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A pair of papers in this week's Nature look at evidence that Enceladus, a moon of Saturn, may have an ocean of liquid water beneath its icy surface. Such an ocean would bode well for Enceladus harboring some kind of extraterrestrial life, in a location close enough for robotic probes to visit.

At the moon's south pole, plumes of water vapor and ice spew into space from cracks in the surface, leading to speculation that an ocean feeds the eruptions. A team of European researchers provides evidence to support that theory in a Nature study published online today, in which they used the Cassini spacecraft to spot salty ice grains in Saturn's E ring. (Scientific American is part of the Nature Publishing Group.)

That ring is largely produced by Enceladus's icy jets, so the presence of sodium in the E ring points to a salty ocean below the moon's surface. The sodium compounds, the authors write, "exhibit a compelling similarity to the predicted composition of a subsurface Enceladus ocean in contact with its rock core."

But the second study, published concurrently, examines the vapor from the moon's plumes, which greatly outweighs the ice grains, from ground-based observatories and does not see the sodium that would be expected if the plumes were indeed geysers from a near-surface saltwater ocean. The research, the study's authors write, shows "that the bulk of mass escaping Enceladus has much lower salt content than ocean models." Evaporation from a deeper ocean might explain the lack of sodium in the vapor, as might a freshwater reservoir on Enceladus.

In a related commentary on the two studies, space scientist John Spencer of the Southwest Research Institute in Boulder, Colo., weighs the two arguments and finds that they may yet fit together. The salty ice grains, he says, would not provide enough sodium to be detected by the ground-based methods—there is too much sodium-free or sodium-poor material to dilute it. "In any case," Spencer writes, "those salty grains provide our current best smoking (or steaming) gun pointing to present-day liquid water near the surface of Enceladus."

Photo of Enceladus from the Cassini spacecraft: NASA/JPL/Space Science Institute

7 Comments

1. 1. sapbucket 04:07 PM 6/24/09

   Water, H20, provides oxygen for atmosphere and hydrogen for fuel, and it is spewing out of this moon. Maybe this is sci-fi, and of course it would require more data to theorize, but a distinct possibilty presents itself: an orbitting craft with a high speed orbit and some type of "scoop" could orbit the moon and collect water from the polar regions. It could also orbit Saturn and collect from this E ring I've heard so much about. This might be a nice place for a space station?

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2. 2. Tucker M 04:40 PM 6/24/09

   Science fiction indeed! Hydrogen works as fuel only because you can burn it - that is, light it in the presence of oxygen, prompting it to combine with the oxygen to form H2O, which releases energy. That's why hydrogen burns so cleanly; its "ash" is water.
   
   Unfortunately, that means it takes at least as much energy to extract hydrogen from water as you get back when you burn it. Which means that getting oxygen from water isn't much help if you're going to burn it all back up with hydrogen - and getting hydrogen fuel from water is only practical if you have a third source of energy (like solar) to separate it from the oxygen. Basically, what you're really proposing is using hydrogen as a sort of fuel cell for storing the solar energy your spaceship gathers. Not a bad idea, but it might be easier to just bring the water you need, rather than burning the fuel it would take to maneuver and scoop up vapor from Enceladus' jets.

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3. 3. hotblack 02:27 AM 6/25/09

   So, bodies in our solar system with the current potential to support life: Callisto, Ganymede, Europa, Titan, and Enceladus... That's quite a few.
   
   A synopsis on the possibilities of & search for extra-terrestrial life in our own solar system would be very interesting.

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4. 4. aurelius 06:34 AM 6/25/09

   Do you think building colonies in other bodies of our solar system is doable with the current techology? And if so, do you think that is possible for one country to prepare such a mission or should it be an internationnal attempt ?
   

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5. 5. tharriss 09:07 AM 6/25/09

   When you look at the expense, delays, and problems with building the International Space station in near Earth orbit, can you imagine the difficulties and expense of a similar effort so far away?
   
   While that sort of thing is technically possible, it seems highly unlikely the nations of Earth would invest in a project like that until the cost/benefit of it changes radically (which is possible over time given new discoveries/new tech).
   
   Of course, with our population continuing to run out of control in the century to come, it seems even less likely we'd invest dwindling resources in such a project. So unless something changes soon, we have a narrowing window in which to make the attempt.
   
   Really the future of exploration, and of mankind in general is going to depend heavily on the current scientific/technical explosion that is going on. We need paradigm shifting discoveries across a wide array of issues just to survive the next few centuries without disaster.

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6. 6. aurelius 09:43 AM 6/25/09

   I think that a human station on the moon is basically the very first step, before even thinking of going somewhere further. I think it will help even psychologically, for pursuing something even bigger afterwards.
   
   Since you spoke for technological progress that is necessary for something like building human stations, I think that the new protocols that have been built(or they are still being developed) for interplanetary communications (or simply space internet) are a very important step forwards to improve communications (what else).
   
   Of course there are much more things to be done, but I think the biggest challenge is to answer the question "why go to the moon? or why go to Mars?". I think that till now, the different countries use space technology mostly for showing-off (apart from the military sci-fi usage they are also hoping to). You can't go far with this way of thinking, because world has much bigger problems now. I think, if scientists/engineers were researching on how to make efficient use of resources in other bodies of our solar system, that would be a very attractive and promising alternative.
   
   Anyways, I don't think we(as humanity) can go far with this (because of both economical and human-resource reasons), if there is no cooperation.

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7. 7. Homeskull in reply to hotblack 02:07 AM 6/26/09

   I'm creating a blog to make solar system astronomy simple and dramatic for students, especially homeschool students www.homeskull.blogspot.com. Can anyone briefly explain why finding (or not finding) sodium in the H2O ejected from Enceladus is so significant?

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