Our recent discussions of the Jovian moons Ganymede and Europa highlight a fact that not so long ago would have seemed absurd. Three of the four bright dots that Galileo saw through his primitive telescope around Jupiter are potential habitats for life. Even battered Callisto gives evidence of an internal ocean, as do, of course, both Ganymede and Europa. But why stop there? Further out, Titan is worth exploring both on the surface and under it, and tiny Enceladus may be both the easiest to study and the most bizarre astrobiological possibility we’ve yet found.
The ‘easy to study’ part comes from the fact that Enceladus conveniently spews vapor from its own internal reservoirs into space, making it possible for a space probe to analyze the contents without ever touching down on the surface. The ‘bizarre’ part comes from the fact that those fissures exist, surely a sign of Saturn’s gravitational grip upon the flexing moon, but also a reminder that these outer moons have leaped into our consciousness as liquid water-bearing places. Remember, it wasn’t that long ago that we assumed Europa itself would be just another crater-scarred, inert ball of rock and ice. The Voyager missions changed everything.
Lee Billings is sufficiently encouraged by facts like these to put Europa at the very top of his list of destinations, speculating in his new essay in Aeon Magazine that our enthusiasm for Mars may be misplaced. We’re always ‘following the water,’ knowing that water helps in the transmission of biochemical energy, nutrients and waste, not to mention its shielding effects against cosmic radiation and its ability to retain warmth. But Billings, the author of Five Billion Years of Solitude (Current, 2013) sees our current Mars efforts as ‘cautious and procedural, perhaps to a fault, as a result of past overreaches in the search for Martian life.’
Indeed, scientists who specialise in Mars have been forced to dial down their dreams, hypothesising ever-smaller windows of opportunity for past life on the red planet, and ever more inaccessible refuges for anything now living there. Native Martians, if they exist at all, are most probably microbes clinging to life almost unreachably deep beneath the surface. This does not diminish the importance of exploring our neighbouring planet, but it must be admitted that there might well be more promising places to seek alien life. Indeed, if following the water is the prime directive in the search for extraterrestrial life, it increasingly appears that we should look beyond Mars to an icy moon of Jupiter called Europa.
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. Credit: NASA/JPL-Caltech
The russet upwellings of mineral salts that mark Europa’s cracks and fissures helped us see that a warm ocean sustained by Jupiter’s tidal forces and the flexing of the interior could exist, and that that ocean could have existed for billions of years. Imagine finding evidence that life of some kind existed under that ice. The discovery would implicate the other moons I’ve mentioned, and could, as Billings reminds us, take us out as far as Pluto in the hunt for subsurface water, looking for tidal heating or radioactive decay as sources of a comfy astrobiological warmth.
Europa, of course, is a very tough nut to crack. For one thing, you’re dealing with magnetic fields around Jupiter that produce extreme radiation hazards not just for manned missions but robotic orbiters, which adds greatly to the cost of any contemplated mission. Then there’s the matter of Europa’s crust, which might be a few kilometers deep or a hundred. Here the Enceladus model may come to our rescue, for just as Enceladus vents subsurface materials into space, so too may Europa. It was just last year that the Hubble Space Telescope was used to detect water vapor here — an estimated 7000 kg of water per second — blown 200 kilometers into space.
Fly a mission through these plumes and it should be possible to learn a great deal about what’s going on by way of chemical and physical processes beneath the ice, perhaps even evidence of biological activity or, as Billings adds with a touch of whimsy, ‘you might even catch a flash-frozen fish.’ For that matter, a robotic lander near a Europan fissure might snare highly interesting results. Sure, Mars is a much easier target, but look at the sheer number of orbiters and landers both in place and planned and contrast that commitment to the less than $1 billion NASA is now targeting as the pricetag for the Europa mission it’s gathering concepts for.
