[X] My Assistant

[Guest_Richard Trigaux_*]

James Oberg Chimes in:
Let Us Drink from the Fountains of Enceladus

The idea is as follows: send a stardust-like mission to capture particules from the Enceladus plume.

I think it is the cheapest way to have infos on what is going on into Enceladus, if it has a biochemistry and how far it evolved.

I allow myself to better the idea: the probe could have three targets.


1) when passing near Saturn, catches ring particules
2) Using Titan as a gravitationnal aid, captures smog particules (fortunately they reach very high)
3) passes into Enceladus plume, captures eventual evidences of biochemistry in Enceladus.

And back to Earth! It even don't need to actually satellise around Saturn, if it is well aimed. The only difficulty is a precise navigation, to aim into a 10x10kms window into the plumes, and a bit of fuel.

The only serious problem is not to bring back some alien bacteria on Earth! Eventually the aerogel containing the Enceladus particules would be coated in something after use, so that there would be no possible contamination, in any way.

Even if the mission fails, a low pass over the Tiger Stripes would allow to obtain precise images of the vents (or more likely zones where the ice is sublimating, like in a comet), provided we have a special shutter compensating for motion blur. Such images would be anyway a necessary preliminary step before sending a lander on Enceladus, and even before designing it (depending on the geometry of the vents, which may be complicated or hazardoous).

[Guest_BruceMoomaw_*]

Which is precisely why we need to know as much as Cassini can possibly tell us about the composition of the plumes. But they definitely are not just plain water -- the plume is about 3-4% each nitrogen and CO2, 1.5% methane, and probably smaller amounts of other organics (acetylene and propane are thought to have been detected) and other substance. We simply don't know how far organosynthesis may have gone in this environment.

It is certainly important, however, NOT to jump to the conclusion that there's a good chance Enceladus is a Fountain of Life, even if this wet and organic environment has existed for hundreds of millions of years. As Chris Chyba has pointed out, the carbonaceous-chondrite asteroids are very rich in both water and fairly complex organics (including amino acids) -- and during the Solar System's early days, they also contained enough Al-26 (known to have been scattered throughout the forming Solar System by a coincidental nearby supernova blast) to warm their interiors to the point that a lot of that water was liquid for tens or even a few hundred million years. But not one carbonaceous meteorite shows the slightest sign that biosynthesis went very far -- which, as Chyba says, is actually the strongest evidence we have that the appearance of life really MAY require a major stroke of chance luck even under favorable conditions, and that life may therefore be rare in the Universe.

In any case, I repeat that it's risky to try to make such a mission do too much else. Flying it by Titan or Io would require some additional clever (and risky) interplanetary billiards. Having it brush through the region outside Saturn's visible rings to collect ring particles might be more practical as a bonus. And I suppose it could not only make more IR observations of Enceladus during the sampling flyby, but perhaps carry ice-penetrating radar to try to get a better idea of just what is going on down there. (Edwin Kite and I have suggested this in the past for the Europa Ice Clipper, to test whether Janusz Eluszewicz is right in his fears that ice-penetrating radar on Europa Orbiter might not be able to punch deeply through it at all. But Bob Pappalardo and others have recently provided evidence that Eluszewicz's fears are unfounded -- and if we're going to send Europa Orbiter there anyway with a large payload of other instruments, it won't cost much to add the radar sounder to it in any case. Besides, even if the radar can't penetrate deeply at some locations on Europa, it may well be able to do so at other places.)

Sushil Atreya and the other scientists most interested in outer-planet entry probes have recently firmly reached the conclusion (which they announced at the November COMPLEX meeting) that you don't really need very deep entry probes (which are hard to design) for the first probes to Saturn, Uranus or Neptune -- although at some point later on they will have their uses, as they will for Jupiter. Instead, they recommend that the next mission after Juno that is specifically directed to study ANY of the giant planets should be a relatively simply New Frontiers mission to fly by Saturn and drop off only two (or maybe just one) comparatively lightweight and cheap Galileo-type vented entry probes to analyze the atmosphere down to about 20 bars, while the flyby craft uses a microwave spectrometer similar to Juno's to measure the water and ammonia levels at much great depths (with the entry probe also providing crucial calibration data for that, such as the Galileo probe has already provided for Juno). If we decide to defer Neptune Orbiter and instead return to Uranus and/or Neptune first with more flyby missions, the same thing could be done there -- although the main craft would carry more instruments to study the planet and its moons. But, again, I think that combining such a Saturn entry probe with an Enceladus sampler presents serious and probably insuperable trajectory problems.