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_*]

That last quote was actually a misinterpretation by Emily Lakdawalla of what Spilker told her, which is that there was some evidence from particle distribution that the E Ring particles were coming off Enceladus as a whole rather than from the vents. That particular theory very quickly became inoperative; it's the vents, all right.

What I can't yet discover is whether the stuff being spewed from them is a water/ammonia mixture (as would have seemed logical), or just plain water. I'm still trying to get clarification on this, but Cassini seems to be indicating that much more of the nitrogen of Saturn's moons is instead in the form of HCN than had been previously been believed.

[ugordan]

What I can't yet discover is whether the stuff being spewed from them is a water/ammonia mixture (as would have seemed logical), or just plain water.

I'm certainly not an expert on this, but haven't there been some mentions recently about ammonia being destroyed by UV sunlight practically immediately so that's one of the reasons it hasn't been detected yet? Personally, though, I'm having a hard time imagining such a rapid breakdown rate which would prevent any traces of NH3 to be seen. I could buy that for the Enceladus' surface spectra which obviously gets a lot of sunlight, but these plumes should conceivably escape from the interior fast enough to bring some ammonia high up before it breaks down. Which makes me wonder: would UVIS be capable of picking up a NH3 signature if a suitable stellar occultation pass could be set up right "through" the plumes? What about INMS?