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

[dvandorn]

The question that comes to my mind is:

If "warm" ice is convecting towards Enceladus' surface and then fountaining out of these south polar vents in significant quantities, could this have been happening for a very large percentage of Enceladus' existence?

Do we have any clue of how much mass is entrained in the E ring? And can we even estimate the rate of mass lost from Enceladus due to this process? Because, for example, even if it's only losing a few tons of material a day, after billions of years, such venting would significantly reduce the mass and size of the body. And what would happen to an icy moon that has lost a significant amount of mass from within -- wouldn't there be signs of global crustal compression?

I guess it depends on what's heating the interior ice and forcing convection of "warm ice" to the surface. Since tidal heating seems unlikely for such a small body, perhaps it's radiogenic? Maybe Enceladus happened to form around a rocky core that, for some as-yet-unguessed reason, had an anomalous amount of radiogenic minerals within it?

If that's the case, then maybe Enceladus started out a lot bigger and has been losing mass -- and size -- for billions of years. Otherwise, you'd have to think that the activity we're seeing now is relatively rare, and we're lucky to be seeing it...

-the other Doug

[jmknapp]

Interesting comments from Dr. Carolyn Porco:

"We suspect it could be caused by cold vents that lead from somewhere in the subsurface, perhaps as far as 1 kilometer down. Water ice is sublimating (changing directly from a solid to a gas state) and the vapors are coming off and building up to high pressure." http://dsc.discovery.com/news/briefs/20051...eladus_spa.html

Since the e-ring has been determined to be particulate, maybe these sublimating water vapor jets have enough pressure to pick up ice particles and send them into space with escape velocity?

Based on a web calculator I get 240 m/sec for escape velocity at the surface of Enceladus.

Also from the article:

"What's puzzling us is how it's getting hot enough," Porco said. "We're still in a quandary over how you'd get this much energy."

[ugordan]

Interesting comments from Dr. Carolyn Porco:

"We suspect it could be caused by cold vents that lead from somewhere in the subsurface, perhaps as far as 1 kilometer down. Water ice is sublimating (changing directly from a solid to a gas state) and the vapors are coming off and building up to high pressure." http://dsc.discovery.com/news/briefs/20051...eladus_spa.html

So they're more or less abanoning the idea of there actually being liquid water below?

Based on a web calculator I get 240 m/sec for escape velocity at the surface of Enceladus.

Views of the solar system says 212 m/s, so that's probably about it. It doesn't mean the ice particles need to have this velocity to escape Enceladus, this figure is a theoretical speed needed for an object to reach infinity from the surface. In reality, Saturn's gravitation is bound to take over long before that so the real escape velocity could be substantially lower than that.

[jmknapp]

So they're more or less abanoning the idea of there actually being liquid water below?

The article also states, not quoting Porco directly:

"Another possibility is that Enceladus' energy source is even hotter than suspected and the water ice is actually melted into an underground liquid that is creating hot springs, similar to the geysers found at Yellowstone National Park and elsewhere on Earth."

However Porco seemed to be highlighting the sublimation theory foremost ("We suspect...").

[ugordan]

Regarding the source of the heat, there is a relatively recent theory that someone mentioned a while ago, probably by someone on this forum, but for the life of me I can't remember who or where it was mentioned.

Basically, it speculates the extra heat on Enceladus comes from a "secondary spin-orbit resonance", and if I understand correctly, comes from Enceladus' orbital eccentricity coupled with its tri-axial shape and its wobbling during each orbit that produces extra heating (hundreds of times more), apart from the usual tidal bulging. It states Enceladus has "just the right shape" for this resonance and that it's probably a relatively short term (geologically speaking) effect.

EDIT: I can understand why Carolyn would prefer the "less" exciting speculation and her being cautious, jumping around saying they've found liquid water on another world without rock-solid proof wouldn't be very wise. It's the same as with the Feb 17 plume images, they didn't scream out loud they may have found plumes, they waited for much more convincing proof. That doesn't mean the evidence so far actually prefers the warm ice theory.