_space/Let_gravity_assist_you">gravity assists</a>”. This essentially means JUICE will fly purposefully toward a planet, just missing it, in order to get pulled in by its gravity and “slingshot” past the other side. It may take time, but it is extremely efficient.</p>
<p>Juice’s first gravity assist in 2024 will go around <em>both</em> Earth and our Moon – <a href="https://www.esa.int/ESA_Multimedia/Videos/2022/03/Juice_s_flyby_of_Earth-Moon_system">the first time this has ever been done</a>. Other gravity assists will take it around Venus in 2025, and Earth (only) in 2026 and 2029, before being kicked out to Jupiter for an arrival in mid-2031. </p>
<hr>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/Fw17N3rdN7s?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<hr>
<h2>What happens when JUICE meets Jupiter?</h2>
<p>Fun fact: it will be the first spacecraft to orbit a moon other than our own! </p>
<p>Usually a spacecraft will orbit the main planet (in this case Jupiter) and merely flyby the moons as it loops past. JUICE will start like this, flying by Callisto, Europa and Ganymede a total of 35 times during its three-year tour of the moons. It will briefly meet <a href="https://europa.nasa.gov/">NASA’s Europa Clipper mission</a> around Europa, complimenting this mission nicely.</p>
<p>But in 2034, JUICE will actually switch its orbit from around Jupiter <a href="https://www.esa.int/ESA_Multimedia/Videos/2022/03/Juice_s_elliptical_orbit_around_Ganymede">to go around Ganymede</a>. This will give it an exceptional view, and nearly a year to study this fascinating moon, probing its internal, surface and atmospheric systems.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/520667/original/file-20230413-28-p06afj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A close-up photo of a conical white rocket with ESA logo on it and a cartoon of Jupiter and Earth" src="https://images.theconversation.com/files/520667/original/file-20230413-28-p06afj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/520667/original/file-20230413-28-p06afj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=900&fit=crop&dpr=1 600w, https://images.theconversation.com/files/520667/original/file-20230413-28-p06afj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=900&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/520667/original/file-20230413-28-p06afj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=900&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/520667/original/file-20230413-28-p06afj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1131&fit=crop&dpr=1 754w, https://images.theconversation.com/files/520667/original/file-20230413-28-p06afj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1131&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/520667/original/file-20230413-28-p06afj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1131&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Ariane 5 VA 260 with JUICE ready for launch on the ELA-3 launch pad at Europe’s Spaceport in Kourou, French Guiana on April 12 2023.</span>
<span class="attribution"><a class="source" href="https://www.esa.int/ESA_Multimedia/Images/2023/04/Ariane_5_VA_260_with_Juice_-_Ready_for_launch">ESA/S. Corvaja</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Of particular interest is the magnetic field. Ganymede is one of only three rocky bodies in our Solar System known to have one (Earth and Mercury being the other two). Questions JUICE will be able to investigate are not just the basic question of what is creating Ganymede’s magnetic field, but also what happens to it as Ganymede travels through the larger field produced by Jupiter itself, and how their complex interactions influence auroras on both Jupiter and Ganymede.</p>
<p>JUICE will also get a chance to study Jupiter itself, looking into characteristics of giant gas planets that might be universal. Could Jupiter be the key to understanding other solar systems, and the hundreds of <a href="https://theconversation.com/stars-with-planets-on-strange-orbits-whats-going-on-56511">exoplanets we have discovered orbiting other stars</a>?</p>
<p>So, we might be waiting a while for JUICE’s arrival at Jupiter, but it will be well worth the wait. Could any of these moons have once supported alien life, and what might we learn about our own Earth, its early oceans, and the conditions needed to spawn life?</p><img src="https://counter.theconversation.com/content/203669/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Eleanor K. Sansom receives funding from the International Centre for Radio Astronomy Research and is supported by the Space Science and Technology Centre at Curtin University and the Australian Research Council (DP230100301).</span></em></p>We’re going to get up close and personal with three of Jupiter’s largest moons like never before.Eleanor K. Sansom, Research Associate, Curtin UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2032072023-04-10T12:10:25Z2023-04-10T12:10:25ZJupiter’s moons hide giant subsurface oceans – two missions are sending spacecraft to see if these moons could support life<figure><img src="https://images.theconversation.com/files/519960/original/file-20230407-28-6r7tcb.jpg?ixlib=rb-1.1.0&rect=51%2C27%2C2224%2C1425&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The surface of Europa – one of Jupiter's moons – is a thick layer of solid ice.</span> <span class="attribution"><a class="source" href="https://solarsystem.nasa.gov/resources/204/europas-stunning-surface/?category=moons/jupiter-moons_europa">NASA/JPL-Caltech/SETI Institute</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>On April 13, 2023, the European Space Agency launched a rocket carrying a spacecraft destined for Jupiter. The <a href="https://www.esa.int/Science_Exploration/Space_Science/Juice">Jupiter Icy Moons Explorer</a> – or JUICE – will spend at least three years on Jupiter’s moons after it arrives in 2031. In October 2024, NASA is also planning to launch a robotic spacecraft named <a href="https://europa.nasa.gov/">Europa Clipper</a> to the Jovian moons, highlighting an increased interest in these distant, but fascinating, places in the solar system.</p>
<p><a href="https://www.michaelmsori.com/">I’m a planetary scientist</a> who studies the <a href="https://scholar.google.com/citations?user=NLWIrYoAAAAJ&hl=en&oi=ao">structure and evolution of solid planets and moons</a> in the solar system. </p>
<p>There are many reasons my colleagues and I are looking forward to getting the data that JUICE and Europa Clipper will hopefully be sending back to Earth in the 2030s. But perhaps the most exciting information will have to do with water. Three of Jupiter’s moons – Europa, Ganymede and Callisto – are home to large, underground oceans of liquid water that could support life.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/519961/original/file-20230407-16-27nqat.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Four moons next to a large red spot on the surface of Jupiter." src="https://images.theconversation.com/files/519961/original/file-20230407-16-27nqat.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/519961/original/file-20230407-16-27nqat.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=857&fit=crop&dpr=1 600w, https://images.theconversation.com/files/519961/original/file-20230407-16-27nqat.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=857&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/519961/original/file-20230407-16-27nqat.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=857&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/519961/original/file-20230407-16-27nqat.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1077&fit=crop&dpr=1 754w, https://images.theconversation.com/files/519961/original/file-20230407-16-27nqat.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1077&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/519961/original/file-20230407-16-27nqat.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1077&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">This composite image shows, from top to bottom, Io, Europa, Ganymede and Callisto next to Jupiter.</span>
<span class="attribution"><a class="source" href="https://solarsystem.nasa.gov/resources/2662/family-portrait-of-the-jovian-system/?category=moons/jupiter-moons_europa">NASA</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Meet Io, Europa, Ganymede and Callisto</h2>
<p>Jupiter has dozens of moons. Four of them in particular are of interest to planetary scientists.</p>
<p>Io, Europa, Ganymede and Callisto are, like Earth’s Moon, relatively large, spherical complex worlds. Two previous NASA missions have sent spacecraft to orbit the Jupiter system and collected data on these moons. The <a href="https://solarsystem.nasa.gov/missions/galileo/overview/">Galileo mission</a> orbited Jupiter from 1995 to 2003 and led to geological discoveries on all four large moons. The <a href="https://www.nasa.gov/mission_pages/juno/main/index.html">Juno mission</a> is still orbiting Jupiter today and has provided scientists with an unprecedented view into Jupiter’s composition, structure and space environment. </p>
<p>These missions and other observations revealed that Io, the closest of the four to its host planet, is <a href="https://doi.org/10.1146/annurev.earth.31.100901.145428">abuzz with</a> <a href="https://doi.org/10.1038/nature22339">geological activity</a>, including lava lakes, volcanic eruptions and tectonically formed mountains. But it is not home to large amounts of water.</p>
<p>Europa, Ganymede and Callisto, in contrast, have icy landscapes. Europa’s surface is a frozen wonderland with a young but complex history, <a href="https://doi.org/10.1038/ngeo2245">possibly including icy analogs</a> of plate tectonics and volcanoes. Ganymede, the largest moon in the entire solar system, is bigger than Mercury and has its own magnetic field <a href="https://doi.org/10.1038/384544a0">generated internally from a liquid metal core</a>. Callisto appears somewhat inert compared to the others, but serves as a valuable time capsule of an ancient past that is no longer accessible on the youthful surfaces of Europa and Io.</p>
<p>Most exciting of all: Europa, Ganymede and Callisto all almost certainly possess <a href="https://www.nasa.gov/specials/ocean-worlds/">underground oceans of liquid water</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/519962/original/file-20230407-16-ddggzn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing a cutaway of Europa." src="https://images.theconversation.com/files/519962/original/file-20230407-16-ddggzn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/519962/original/file-20230407-16-ddggzn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=570&fit=crop&dpr=1 600w, https://images.theconversation.com/files/519962/original/file-20230407-16-ddggzn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=570&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/519962/original/file-20230407-16-ddggzn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=570&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/519962/original/file-20230407-16-ddggzn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=716&fit=crop&dpr=1 754w, https://images.theconversation.com/files/519962/original/file-20230407-16-ddggzn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=716&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/519962/original/file-20230407-16-ddggzn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=716&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Warmth from Europa’s interior and tidal energy from Jupiter likely maintain a massive liquid ocean beneath the moon’s icy surface.</span>
<span class="attribution"><a class="source" href="https://photojournal.jpl.nasa.gov/jpeg/PIA24477.jpg">NASA/JPL-Caltech/Michael Carroll</a></span>
</figcaption>
</figure>
<h2>Ocean worlds</h2>
<p>Europa, Ganymede and Callisto have chilly surfaces that are <a href="https://europa.nasa.gov/resources/114/daytime-temperatures-on-europa/">hundreds of degrees below zero</a>. At these temperatures, ice behaves like solid rock. </p>
<p>But <a href="https://theconversation.com/how-has-the-inside-of-the-earth-stayed-as-hot-as-the-suns-surface-for-billions-of-years-193277">just like Earth</a>, the deeper underground you go on these moons, the hotter it gets. Go down far enough and you eventually reach the temperature where ice melts into water. Exactly how far down this transition occurs on each of the moons is a <a href="https://doi.org/10.1016/j.icarus.2005.03.013">subject of debate</a> that scientists hope to resolve with JUICE and Europa Clipper. While the exact depths are still uncertain, scientists are confident that these oceans exist. </p>
<p>The best evidence of these oceans comes from Jupiter’s magnetic field. Saltwater is electrically conductive. So as these moons travel through Jupiter’s magnetic field, they <a href="https://doi.org/10.1126/science.289.5483.1340">generate a secondary, smaller magnetic field</a> that signals to researchers the presence of an underground ocean. Using this technique, planetary scientists have been able to show that the three <a href="https://doi.org/10.1038/27394">moons contain underground oceans</a>. And these oceans are not small – Europa’s ocean alone might have more than <a href="https://solarsystem.nasa.gov/moons/jupiter-moons/europa/overview/">double the water</a> of all of Earth’s oceans combined.</p>
<p>An obvious and tantalizing next question is whether these oceans can support extraterrestrial life. Liquid water is an important piece of what makes for a habitable world, but far from the only requirement for life. Life also needs <a href="https://astrobiology.nasa.gov/education/primer/">energy and certain chemical compounds</a> in addition to water to flourish. Because these oceans are hidden beneath miles of solid ice, <a href="https://doi.org/10.1126/science.1060081">sunlight and photosynthesis are out</a>. But it’s possible other sources could provide the needed ingredients.</p>
<p>On Europa, for example, the liquid water ocean <a href="https://solarsystem.nasa.gov/moons/jupiter-moons/europa/overview/">overlays a rocky interior</a>. That rocky seafloor could provide energy and chemicals through underwater volcanoes that could make Europa’s ocean habitable. But it is also possible that Europa’s ocean is a sterile, inhospitable place – scientists need more data to answer these questions. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/519967/original/file-20230407-16-sd1vga.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Artist's impression of the JUICE spacecraft approaching Jupiter and the jovian moons." src="https://images.theconversation.com/files/519967/original/file-20230407-16-sd1vga.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/519967/original/file-20230407-16-sd1vga.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=339&fit=crop&dpr=1 600w, https://images.theconversation.com/files/519967/original/file-20230407-16-sd1vga.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=339&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/519967/original/file-20230407-16-sd1vga.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=339&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/519967/original/file-20230407-16-sd1vga.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=426&fit=crop&dpr=1 754w, https://images.theconversation.com/files/519967/original/file-20230407-16-sd1vga.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=426&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/519967/original/file-20230407-16-sd1vga.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=426&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Jupiter Icy Moons Explorer spacecraft will travel for eight years before reaching Jupiter.</span>
<span class="attribution"><a class="source" href="https://sci.esa.int/web/juice/-/59334-exploring-jupiter">ESA/ATG medialab/NASA/JPL/University of Arizona/J. Nichols</a></span>
</figcaption>
</figure>
<h2>Upcoming missions from ESA and NASA</h2>
<p>JUICE and Europa Clipper are set up to give scientists game-changing information about the potential habitability of Jupiter’s moons. While both missions will gather data on multiple moons, JUICE will spend time orbiting and focusing on Ganymede, and Europa Clipper will make dozens of close flybys of Europa.</p>
