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Landing Sites on Europa

A paper just published online by the journal Astrobiology examines what a Europa lander could accomplish on the surface. It’s part of the process of future mission building even if that future is deeply uncertain — we’re a long way from a Europa lander, and funding even a far less demanding flyby mission is problematic in the current environment. But Robert Pappalardo, lead author of the study at JPL, explains the rationale for a close-up study of the icy world:

“If one day humans send a robotic lander to the surface of Europa, we need to know what to look for and what tools it should carry. There is still a lot of preparation that is needed before we could land on Europa, but studies like these will help us focus on the technologies required to get us there, and on the data needed to help us scout out possible landing locations. Europa is the most likely place in our solar system beyond Earth to have life today, and a landed mission would be the best way to search for signs of life.”

The image below, which offers a pole-to-pole view of Europa by overlaying higher resolution mosaics over a lower resolution global view obtained during Galileo flybys, shows the vivid linear features (lineae) whose color has been enhanced to highlight the red markings associated with many of them. Some of these features may well have biomarkers near them that have reached the surface from the global ocean beneath. Modeling their formation presents the possibility of fracturing caused by processes in the ice shell itself, with some models suggestive of liquids pushing through the fractures to form the numerous ridges we see on the surface. It’s precisely here that we could find exchanges of material between the surface, the icy shell and the ocean.


Image: The terrain in this view stretches from the side of Europa that always trails in its orbit at left (west), to the side that faces away from Jupiter at right (east). In addition to the lineae, the regional-scale images contain many interesting features, including lenticulae (small spots), chaos terrain, maculae (large spots), and the unusual bright band known as Agenor Linea in the south. The mosaic was constructed from individual images obtained by the Solid State Imaging (SSI) system on NASA’s Galileo spacecraft during six flybys of Europa between 1996 and 1999. Credit: NASA/JPL-Caltech/University of Arizona.

Radiation is obviously a factor near Europa, one that will have a huge impact on hardening a lander for survival but also on choosing the most likely landing site. The paper points out that many of the darkest features on the moon also seem to be the youngest and are therefore likely to be less processed by radiation. The team, whose members were drawn from a number of NASA centers and universities, made lower radiation regions a priority for choosing sites where a lander would operate.

Europa’s so-called ‘chaos’ regions — marked by jumbles of ridges, plains and cracks — are the most likely targets because of their apparently young age and their associated dark plains that may consist of frozen fluid from the ocean. The image of suggested landing sites below is drawn from the paper, with associated caption.


Image: Candidate landing sites on Europa. Top: Blue contours show radiation intensity on Europa’s surface, as labeled with the geographic extent to which electrons of a given energy affect the surface and how deeply they penetrate (excluding the effects of secondary particles)… Candidate landing sites are indicated by red circles on the global map and shown in regional scale images at bottom. Left: Dark plains associated with chaos in the Galileo E25 region. Center: The chaos terrains Thera and Thrace Maculae. Right: Dark chaotic terrain in the Galileo E17 regional mosaic. Each candidate site satisfies the criteria of low-albedo, youthful material that appears to have originated from the subsurface and is outside the most intense radiation regions on the satellite. Credit: Pappalardo et al. (full citation below).

Two candidates stand out: “Thera and Thrace Maculae present very attractive targets for exploration on the basis of their low albedo, relatively young age (they have disrupted the preexisting terrain), and likely endogenic origin. It has been suggested that water may exist beneath Thera Macula today.” The problem is that we don’t have a view of Europa’s surface detailed enough to make many further inferences without more data from reconnaissance missions. This is going to be one tough place to touch down on safely, as the paper makes clear:

The highest-resolution images of Europa’s surface currently available are the handful acquired by the Galileo spacecraft with resolutions that range from 6 to 12 m/pixel. These show a surface that is rough down to the pixel level, containing fractures, slopes, and scarps. Most daunting are plates and matrix material resulting from chaos formation…, although these are scientifically very attractive places to explore. Imaging with resolution of 4 m/pixel of very young and active terrain on Saturn’s satellite Enceladus—in a portion of Enceladus that resembles Europa’s surface at comparable (tens of meters) resolution—reveals a landscape with many large ice boulders down to the resolution limit.

