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

[scalbers]

My guess is that the rays are actual streamers of material instead of sun rays. This somewhat reminds me of cometary jets. Are cometary jets presumed to be liquid or vapor generally? I suppose a geyser on earth can also emit either vapor (condensing into steam) or liquid water. Would a determination of ice particle size help constrain whether it was likely to be steam or water?

[JRehling]

My guess is that the rays are actual streamers of material instead of sun rays. This somewhat reminds me of cometary jets. Are cometary jets presumed to be liquid or vapor generally? I suppose a geyser on earth can also emit either vapor (condensing into steam) or liquid water. Would a determination of ice particle size help constrain whether it was likely to be steam or water?

There is clearly some anisotropy going on here, and I think we can rule out the solar illumination and the camera as possible sources... It appears as though these fountains have a considerable non-vertical component in their initial emission, which means that this isn't just a mist rising lazily up from warm ice -- these are geysers.

We see more than three fountains (more like eight or nine, plus possibly more minor ones), so I agree that the tiger stripes are probably active in selective locations, and not everywhere along a stripe once.

As for the dynamics, we surely have some sort of pressure below. The crust may be moving, although in what way, I don't claim to know. Surely if the volume of emission falls below a certain rate at any location, rapid freezing will overwhelm the process and pinch a fault (locally) closed.

I think that each tiger stripe overlies a warm area about as wide as the area *between* the stripes, with the stripe being the place where emission can take place. This activity probably shifts over time, although it may be going on all the time *somewhere*. For example, maybe there are sixty or so places where fountains can spray out, but at any given time, only ten or so are actually spewing. And, yes, I pulled those numbers out of thin air.

I'm not sure what kind of mission would target Enceladus next. An orbiter might face a mechanical hazard from the plumes. The question is if a stable orbit could fly above the plumes. If the plumes are all highly localized, one solution would be an inclined orbit that misses the full blast of the spray. A lander is always an option, and seismology would be interesting. Another possible followup would be a Saturn orbiter -- perhaps one that observes both Enceladus and the rings without sacrificing too much in design to the dual needs? It seems less likely that a focused Enceladus+Titan mission could do much beyond what Cassini already provides. Other than quaint images of opportunity, it seems like a mission dedicated to one of those high-priority moons would not offer much in terms of performing science at the other. An incremental improvement on Cassini would fit the bill, but I think any Titan followup will be a quantum leap from Cassini to the next thing (eg, aerobot).

[tedstryk]

This makes me wonder about Europa, where high phase coverage is extremely limited. Also, a volcano of equal force would have a smaller plume at Europa, since there would be much stronger gravity.