<p>Both of the spacecraft will carry a suite of scientific instruments built specifically to investigate the oceans. Onboard radar will allow JUICE and Europa Clipper <a href="https://rslab.disi.unitn.it/rime/">to probe into the moons’</a> <a href="https://europa.nasa.gov/spacecraft/instruments/reason/">outer layers of solid ice</a>. Radar could reveal any small pockets of liquid water in the ice, or, in the case of Europa, which has a thinner outer ice layer than Ganymede and Callisto, <a href="https://doi.org/10.1016/j.icarus.2016.08.014">hopefully detect the larger ocean</a>. </p>
<p><a href="https://europa.nasa.gov/spacecraft/instruments/ecm/">Magnetometers will also be</a> <a href="https://www.esa.int/Science_Exploration/Space_Science/Juice_factsheet">on both missions</a>. These tools will give scientists the opportunity to study the secondary magnetic fields produced by the interaction of conductive oceans with Jupiter’s field in great detail and will hopefully give researchers clues to salinity and volumes of the oceans. </p>
<p>Scientists will also observe small variations in the moons’ gravitational pulls by tracking subtle movements in both spacecrafts’ orbits, which could help determine if Europa’s seafloor has volcanoes that <a href="https://doi.org/10.1016/j.icarus.2019.02.025">provide the needed energy and chemistry</a> for the ocean to support life.</p>
<p>Finally, both craft will carry a host of cameras and light sensors that will provide unprecedented images of the geology and composition of the moons’ icy surfaces. </p>
<p>Maybe one day, a spacecraft will be able to drill through the miles of solid ice on Europa, Ganymede or Callisto and explore oceans directly. Until then, observations from spacecraft like JUICE and Europa Clipper are scientists’ best bet for learning about these ocean worlds.</p>
<p>When Galileo discovered these moons in 1609, they were the first objects known to directly orbit another planet. Their discovery was the final nail in the coffin of the theory that Earth – and humanity – resides at the center of the universe. Maybe these worlds have another humbling surprise in store.</p><img src="https://counter.theconversation.com/content/203207/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Michael Sori receives funding from NASA. </span></em></p>The Jupiter Icy Moons Explorer and Europa Clipper missions will arrive at Jupiter in the 2030s and provide researchers with unprecedented access to the icy moons orbiting the gas giant.Mike Sori, Assistant Professor of Planetary Science, Purdue UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1463582020-09-18T11:50:53Z2020-09-18T11:50:53ZThe four most promising worlds for alien life in the solar system<figure><img src="https://images.theconversation.com/files/358659/original/file-20200917-14-1qdn4n4.jpg?ixlib=rb-1.1.0&rect=36%2C36%2C1238%2C782&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">NASA's Curiosity Rover takes a selfie on Mars in June, 2018.</span> <span class="attribution"><a class="source" href="https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA22486">NASA/JPL-Caltech/MSSS</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>The Earth’s biosphere contains all the known ingredients necessary for life as we know it. Broadly speaking these are: liquid water, at least one source of energy, and an inventory of biologically useful elements and molecules.</p>
<p>But the recent discovery of possibly biogenic phosphine <a href="https://theconversation.com/venus-could-it-really-harbour-life-new-study-springs-a-surprise-145981">in the clouds of Venus</a> reminds us that at least some of these ingredients exist elsewhere in the solar system too. So where are the other most promising locations for extra-terrestrial life?</p>
<h2>Mars</h2>
<p>Mars is one of the most Earth-like worlds in the solar system. It has a 24.5-hour day, polar ice caps that expand and contract with the seasons, and a large array of surface features that were sculpted by water during the planet’s history.</p>
<figure class="align-center ">
<img alt="Red planet Mars in space with polar ice caps visible" src="https://images.theconversation.com/files/358594/original/file-20200917-24-fwl0h9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/358594/original/file-20200917-24-fwl0h9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/358594/original/file-20200917-24-fwl0h9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/358594/original/file-20200917-24-fwl0h9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/358594/original/file-20200917-24-fwl0h9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/358594/original/file-20200917-24-fwl0h9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/358594/original/file-20200917-24-fwl0h9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Mars has polar ice caps.</span>
<span class="attribution"><a class="source" href="https://upload.wikimedia.org/wikipedia/commons/0/02/OSIRIS_Mars_true_color.jpg">ESA & MPS for OSIRIS Team MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA)</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>The detection of <a href="https://www.sciencemag.org/news/2018/07/liquid-water-spied-deep-below-polar-ice-cap-mars">a lake beneath</a> the southern polar ice cap and methane in the Martian atmosphere (which varies with the seasons and even the <a href="https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GL083800">time of day</a>) make Mars a very interesting candidate for life. Methane is significant as it can be produced by biological processes. But the actual source for the methane on Mars is not yet known.</p>
<p>It is possible that life may have gained a foothold, given the <a href="https://advances.sciencemag.org/content/4/6/eaar3330">evidence</a> that the planet once had a much more benign environment. Today, Mars has a very thin, dry atmosphere comprised almost entirely of carbon dioxide. This offers scant protection from solar and cosmic radiation. If Mars has managed to retain some reserves of water beneath its surface, it is not impossible that life may still exist. </p>
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Read more:
<a href="https://theconversation.com/life-on-mars-europe-commits-to-groundbreaking-mission-to-bring-back-rocks-to-earth-128328">Life on Mars? Europe commits to groundbreaking mission to bring back rocks to Earth</a>
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<h2>Europa</h2>
<p>Europa was discovered by Galileo Galilei in 1610, along with Jupiter’s three other larger moons. It is slightly smaller than Earth’s moon and orbits the gas giant at a distance of some 670,000km once every 3.5 days. Europa is constantly squeezed and stretched by the competing gravitational fields of Jupiter and the other <a href="https://www.universetoday.com/44796/galilean-moons/">Galilean moons</a>, a process known as tidal flexing. </p>
<p>The moon is believed to be a geologically active world, like the Earth, because the strong tidal flexing heats its rocky, metallic interior and keeps it partially molten.</p>
<figure class="align-center ">
<img alt="Jupiter's white with brown streaks moon Europa in space," src="https://images.theconversation.com/files/358637/original/file-20200917-14-1hfzvc8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/358637/original/file-20200917-14-1hfzvc8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=444&fit=crop&dpr=1 600w, https://images.theconversation.com/files/358637/original/file-20200917-14-1hfzvc8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=444&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/358637/original/file-20200917-14-1hfzvc8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=444&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/358637/original/file-20200917-14-1hfzvc8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=557&fit=crop&dpr=1 754w, https://images.theconversation.com/files/358637/original/file-20200917-14-1hfzvc8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=557&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/358637/original/file-20200917-14-1hfzvc8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=557&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Europa’s icy surface is a good sign for alien hunters.</span>
<span class="attribution"><a class="source" href="https://photojournal.jpl.nasa.gov/catalog/PIA19048">NASA/JPL-Caltech/SETI Institute</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>The surface of Europa is a vast expanse of water ice. Many scientists think that beneath the frozen surface is a layer of liquid water – a global ocean – which is prevented from freezing by the heat from flexing and which maybe over 100km deep. </p>
<p>Evidence for this ocean includes geysers erupting through <a href="https://www.nature.com/articles/s41550-019-0933-6">cracks in the surface ice</a>, a <a href="http://ffden-2.phys.uaf.edu/webproj/212_spring_2015/Justin_Long/Justin_Long/magnetic.html">weak magnetic field</a> and <a href="https://www.sciencedirect.com/science/article/abs/pii/S0019103599961870?via%3Dihub">chaotic terrain</a> on the surface, which could have been deformed by ocean currents swirling beneath. This icy shield insulates the subsurface ocean from the extreme cold and vacuum of space, as well as Jupiter’s ferocious radiation belts.</p>
<p>At the bottom of this ocean world it is conceivable that we might find <a href="https://oceanservice.noaa.gov/facts/vents.html">hydrothermal vents</a> and ocean floor volcanoes. On Earth, such features often support very rich and diverse ecosystems.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/europa-there-may-be-life-on-jupiters-moon-and-two-new-missions-will-pave-the-way-for-finding-it-122551">Europa: there may be life on Jupiter's moon and two new missions will pave the way for finding it</a>
</strong>
</em>
</p>
<hr>
<h2>Enceladus</h2>
<p>Like Europa, <a href="https://solarsystem.nasa.gov/moons/saturn-moons/enceladus/in-depth/">Enceladus</a> is an ice-covered moon with a subsurface ocean of liquid water. Enceladus orbits Saturn and first came to the attention of scientists as a potentially habitable world following the <a href="https://solarsystem.nasa.gov/resources/806/bursting-at-the-seams-the-geyser-basin-of-enceladus/">surprise discovery</a> of enormous geysers near the moon’s south pole.</p>
<p>These jets of water escape from large cracks on the surface and, given Enceladus’ weak gravitational field, spray out into space. They are clear evidence of an underground store of liquid water.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"906891543780323328"}"></div></p>
<p>Not only was water detected in these geysers but also an array of organic molecules and, crucially, tiny grains of rocky silicate particles that can only be present if the sub-surface ocean water was in physical contact with the rocky ocean floor at a <a href="https://solarsystem.nasa.gov/missions/cassini/science/enceladus/">temperature of at least 90˚C</a>. This is very strong evidence for the existence of hydrothermal vents on the ocean floor, providing the chemistry needed for life and localised sources of energy. </p>
<h2>Titan</h2>
<p>Titan is the largest moon of Saturn and the only moon in the solar system with a substantial atmosphere. It contains a thick orange haze of complex organic molecules and a methane weather system in place of water – complete with seasonal rains, dry periods and surface sand dunes created by wind.</p>
<figure class="align-center ">
<img alt="Yellow/orange moon Titan in space" src="https://images.theconversation.com/files/358645/original/file-20200917-16-17xgwya.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/358645/original/file-20200917-16-17xgwya.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/358645/original/file-20200917-16-17xgwya.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/358645/original/file-20200917-16-17xgwya.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/358645/original/file-20200917-16-17xgwya.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/358645/original/file-20200917-16-17xgwya.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/358645/original/file-20200917-16-17xgwya.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Titan’s atmosphere makes it look like a fuzzy orange ball.</span>
<span class="attribution"><a class="source" href="https://photojournal.jpl.nasa.gov/catalog/PIA14602">NASA/JPL-Caltech/Space Science Institute</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>The atmosphere consists mostly of nitrogen, an important chemical element used in the construction of proteins in all known forms of life. Radar observations have detected the presence of <a href="https://theconversation.com/titan-first-global-map-uncovers-secrets-of-a-potentially-habitable-moon-of-saturn-126985">rivers and lakes</a> of liquid methane and ethane and possibly the presence of cryovolcanoes – volcano-like features that erupt liquid water rather than lava. This suggests that Titan, like Europa and Enceladus, has a sub-surface reserve of liquid water.</p>
<p>At such an enormous distance from the Sun, the surface temperatures on Titan are a frigid -180˚C – way too cold for liquid water. However, the bountiful chemicals available on Titan has raised speculation that lifeforms – potentially with fundamentally different chemistry to terrestrial organisms – <a href="https://www.space.com/8547-strange-discovery-titan-leads-speculation-alien-life.html">could exist</a> there.</p><img src="https://counter.theconversation.com/content/146358/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Gareth Dorrian does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The clouds of Venus may harbour alien life. But where else?Gareth Dorrian, Post Doctoral Research Fellow in Space Science, University of BirminghamLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1225512019-08-28T10:21:49Z2019-08-28T10:21:49ZEuropa: there may be life on Jupiter’s moon and two new missions will pave the way for finding it<figure><img src="https://images.theconversation.com/files/289801/original/file-20190828-184217-tucepa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Enigmatic Europa.</span> <span class="attribution"><span class="source">NASA</span></span></figcaption></figure><p>It’s brilliant news. In just over a decade, there will be two spacecraft exploring <a href="https://theconversation.com/the-moon-was-a-first-step-mars-will-test-our-capabilities-but-europa-is-the-prize-37253">one of the most habitable worlds</a> in the solar system – Jupiter’s moon Europa. That’s thanks to a recent announcement by NASA that the orbiter <a href="https://www.jpl.nasa.gov/news/news.php?feature=7480">Europa Clipper</a> has been given the go ahead, scheduled to reach the moon at the beginning of the 2030s.</p>
<p>In April this year, the European Space Agency also <a href="http://sci.esa.int/juice/61286-review-board-gives-juice-the-all-clear/">approved development</a> of the Jupiter Icy Moons Explorer (<a href="http://sci.esa.int/juice/">JUICE</a>), which is currently slated to reach the Jupiter system in 2029.</p>
<p>At the dawn of the space age, it was imagined that all life was ultimately dependent on energy from the sun. The frozen ice ball moons of the outer planets seemed unlikely abodes for any kind of life. Discoveries of thriving ecosystems at the bottom the oceans of Earth, relying on hydrothermal vents for both energy and molecular fuel, changed all that. Now we know that life can thrive in environments that are completely isolated from the sun.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/XotF9fzo4Vo?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>Europa is thought to be able to harbour simple, microbial life in its liquid, <a href="https://europa.nasa.gov/about-europa/ocean/">internal ocean</a> beneath its icy surface. That is because it has each of three essential prerequisites for life in abundance: a source of biochemically useful molecules, a source of energy and a liquid solvent (water) in which dissolved substances can chemically react with each other. </p>
<p>Europa’s energy comes from a combination of its slightly elliptical orbit about Jupiter and its gravitational interaction with two other moons. This combination of forces subject Europa to a tidal variation in gravity with each orbit, causing it to <a href="https://www.nature.com/articles/325133a0">flex and release heat</a>, which prevents the water from freezing. </p>
<p>Europa’s biochemically useful molecules may come from <a href="https://theconversation.com/building-blocks-of-life-found-among-organic-compounds-on-comet-67p-what-philae-discoveries-mean-45379">impacts by comets</a> or from deep within the moon’s rocky core.</p>
<h2>Ice penetrating radar</h2>