Image: Reddish spots and shallow pits pepper the enigmatic ridged surface of Europa in this view combining information from images taken by NASA’s Galileo spacecraft during two different orbits around Jupiter. The spots and pits visible in this region of Europa’s northern hemisphere are each about 10 kilometers across. The dark spots are called “lenticulae,” the Latin term for freckles. Their similar sizes and spacing suggest that Europa’s icy shell may be churning away like a lava lamp, with warmer ice moving upward from the bottom of the ice shell while colder ice near the surface sinks downward. Other evidence has shown that Europa likely has a deep melted ocean under its icy shell. Ruddy ice erupting onto the surface to form the lenticulae may hold clues to the composition of the ocean and to whether it could support life. Credit: NASA/JPL/University of Arizona/University of Colorado.
Billings ends his essay with characteristic eloquence:
Even if Mars proves totally, irrevocably dead, one can still squint up at its ruddy disk in the night sky, and envision a better future for it. Someday, humans might walk there, perhaps even live. No one has such dreams for Europa. If Mars is a warped mirror we stare into, while imagining ourselves as explorers in some pleasantly familiar frontier future, then Europa must be a locked door, or maybe a matte-black monolith, cold and indifferent, an abyss that might, some day, gaze back at us, if only we could first convince ourselves to look.
I like that, especially the nod to Clarke’s monoliths, and I thought about the distance between Bradbury and Clarke as I absorbed Lee’s essay. Clarke went to Mars as well, in The Sands of Mars (1951), his first published novel, while Bradbury’s Mars was a splendid, visionary dream sequence. Both writers depicted a Mars that could be tamed by humans, but it’s the mysterious Europa of Clarke’s Space Odyssey series that draws me more.
Clarke had planned to delay 2061: Odyssey Three until the Galileo mission to Jupiter was operational, but he went ahead after that mission’s launch delay, so that when the book was published in 1987, it couldn’t have drawn on any of the Galileo findings. But even with Galileo’s imagery, Europa’s hidden depths are still enigmatic, their exciting promise hidden by their layered ice. Clarke’s Europa would be all about transformation as an ignited Jupiter (‘Lucifer’) heated up all the Jovian moons to bring life to a once desolate system.
What might come out of a thawed Europan ocean in a scenario like that? Life is all about transfiguration — it emerges out of an environment, changes and is changed by that environment — and we are left to wonder how complex it might become given the right mix of oxidized mineral salts filtering back down through the fractured Europan ice and the chemical reactions near deep water hydrothermal vents. The prospect is so compelling, the possibilities so alien to our earlier conceptions of the Galilean moons, that surely we can come up with a mission following up ESA’s Jupiter Icy Moons Explorer (JUICE) to make the 2030s the decade of Europa.
Given that Enceladus may indeed be the “easiest to study”, I’m not clear why Europa seems to be the only target of exploration that is seriously discussed for missions, and that Enceladus isn’t at the top of the list instead. Is there reason to believe there is less likelihood for life there? Or is it just that Europa has a certain historical “sexiness” at being the first moon discovered to have a subsurface ocean? Are there other scientific factors at play that make Enceladus a less attractive target?
I would think that an orbiter around Enceladus, continually scooping up and analyzing plume material, would be far more effective in assaying for possible life there than flybys of Europa necessitated by the radiation environment.
Europa sounds like the best possibility, if we can get hold of that water vapor being spewed into space (a lander dropped near or in one of those thin areas would be even better, but much less likely). Actual mineral salts means we’ve got rock in contact with the water, and now we just need energy to create a situation where life could theoretically develop to the best of our knowledge about abiogenesis.
Not so sure about Ganymede and Callisto, with the water layers interwoven with special Ice states.
The one big gripe I have with these missions is the length of time to get there due to the great distances. But if we could those cracks look mighty interesting.
1) They are easy to find and at their bottom there would be less ice to melt through.
2) The crack material has substantial salt which would lower the melting point of the ice.
3) The ice in the cracks is mostly likely slushing, at least a lower depths due to the great forces that Jupiter exerts on them.
4) They give better radiation protection if they are at an angle with the radiation stream.
I don’t think we would need to go down far to find a region where life could have gained a foothold and held on to it.
