[X] My Assistant

[vexgizmo]

OK, it's time to have it out. Is Enceladus really spewing water, or are its fractures effectively sublimating warm ice like a comet?

Have a careful read of the Enceladus Science papers (specifically Porco et al vs. Spencer et al.) and you will see that the evidence for water is equivocal, and arguably circular. The prime piece of evidence for liquid water (Porco et al) is the inferred high ice/vapor ratio of the plume (top of p. 1398). This is inferred from scattering models and assumptions of plume particle sizes and argued unlikelihood of particle entrainment in sublimating gas (explained briefly in their note 30, and into p. 1399). Should we hang our conclusions, exploration strategies, and hopes for life on moels of ice/vapor ratio, particle size assumptions, and inferred difficulty of entraining particles in sublimated gas?

Instead (Spencer et al), the fractures of Enceladus may simply expose warm (T ~ 180K) ice which sublimates like a comet (p. 1405).

Show me the water.

[Guest_BruceMoomaw_*]

Well, yeah, but my point was that Baragiola doesn't seem to have any concrete reason for believing the latter -- just that it's a possibility -- and that, if Matson & company are right, the heat level contacting the bottom of the ice is so high that there MUST be a liquid water layer.

The difficulty is how to determine this one way or the other, if there AREN'T liquid-water vents coming all the way to the top. Enceladus' ice layer is probably too deep for a Europa-type radar sounder to punch through all the way to a liquid-water layer -- we might have to depend on very sensitive gravity mapping, of the sort that only an orbiter could do. And in that case, it might be more scientifically cost-effective to jump directly to a lander, since even if an orbiter confirmed the existence of liquid water that would provide no evidence that it contained biologically interesting material (which is the central purpose of Enceladan exploration).

[JRehling]

I'll re-mention my mega-strategy for a Europa mission that makes some sense for Enceladus as well:

Put a lander with a seismic package into an area of key interest. Shortly after it lands, have an impactor land a short distance away, creating a seismic thump of known dimension. That should map the local crustal depth quite accurately. The impactor would return Ranger-style imagery as it closes in. Of course, the lander would return descent/surface imaging of its own site. Meanwhile, a flyby craft images the impact plume and comes back to Earth with a sample from the plume.

I think that would make a great Europa suite which, yes, would be very expensive but less than JIMO (or a war), and would utilize almost every component for double-duty of some kind.

Enceladus doesn't quite require the plume since it makes its own, but the suite might perform very well there, too.