<p>Both Europa Clipper and JUICE will carry special radar instruments to probe beneath Europa’s surface ice. This is not a new technique, radar has been used since the 1970s to find sub-glacial lakes in <a href="http://www.antarcticglaciers.org/glacier-processes/glacial-lakes/subglacial-lakes/">Antarctica</a> and, more recently, on <a href="https://science.sciencemag.org/content/361/6401/490">Mars</a>. </p>
<p>As it happens, Europa may offer an even more suitable environment in which to try this out because the colder ice gets, the more transparent it becomes to radar. Being so far from the sun, typical daytime surface temperatures at Europa are -170°C. The goal at Europa is to establish the depth at which the ice sheet gives way to a global ocean of liquid water. Current models predicts that is at a depth of <a href="https://solarsystem.nasa.gov/moons/jupiter-moons/europa/in-depth/">15-25km</a>. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/289823/original/file-20190828-184234-ylqt4i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/289823/original/file-20190828-184234-ylqt4i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=528&fit=crop&dpr=1 600w, https://images.theconversation.com/files/289823/original/file-20190828-184234-ylqt4i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=528&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/289823/original/file-20190828-184234-ylqt4i.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=528&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/289823/original/file-20190828-184234-ylqt4i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=664&fit=crop&dpr=1 754w, https://images.theconversation.com/files/289823/original/file-20190828-184234-ylqt4i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=664&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/289823/original/file-20190828-184234-ylqt4i.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=664&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Europa Clipper with Jupiter in the background.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech</span></span>
</figcaption>
</figure>
<p>However, liquid water may also be found much closer to the surface, which would be easier to get to. Evidence from Hubble Space Telescope images <a href="https://www.nasa.gov/press-release/nasa-s-hubble-spots-possible-water-plumes-erupting-on-jupiters-moon-europa">appear to show</a> plumes of liquid water erupting from the southern hemisphere. Production of these plumes might function something like a volcano, with liquid water welling up from the ocean below. </p>
<p>Water, under sufficient pressure, will force its way through fractures and voids inside the ice, eventually reaching the surface to erupt as geysers. During this process, any liquid water that doesn’t quite make it to the surface may nonetheless fill <a href="https://science.nasa.gov/science-news/science-at-nasa/2011/16nov_europa">voids and cracks</a> within the ice, forming something very similar to the sub-glacial lakes of Mars and Antarctica. </p>
<p>The missions should be able to find these features if they exist. All of this contributes to one of the ultimate goals of these missions, which is to scout out the best location for a future lander which could one day drill through the ice and reach the enigmatic ocean realm beneath.</p>
<h2>Gravity maps</h2>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/289815/original/file-20190828-184196-xifp4j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/289815/original/file-20190828-184196-xifp4j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=776&fit=crop&dpr=1 600w, https://images.theconversation.com/files/289815/original/file-20190828-184196-xifp4j.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=776&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/289815/original/file-20190828-184196-xifp4j.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=776&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/289815/original/file-20190828-184196-xifp4j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=976&fit=crop&dpr=1 754w, https://images.theconversation.com/files/289815/original/file-20190828-184196-xifp4j.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=976&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/289815/original/file-20190828-184196-xifp4j.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=976&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Europa’s interior.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>Spacecraft travelling near the surface of a planet or moon can use slight changes in rocket speed to detect subtle variations in the gravitational field of that object. Such “gravitational anomalies” are caused by changes in the density of material under the planetary surface as the spacecraft flies overhead. </p>
<p>For example, denser rock that one might find in a mountain range can cause the spacecraft to experience a measureable extra gravitational tug. Detection of gravitational anomalies on Earth has been used for many years to identify subterranean structures such as oil fields, metal deposits and the famous dinosaur-destroying impact crater at <a href="https://www.lpi.usra.edu/science/kring/Chicxulub/discovery/">Chixculub</a> in Mexico.</p>
<p>JUICE and Europa Clipper will also be able to detect gravitational anomalies and potentially allow scientists to find interesting features at the bottom of the ocean. A smooth ocean floor with small gravitational anomalies would actually be a <a href="https://www.sciencedirect.com/science/article/abs/pii/S0019103517308527?via%3Dihub">boon to the prospects of life</a>, as it would imply more heat flow from the moon’s interior. </p>
<h2>Getting through the ice</h2>
<p>But to ultimately find life on Europa, we have to get beneath the ice by one day putting a lander on the surface, potentially carrying a submarine. Even if Europa Clipper and JUICE do identify where the ice is thinnest, this will be challenging. </p>
<p>Europa is close to Jupiter, meaning that spacecraft need lots of fuel to change their velocity enough that they can get out of the planet’s massive gravity field and enter into orbit about the moon. JUICE, in fact, will become the first spacecraft to perform this manoeuvre at Ganymede, one of Jupiter’s other moons, and it will use 3,000 kg of fuel to do it on the same journey.</p>
<p>There are also huge amounts of harmful radiation at Jupiter, which can <a href="https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=1134214">damage spacecraft</a> in the long run. Europa Clipper will therefore stay in long looping orbits about Jupiter, repeatedly taking it out of the radiation field. It will study Europa by instead performing flybys of the moon.</p>
<p>The lack of substantial atmosphere at Europa poses another problem. It means we can’t slow a lander with heat shields and parachutes. Everything must be done with rockets, requiring yet more fuel. The lack of atmosphere also offers little protection from radiation while the lander is on the surface.</p>
<p>Even if a spacecraft survives a landing, there is the matter of the ice itself. Using a mechanical drill to bore through many miles of super-cold ice, which is as hard as granite, is unlikely. Instead more exotic means of getting through are being considered, such as using <a href="https://www.universetoday.com/140499/archimedes-digging-into-the-ice-on-europa-with-lasers/">lasers</a> or heat from a <a href="https://interestingengineering.com/nuclear-powered-drilling-bot-to-look-for-life-on-europa">nuclear reactor</a> to melt through the ice. </p>
<p>Another consideration is that Europa, currently, is a pristine environment. That means these complex tasks must be done without inadvertently contaminating the ocean with pollutants from the spacecraft, or any terrestrial microbes which may have hitched a ride.</p>
<p>But one way or another, we will get there. The final challenge might then be ensuring that the spacecraft or submarine, having finally reached the ocean, doesn’t get eaten by something swimming around in the deep.</p><img src="https://counter.theconversation.com/content/122551/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Gareth Dorrian does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>NASA’s Europa Clipper mission just got the green light - here’s what it could achieve.Gareth Dorrian, Post Doctoral Research Fellow in Space Science, University of BirminghamLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1186612019-06-13T14:48:32Z2019-06-13T14:48:32ZLife on Jupiter’s moon Europa? Discovery of table salt on the surface boosts hopes<figure><img src="https://images.theconversation.com/files/279316/original/file-20190613-32331-z2nvyh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Varied terrain on Europa.</span> <span class="attribution"><a class="source" href="https://photojournal.jpl.nasa.gov/catalog/PIA19048">NASA/JPL-Caltech/SETI Institute</a></span></figcaption></figure><p>Europa, a frozen moon around Jupiter, is believed to be <a href="https://theconversation.com/the-moon-was-a-first-step-mars-will-test-our-capabilities-but-europa-is-the-prize-37253">one of the most habitable worlds</a> in the solar system. It was first imaged in detail by the <a href="https://voyager.jpl.nasa.gov/">Voyager 1</a> probe in 1979, revealing a surface almost devoid of large craters. This suggested that water regularly floods up from inside, resurfacing the satellite. Europa is also criss-crossed with long troughs, folds and ridges, potentially made of icebergs floating around in melt-water or slush.</p>
<p>But it was in the late 1990s that Europa got really interesting. The Galileo mission found evidence that it had a <a href="https://www.nytimes.com/2018/10/08/science/margaret-kivelson-europa.html">sub-surface liquid salt water ocean</a>. The fact that it is salty gives us clues that the water may be in contact with rock – a process that could provide energy in the water to feed microbial life. </p>
<p>But the observations were too few and limited for us to separately tell how deep and how salty the ocean is – let alone what kind of salts there are. Now a new study, <a href="https://advances.sciencemag.org/content/5/6/eaaw7123">published in Science Advances</a>, shows it may well be normal table salt (sodium chloride) – just like on Earth. This has important implications for the potential existence of life in Europa’s hidden depths.</p>
<p>Scientists believe that hydrothermal circulation within the ocean, possibly driven by <a href="https://oceanservice.noaa.gov/facts/vents.html">hydrothermal vents</a> might naturally enrich the ocean in sodium chloride, via chemical reactions between the ocean and rock. On Earth, hydrothermal vents are thought to be a <a href="https://theconversation.com/weve-been-wrong-about-the-origins-of-life-for-90-years-63744">source of life</a>, such as bacteria. Plumes emanating from the south pole of Saturn’s moon Enceladus, which has a similar ocean, have been found to contain sodium chloride, making both Europa and Enceladus even more enticing targets for exploration.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/279318/original/file-20190613-32342-1kl0900.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/279318/original/file-20190613-32342-1kl0900.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=381&fit=crop&dpr=1 600w, https://images.theconversation.com/files/279318/original/file-20190613-32342-1kl0900.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=381&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/279318/original/file-20190613-32342-1kl0900.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=381&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/279318/original/file-20190613-32342-1kl0900.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=479&fit=crop&dpr=1 754w, https://images.theconversation.com/files/279318/original/file-20190613-32342-1kl0900.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=479&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/279318/original/file-20190613-32342-1kl0900.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=479&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Chaos regions on Europa’s trailing hemisphere.</span>
<span class="attribution"><span class="source">NASA/JPL</span></span>
</figcaption>
</figure>
<p>If we look at the spectrum (the breakdown of light according to wavelength) of light reflected from the surface, we can infer what substances are there. This shows evidence of water ice. But there are also two other materials: “hydrated” sulphuric acid and sulphate salt. Where do they come from? For scientists studying the interior of Europa, or those examining the astrobiological potential of the moon’s ocean, the really interesting question is: do they come from inside Europa?</p>
<p>Like our moon and Earth, Europa is <a href="https://en.wikipedia.org/wiki/Tidal_locking">tidally locked</a> to Jupiter, meaning that it always presents the same side to the giant planet. Galileo observations revealed the presence of “hydrated” sulphuric acid on the side of Europa that faces backwards along its orbit, the trailing hemisphere. To make sulphuric acid in water ice you need a source of sulphur, and energy to drive the chemical reaction. Some of this may come up from inside the moon in the form of sulphate salts, some of it can be delivered by meteorites, but the most likely explanation is that it comes from its sibling <a href="https://solarsystem.nasa.gov/moons/jupiter-moons/io/in-depth/">volcanic moon, Io</a>.</p>
<p>Sulphur would be ejected into space from volcanoes on Io and eventually make its way to Europa. Moving faster than Europa, the sulphur would most likely hit the trailing side of Europa and implant itself in the ice. The energy required for it to do this <a href="https://www.jpl.nasa.gov/news/news.php?feature=7191">would come from electrons</a> in Jupiter’s radiation belts. For the most part, they go around Jupiter faster than Europa, <a href="https://photojournal.jpl.nasa.gov/catalog/PIA16921">hit its trailing side and deliver tonnes of energy</a>.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/279317/original/file-20190613-32321-1jcl8p3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/279317/original/file-20190613-32321-1jcl8p3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=572&fit=crop&dpr=1 600w, https://images.theconversation.com/files/279317/original/file-20190613-32321-1jcl8p3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=572&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/279317/original/file-20190613-32321-1jcl8p3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=572&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/279317/original/file-20190613-32321-1jcl8p3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=718&fit=crop&dpr=1 754w, https://images.theconversation.com/files/279317/original/file-20190613-32321-1jcl8p3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=718&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/279317/original/file-20190613-32321-1jcl8p3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=718&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Concentrations of sulphuric acid on the surface. The trailing hemisphere is to the upper left where the concentrations are higher.</span>
<span class="attribution"><span class="source">NASA/JPL</span></span>
</figcaption>
</figure>
<p>Measurements have also shown evidence for sulphate salts, such as <a href="https://www.epsomsaltcouncil.org/uses-benefits/">magnesium sulphate (Epsom salts)</a> but it has remained unclear where it comes from.</p>
<p>The team behind the new study reasoned that the side of Europa facing along its orbit, the leading hemisphere, which is shielded from the sulphur bombardment, might be the best place to look for evidence of what salts actually exist inside Europa. </p>