My best bet to look for life would be to probe the plumes of Europa and Enceladus using nanopore based devices for detecting nucleic acid or their analogues:
http://online.liebertpub.com/doi/abs/10.1089/ast.2013.1120
@Tulse,
Enceladus is very interesting but I think that one of the fears there is that the activity and possible lake/ocean might be limited in time and space (south pole only). If it’s really a relatively short lived phenomenon (on geological time scales) that might be not as interesting from the life point of view. After all, Mimas is very similar but apparently dead. Also, the traveling time to Saturn is much longer.
Europa seems to have a global ocean and it probably had it for a very long time. The crust might be thin enough for ocean interaction with the radiation replenished oxidizers (a source of energy) on the surface. Having said that, I’d be thrilled by an Enceladus mission instead of yet another Mars mission.
Unfortunately, NASA is completely Mars obsessed and it has spent/allocated $5B to it lately (Curiosity $2.5B, Maven $0.5B, Insight $0.5B,MSL-2 $1.5B).
Consequently, there’s no money for Europa for the foreseeable future.
My biggest fear is the sample return mission : a hugely expensive endeavor that might suck up resources from all other planetary missions. And all this without having found even basic organics on Mars to take back : Mars is looking a lot less habitable than it looked in the 70s.
With regard to extra terrestrial exploration , my feeling is that we are all trying to run before we can walk .A first priority must surely be the development and production of vehicles capable of carrying human beings in safety over the enormous distances involved in Space travel even within the Solar system and of transporting the equipment and stores required by future exploration teams to the many destinations currently under discussion . The impatience which both scientists and engineers are exhibiting in their eagerness to investigate further the fascinating discoveries made by unmanned devices travelling deep into the Solar system , is understandable .But there is little point in premature attempts to launch human beings on space ventures into an environment so much more extreme than that in which they have evolved and in which they are likely to be exposed to experiences for which they are completely unprepared both physically and mentally . While we may be able to make a mad dash to Mars within the next tor three decades ,properly planned and organised manned exploration missions are unlikely ,in my view , to be feasible for another two or three centuries, at the earliest. Meantime it is still possible to gain a great deal more information by employing unmanned probes and the advances in robotics
I’m an advocate of fast flyby’s. Like the extremely successful Voyager 2, the only probe to pass by the ice giants, and like today’s New Horizons. Some advantages I imagine of flyby’s rather than orbiters:
– Early results, 7 or so years shorter travel time.
– More modern instruments at work at arrival.
– More mass to instruments and less mass to fuel and shielding.
– Could include impactors or splitting up on arrival to observe from different angles at the same time.
– Would give data to help design a 10+ year long orbital mission later.
– Could afterwards study the heliopause or even like New Horizons maybe a Kuiper Belt object. And of course like all other outer planetary probes, on the way have another close look at Jupiter with better than ever instruments.
– Cheaper. $1 billion to Europa is good for a flyby this decade, but poor for an orbiter in the 2030s. Cheapness and quickness tend to be politically more apealling too.
Sample return missions to Europa do not necessarily have to be billion-plus dollar projects. There is a proposed low cost, Discovery-class Enceladus sample return mission concept called LIFE (Life Investigation For Enceladus) that would use aerogel collectors (of the sort used in NASA’s Stardust mission) to secure samples from the polar plumes of Enceladus during multiple passes by this moon. Initial studies show that the same hardware could be used to secure samples of material from Europa’s recently discovered plumes as well as material from volcanic plumes of Io and Jupiter’s Gossamer Rings (indirectly sampling Amalthea and it smaller inner moon siblings in the process). Check out the following for a fuller discussion: http://www.drewexmachina.com/2014/03/27/a-europa-io-sample-return-mission/
I wonder what the change of pressure involved in being erupted into space would do to any organisms that might be in the oceans on these icy moons. I guess it wouldn’t do them any favours, and that sampling the plumes would give at best some biochemistry rather than intact micro-organisms. How long would biomolecules last in the radiation environment near Europa or Enceladus?