All of which puts the focus on existing mission candidates like Europa Clipper. Planetary geologist Philip Horzempa provided a recent update on this concept, which could launch as early as 2021 depending on ever-present budgeting fluctuations. Europa Clipper would not be a lander but a Jupiter orbiter that, over the course of two and a half years, would perform 32 flybys of Europa, the closest as low as 25 kilometers. According to Horzempa, the mission is seen as a precursor to a future lander, with a reconnaissance camera included as part of the package to provide lander-scale characterization of the surface with resolutions down to 0.5 meters.


Image: This artist’s concept shows a simulated view from the surface of Jupiter’s moon Europa. Europa’s potentially rough, icy surface, tinged with reddish areas that scientists hope to learn more about, can be seen in the foreground. The giant planet Jupiter looms over the horizon. Image credit: NASA/JPL-Caltech.

A future team of Europa lander specialists would study a selection of perhaps fifteen potential landing sites to down-select to a primary and a backup. Read Horzempa’s essay for more on the instruments being designed for the mission, which will have to survive intense radiation exposure through the use of 150 kilograms of dedicated radiation shielding. The Clipper team is weighing numerous options including mini-probes (nanosats) that might orbit or even make a hard landing on Europa. As we wait to see what plays out on the funding front (and remember the ongoing cost of the James Webb Space Telescope), work on the Europa Clipper design continues even as we ponder the most effective sites for safe operations and science on the surface.

The paper is Pappalardo et al., “Science Potential from a Europa Lander,” published online by Astrobiology August 7, 2013 (full text). This presentation of the Europa Summer Study Report to the Outer Planets Assessment Group also offers helpful background.


Comments on this entry are closed.

  • Tulse August 9, 2013, 15:22

    How stable is Europa’s surface? Have we had high-res imaging of its surface long enough to know the likelihood of a landing site chosen at launch still being there by the time a lander arrives?

  • Joy August 9, 2013, 15:24

    ” 150 kilograms of dedicated radiation shielding”

    IMO, Europa belongs in the “too hard” box until there is a low cost heavy lift booster. Even then, I would rather send a drilling rig to Mars to sink a well down to the liquid water level of the crust – a hard task, but still a lot easier than doing anything around Jupiter.

  • Alex Tolley August 9, 2013, 18:58

    Since the proposed lander is stationary, the landing has to be extremely precise to hit the target. But even this would be heartbreaking if the cameras saw something very interesting (like dead macro life), but out of reach. When so much of the reason for selecting this target is astrobiology, I would have thought that you would want a mobile lander so that you could look for promising spots to take samples, for example an area that was rich in carbon compounds.

    Given how little detail we have of the surface, a good orbital mission providing high resolution images of the whole moon seems far more sensible as a preparatory mission, with a later, mobile lander to exploit the new knowledge. A detailed heat map might even suggest active upwelling sites that would make better lander targets as the material would be fresh.

  • Michael August 10, 2013, 3:28

    Maybe a dumb lander with laser focusing equipment and results reflecting materials could use a laser produced from a craft in orbit to conduct experiments. Less weight to the ground will save on mission mass. Incidentally one of my friends at work has a nephew who is working on an Europa impactor probe design ~24000 g impact deceleration, harsh!

  • coacervate August 11, 2013, 5:28

    Give me an ice axe, a microscope, 3 months worth of oxygen and 6 months worth of good scotch and I’m gone.

  • David Cummings August 11, 2013, 8:23

    “The Europa Jupiter System Mission – Laplace (EJSM/Laplace) was a proposed joint NASA/ESA unmanned space mission slated to launch around 2020 for the in-depth exploration of Jupiter’s moons with a focus on Europa, Ganymede and Jupiter’s magnetosphere. The mission would comprise at least two independent elements, NASA’s Jupiter Europa Orbiter (JEO) and ESA’s Jupiter Ganymede Orbiter (JGO), to perform coordinated studies of the Jovian system.

    The Japan Aerospace Exploration Agency (JAXA) and the Russian Federal Space Agency (Roscosmos) had expressed their interest in contributing to EJSM/Laplace, although no deals had been finalized. JEO was estimated to cost $4.7 billion,[1] while ESA would spend $1.0 billion (€710 million) on JGO.[2]

    In April 2011, ESA stated that it seemed unlikely that a joint US–European mission will happen in the early 2020s given NASA’s budget, so ESA is investigating the possibility of proceeding with a European-led mission.[3] The ESA-led mission is called the Jupiter Icy Moon Explorer (JUICE) and will be based on the JGO design. Selection of JUICE for the L1 launch slot of ESA’s Cosmic Vision science programme was announced on May 2, 2012.[4]”


  • Horatio Trobinson August 11, 2013, 16:01

    re: “Satellites doing a hard landing”

    Here’s an idea:
    Landing doesn’t need to be too hard, not if we can position the craft so that it lands directly, perpendicularly on a geyser.