<p>In the visible part of a spectrum there are distinct features called “colour centres” that appear when irradiated by very energetic electrons. The researchers used the powerful <a href="https://theconversation.com/telescopes-on-the-ground-may-be-cheaper-but-hubble-shows-why-they-are-not-enough-40724">Hubble Space Telescope </a> to look for evidence of these colour centres in Europa’s spectrum and discovered a feature located exclusively on the side of the moon facing along its orbit, showing evidence for sodium chloride.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/279384/original/file-20190613-32342-1mp8ym6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/279384/original/file-20190613-32342-1mp8ym6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=300&fit=crop&dpr=1 600w, https://images.theconversation.com/files/279384/original/file-20190613-32342-1mp8ym6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=300&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/279384/original/file-20190613-32342-1mp8ym6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=300&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/279384/original/file-20190613-32342-1mp8ym6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=377&fit=crop&dpr=1 754w, https://images.theconversation.com/files/279384/original/file-20190613-32342-1mp8ym6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=377&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/279384/original/file-20190613-32342-1mp8ym6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=377&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Europa in natural colour on the left, and false colour on the right. The brown/red regions on the right might correspond to the sulphuric acid regions, the yellow-ish terrain on the left is now thought to be produced by sodium chloride.</span>
<span class="attribution"><span class="source">NASA/JPL/University of Arizona</span></span>
</figcaption>
</figure>
<h2>Type of salt</h2>
<p>Although there were some hints of salts in the Galileo observations, the newer Hubble data has allowed the scientists to narrow it down to a region on the leading hemisphere called the chaos terrain, and not in regions where the sulphur chemistry could be driven by radiation. That means they really are likely to come from Europa’s interior.</p>
<p>Life, as we know it, needs liquid water and energy. That Europa has a liquid ocean at all tells us that there is liquid water and a source of energy to stop it from freezing. But the chemical make-up of the ocean is also crucial. Brine, “salty water”, has a lower freezing point than pure water, meaning it makes the water more habitable.</p>
<p>Salt, specifically the sodium ions in table salt, is also crucial for a whole range of metabolic processes in plant and animal life. By contrast some other salts, such as sulphates, <a href="https://theconversation.com/what-on-earth-could-live-in-a-salt-water-lake-on-mars-an-expert-explains-101148">might inhibit life</a> if present in large quantities. The researchers were keen to point out that they might just be seeing the end-point of a complicated chain of sub-surface processes – the salt might just be part of the natural ice layers. But, for those hoping there is life on Europa, the discovery of sodium chloride is good news.</p><img src="https://counter.theconversation.com/content/118661/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Arridge receives funding from the Royal Society and the Science and Technology Facilities Council.</span></em></p>Whether anything could live in Europa’s subsurface ocean depends on what kind of salt it contains. Now scientists have found out.Chris Arridge, Research Fellow/Lecturer, Lancaster UniversityLicensed 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>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/xrGAQCq9BMU?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<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>
</figure>
<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>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/_dafbHGxNOE?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<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/965072018-05-14T15:11:24Z2018-05-14T15:11:24ZSigns of water plumes boost chances of finding life on Jupiter’s moon Europa<figure><img src="https://images.theconversation.com/files/218761/original/file-20180514-178757-kdxbd5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Artist's impression of the Europa clipper mission.</span> <span class="attribution"><span class="source">NASA</span></span></figcaption></figure><p>Along with Mars, Jupiter’s moon Europa has long captured the imagination of science fiction writers as a potential place for life in the solar system beyond Earth. In science fact, missions have found hints of a subsurface water ocean below the icy crust of the moon. And where there’s warm, liquid water, and the right chemistry, <a href="https://theconversation.com/the-moon-was-a-first-step-mars-will-test-our-capabilities-but-europa-is-the-prize-37253">there could indeed be life</a>.</p>
<p>Finding out whether this is the case is not going to be easy though. One complicated and expensive solution would be landing on the moon and drilling a hole through the ice to sample the water beneath. But now research has thrown up a better option. The exciting results, <a href="http://nature.com/articles/doi:10.1038/s41550-018-0450-z">published in Nature Astronomy</a>, suggest there may be plumes emanating from Europa’s ocean – meaning a spacecraft could simply fly though them to test the water. The findings are important for the upcoming <a href="https://www.nasa.gov/europa/">Europa Clipper</a> missions and <a href="http://sci.esa.int/juice/">JUICE</a> missions. </p>
<p>It’s not the first time it’s been suggested that there are geyser-like features on the moon. The Hubble Space Telescope saw <a href="https://www.nasa.gov/press-release/nasa-s-hubble-spots-possible-water-plumes-erupting-on-jupiters-moon-europa">transient signs of plumes</a> from Europa’s subsurface ocean in 2012 and 2016. However, the result was controversial – the data was after all captured from far away (Hubble orbits the Earth). The new evidence instead comes from an actual flyby of Europa by the <a href="https://www.jpl.nasa.gov/missions/galileo/">Galileo mission</a> in 1997 – significantly strengthening the evidence that there are plumes on the moon.</p>
<p>We don’t know exactly how thick Europa’s ice shell is or how deep its subsurface ocean is. A 2011 study showed that there are locations where <a href="https://science.nasa.gov/science-news/science-at-nasa/2011/16nov_europa">water may be relatively close to the surface</a> in great lakes, near chopped up icy “chaos regions”, which are similar to some Antarctic structures on Earth. </p>
<h2>Lessons from Enceladus</h2>
<p>The <a href="https://theconversation.com/bittersweet-feeling-as-cassini-mission-embarks-on-its-grand-finale-ahead-of-death-plunge-76670">Cassini mission to Saturn</a> discovered huge plumes of water coming from the small moon Enceladus. The first hints were from magnetic field deflections and an abundance of charged particles in a certain region of the moon. We know that the dense gas of newly emerged molecules and atoms in a watery plume becomes charged (ionised) as electrons are knocked off. This makes it electrically conducting, causing changes to surrounding magnetic fields.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/164865/original/image-20170411-26720-1avikn7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/164865/original/image-20170411-26720-1avikn7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/164865/original/image-20170411-26720-1avikn7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=218&fit=crop&dpr=1 600w, https://images.theconversation.com/files/164865/original/image-20170411-26720-1avikn7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=218&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/164865/original/image-20170411-26720-1avikn7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=218&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/164865/original/image-20170411-26720-1avikn7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=274&fit=crop&dpr=1 754w, https://images.theconversation.com/files/164865/original/image-20170411-26720-1avikn7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=274&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/164865/original/image-20170411-26720-1avikn7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=274&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Enceladus’s south polar plumes, as seen by Cassini November 30 2010.</span>
<span class="attribution"><a class="source" href="https://photojournal.jpl.nasa.gov/catalog/PIA17184">NASA/JPL-Caltech/Space Science Institute</a></span>
</figcaption>
</figure>
<p>Next, the plumes were actually spotted in spectacular images, emanating from what looks like tiger stripes near the south pole. There is evidence from gravity measurements that the source is a subsurface ocean.</p>
<p>Cassini flew past Enceladus 22 times, enabling exploration of the plumes ejected directly from the ocean below. As well as simple water, ions and charged grains in the plumes, Cassini found sodium – a sign that the ocean is salty. <a href="https://theconversation.com/icy-plumes-bursting-from-saturns-moon-enceladus-suggest-it-could-harbour-life-38673">It also found silicates</a>, which indicate a sandy ocean floor and potentially the existence of hydrothermal vents. </p>
<p>This is important as chemical reactions between sand and water can provide enough energy in the water to feed microbial life (and tends to happen near hydrothermal vents on Earth). Finally, in 2107, Cassini also discovered hydrogen in the plumes, which should be a byproduct of such water-sand reactions. This is as close as you can get to a proof that it is <a href="https://theconversation.com/nasa-saturn-moon-enceladus-is-able-to-host-life-its-time-for-a-new-mission-76102">a suitable candidate to host life</a>.</p>
<p>Following these exciting discoveries, the hunt was on for plumes at Europa. Based on the Hubble measurements, estimates in 2012 showed that the amount of water released in the Europa plumes could be a factor 30 times that of Enceladus. The plumes appeared to have a height of some 200km. Like Enceladus, the floor of Europa’s ocean <a href="https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2016GL068547">is likely in contact with sand and rock</a>. This is in contrast to some other moons with subsurface oceans – including Ganymede and Callisto – where the ocean floor is ice.</p>
<p>In the new study, magnetometer data from a Galileo flyby less than 400km above Europa’s icy surface was reexamined and compared with a modern computer model of how charged gas on Europa should behave. The results – based on an observed deflection and decrease in the observed magnetic field over a distance of 1,000km – imply that there’s a dense region of charged particles. This is very likely to be the result of a plume, making it the best direct evidence for such an occurence yet.</p>
<h2>Upcoming missions</h2>
<p>As with Enceladus, the Europa plumes offer the tantalising prospect of directly sampling material from the subsurface ocean. Two future missions will be able to explore this. The European Space Agency’s <a href="http://sci.esa.int/juice/">JUICE mission</a>, which I am involved in developing, is due to launch in 2022 and will arrive in the Jupiter system on 2030. Two close flybys of Europa are planned as part of a sequence, before going into orbit around the moon Ganymede in 2032. </p>
<p>NASA’s <a href="https://www.nasa.gov/europa/">Europa Clipper</a> will perform 45 flybys of Europa. Both these missions can explore the plumes in the same way the Cassini orbiter did at Enceladus. Following these, landers or penetrators at Europa have been proposed (but yet to secure funding). In the meantime, sampling the plumes could provide many exciting insights into what’s going on in the ocean. If we are really lucky we may even be able to detect signatures of biological activity. Unfortunately, Cassini was not equipped to look for such signatures at Enceladus.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/218702/original/file-20180513-34018-8x5odj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/218702/original/file-20180513-34018-8x5odj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=443&fit=crop&dpr=1 600w, https://images.theconversation.com/files/218702/original/file-20180513-34018-8x5odj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=443&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/218702/original/file-20180513-34018-8x5odj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=443&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/218702/original/file-20180513-34018-8x5odj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=557&fit=crop&dpr=1 754w, https://images.theconversation.com/files/218702/original/file-20180513-34018-8x5odj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=557&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/218702/original/file-20180513-34018-8x5odj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=557&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">NASA/JPL-Caltech/SETI Institute</span></span>
</figcaption>
</figure>
<p>This means there are now four likely locations for life beyond Earth in our solar systems. First Mars, where <a href="https://theconversation.com/our-rover-could-discover-life-on-mars-heres-what-it-would-take-to-prove-it-89625">conditions were right for life</a> to form 3.8 billion years ago. We will explore this further with the <a href="http://exploration.esa.int/mars/48088-mission-overview/">ExoMars 2020 rover</a>, <a href="https://theconversation.com/decades-of-attempts-show-how-hard-it-is-to-land-on-mars-heres-how-we-plan-to-succeed-in-2021-69734">which I am also involved in developing</a>. This will be able to drill up to two metres underneath the surface to search for biomarkers, as well as the NASA Mars 2020 rover and the related <a href="https://www.space.com/40570-nasa-sending-helicopter-to-mars.html">helicopter recently announced</a>. </p>
<p>But on Europa and Enceladus there could actually be life now, and sampling the plumes will help reveal whether this is the case. At Saturn’s moon Titan, we have also found signs of complex prebiotic chemistry that once gave rise to life on Earth. This means it <a href="https://theconversation.com/saturns-moon-titan-may-harbour-simple-life-forms-and-reveal-how-organisms-first-formed-on-earth-81527">is a location for future or perhaps current life</a>.</p>
<p>As well as the planned missions to Mars and Europa, it is therefore also important that we also return to the Saturn system to track down where there may be life elsewhere. NASA’s <a href="https://www.space.com/36598-dragonfly-quadcopter-saturn-moon-titan-explorer.html">Dragonfly quadcopter</a> proposed for Titan is one possibility. </p>
<p>With so many promising candidates for life in our own solar system, it is exciting to think that it could be just a few years until we discover some form of microbial alien life.</p><img src="https://counter.theconversation.com/content/96507/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Andrew Coates receives funding from STFC and UKSA. </span></em></p>We could find evidence of life on Europa within a couple of decades.Andrew Coates, Professor of Physics, Deputy Director (Solar System) at the Mullard Space Science Laboratory, UCLLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/735082017-02-23T19:23:44Z2017-02-23T19:23:44ZThe search for extraterrestrial life in the water worlds close to home<figure><img src="https://images.theconversation.com/files/158021/original/image-20170223-32094-bd6imx.jpg?ixlib=rb-1.1.0&rect=308%2C222%2C1089%2C769&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A likely candidate for life: Saturn's icy moon Enceladus.</span> <span class="attribution"><a class="source" href="https://saturn.jpl.nasa.gov/resources/7597/?category=images">NASA/JPL-Caltech/Space Science Institute</a></span></figcaption></figure><p>The discovery of <a href="https://theconversation.com/seven-earth-sized-planets-discovered-orbiting-a-nearby-star-73352">seven exoplanets around a star</a> 40 light years from our Sun has raised the possibility that they could <a href="https://exoplanets.nasa.gov/news/1419/nasa-telescope-reveals-largest-batch-of-earth-size-habitable-zone-planets-around-single-star/">harbour life</a>. </p>
<p>Why? Because the astronomers who made the discovery believe some of the planets may have liquid water. And on Earth, wherever there is liquid water, there is life. </p>
<p>But we believe we can look much closer to Earth for potential candidates for evidence of extraterrestrial life, as we state this month in the <a href="https://doi.org/10.1017/S1473550416000483">International Journal of Astrobiology</a>.</p>
<p>Recent discoveries by the NASA Voyager and Cassini space missions infer the presence of liquid oceans beneath a sea ice crust on some of the moons of Jupiter and Saturn. </p>
<p>These provide the most likely sites for finding extraterrestial life in our solar system.</p>
