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

[edstrick]

I doubt there's enough parallax during the high-phase sequence to strongly constrain the plume's sources along the line of sight, but from postings in this thread, it's going to be pretty easy to see where lines of sight to plume bases cross the terminator and cross tiger stripes near the terminator. I very strongly suspect there are multiple vents along each of the tiger stripes, with most relatively weak. This seems to me to suggest that either there are relatively few extra-warm spots exposed within a stripe at one time, the hottest being discrete plume sources, or that a more active gysering source may be involved.

I can, however, imagine a vent with the hottest ice (with the highest vapor pressure) at the bottom, spewing upwards through a fissure or pipe, producing relatively collimated plumes like we seem to see in these pics.

[ugordan]

Regarding the possibility of more intense Enceladus investigation during the (hopefully) extended mission, how long will it be until the south pole dips into years-long darkness?
I take it any extended mission will need focus on the south pole observations early on to ensure good coverage of the area while it's still receiving some sunlight. Might be interesting to repeatedly fly above the tiger stripes at a very low altitude and look for small changes in the fissures/try to locate the hotspots, at the same time sniffing out the plume materials to find out the composition of the heavier components.

Optional gravitational passes could (as well as CIRS nighttime temperature mapping), of course, be carried out later on when the focus shifts on Titan flybys.

[jmknapp]

We're set for a Christmas rerun:



The above is oriented with north pointing straight up.

[ugordan]

The above is oriented with north pointing straight up.

That's practically the same viewing geometry, it should really provide clues to the temporal variability of the outgassing. The February images seem to show a slightly weaker outgassing effect, possibly due to less favorable viewing conditions. I wonder whether we'll see even more violent plumes than now or their virtual absence... It would be a nice Christmas present to be there just as there's another major eruption like the one that was supposedly responsible for a large increase in oxygen atoms in the rings, detected prior to Cassini's arrival...

[jmknapp]

That's practically the same viewing geometry, it should really provide clues to the temporal variability of the outgassing.

I'm hoping that they take more images at different points during the flyby. The orientation of the crescent changes quite a lot during the flyby, & it's convincing to see that regardless of that orientation, the fountains remain at the purported location.

For the Nov. 27 flyby, images were taken from 144,000 - 174,000 km. Taking the images at the extremes of this range, and rotating them so north is up yields:



raw images:
N00043446.jpg
N00043428.jpg

So the fountains remain due south as the crescent rotates around. It might be interesting to see how their appearance changes at more points during the Dec. 25 flyby, different solar phase angles, etc.