    Of course a special shield would be needed to protect it, as water crystallises into sleet and hail very quickly, but it’s possible a relatively lightweight (and easy to deploy) inflatable shield can do that job.

    Is this too crazy of an idea?

  • Enzo August 11, 2013, 18:01

    Talking of landing on Europa is premature : we haven’t even had a proper survey yet. And there will not be one for the foreseeable future : NASA has allocated most of the current funds to Mars. Even the plutonium is being used for Mars where solar panels work well.
    I won’t believe in the Europa Clipper or similar missions until they are on the launching pad as I have seen heaps of similar announcements followed by cancellations (Europa Orbiter, JIMO, JGO, Clipper, all talk and no action).
    The closest thing to an Europa mission seems to be the two flyby from JUICE around 2030 on its way to Ganymede. At least it will be a modern mission with ground penetrating radar.

  • Doug M. August 12, 2013, 10:06

    What Enzo said.

    Barring something truly unexpected happening, there will be no probes to Jupiter between the death of JUNO (October 2017) and the arrival of JUICE (currently scheduled for 2030, but don’t hold your breath).

    Let me emphasize that: we’re almost certainly going to have a stretch of 13 years (and probably more) in which outer planet exploration is going to go dark. No probes whatsoever, to Jupiter, Saturn, Uranus or Neptune. No flybys, no orbiters, no landers… nothing.

    Doug M.

  • Doug M. August 12, 2013, 10:16

    By coincidence, it just so happens that Cassini’s final orbit will take place just a couple of months before JUNO’s fiery demise. Both probes will end by plunging into the atmospheres of their respective planets. So, we’ll go in just a few weeks from having orbiters around both gas giant planets to having orbiters around none. The only human assets left active beyond the asteroid belt will be the two Voyagers (expected to go dark sometime in the 2020s as their RTGs wind down) and New Horizon, all flying through the darkness beyond the orbit of Pluto.

    And that will be it for a good long while. It takes years to plan and build an outer planets probe, and more years to get it there. If we started tomorrow, we wouldn’t see one arrive before the middle of he next decade.

    And we’re not starting tomorrow. With the sole exception of JUICE, not one mission to the outer planets has been approved. As Enzo correctly notes, they’ve all been cancelled. And JUICE is still in the planning stage, nearly a decade away from launch, and thus highly vulnerable to budget cuts and delays.

    TLDR: we’re not going to Europa any time soon. Personally, I won’t be surprised if our next visit doesn’t happen until well into the 2030s, twenty years or more from now.

    Doug M.

  • Rob Flores August 12, 2013, 11:09

    I’ve done this type of landing before, Steep cliffs, treacherous canyons limited fuel, 25 cents a try. Very hazzardous.
    Only Venus would be harder to land on IMO. Even if these Ice projections that are theorized to exist on the surface are a few meters high
    I think any mobile surface lander is out of the question. Better to use
    a surface base for deep Ice exploration.

    Speaking of which can the lethal radiation on the surface have a costant direction it’s coming from?
    Would there be a position close to an ice cliff where the radiation is blocked/shadowed out.?

  • Bob August 12, 2013, 12:21

    I highly recommend to those interested a new movie called Europa Report, a sci-fi thriller about a mission to Europa to search for life. It is make in a hyper realistic style and concentrates of science. In other words, it does not devolve into a bug hunt.


  • Doug M. August 12, 2013, 16:20

    “Speaking of which can the lethal radiation on the surface have a costant direction it’s coming from?”

    It comes from all directions, but (we think) most heavily from the apex of the trailing hemisphere. Levels are lower, though still crazy high, at high latitudes and in the forward hemisphere.

    A complicating factor is that it includes multiple types of “radiation”. There are electrons and protons at various energies, ions of various atoms, and — at the surface — bremsstrahlung radiation that goes well up into the X-rays. It’s a challenging environment.

    Doug M.

  • andy August 12, 2013, 18:11

    The giant planet Jupiter looms over the horizon.

    Is that bump mapping on Jupiter (more visible in the full-res version here) at all realistic? It seems a bit extreme to me.