@andy May 8, 2014 at 13:21
‘I wonder what the change of pressure involved in being erupted into space would do to any organisms that might be in the oceans on these icy moons… How long would biomolecules last in the radiation environment near Europa or Enceladus?’
Any dissolved gases in the cell would expand rapidly destroying the cell, not a good outlook and as for the radiation that outlook does not look good either!
Here is a neat program to look at pictures of celestial bodies,
http://webmap.lroc.asu.edu/lunaserv.html
Europa and Ganymede are there as well as is Enceladus.
I like these types of programs as you can get a feel for the object you are looking at.
A Reluctant Dance Towards Europa
or, Why A Credible Europa Mission is Likely to Cost ~$2B
Posted by Van Kane
2014/05/14 12:42 CDT
Topics: FY2015 NASA Budget, Jupiter’s moons, Europa, Space Policy, Decadal Survey, Future Mission Concepts, spacecraft
For the last two years, NASA has been the shy partner refusing to get on the dance floor, and Congress has been the aggressive partner insisting on a dance now. Recently, NASA has said maybe on another night but only if it’s a cheap date. While NASA says no for now, Congress looks to be willing to slip the band a cool $100M – on top of $150M already paid – to keep the music playing, but (to keep the metaphor going) has not been willing to fully commit itself to paying the bigger bill to rent the dance hall.
The dance, of course, is the continuing attempt by Congress to have NASA commit to a mission to explore Europa, and NASA managers’ attempts to delay a mission well into the 2020s. NASA is also seeking ideas for alternatives to the current $2B Europa Clipper concept that would cost no more than $1B but that also would presumably be much less capable.
(I should make it clear that NASA’s managers in this context are its most senior managers who have to try to balance the demands of an underfunded human spaceflight program against requests for several exciting science missions. They are in a tough spot between the restrictions placed on them by the President’s budget office and Congress’ requests, with too little money the common denominator.)
Full article here:
http://www.planetary.org/blogs/guest-blogs/van-kane/20140514-nasas-reluctant-dance-towards-europa.html
A Europa-Io Sample Return Mission
By Drew Lepage
March 27, 2014
A couple of weeks ago the Obama Administration released its proposed budget for FY2015. NASA’s budget (which is almost certainly subject to change by Congress as has been the case for decades) would stay essentially flat at $17.5 billion and Planetary Science would get nearly $1.3 billion or just $65 million less than what Congress approved for the current fiscal year. Included in the budget is $15 million for continued studies of a mission to Jupiter’s moon, Europa, in the 2020s. But instead of a full blown flagship-class mission, the Administration is proposing that the Europa mission have a cost target of under a billion dollars. This is just a fraction of the cost of missions like the proposed $2.1 billion Europa Clipper currently under study which itself is a fraction of the cost of the earlier proposed $4.7 billion Europa Orbiter.
As the planetary science community scrambles to figure out how to meet such a tight budget cap to such a difficult-to-reach (but scientifically fascinating) target like Europa, I would like to make a suggestion: A sample return mission to Europa.
Full article here:
http://www.drewexmachina.com/2014/03/27/a-europa-io-sample-return-mission/
Enceladus is a tiny world and could be a captured comet. Europa, on the other hand, is a sizable world with terrestrial-like composition and geology beneath its surface. Titan also shows evidence of terrestrial character in the existence of radiogenic argon, produced from the decay of potassium. The close relationship between geology and microbiology suggested by extremophiles found on Earth, from the ocean floor at the mid-ocean ridge to the bottom of our deepest caves, suggests that Europa’s subsurface environment has a high probability of being analogous to conditions on Earth from which life arose. Also, for the brief time in which any organic molecules would be exposed to the vacuum of space, much would survive that could be analyzed by a flyby spacecraft with the appropriate instrumentation. Some microbes are remarkably hardy under vacuum conditions, and regardless of those, plankton and diatoms have structures that are not easily destroyed under any conditions.