<h2>Just like on Earth</h2>
<p>The independent scientist <a href="http://www.jameslovelock.org/">James Lovelock</a>, best known for developing the Gaia hypothesis, was contracted to NASA in the 1960s to develop atmospheric and planetary sensors for the Viking probes subsequently deployed to Mars in 1975.</p>
<p>Following a precursory Earth-based assessment, Lovelock theorised that the red planet was likely devoid of life because of atmospheric chemical equilibrium. In contrast, Earth’s atmosphere is in dynamic flux due to the biological activity that takes place on the surface. </p>
<p>Notwithstanding the continued ambiguity as to whether or not life is, or ever has been, present on Mars, Lovelock set a powerful precedent for the emerging field of astrobiology – the comparative approach with Earth in the search for extra-terrestrial life. </p>
<h2>Energy and life</h2>
<p>In our endeavour to answer the question of whether we are alone in the Universe, we have a solitary clue: “follow the energy”. </p>
<p>Earth is our only point of reference, and life on Earth requires energy – thermal energy for melting water and chemical energy for maintaining life. That’s it. Just two forms of energy define the cosmic imperative for life as we know it. </p>
<p>But ironically, we do not know when, where or how life originated on Earth. </p>
<p>What we do know is that the oldest and most abundant life forms on the planet are microorganisms. Biological adaptation is not restricted by structural simplicity, because microbes occupy every conceivable ecological niche on Earth. </p>
<p>If we accept the simple prokaryotic cell as being life’s universal blueprint, then ET is either an amalgamation of microbes or is still a microbe.</p>
<h2>Follow the energy = follow the water</h2>
<p>The mandate to “follow the energy” is synonymous with “follow the water”. The recent discovery of evidence of <a href="https://www.nasa.gov/press-release/nasa-confirms-evidence-that-liquid-water-flows-on-today-s-mars">liquid water on the surface of Mars</a> is therefore intriguing, but there is a lot more of it on Jupiter’s <a href="http://solarsystem.nasa.gov/planets/europa">Europa</a> and Saturn’s <a href="http://solarsystem.nasa.gov/planets/enceladus">Enceladus</a>. </p>
<p>These moons are compelling targets for astrobiology because of the <a href="https://theconversation.com/new-water-plumes-from-jupiters-moon-europa-raise-hopes-of-detecting-microbial-life-66019">inferred presence of oceans</a> beneath a sea ice crust that have persisted over geological time scales. </p>
<p>A new interpretation of data collected by the Cassini spacecraft suggests that the <a href="https://www.nasa.gov/press-release/cassini-finds-global-ocean-in-saturns-moon-enceladus">ocean beneath the ice on Enceladus</a> is not just confined to the south polar region. Like <a href="https://www.nasa.gov/feature/jpl/europas-ocean-may-have-an-earthlike-chemical-balance">Europa</a>, it is global. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/158024/original/image-20170223-32121-11mcs1n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/158024/original/image-20170223-32121-11mcs1n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/158024/original/image-20170223-32121-11mcs1n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=375&fit=crop&dpr=1 600w, https://images.theconversation.com/files/158024/original/image-20170223-32121-11mcs1n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=375&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/158024/original/image-20170223-32121-11mcs1n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=375&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/158024/original/image-20170223-32121-11mcs1n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=471&fit=crop&dpr=1 754w, https://images.theconversation.com/files/158024/original/image-20170223-32121-11mcs1n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=471&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/158024/original/image-20170223-32121-11mcs1n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=471&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">An artist’s rendering of Saturn’s moon Enceladus shows possible hydrothermal activity that may take place on and under the seafloor of the moon’s subsurface ocean.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech</span></span>
</figcaption>
</figure>
<p>It now also appears that <a href="http://www.jpl.nasa.gov/news/news.php?release=2014-300">Europa’s ice shell comprises a mobile, plate tectonic-like system</a> that overlies warm convecting ice and a salty seawater reservoir that is 30-35 times the volume of Earth’s ocean. </p>
<p>Should more water equate to more life? Not necessarily. There are many biological constraints on habitability in extreme environments. </p>
<p>Life as we know it appears to be absent on the surface of Europa and Enceladus because of ionising radiation and extremely low temperatures. Photosynthesis as we know it is also very unlikely to occur under ice that is kilometres thick.</p>
<p>Hydrothermal vents, a habitat for deep-sea ecosystems on Earth, may or may not exist on the moons.</p>
<p>So is this the end of comparison with Earth and end of story? Actually no, because it’s feasible that microorganisms that currently inhabit sea ice on Earth could also inhabit the ice water-interface and ice fissures on Europa or Enceladus. </p>
<h2>Life in extreme conditions</h2>
<p>The molecular basis for adaptation is not completely understood, but <a href="https://theconversation.com/au/topics/extremophiles-5967">extremophiles</a> (organisms that live in extreme conditions) must tolerate steep gradients in temperature, salinity, acidity and inorganic nutrients, as well as dissolved gas and light signatures. </p>
<p>Stress-related fissures in the ice shells of Europa and Enceladus are complex, and our understanding of their topography is based on theoretical modelling. But fissures appear to actively exchange liquid from the subsurface oceans to the ice exteriors. </p>
<p>The physiological demands on any microbial organisms would be exceptional, but these features could harbour small-scale, biologically permissive domains. Even brief periods of photosynthesis might be possible. </p>
<p>Extremophiles are relevant reference organisms because they adapt to multiple stressors in ways we don’t completely understand.</p>
<p>Life on these moons may be possible, but how likely is it? The comparative approach calls for an understanding of how these microbes respond to multiple stressors and the limits to which they can be pushed. </p>
<p>But the search for extra-terrestrial life is impeded because we lack a framework linking the capacity for adaptation with environmental variability. Future research and exploration to these moons will benefit from experimental work that defines life’s limits in the sea ice ecosystem. </p>
<p>Ultimately, we need to characterise theoretical biological limits that are distinct from the limits imposed on Earth-based analogues.</p><img src="https://counter.theconversation.com/content/73508/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Andrew Martin receives funding from the Australian Research Council's Special Research Initiative for Antarctic Gateway Partnership (Project ID SR140300001). </span></em></p><p class="fine-print"><em><span>Andrew McMinn receives funding from Australian Antarctic Science Grants, Australian Research Council. </span></em></p>There has been much excitement this week about the possibility of water – and life – on some newly discovered exoplanets. But we can look closer to home for evidence of ET.Andrew Martin, Sea ice microbial physiologist, University of TasmaniaAndrew McMinn, Professor of Antarctic Science, University of TasmaniaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/634172016-08-03T11:35:47Z2016-08-03T11:35:47ZSpace submarines will allow us to explore the seas of icy moons<figure><img src="https://images.theconversation.com/files/132778/original/image-20160802-17177-wta4kg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Artist's impression of a cryobot and submarine in the ice on Jupiter's Europa</span> <span class="attribution"><span class="source">NASA/JPL</span></span></figcaption></figure><p>One of the most profound and exciting breakthroughs in planetary science in the last two decades has been the discovery of <a href="http://www.jpl.nasa.gov/news/news.php?feature=4635">liquid methane lakes</a> on the surface of Saturn’s largest moon Titan, and <a href="http://solarsystem.nasa.gov/europa/overview.cfm">liquid oceans</a> under the icy surfaces of many of the giant gas planets’ other moons. Thrillingly, these some of these “waters” <a href="https://theconversation.com/the-moon-was-a-first-step-mars-will-test-our-capabilities-but-europa-is-the-prize-37253">may actually harbour life</a>.</p>
<p>Unfortunately, we don’t know much about them. Probes such as Juno and Cassini can only get so close. Also, subsurface oceans can only be sensed indirectly. The European Space Agency’s <a href="http://www.esa.int/Our_Activities/Space_Science/Cassini-Huygens/Huygens_spacecraft">Huygens</a> probe did land on Titan in 2005, but on a solid surface rather than on liquid. So how can we explore these seas? </p>
<p>An exciting idea being explored is developing submarines to send through space to the moons. Over the next two years, NASA is devoting half a million dollars to researching the prospect of <a href="https://www.nasa.gov/content/titan-submarine-exploring-the-depths-of-kraken">sending such a vehicle to Titan</a>. But there are <a href="http://www.kiss.caltech.edu/workshops/titan2010/presentations/aharonson.pdf">other studies out there, too</a> – with targets including Jupiter’s Europa and Ganymede, and Saturn’s Enceladus. But are such missions actually <a href="http://dx.doi.org/10.1016/j.cryogenics.2015.09.009">within our technological reach</a>?</p>
<h2>The challenges of a Titan submarine</h2>
<p><a href="https://saturn.jpl.nasa.gov/resources/725/">Kraken Mare</a> is thought to be the largest sea on Titan with an area of 400,000 square kilometres – larger than Earth’s Caspian Sea. But it’s not made of water – we have good evidence that this is instead a <a href="http://www.esa.int/Our_Activities/Space_Science/Cassini-Huygens/Profile_of_a_methane_sea_on_Titan">lake of methane</a>, ethane and nitrogen.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/132758/original/image-20160802-17177-14aq5vd.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/132758/original/image-20160802-17177-14aq5vd.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=366&fit=crop&dpr=1 600w, https://images.theconversation.com/files/132758/original/image-20160802-17177-14aq5vd.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=366&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/132758/original/image-20160802-17177-14aq5vd.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=366&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/132758/original/image-20160802-17177-14aq5vd.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=460&fit=crop&dpr=1 754w, https://images.theconversation.com/files/132758/original/image-20160802-17177-14aq5vd.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=460&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/132758/original/image-20160802-17177-14aq5vd.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=460&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Cassini radar image of the northern region of Kracken Mare on Titan showing the large island of Mayda Insula.</span>
<span class="attribution"><span class="source">NASA/Jet Propulsion Laboratory-Caltech/Agenzia Spaziale Italiana.</span></span>
</figcaption>
</figure>
<p>So what would a submarine on Titan look like? It turns out that a design like a traditional submarine, with a high “aspect ratio” (ten times as long as it is wide), would minimise drag and could fit inside a launch vehicle. Most deep space missions operate autonomously and a submarine would be no different. However, they would have to go to the surface for periods of time. Radio and microwave signals get absorbed very quickly in oceans, so to send a signal back to Earth the antenna would have to be above the surface. </p>
<p>Another issue is electrical power – this obviously cannot be provided by solar panels as it is on many spacecraft. As part of a <a href="http://dx.doi.org/10.1016/j.cryogenics.2015.09.009">recent study</a>, engineers investigated various alternatives, including compact nuclear reactors and fuel cells, but concluded these were too heavy. Instead, they proposed that electricity could be generated from the radioactive decay of plutonium – a technique <a href="http://mars.nasa.gov/mars2020/files/mep/MMRTG_FactSheet_update_10-2-13.pdf">similar to that powering Cassini</a>.</p>
<p>Some of the shallow shorelines of Kraken Mare are only 30-40 metres deep but it is thought to be 150 metres at its deepest. As you dive down beneath the surface the pressure increases because of the weight of the liquid above. On Earth, you can feel this in your ears when swimming underwater. Liquid methane is about half as dense as water and gravity on Titan is about seven times weaker than Earth, similar to our moon. So submarines diving down 150 meters on Titan don’t need to withstand the same pressure as they would on Earth.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/NnKxbdpLP5E?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Credit: NASA/NIAC.</span></figcaption>
</figure>
<p>A huge difficulty with these missions is to package the submarine into a system that can be launched on a rocket, survive in deep space during the roughly seven-year cruise to Titan, and then make it through a hypersonic descent to the ocean. It turns out that spaceplanes, such as the <a href="https://www.theguardian.com/science/2010/dec/01/space-vehicle-earth">X-37</a>, are ideal and would work well when descending into Titan’s thick hydrocarbon atmosphere. The spaceplane would launch from Earth on top of a rocket with the submarine inside. Once at the Saturnian system, the spaceplane would then land on Kraken Mare and deploy the submarine.</p>
<p>But perhaps the hardest thing will be to control the temperature inside the submarine – even though the sea is a somewhat frigid -180°C, the radioactive decay of the plutonium produces a lot of heat that needs to be dissipated.</p>
<h2>Descending to the depths of subsurface oceans</h2>
<p>Some tens of kilometres below the icy surface of Europa, meanwhile, we have good evidence that there could be a liquid salt water ocean. In fact, there could be subsurface liquid water oceans on a number of the moons of Jupiter, Saturn, and possibly Uranus and Neptune. As water is a prerequisite for life on Earth, this raises the exciting notion that these moons may be habitable. This is why many planetary scientists are interested in ideas to explore under the ice – either with submarines or <a href="http://www.jpl.nasa.gov/missions/europa-mission/">ice penetrating radar</a>.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/132757/original/image-20160802-17187-1swnp9i.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/132757/original/image-20160802-17187-1swnp9i.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=874&fit=crop&dpr=1 600w, https://images.theconversation.com/files/132757/original/image-20160802-17187-1swnp9i.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=874&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/132757/original/image-20160802-17187-1swnp9i.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=874&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/132757/original/image-20160802-17187-1swnp9i.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1098&fit=crop&dpr=1 754w, https://images.theconversation.com/files/132757/original/image-20160802-17187-1swnp9i.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1098&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/132757/original/image-20160802-17187-1swnp9i.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1098&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Travel to Europa.</span>
<span class="attribution"><span class="source">NASA/JPL</span></span>
</figcaption>
</figure>
<p>However, getting a submarine through at least 5km of ice makes putting a submarine on Titan look very easy. Cryobots – robotic devices that penetrate ice by <a href="http://www.jpl.nasa.gov/releases/2002/release_2002_6.html">melting it, allowing gravity to pull the robot downwards</a> – have been proposed as a way to <a href="http://www.jpl.nasa.gov/news/news.php?release=2013-077">deliver a submarine</a> into Europa’s oceans.</p>
<p>But energy is needed both to heat up the ice and then melt it -– a typical power station would be able to provide this in about five minutes. But it’s not going to be practical to send a power station to Europa. And with the amount of power available to most spacecraft, it would take a cryobot about eight years to get through the ice.</p>
<p>One way this problem can be solved is to use a compact nuclear fission reactor, which will do the job in about six weeks. But such a nuclear reactor wouldn’t fit into the cryobot. One problem solved, another is created. To get around this, <a href="http://www.igsoc.org:8080/annals/55/65/a65A200.pdf">one idea</a> involves leaving the reactor on the surface and sending the electrical power to the descending cryobot as light along a fibre-optic cable. Once the cryobot has reached the ocean it would deploy a submarine to take measurements. Communications with the cryobot could be achieved by sound waves in the ocean (think whales talking to each other) and then sent back up the connection to the surface vehicle for transmission to Earth.</p>
<p>Amazingly, these ideas have actually been <a href="https://www.newscientist.com/article/dn1786-ice-melting-robot-passes-arctic-test/">tested in Antarctica</a>. But one significant challenge is that, as the water melts, sediments build up ahead of the probe. Another is that the cryobot and submarine would have to undergo expensive extreme <a href="https://planetaryprotection.arc.nasa.gov/about">sterilisation</a> to avoid introducing any contamination to an environment that may harbour life.</p>
<p>So there are big hurdles to clear. But NASA does appear committed. It’s mission concept could possibly executed in the mid 2040s. And after Titan, who knows, we may even be hunting for <a href="https://en.wikipedia.org/wiki/Hydrothermal_vent">hydrothermal vents</a> on Europa.</p><img src="https://counter.theconversation.com/content/63417/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Arridge receives funding from the Science and Technology Facilities Council (STFC), the Royal Society and the Royal Astronomical Society. He also provides scientific advice to STFC and the UK Space Agency on solar system exploration.</span></em></p>We could be exploring the oceans of Jupiter’s and Saturn’s icy moons in a couple of decades. Here’s what we need to work out.Chris Arridge, Research Fellow/Lecturer, Lancaster UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/535832016-01-26T15:22:16Z2016-01-26T15:22:16ZExciting missions that could unlock secrets of the solar system in 2016<figure><img src="https://images.theconversation.com/files/109045/original/image-20160122-437-1nh62go.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Juno in front of Jupiter.</span> <span class="attribution"><span class="source">NASA/JPL</span></span></figcaption></figure><p>From the mystery of methane on Mars to how Jupiter formed and whether there is microbial life on Saturn’s moon Enceladus, there are many questions about our solar system waiting to be answered this year.</p>
<p>For planetary scientists, 2016 is a year of grand finales, anniversaries and planning major new missions. Let’s take a look at some of the most exciting possibilities. </p>
<h2>Mars</h2>
<p>In July 1976, NASA’s Viking Landers were the first probes to successfully reach the Martian surface. An immensely successful series of Mars landers followed. </p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/109043/original/image-20160122-403-qx3blr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/109043/original/image-20160122-403-qx3blr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=900&fit=crop&dpr=1 600w, https://images.theconversation.com/files/109043/original/image-20160122-403-qx3blr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=900&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/109043/original/image-20160122-403-qx3blr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=900&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/109043/original/image-20160122-403-qx3blr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1132&fit=crop&dpr=1 754w, https://images.theconversation.com/files/109043/original/image-20160122-403-qx3blr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1132&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/109043/original/image-20160122-403-qx3blr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1132&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The ExoMars 2016 Trace Gas Orbiter being moved.</span>
<span class="attribution"><a class="source" href="http://exploration.esa.int/jump.cfm?oid=57174">TsENKI/ESA</a></span>
</figcaption>
</figure>
<p>NASA’s Curiosity Rover is the latest. In 2016, Curiosity will pick its way through its current position in the Bagnold dunes – a band along the north-western flank of a 5.5km high mountain inside Gale Crater called Mount Sharp – and continue its drive up the mountain to reach iron-oxide layers (rust is a kind of iron oxide) and a clay-rich horizon – both believed to have formed from the reaction between water and Mars’ crust. We know that lakes filled the Gale Crater around 3.8 billion years ago. Curiosity will photograph, drill and analyse to find out more about Mars’ past warm and wet environment.</p>
<p>Europe is also aiming for Mars. ESA’s <a href="http://exploration.esa.int/mars/46475-trace-gas-orbiter/">ExoMars Trace Gas Orbiter</a> will launch on a Russian rocket in March and get there in October. It will follow up Curiosity’s discovery of traces of methane in Mars’ atmosphere, which could be a result of cosmic dust, geological processes or even past microbial life. ExoMars will test for current geological processes that might be releasing the methane. </p>
<p>It will also drop a simple, small lander to the surface. If it performs as planned then it is likely that a more ambitious ExoMars Rover – a two-metre drill on wheels with science instrumentation designed to test for traces of ancient life – will launch between 2018 and 2020. If ExoMars goes ahead as planned then the €150m or so needed to complete it could lead to postponements of other possible projects such as a mission to return material from Mars’ moon Phobos.</p>
<h2>Moon</h2>
<p>The moon also has a landmark anniversary: it is 50 years since the first successful robotic landing on its surface by the Soviet Union’s Luna 9. The Russians have always maintained a keen interest in the moon. Meanwhile, ESA has offered European countries <a href="http://www.bbc.co.uk/news/science-environment-34504067">a plan to collaborate with RosCosmos</a>, the Russian Space Agency, to start a new lunar exploration programme – with an initial focus on sampling the previously unstudied South Pole Aitken region. But budgets are limited. A decision at the European Council of Ministers in November about space priorities will be difficult, with projects targeting the moon, Mars’ moon Phobos and Mars all competing for funds.</p>
<p>Meanwhile, US company <a href="https://www.astrobotic.com/">Astrobotic Technology</a> hopes to be the first private lunar lander and rover mission in 2016. </p>
<h2>Outer solar system</h2>
<p>The <a href="https://www.nasa.gov/mission_pages/juno/main/index.html">Juno NASA spacecraft</a> will reach Jupiter in July. Juno will orbit Jupiter 32 times for a year helping us to answer questions about how the planet formed, how much water exists inside its atmosphere and how its mighty magnetosphere works.</p>
<p>Meanwhile, the <a href="http://saturn.jpl.nasa.gov/">Cassini mission</a> will begin a gradual grand finale in September, orbiting between Saturn and its outermost ring while flying past the moons Titan and Enceladus before crashing into Saturn in 2017. This will provide a last opportunity to analyse the water-rich geysers on Enceladus. In 2015, <a href="https://theconversation.com/the-chemistry-that-could-feed-life-within-saturns-moon-enceladus-study-gives-clue-ahead-of-flyby-49683">researchers even suggested</a> that certain chemical reactions inside its internal ocean may provide enough energy to feed microbial life. The study predicted that these would create molecular hydrogen that should be detectable in the plumes. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/109042/original/image-20160122-437-brzfjw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/109042/original/image-20160122-437-brzfjw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=707&fit=crop&dpr=1 600w, https://images.theconversation.com/files/109042/original/image-20160122-437-brzfjw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=707&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/109042/original/image-20160122-437-brzfjw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=707&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/109042/original/image-20160122-437-brzfjw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=888&fit=crop&dpr=1 754w, https://images.theconversation.com/files/109042/original/image-20160122-437-brzfjw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=888&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/109042/original/image-20160122-437-brzfjw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=888&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Enceladus craters and complex fractured terrains.</span>
<span class="attribution"><a class="source" href="http://www.esa.int/spaceinimages/Images/2007/03/Enceladus_craters_and_complex_fractured_terrains">ESA</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>An even more exciting candidate for life in our solar system is Jupiter’s moon Europa, which has a fractured crust of ice thought to overly an ocean which might harbour life. It would be nice if Europe got involved in exploring this, perhaps by contributing a “penetrator”, a light probe designed to bury itself on a body’s surface, to a planned <a href="http://www.jpl.nasa.gov/missions/europa-mission/">NASA fly by mission</a>. </p>
<p>A tiny member of the outer solar system is <a href="https://theconversation.com/explainer-what-philae-did-in-its-60-hours-on-comet-67p-34289">comet 67p/Churyumov-Gerasimenko</a>. In 2015, the Rosetta mission achieved a remarkable feat by landing on the 4km-wide cometary nucleus. Rosetta will be crashed into the comet in September – look out for some spectacular close-up images.</p>
<p>A NASA mission called <a href="http://www.asteroidmission.org/">Osiris Rex</a> to sample a carbonaceous asteroid called Bennu will be launched in September on a seven-year round trip. The mission could help us better understand the materials that make up our planets. Fittingly it comes on the tenth anniversary of the Stardust mission which returned samples from <a href="http://www.ncbi.nlm.nih.gov/pubmed/15205524">Jupiter Family Comet 81P/Wild2</a> and changed our view of what comets are made of. </p>
<p>So there’s a lot to look forward to. But aside from European, Russian and US missions, let’s not forget that China will steadily continue to build a space station and plans to go on to Mars and the <a href="https://theconversation.com/chinas-plan-to-be-first-to-far-side-of-the-moon-could-unveil-inner-lunar-secrets-53253">far side of the Moon</a>. India hopes to launch its first astronauts into orbit, and the Japanese Hayabusa2 mission will continue its journey to return samples from an asteroid. </p>
<p>It is impossible to determine what the greatest highlight of space science will be in 2016. But it might not even come from the glamour of space missions. Each year, 50,000 tonnes of cosmic dust and material from bodies in the solar system comes to planet Earth – and that can lead to unexpectedly great discoveries.</p><img src="https://counter.theconversation.com/content/53583/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>John Bridges receives funding from STFC, UKSA</span></em></p>Missions including ExoMars, Juno and Rosetta could make some major discoveries in 2016.John Bridges, Professor of Planetary Science, University of LeicesterLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/438462015-07-08T06:08:18Z2015-07-08T06:08:18ZThe search for life beneath the ice: why we’re going back to Europa<figure><img src="https://images.theconversation.com/files/87566/original/image-20150707-1274-aii21a.jpg?ixlib=rb-1.1.0&rect=39%2C243%2C984%2C789&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An artist's concept of a plume of water vapour thought to be ejected off the surface of Europa. Could life be beneath?
</span> <span class="attribution"><span class="source">NASA</span></span></figcaption></figure><p>Last month NASA gave the <a href="http://www.nasa.gov/press-release/all-systems-go-for-nasas-mission-to-jupiter-moon-europa">“all systems go”</a> for a new mission to Europa. But <a href="https://theconversation.com/europa-attempt-no-landing-here-but-a-fly-by-is-fine-43845">why go back</a>? After all, we’re still sifting through the data from the <a href="http://solarsystem.nasa.gov/galileo/">Galileo probes fly-bys</a> from more than a decade ago.</p>
<p>The short answer: it’s all about life. </p>
<p>The Jovian moons – named after Jupiter’s lovers by <a href="https://en.wikipedia.org/wiki/Simon_Marius">Simon Marius</a> – have been a source of scientific speculation since Galileo trained his telescope on Jupiter in 1610, announcing his discovery in the <a href="https://en.wikipedia.org/wiki/Sidereus_Nuncius">Sidereal Messenger</a>. </p>
<p>But the idea that Europa and other moons of Jupiter might harbour life is relatively new, as is the notion they might have hidden oceans beneath their icy surfaces. Indeed, these speculations demonstrate just how fast our conceptions of the solar system, and life, can change.</p>
<h2>Speculative science, speculative fiction</h2>
<p>A generation of space scientists and enthusiasts who grew up on Robert A. Heinlein’s “<a href="http://www.heinleinsociety.org/rah/works/novels/heinleinjuveniles.html">juveniles</a>” will fondly remember <a href="https://en.wikipedia.org/wiki/Farmer_in_the_Sky">Farmer in the Sky</a>, written in 1950, when the Jovian moons were believed to be rocky, like our own Moon.</p>
<p>But in the late 1950s and continuing through the early 1970s, a growing body of telescopic data suggested that some of these moons, in particular <a href="https://solarsystem.nasa.gov/planets/profile.cfm?Object=Jup_Callisto">Callisto</a>, <a href="https://solarsystem.nasa.gov/planets/profile.cfm?Object=Jup_Ganymede">Ganymede</a> and <a href="https://solarsystem.nasa.gov/planets/profile.cfm?Object=Jup_Europa">Europa</a>, were <a href="https://www.math.washington.edu/%7Egreenber/EuropaHistory.html">covered in water ice</a>. This speculation came from their high albedo, a measure of how much they light they reflect. With an albedo of 0.64, Europa is one of the most reflective bodies in the solar system. </p>
<p>In 1971, Carl Sagan suggested that the Jovian moons, including Europa, were of <a href="http://adsabs.harvard.edu/full/1971ssrv...11..827s">“major…exobiological significance”</a>. In other words: they might harbour life.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/87586/original/image-20150707-1311-ml9u2x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/87586/original/image-20150707-1311-ml9u2x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/87586/original/image-20150707-1311-ml9u2x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=580&fit=crop&dpr=1 600w, https://images.theconversation.com/files/87586/original/image-20150707-1311-ml9u2x.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=580&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/87586/original/image-20150707-1311-ml9u2x.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=580&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/87586/original/image-20150707-1311-ml9u2x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=728&fit=crop&dpr=1 754w, https://images.theconversation.com/files/87586/original/image-20150707-1311-ml9u2x.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=728&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/87586/original/image-20150707-1311-ml9u2x.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=728&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Europa as seen by Voyager 2 during its close encounter in 1979.</span>
<span class="attribution"><span class="source">NASA/JPL</span></span>
</figcaption>
</figure>