  • Enzo August 12, 2013, 20:32

    “No probes whatsoever, to Jupiter, Saturn, Uranus or Neptune.”

    The most painful thing is not just the lack of budget, but the overallocation to Mars. NASA chose Curiosity ($2.5B), MAVEN ($0.5), Insight ($0.5) and Curiosity 2 ($1.5B). Total $5B, ll for Mars .A much more balanced choice could have been Curiosity ($2.5B), MAVEN ($0.5) and Europa Clipper ($2B), same total. Personally I would have preferred Curiosity ($2.5B), Titan MARE ($0.5) and Europa Clipper ($2B), but that’s me.
    Besides, nothing revolutionary has been discovered on Mars that now looks a lot less habitable than in the 70s.

    Coordination with ESA would help. Instead they seem to often replicate missions (MESSENGER-Bepi Colombo, MSL2-ExoMars rovers, MAVEN-Trace Gas Orbiter). Even if not identical, there’s a lot of overlap that would allow precious savings (=> more missions) if they were shared.

    Regarding JUICE Europa flybys, I’m more confident : ESA tends not to cancel missions, even when it should :-) Like in the case of ExoMars, terminally damaged when NASA reneged on its promised landing system for budget reasons only to announce their very own rover (MSL2) a short time later. Instead of cancelling ExoMars, ESA is going ahead with the Russians whose track record in planetary exploration has been very poor recently.

    China and India are planning their own Mars orbiters too, so more of the same. YAWN.

  • coolstar August 12, 2013, 20:48

    @Rob Flores Venus is so EASY to land on that at least 5 probes have done it without a parachute! Venera 11-14 all ejected their parachutes at around 50 km, while one of the 4 sub-probes of Pioneer Venus 2 had no parachute and survived on the ground for about an hour. It’s SURVIVING once you land, that is the hard thing on Venus……

  • Doug M. August 13, 2013, 18:03

    Mars is perceived as popular. And then of course, there’s the obsession with putting humans on Mars. The two combine to make NASA pretty Mars-obsessed, yes.

    Bepi-Colombo is actually pretty different from MESSENGER. It has a significantly different instrument suite, and it’s actually going to split into two orbiters once it arrives. One will be in a low orbit (mostly lower than MESSENGER’s, though with a higher periapsis) and will study hell out of the surface. The other will be in a higher orbit and will study Mercury’s magnetosphere and interactions with the Sun. Also, Bepi-Colombo was originally going to drop a little lander, which would have been cool as hell, but which got cancelled for budget reasons.

    Anyway, two Mercury orbiters over a decade apart doesn’t seem like overkill. Especially given that Mercury had hardly been explored at all before MESSENGER — there’d only been the single Mariner flyby 45 years earlier.

    India hopes to launch its Mars orbiter, Mangalyaan-1, this December. Its scientific value will be modest — close to nil, really; it has a small science package that’s largely redundant with stuff that’s already been in orbit for years. But, hey, proof-of-concept.

    Doug M.

  • Horatio Trobinson August 13, 2013, 20:01

    I suppose that it all comes down to making more effective PR work, teaching the general public that Mars is pretty much already covered for the time being, and the really interesting targets of Europa, Titan and possibly Enceladus await eagerly.

  • Enzo August 14, 2013, 6:32

    “Anyway, two Mercury orbiters over a decade apart doesn’t seem like overkill. ”

    If you put it into the current context which is no money for the foreseeable future for Europa or Titan and, if you also add that it takes some 15-20 yrs from approval to arrival to one of these two places, then spending some $1.3 B on another Mercury orbiter does seem a bit extravagant.
    I guess ESA is also limited by the fact that they have no RTG (otherwise they could go to Titan) and no rad hard enough hw (otherwise they could go to Europa).
    Ulysses flew with a NASA provided RTG.

  • ljk August 14, 2013, 19:56
  • Doug M. August 15, 2013, 4:05

    @Enzo, I would disagree. That’s only one flyby and two orbiters in almost 60 years of Mercury exploration. That will put Mercury a bit ahead of Saturn (three flybys, one orbiter) but well behind Jupiter (seven flybys, two orbiters).

    Also, we can be pretty sure that those will be the last Mercury missions until… oh, let’s say at least 2040.

    Doug M.

  • Doug M. August 15, 2013, 4:10

    You know that JUICE is going to do Europa flybys, right?

