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_*]

On another matter regarding the plumes: may we assume that if the plumes are sometimes sending ice particles into space with escape velocity, the plumes also sometimes emit particles with less than escape velocity that will impact somewhere downrange on the moon?

If so, then is there then effectively a rain of ice particles impacting the surface, resulting in accumulation and even erosion in the preferred impact spots? After all, the particles would impact with about the same velocity they left the plume with, up to 240 m/sec. Truly a "hard rain" falling.

It's been assumed since Voyager that this is the likely explanation for Enceladus' extremely high albedo -- it's refrosting itself, all over its surface. (Presumably, when such impacts vaporize some of the ice in the particles, it quickly refreezes again a short distance away.)

[jmknapp]

It's been assumed since Voyager that this is the likely explanation for Enceladus' extremely high albedo -- it's refrosting itself, all over its surface.  (Presumably, when such impacts vaporize some of the ice in the particles, it quickly refreezes again a short distance away.)

Seems like the process is becoming a lot more constrained, knowing that the ice jets are coming from (approximately) the south pole.

A while back ugordan and I were discussing the escape velocity & I came up with a little simulation predicting what would happen to a particle emitted from the south pole. I refined the program some more recently, and now it allows prediction of the path of a particle emitted from any point on the surface, and in any direction (azimuth and elevation from the "vent" location). Some interesting asymmetries are evident resulting from the moon's rotation and the three-body situation involving Saturn's strong gravity.

Take the case of a vent located at 180W, 80S (10 degrees from the south pole) and with a plume direction of 70 degrees elevation. Rotating that plume 360 degrees in 5-degree steps (think of it kind of as a rotating sprinkler) results in a surprising asymmetrical pattern. This map shows the predicted impact points, varying the plume velocity from 0-220 m/sec (approx. escape velocity) in 1 m/sec steps (click for larger version):



The impact points are preferentially towards the center, which is the anti-Saturn (180-degree) meridian, offset to the west a little due to the moon's rotation.

That's just the result with the plume at one location, but interestingly a simlar pattern persists even if the plume location is moved (click on any for a larger version):

0W 80S:


90E 80S


270E 80S:


Not sure if it's my imagination, but it seems like the patterns line up with some of the features on Enceladus. Interesting anyway.

[ugordan]

Not sure if it's my imagination, but it seems like the patterns line up with some of the features on Enceladus. Interesting anyway.

Outstanding work, Joe!
I'm curious: are those Matlab simulations or something you programmed for yourself?

One thing that could be done to further investigate the patterns would be to integrate across all tiger stripes and all angles/speeds and see if the "fallout" map would preferentially exclude some areas of the moon and then compare with the albedo and crater saturations of those regions.
That would probably be grounds for a scientific paper, though

What you did already suggests there indeed are some areas in the north that should be very depleted of snowfall.
Once again, great work!

[jmknapp]

I'm curious: are those Matlab simulations or something you programmed for yourself?

One thing that could be done to further investigate the patterns would be to integrate across all tiger stripes and all angles/speeds and see if the "fallout" map would preferentially exclude some areas of the moon and then compare with the albedo and crater saturations of those regions.

I programmed it in C, using the CSPICE library to determine the positions of Enceladus and Saturn over time, and a Runge-Kutta integration to determine the particle trajectory. One thing about doing a lot of integrations though across the tiger stripes or whatever: each map takes a few hours to generate on my machine! So I'm wondering how exactly to plan it out that would give relevant results and not waste a week of number-crunching.

[ugordan]

I programmed it in C, using the CSPICE library to determine the positions of Enceladus and Saturn over time, and a Runge-Kutta integration to determine the particle trajectory. One thing about doing a lot of integrations though across the tiger stripes or whatever: each map takes a few hours to generate on my machine! So I'm wondering how exactly to plan it out that would give relevant results and not waste a week of number-crunching.

It's been a while since I studied different integration methods, but isn't there a time step that's adjustable for different levels of precision? Or are the stability constraints too tight? I'm probably talking jibberish here...
Out of curiosity, what machine are you running the sims on?