<p>The early 1970s also saw the first speculation that some outer moons of the solar system, including Europa, might hide an ocean beneath their surfaces. It was initially suggested this might be due to <a href="http://www.sciencedirect.com/science/article/pii/0019103571900728">radiative heating</a>, although it was later proposed that the heat might come from <a href="http://www.researchgate.net/profile/Stanton_Peale/publication/6068304_Melting_of_io_by_tidal_dissipation/links/0046353bf266de44dc000000.pdf">tidal forces induced by Jupiter</a>, especially because of the synchronous orbits of the three innermost Galilean moons: Io, Europa and Ganymede. </p>
<p>The 1979 <a href="http://voyager.jpl.nasa.gov/">Voyager</a> fly-bys confirmed that Callisto, Europa and Ganymede moons were covered in ice and that Io was extremely volcanic. The <a href="http://www.jpl.nasa.gov/spaceimages/details.php?id=PIA00459">best images</a> of Europa were taken by Voyager 2 from a range of 204,400 kilometres, showing Europa to be “billiard ball” smooth.</p>
<h2>Not too hot, not too cold…</h2>
<p>Things took a turn following the discovery by Robert Ballard’s <a href="http://www.britannica.com/biography/Robert-Ballard-American-oceanographer">1977 expedition</a> of entire ecosystems thriving near hydrothermal vents in the deep ocean. These vents existed in the “midnight zone”, without sunlight and photosynthesis, and changed the way we thought about life. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/87587/original/image-20150707-1281-5c8fdm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/87587/original/image-20150707-1281-5c8fdm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/87587/original/image-20150707-1281-5c8fdm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=884&fit=crop&dpr=1 600w, https://images.theconversation.com/files/87587/original/image-20150707-1281-5c8fdm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=884&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/87587/original/image-20150707-1281-5c8fdm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=884&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/87587/original/image-20150707-1281-5c8fdm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1111&fit=crop&dpr=1 754w, https://images.theconversation.com/files/87587/original/image-20150707-1281-5c8fdm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1111&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/87587/original/image-20150707-1281-5c8fdm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1111&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 discovery of life around deep ocean vents, like this one, raised the exciting prospect of life existing under the ocean on Europa.</span>
<span class="attribution"><span class="source">P. Rona/NOAA</span></span>
</figcaption>
</figure>
<p>In 1980, scientists Gerald Feinberg and Robert Shapiro <a href="https://books.google.com.au/books?id=ZECsAAAAIAAJ&q=shapiro+1980+life+beyond+earth&dq=shapiro+1980+life+beyond+earth&hl=en&sa=X&ei=53KPVY7cBMnq8AWw55ko&ved=0CBwQ6AEwAA">hypothesised</a> that deep sea volcanism might support life on the Jovian moons. The <a href="https://books.google.com.au/books?id=BnyjmtIR7McC&pg=PA159&lpg=PA159&dq=shapiro+feinberg+europa&source=bl&ots=nPcdPCEKt1&sig=MJTG2WmynW7tUsNqBQU33w0IpbI&hl=en&sa=X&ei=fHGPVemPAeLlmAXemIFQ&ved=0CB0Q6AEwAA#v=onepage&q=shapiro%20feinberg%20europa&f=false">Feinberg-Shapiro hypothesis</a> is one of the major reasons for the current interest in Europa by astrobiologists. </p>
<p>In essence, it was proposed there might be a <a href="http://www.sciencedirect.com/science/article/pii/0273117787903644">tidally heated habitable zone</a> around giant planets, similar to the habitable, or “<a href="https://en.wikipedia.org/wiki/Goldilocks_planet">Goldilocks</a>” zone around a star: where it’s not too hot, not too cold, and where liquid water and life can exist.</p>
<p>The idea of life on the Jovian moons was quickly picked up by science fiction writers. In <a href="http://www.arthurcclarke.net/?scifi=1&type=1">Arthur C. Clarke’s</a> 2010: Odyssey two (1982) and 2061: Odyssey three (1988), aliens transform Jupiter into a star kick-starting the evolution of life on Europa, transforming it into a tropical ocean world forbidden to humans.</p>
<p>In Bruce Sterling’s 1985 <a href="https://www.sfwa.org/nebula-awards/">Nebula Award</a> nominee, <a href="https://en.wikipedia.org/wiki/Schismatrix">Schismatrix</a>, Europa’s ocean is colonised by a group of genetically transformed post-human species. </p>
<h2>Fire and ice</h2>
<p>Europa and life were thus well and truly established in the minds of science fiction writers, planetary scientists, exobiologists and the public by the time NASA’s extraordinary <a href="http://science.nasa.gov/missions/galileo/">Galileo mission</a> began taking images of Europa in 1996. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/87565/original/image-20150707-1271-1g2jvuf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/87565/original/image-20150707-1271-1g2jvuf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/87565/original/image-20150707-1271-1g2jvuf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=444&fit=crop&dpr=1 600w, https://images.theconversation.com/files/87565/original/image-20150707-1271-1g2jvuf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=444&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/87565/original/image-20150707-1271-1g2jvuf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=444&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/87565/original/image-20150707-1271-1g2jvuf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=557&fit=crop&dpr=1 754w, https://images.theconversation.com/files/87565/original/image-20150707-1271-1g2jvuf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=557&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/87565/original/image-20150707-1271-1g2jvuf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=557&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">This is the colour view of Europa from Galileo, taken in the 1990s, that shows the largest portion of the moon’s surface at the highest resolution.</span>
<span class="attribution"><span class="source">NASA/JPL</span></span>
</figcaption>
</figure>
<p>By the completion of its primary mission on December 7 1997, Galileo had made eleven encounters with Europa. Galileo’s extended mission became one of “fire and ice”: its twin foci were Io’s vulcanism and Europa’s icy oceans. The Europa fly-bys took the probe to within a few hundred kilometres of the moon’s surface.</p>
<p>These extensive observations of Europa by the Galileo mission were compelling evidence for a liquid water ocean some 100 to 200 kilometres thick on which “floats” an outer shell of ice. Magnetometer measurements indicate the ocean is free flowing and salty. </p>
<p>Galileo also provided spectacular views of the icy terrain: ridges, slip faults and “ice-bergs”, all adding to the picture of a surface only 10-100 million years old, which is young by the four to five billion year <a href="http://earthguide.ucsd.edu/virtualmuseum/ita/05_3.shtml">age of the solar system</a>. </p>
<p>The spacecraft, nearly out of fuel after an extended mission, was deliberately crashed into Jupiter on 21 September 2003 to protect Europa from possible contamination.</p>
<h2>Europa Report</h2>
<p>The data Galileo collected are still revealing <a href="http://solarsystem.nasa.gov/galileo/news/index.cfm">new important finds</a>. There evidence of clay-like minerals on the surface, possibly from asteroid or meteorite collision, and signs of sea salt, discoloured by radiation, making up some of the dark patches observed by both Voyager and Galileo.</p>
<p>A whole new generation of scientists is eagerly awaiting the data from the new mission. Astrobiology has become, since the early 2000s, a whole new <a href="https://astrobiology.nasa.gov/education-resources/">science discipline</a>. This “<a href="https://www.nasa.gov/press-release/all-systems-go-for-nasas-mission-to-jupiter-moon-europa">alien ocean</a>” mission is clumsily named, at present, <a href="http://solarsystem.nasa.gov/missions/profile.cfm?MCode=EuropaFlyby">Europa Multiple Flyby Mission</a>. </p>
<p>So the new mission, slated for a rendezvous with Europa in 2030, won’t involve a lander. And until we can send a probe into the icy depths of Europa’s sea, speculation about what might be lurking there, à la Sebastián Cordero’s <a href="http://www.magnetreleasing.com/europareport/">Europa Report</a>, will remain the domain of science fiction and scientists’ fantasy. Maybe one day, it will be science fact. Europa, here we come.</p><img src="https://counter.theconversation.com/content/43846/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Jupiter’s moon Europa is one of the most enticing objects in our solar system, and a future NASA mission may help reveal whether it is a suitable for life.Morgan Saletta, PhD, History and Philosophy of Science, The University of MelbourneKevin Orrman-Rossiter, Graduate Student, History & Philosophy of Science, The University of MelbourneLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/438452015-06-25T04:37:50Z2015-06-25T04:37:50ZEuropa: attempt no landing here, but a fly-by is fine!<figure><img src="https://images.theconversation.com/files/86343/original/image-20150625-12998-ehiuwn.jpg?ixlib=rb-1.1.0&rect=0%2C72%2C2300%2C1425&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">What mysteries lie beneath your icy crust, Europa?</span> <span class="attribution"><span class="source">NASA/JPL-Caltech/SETI Institute</span></span></figcaption></figure><p>NASA has now formally started to pack its bags for the next big discovery mission, this time heading to Jupiter’s icy moon <a href="https://solarsystem.nasa.gov/planets/profile.cfm?Object=Jup_Europa">Europa</a>. Last month NASA announced <a href="http://www.nasa.gov/press-release/nasa-s-europa-mission-begins-with-selection-of-science-instruments">the instruments</a> that will fly on this trip and now has formally moved it from <a href="http://www.jpl.nasa.gov/missions/europa/">“concept” to “development”</a> stage. </p>
<p>Formally known as Europa Clipper, the mission will be known as <a href="http://solarsystem.nasa.gov/missions/profile.cfm?MCode=EuropaFlyby">Europa Multiple Flyby Mission</a>, at least until a more glamorous name is picked. It’s slated for a possible launch in 2025 and will arrive hot on the heels of the European Space Agency’s (ESA) Jupiter Icy Moons Explorer (<a href="https://theconversation.com/the-anticipation-of-some-freshly-squeezed-results-6991">JUICE</a>) mission, which will be well into its investigation of Europa’s neighbour <a href="https://solarsystem.nasa.gov/planets/profile.cfm?Object=Jup_Ganymede">Ganymede</a> by then. </p>
<p>It has not been an easy journey to get the mission to this stage. It is to the credit of a massive team of scientists, engineers and science communicators engaging with policy makers that <a href="https://theconversation.com/us-plans-to-answer-the-lure-of-europa-33990">this has happened at all</a>. </p>
<h2>The lure of Europa</h2>
<p>We’re still sifting through the massive amount of data that the <a href="http://science.nasa.gov/missions/galileo/">Galileo spacecraft</a> has beamed back from the Jupiter system, so why go back? </p>
<p>It is actually the tentative peek that Galileo gave us into the mysterious icy moon that is a prime motivator for a return trip. Of all the discoveries that this (<a href="http://www.space.com/18632-galileo-spacecraft.html">at times struggling</a>) spacecraft made, the most famous was the evidence it collected for a moon-wide ocean beneath Europa’s icy crust.</p>
<p>Based on data from Galileo, and follow up measurements from the Hubble Space Telescope, we have gathered clues that any ocean under the ice would be a rather cosy place to be. It might even be the best place for life in our solar system, apart from our own home.</p>
<p>But the presence of an ocean is still only one theory of many as to Europa’s inner makeup. To help settle the matter, NASA’s new mission will fly with an <a href="http://www.astrobio.net/topic/solar-system/jupiter/europa/radar-techniques-used-in-antarctica-will-scour-europa-for-life-supporting-environments/">ice-penetrating radar</a>, built by the University of Austin in Texas, which will work with a number of other instruments to gain a better picture of what may lie beneath the cold crust. </p>
<p>Those follow-up measurement by the Hubble Space telescope <a href="https://theconversation.com/europa-the-new-spa-destination-of-the-solar-system-21460">spotted potential geysers from Europa’s surface</a>. So to map these out, the new mission will also carry a thermal imaging camera, with the hope of discovering features like the “<a href="http://solarsystem.nasa.gov/scitech/display.cfm?ST_ID=1889">tiger stripes</a>” of Saturn’s moon Enceladus. </p>
<h2>State of the art snaps</h2>
<p>Also, the Galileo mission ended dramatically in 2003 (with the probe <a href="http://www.nasa.gov/missions/solarsystem/galileo_impact.html">hurling itself</a> into the depths of Jupiter). The mission was launched in 1989, and although it would have flown with state-of-the-art equipment for the time, can you recall state-of-the-art what was in the 1980’s?</p>
<p>Just imagining the fantastic pictures this new Europa mission will yield brings me out in goose bumps. And capturing high resolution is exactly the plan, with this mission flying an instrument, Europa Imaging System (EIS), that will resolve the icy surface down to a resolution of 50 metres. </p>
<p>Preparations are already well underway for us to interpret the data that the mission will send back. In fact, there have been a few leaps in our understanding of Europa this year already. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/86342/original/image-20150625-12990-w9t3bq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/86342/original/image-20150625-12990-w9t3bq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/86342/original/image-20150625-12990-w9t3bq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=265&fit=crop&dpr=1 600w, https://images.theconversation.com/files/86342/original/image-20150625-12990-w9t3bq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=265&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/86342/original/image-20150625-12990-w9t3bq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=265&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/86342/original/image-20150625-12990-w9t3bq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=333&fit=crop&dpr=1 754w, https://images.theconversation.com/files/86342/original/image-20150625-12990-w9t3bq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=333&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/86342/original/image-20150625-12990-w9t3bq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=333&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Bizarre features on Europa’s icy surface suggest a warm interior.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech</span></span>
</figcaption>
</figure>
<h2>What else is there?</h2>
<p>Although we refer to Europa and its companions, Ganymede and Callisto, as being “icy”, it’s pretty well understood that there’s a significant fraction of other “stuff” on these moons. There are a number of candidates as to what this is, such as magnesium sulfate and sulfuric acid, but a new possibility was outlined earlier this year: humble table salt.</p>
<p>While the optical properties of salt as we know it don’t fit with what we’ve seen from Europa, NASA scientists discovered that <a href="http://mashable.com/2015/05/12/europa-jupiter-moon-salt-ocean/">radiation-damaged salt does</a>. That’s pertinent, because the radiation on the top of Europa’s surface – mainly coming from Jupiter – is actually very high. So salt that seeps there could be damaged and create the “dirty ice” that we see on the surface. </p>
<p>More analysis of the light reflected off Europa by the new spacecraft could very well show if this radiation-damaged salt – or indeed any of the other candidates – are there on Europa. </p>
<h2>What lies under the ice?</h2>
<p>At the same time, researchers have been out in the field, investigating places that are rather like Europa here on Earth. In 2014 a group tested how effective a <a href="http://spie.org/x113852.xml">small robot</a> was at burrowing though the ice on the <a href="http://www.antarcticglaciers.org/antarctica/photographs/mcmurdo/">McMurdo ice shelf</a> in Antarctica. </p>
<p>Hopefully we’ll see more of the use of these types of probes to study the <a href="https://theconversation.com/life-in-lake-vostok-the-link-between-antarctica-and-extra-terrestrials-5334">lakes trapped in the Antarctic ice</a>. Aside from the knowledge we might gain about our own polar environment, we’ll learn more about how to control these robots when they are 628 million kilometres away on one of Jupiter’s moons. </p>
<p>With all going well through the design phase, this new Europa mission will be on its way in 2025 and be sending us data from the enigmatic moon in the 2030s. Initially it looks like it will fly-by Europa 45 times, but hopefully a mission extension will be on the cards too. Perhaps by then we’ll have a plan to land on the ice and burrow into any potential ocean on the way. </p>
<p>I hope Arthur C Clarke wouldn’t have been too cross.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/38EDhpxzn2g?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Final scene from 2010: The Year We Make Contact, including the haunting words from the makers of the monoliths.</span></figcaption>
</figure><img src="https://counter.theconversation.com/content/43845/count.gif" alt="The Conversation" width="1" height="1" />
NASA has now formally started to pack its bags for the next big discovery mission, this time heading to Jupiter’s icy moon Europa. Last month NASA announced the instruments that will fly on this trip and…Helen Maynard-Casely, Instrument Scientist, Australian Nuclear Science and Technology OrganisationLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/386732015-03-11T19:35:43Z2015-03-11T19:35:43ZIcy plumes bursting from Saturn’s moon Enceladus suggest it could harbour life<figure><img src="https://images.theconversation.com/files/74519/original/image-20150311-24188-hpeflk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">With geysers bursting through an icy crust, Enceladus is a tiny moon with a big personality.</span> <span class="attribution"><span class="source">Hsiang-Wen Hsu et al/Nature</span>, <span class="license">Author provided</span></span></figcaption></figure><p>The <a href="http://saturn.jpl.nasa.gov/mission/introduction/">Cassini</a> mission that has investigated Saturn since 2004 has revealed much about the giant planet and its many moons. Perhaps most tantalising is the discovery that the moon Enceladus is the source of strong geysers ejecting plumes of water and ice.</p>
<p>A new <a href="http://www.google.com/url?q=http%3A%2F%2Fdx.doi.org%2F10.1038%2Fnature14262&sa=D&sntz=1&usg=AFQjCNGdOviBn9Rlh1do4S58gDVPgMfNDA">study of Cassini data</a> published in Nature by Hsiang-Wen Hsu and colleagues reveals these plumes are laced with grains of sand. This indicates that hydrothermal activity may be at work in Enceladus’ sub-surface ocean, and propels this tiny moon into the extremely exclusive club of locations that could harbour life. </p>
<p>The club’s only current member is Earth, of course – although it’s very possible that <a href="https://theconversation.com/the-moon-was-a-first-step-mars-will-test-our-capabilities-but-europa-is-the-prize-37253">Europa</a>, one of Jupiter’s moons, is, like Enceladus, also a candidate. What they have in common is that they host liquid oceans of salty water that exists in contact with a rocky, silicate seabed from which the oceans can absorb complex minerals and elements.</p>
<h2>A bit of a geyser</h2>
<p>With a diameter of just 500km Enceladus is nevertheless the sixth largest of Saturn’s more than 60 moons, orbiting at a distance of just two planet-widths. Cassini has shown that Enceladus is the source of huge geysers of neutral water-rich gas and ice grains erupting at a rate of 100-300kg per second. This makes Enceladus the second most active object, after Jupiter’s moon Io which ejects one tonne per second of sulphur-rich material. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/74535/original/image-20150311-24212-1djlagy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/74535/original/image-20150311-24212-1djlagy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/74535/original/image-20150311-24212-1djlagy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=704&fit=crop&dpr=1 600w, https://images.theconversation.com/files/74535/original/image-20150311-24212-1djlagy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=704&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/74535/original/image-20150311-24212-1djlagy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=704&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/74535/original/image-20150311-24212-1djlagy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=885&fit=crop&dpr=1 754w, https://images.theconversation.com/files/74535/original/image-20150311-24212-1djlagy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=885&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/74535/original/image-20150311-24212-1djlagy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=885&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">How the plumes are formed, from beneath Enceladus’ surface.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>Gravity measurements have shown that there is at least a local and <a href="http://www.sciencemag.org/content/344/6179/78.short">possibly a global ocean</a> under Enceladus’ icy crust, and some of the emitted grains are <a href="http://www.nature.com/nature/journal/v459/n7250/full/nature08046.html">rich in sodium salt</a>, which indicates the presence of a salty ocean. Now we also discover that some are silicate-rich, and analysis shows that these may have been produced close to hydrothermal vents at temperatures above 90°C. This raises the interesting comparison with <a href="http://www.lostcity.washington.edu/science/biology/newlife.html">hydrothermal vents on Earth</a>, which may have played a role in the origin of life on our planet.</p>
<h2>The recipe for life</h2>
<p>For life as we know it to exist, four key ingredients are important: liquid water; the right chemistry involving the elements carbon, hydrogen, nitrogen, oxygen, phosphorus and sulphur; a source of heat; and enough time for life to develop. While we know these conditions exist on Earth, planetary research throughout the solar system shows that it may exist on other objects too, and the details from this paper pushes Enceladus towards the top of the list.</p>
<p>We know liquid water oceans exist on several objects in our solar system. These include Earth with its surface oceans, and Jupiter’s moons Europa, Ganymede and Callisto, and Saturn’s moons Titan and Enceladus where the oceans are below the surface. Water has also played a vital role in Mars’ history: Geronimo Villanueva and colleagues recently showed that there may have been enough water on Mars to cover the planet in <a href="http://www.sciencemag.org/content/early/2015/03/04/science.aaa3630">an ocean 137 metres deep</a> around 3.8 billion years ago –- about the time when life was starting on Earth. </p>
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<figcaption>
<span class="caption">The view from Cassini towards the geyser region of Enceladus.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>There may also be water on the dwarf planets <a href="https://theconversation.com/dawn-eases-into-orbit-around-the-dwarf-planet-ceres-38398">Ceres</a> and Pluto, Neptune’s moon Triton, and several other objects in the solar system – but only further investigation will tell. Two other objects have lakes and oceans, but not of water. Titan has lakes of methane and ethane, for example – the only extraterrestrial object we know of with liquid on the surface – and volcanic Io has a <a href="http://www.sciencemag.org/content/332/6034/1186.short">subsurface ocean of liquid magma</a>.</p>
<h2>A shortlist for extraterrestrial life</h2>
<p>So where are the best places to look for life in our solar system? The short list now seems to be Mars, Europa and Enceladus. At Mars the most likely time for life to have existed is 3.8 billion years ago when water was present, so the <a href="http://exploration.esa.int/mars/45084-exomars-rover/">ESA-Russia ExoMars rover</a> due for launch in 2018 will focus on drilling 2m below the present surface’s harsh oxidising and radiation-rich environment to search for buried evidence from the past. It carries our PanCam instrument which will provide context for the mission.</p>
<p>As for right now, Mars may be a less good candidate for life. Following a catastrophic collision about 3.8 billion years ago the planet underwent massive climate change, volcanic activity stopped, and the planet’s magnetic field disappeared. But the recent confirmation by Curiosity of the presence of methane is tantalising. At Europa, <a href="http://sci.esa.int/juice/">ESA’s JUICE mission</a> and the proposed <a href="http://www.jpl.nasa.gov/missions/europa-clipper/">NASA Europa Clipper</a> may bring more clues in the 2030s, but further missions to Enceladus have yet to make it past the proposal stage.</p>
<p>Nevertheless, this leaves Europa and Enceladus as prime sites where conditions may be suitable for life to exist now – but who knows which other solar system objects could be the next to join the club.</p><img src="https://counter.theconversation.com/content/38673/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Andrew Coates receives funding from STFC and the UK Space Agency.</span></em></p>Saturn’s tiny moon Enceladus joins Europa and Mars as possible locations for life beyond Earth.Andrew Coates, Professor of Physics, Head of Planetary Science at the Mullard Space Science Laboratory, UCLLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/372532015-02-06T14:29:38Z2015-02-06T14:29:38ZThe Moon was a first step, Mars will test our capabilities, but Europa is the prize<figure><img src="https://images.theconversation.com/files/71311/original/image-20150206-28594-180ndar.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The prize, Europa, a watery world.</span> <span class="attribution"><a class="source" href="http://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=11176">NASA</a></span></figcaption></figure><p>The icy moon Europa is perhaps the most tantalising destination in our solar system. Scientists have been trying for years to kickstart a mission to Jupiter’s most enigmatic moon, with very Earth-like concerns over costs keeping missions grounded until now. </p>
<p>The European Space Agency’s ambitious mission to Jupiter, <a href="http://sci.esa.int/juice/">JUICE</a>, will visit its fire-and-ice moons – volcanic Io, icy Europa, giant Ganymede, and cratered Callisto – in the 2030s. But it will only provide a glimpse of Europa’s surface from a couple of close flybys. With the announcement of the NASA-led <a href="http://www.jpl.nasa.gov/missions/europa-clipper/">Europa Clipper</a> mission, now it looks like a much closer inspection of Europa is on the cards. </p>
<p>It’s hard to overstate the excitement among planetary scientists, after so many years of waiting in the wings while all eyes were on Mars. This is truly a quest to understand what makes a world habitable. </p>
<h2>A watery world</h2>
<p>Europa is the smallest and smoothest of the four Galilean moons. At 1,940 miles across, it is roughly a quarter of the size of Earth, composed of a mixture of ices and rocks. When the <a href="http://solarsystem.nasa.gov/galileo/">Galileo</a> spacecraft flew over Europa in the 1990s, it uncovered evidence of a global sub-surface ocean: vast, deep, dark waters hidden beneath the ice crust. </p>
<p>The water doesn’t freeze completely because it’s constantly kneaded by powerful tidal forces as the moon orbits around Jupiter once every 3.5 days. What’s more, the ocean is believed to be in direct contact with the surface ices and the moon’s silicate mantle, which brings together all the necessary ingredients for a habitable environment: liquid water, a source of energy, and a source of minerals/nutrients. We know that life on Earth can exist in even the most extreme environmental conditions (for example, bacteria known as <a href="http://oceanservice.noaa.gov/facts/extremophile.html">extremophiles</a>), so maybe – just maybe – Europa’s hidden ocean could support life.</p>
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<figcaption>
<span class="caption">The Galilean moons of Jupiter: Io, Europa, Ganymede and Callisto.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<h2>What to look for</h2>
<p>Neither JUICE nor Clipper will reach the surface or the ocean below – that’s too great a technological challenge for now. But if habitable conditions for life are discovered beyond Earth, particularly somewhere as far from the Sun as Jupiter and its moons, this could mean that habitable conditions are commonplace throughout our universe. </p>
<p>We must begin to explore Europa via orbital reconnaissance: to image and perform spectral analysis of the composition and geology of the surface, and the radiation, magnetic, electric and plasma fields that sweep across it. With ice penetrating radar we can probe through the icy crust, even as far as the hidden ocean to understand the forces that shape this icy world.</p>
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<figcaption>
<span class="caption">Europa’s ‘chaos terrain’, caused by repeated freezing and melting.</span>
<span class="attribution"><a class="source" href="http://commons.wikimedia.org/wiki/File:Europa_Chaos.jpg">NASA</a></span>
</figcaption>
</figure>
<p>Europa’s fractured and cracked surface is geologically quite young, and relatively crater-free. The structures that the Galileo probe observed from orbit suggest freeze-melt processes that trap icy burgs into frozen seas, creating the scarred patterns known as <a href="http://io9.com/5859715/what-causes-europas-mysterious-chaos-terrain">chaos terrain</a>. Dark parallel ridges criss-cross the bright planes, possibly due to tectonics or other geologic processes. </p>
<p>Most surprising was Hubble’s observations in 2012, which showed evidence of huge plumes or geysers erupting tens of kilometres over Europa’s south pole, potentially contributing to a very thin atmosphere. If we could directly sample those plumes we might just get a glimpse of the composition of the deep ocean. </p>
<h2>Sooner rather than later</h2>
<p>So for all these reasons and more, Europa remains the highest priority target for a future mission. That there are two missions to the Jupiter system stems from years of study within NASA and ESA. At one point a joint mission, the <a href="http://sci.esa.int/ejsm-laplace/42291-summary/">Europa-Jupiter System Mission</a>, was planned but was not taken forward due to funding constraints.</p>
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<figcaption>
<span class="caption">The Jupiter Icy Moon Explorer, JUICE, and its instruments.</span>
<span class="attribution"><span class="source">ESA</span></span>
</figcaption>
</figure>
<p>Today, JUICE is full-steam ahead, the project having passed through a full study and definition phase towards now building the spacecraft. If all goes to plan it would launch in 2022 and reach Jupiter in 2030. After two years of multiple fly-bys exploring Jupiter, its moons, rings and magnetosphere, it will become humankind’s first orbiter of an icy moon, targeting Ganymede in late 2032. If NASA’s recently announced funding is confirmed Europa Clipper may proceed even faster, using a new rocket (the <a href="http://www.nasa.gov/exploration/systems/sls/">Space Launch System</a>) to propel it towards Europa in only a few years, potentially arriving just before or even at the same time as JUICE. </p>
<p>Clipper will conduct multiple flybys of Europa (maybe 45 or more over three years) without entering orbit directly, but will provide the high-resolution reconnaissance necessary to ultimately choose a landing site for some future robotic explorer. Although that future landing mission is beyond the funding horizon right now, it’s exciting to think that we’ll one day see images from that icy and harsh environment, with Jupiter suspended in the black skies above.</p><img src="https://counter.theconversation.com/content/37253/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Leigh Fletcher receives funding from the Royal Society as a University Research Fellow.</span></em></p>The icy moon Europa is perhaps the most tantalising destination in our solar system. Scientists have been trying for years to kickstart a mission to Jupiter’s most enigmatic moon, with very Earth-like…Leigh Fletcher, Royal Society Research Fellow, University of OxfordLicensed as Creative Commons – attribution, no derivatives.