    The ESA is totally capable of developing RTGs — Europe has a bigger nuclear industry than the US — and heavily hardened electronics. But with about half of NASA’s budget, it wouldn’t really be cost effective for them; they’re just not going to be doing that many missions that need those things.

    Doug M.

  • Enzo August 18, 2013, 23:23

    @ Doug M.

    Europe is technically capable of producing a RTG, but I’m not sure it would be a politically wise move over there. There is a strong aversion in the general population over there for anything nuclear.
    Some time ago I read something about ESA using americium for RTGs. I just checked and it looks like they are at least financing more work :

    Maybe americium doesn’t sound as threatening as plutonium to the masses.
    Or maybe there are some more technical reasons outlined here :

    Regarding Mercury, you count a mission to Europa and Titan as missions to Jupiter and Saturn. They are not, they are missions to Europa and Titan, worlds in their own right which never got an orbiter. JUICE is a mission to Ganymede, not Jupiter.
    Besides Mercury is geologically dead, with no volatiles (with the exception of a bit of comet ice at the poles) and a scorching temperature.
    Comet ice is interesting, but it would be much better examining it uncontaminated from a comet.

    Europa has an ocean which has interacted with the surface in geologically recent times and two likely sources of energy useful for life (the compounds created on the surface and the volcanic activity at the bottom).
    Titan has an interesting geology and alternative weather that leaves Mercury for dead and a very very interesting organic chemistry on the surface.

  • Doug M. August 20, 2013, 4:25

    @Enzo, I’m not sure what you’re talking about. I’m counting missions completed, en route, or clearlys going to launch. That gives the following:

    Mercury, orbiters — MESSENGER, BepiColombo = 2 orbiters
    Jupiter, flybys — 2xPioneers, 2xVoyagers, New Horizon, Cassini, Odyssey=7 flybys
    Jupiter, orbiters — Galileo, Juno = 2 orbiters
    Saturn, all — 1 Pioneer, 2xVoyagers, Cassini = 3 flybys, 1 orbiter

    There have been no specialized missions to Europa or Titan; Galileo and Cassini were both hybrid missions, studying both the primary and the moons. Juno will be the first specialized mission to the outer planets; she’ll study Jupiter only, almost completely ignoring the moons.

    You seem to be arguing that Mercury is inherently less interesting than the outer planets. I’m not sure I agree. Mercury is a terrestrial planet, which makes it inherently interesting (at least to us). We’ve already learned all sorts of interesting things, from the presence of ice to the fact that Mercury had a major resurfacing event around 4 gya. (Wow, terrestrial planets seem to have a lot of resurfacing events.) Also, since a great many exoplanets seem to be in Mercurian orbits (or closer), Mercury may have some useful insights for us.

    Anyway, the die is cast — we’re getting BepiColombo, but nothing to Jupiter between Juno and JUICE. Whether we agree with that or not, it appears that’s how it will be.

    Doug M.

  • Doug M. August 20, 2013, 4:33

    As to americium: less threatening, probably yes. Also, americium has one advantage compared to plutonium, and one great disadvantage. The disadvantage is it produces much less energy per gram. So an americium RTG is going to be a lot heavier, which in a space context is all kinds of bad.

    The advantage is that americium’s half-life is more than 5X longer than plutonium’s — ~430 years as opposed to ~82. So far, only the Pioneers have died from running out of power, and only the Voyagers are going to. (Every other space probe will die from some other cause, most typically running out of propellant for station keeping.) But as we build longer-lived probes with ever more extended missions, americium is going to look more and more attractive.

    Doug M.

  • ljk September 11, 2013, 15:13

    NASA Maps Out Goals for Europa Landing

    By SpaceNews Staff | Sep. 2, 2013

    Depiction of Europa’s surface and suspected subsurface ocean. Credit: NASA/JPL-Caltech artist’s concept

    The top priority of a robotic lander mission to Jupiter’s potentially life-supporting moon Europa should be investigating the composition and chemistry of its subsurface ocean, scientists say.

    Such a mission should also aim to determine the thickness and dynamics of the moon’s ice shell and characterize the surface geology of Europa in detail, a NASA-appointed “science definition team” reports in a new study in the journal Astrobiology.

    “If one day humans send a robotic lander to the surface of Europa, we need to know what to look for and what tools it should carry,” study lead author Robert Pappalardo of NASA’s Jet Propulsion Laboratory in Pasadena, Calif., said in a statement.

