Enceladus Plume Search, Nov. 27 Options

[jmknapp]

Interesting item in the science plan kernel (S16) just released to the NAIF website:

OBSERVATION_ID: S1629

SEQUENCE: S16

OBSERVATION_TITLE: Plume Search

SCIENCE_OBJECTIVE: Hope to detect/observe plumes, whether from volcanic activity or geysers.

OBS_DESCRIPTION: Point and stare.

SUBSYSTEM: ISS

PRIMARY_POINTING: ISS_NAC to Enceladus (0.0,5.0,0.0 deg. offset)

REQUEST_ID: ISS_018EN_PLUMES001_PRIME

REQUEST_TITLE: ENCELADUS Geyser/Plume Search

REQ_DESCRIPTION: 1;ENCELADUS Geyser/Plume Search 1x1xNPp -- 3 different exposures

BEGIN_TIME: 2005 NOV 27 19:00:00 UTC

END_TIME: 2005 NOV 27 20:00:00 UTC

[Guest_BruceMoomaw_*]

If it was water vapor escaping from exposed ice, wouldn't it be a diffuse cloud over the area, rather than concentrated in fountains or jets? And would the water molecules or other material have the escape velocity needed to join the e-ring? Are the linear features in images like that below then rays of sunlight shining through a diffuse cloud (like sunbeams through clouds or forest cover on Earth) rather than the representing the fountains themselves?

And yet they are using the term fountains, which would imply some sort of pressurized spray, no?

What they're referring to is the possibility that ice is rising to the surface in the hottest spots which -- although still cold enough to be solid -- is warm enough that water vapor sublimates off it like crazy, but only in those limited places, and then refreezes as a cloud of microscopic ice particles.

We are definitely looking at genuine, honest-to-God separate plumes here, just as we are with comet nuclei.

As for Europa plumes, don't forget that Galileo made at least one intensive search for them using a similar technique, and came up totally empty-handed. I think Europa is currently in the cold, thick-crust portion of its tidal-heating cycle, so that plumes of any significant size are rare or actually nonexistent. In another few tens of millions of years, it will be a different matter.

But as for Enceladus: while we now know that there are indeed geysers, we still have no idea just what's driving them -- and may not know for a long time. (We apparently don't even know yet how much ammonia is mixed with the water.) For a summary of the current debate, see

http://www.agu.org/cgi-bin/SFgate/SFgate?&...t;P32A-04"

http://www.agu.org/cgi-bin/SFgate/SFgate?&...t;P32A-05"