    “There is still a lot of preparation that is needed before we could land on Europa, but studies like these will help us focus on the technologies required to get us there, and on the data needed to help us scout out possible landing locations,” Pappalardo added.

    Scientists are eager to learn if Europa’s huge subsurface ocean harbors alien life.

    Full article here:


  • ljk September 19, 2013, 14:17

    New Molecules Detected in Io’s Atmosphere

    by SHANNON HALL on SEPTEMBER 18, 2013

    Io – Jupiter’s innermost Galilean moon – is the most geologically active body in the Solar System. With over 400 active volcanic regions, plumes of sulfur can climb as high as 300 miles above the surface. It is dotted with more than 100 mountains, some of which are taller than Mount Everest. In between the volcanoes and mountains there are extensive lava flows and floodplains of liquid rock.

    Intense volcanic activity leads to a thin atmosphere consisting mainly of sulfur dioxide (SO2), with minor species including sulfur monoxide (SO), sodium chloride (NaCl), and atomic sulfur and oxygen. Despite Io’s close proximity to the Earth the composition of its atmosphere remains poorly constrained.

    Models predict a variety of other molecules that should be present but have not been observed yet.

    Recently a team of astronomers from institutions across the United States, France, and Sweden, set out to better constrain Io’s atmosphere. They detected the second-most abundant isotope of sulfur (34-S) and tentatively detected potassium chloride (KCl). The latter is produced in volcanic plumes – suggesting that these plumes continuously contribute to Io’s atmosphere.

    Expected yet undetected molecular species include potassium chloride (KCl), silicone monoxide (SiO), disulfur monoxide (S2O), and various isotopes of sulfur. Most of these elements emit in radio wavelengths.

    “Depending on their geometry, some molecules emit at well known frequencies when they change rotational state,” Dr. Arielle Moullet, lead author on the study, told Universe Today. “These spectral features are called rotational lines and show up in the (sub)millimeter spectral range.”
    These observations were therefore obtained at the Atacama Pathfinder Experiment (APEX) antenna – a radio telescope located 16,700 feet above sea level in northern Chile. The main dish has a diameter of 12 meters, and is a prototype antenna for the Atacama Large Millimeter Array (ALMA).

    Full article here:


  • ljk November 23, 2013, 12:00

    A Story of Planetary Seduction: The Captivating Charms of Europa

    By Leonidas Papadopoulos

    Here’s Europa for a shilling
    No one minds, and she’s quite willing;
    Spotless sheets her charms enfold,
    She’ll light a fire if it be cold:
    No need to have turn’d bull, dear Jove,
    The day you sought Europa’s love.

    — Antipater of Thessalonica, 1st century AD

    Although the Greek poets of antiquity praised the unsurpassed beauty of the mythological maiden princess, they could never have imagined that hundred of million of kilometers away lay a real world of equal beauty and intrigue that would captivate the hearts and minds of astronomers, planetary scientists, and space advocates alike, up to this day. And even though scientists do not have to metamorphosise into a bull in order to cover the vast distances to go to Europa enchanted by its inviting charms, nevertheless making physical contact and landing on the distant moon presents one of the hardest engineering challenges.

    Europa was one of the first things Italian astronomer Galileo Galilei saw in 1610 when he turned his telescope upward to examine the heavens for the first time, during a set of observations that would change the world forever. For the next 350 years, Europa, like most of the things that astronomers observed through a telescope, remained just a point of light in the sky.

    All this changed with the advent of the Space Age, when these points of light started to transform into real and exciting worlds just like our own. Still, Europa holds a special place among them, for many in the scientific community view it as the single, best place in the Solar System to hold the possibility of supporting extraterrestrial life today.

    Prior to space exploration, astronomers believed for decades that the moons of the outer planets in our Solar System were frozen and boring chunks of rock and ice. After all, conventional wisdom held that so far from the Sun, every Solar System body would be a denizen of a vast icy planetary graveyard. But the Voyager probes’ fly-bys during the 1970s and ’80s revealed a very different picture. An assortment of dynamic, active, and ever-changing moons orbiting their equally fascinating planets, in setups that could best be described as mini solar systems in their own right.

    And exploration of Europa brought its own fascinating discoveries: a Jovian moon that, unlike Saturn’s Titan, only holds a very tenuous atmosphere of molecular oxygen, created by the breakup of the surface water ice from the radiation around Jupiter. But the real treat proved to be its interior, which is considered a promised land for astrobiology research, more so than even Titan’s surface itself.

    Full article here: