Enceladus Plume Search, Nov. 27 |
Enceladus Plume Search, Nov. 27 |
Nov 24 2005, 04:01 PM
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#1
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Senior Member Group: Members Posts: 1465 Joined: 9-February 04 From: Columbus OH USA Member No.: 13 |
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 -------------------- |
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Nov 29 2005, 07:50 AM
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#2
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Senior Member Group: Members Posts: 1870 Joined: 20-February 05 Member No.: 174 |
Regarding the plume images: Feb 20, I posted:
http://www.unmannedspaceflight.com/index.p...topic=691&st=45 "Regarding the image<s> of Enceladus with a possible plume in the south polar region. There is a series of short exposure images of the crescent on the JPL RAW pictures pages and a longer exposure (posted on the CICLOPS web page as "862-1905-3", cleaned up and without JPG artifacts). An even longer exposure on the JPL RAW pages is N00028218. The images show Enceladus as a thin crescent, illuminated by sunlight from about a 4:30 clock angle and as a fatter crescent, illuminated by Saturn from the 9:00 clock angle. The unilluminated side of the moon between the crescents is visible in silhouette against a lighter background. This background is *NOT* the ring-lit nightside of saturn, 1.) since the dayside of saturn is to the left and out of the image, and 2.) because all images show stars or nearly horizontal star-trails, all parallel, tilted slightly down to the right, and varying in length in proportion to the exposure. I have to conclude that we are probably seeing the diffuse E-Ring in forward scattering, with Enceladus between the spacecraft and the bulk of the E-Ring. I'm attaching a composite image with the two images named above, and two spatial-bandpass-filtered enhancements of 862-1905-3. These have been processed to enhance fine detail in the plumelike feature close to the moon's limb, and details further away from the limb. None of the images, including the long exposure N00028218, show any trace of the feature against the darkside of the moon above the sunlit crescent, and structures in the plumelike feature converge on the bright limb just like cometary jets seen at comets Halley and Borelly and Wild. There seem to be maybe 3 "sources" for the main plume-like feature and a fainter single-source plume-like feature to the right. Except for a faint diagonal line "behind" Enceladus, visible in the last picture, which I suspect is a camera artifact or something, all features in this image seem consistent with the plume-like feature being real, not light scattered by contamination in the camera (which is a problem with the NA camera) or a lens-flare. I would have to see the images of other moons with simlar faux-plume features referred to a couple days ago by a team member (earlier in this thread) and apply contrast stretching and enhancement to them (using clean versions, not RAW's from the JPL website) to convince me this feature is not real and is not active plumes from Enceladus. " (See original post for the picture) NOW..... VolcanoPele... tell me again this waas just the same old problem with scattered light in the camera....? |
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Nov 29 2005, 07:30 PM
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Senior Member Group: Moderator Posts: 3242 Joined: 11-February 04 From: Tucson, AZ Member No.: 23 |
QUOTE (edstrick @ Nov 29 2005, 12:50 AM) NOW..... VolcanoPele... tell me again this waas just the same old problem with scattered light in the camera....? For quite a while, scattered light in the camera was thought to be the cause of the plume appearance. this changed, as the caption for the January image mentioned, we took additional high phase images of the other satellites that showed that plume like features only appeared with certain twist angles of the camera, which did not match the January and February images, thus showing that the plume was real. This weekend's images sealed the deal. We could have gone to press with the plumes story months ago. But it was important that we rule out artifact before hand. Just because it quacks like a duck and looks like duck doesn't rule out that it isn't a robotic duck. You have to look underneath and look for the on-off switch to seal the deal. Some where in there was a good analogy. Don't know where it went. -------------------- &@^^!% Jim! I'm a geologist, not a physicist!
The Gish Bar Times - A Blog all about Jupiter's Moon Io |
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Nov 29 2005, 08:08 PM
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#4
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Senior Member Group: Members Posts: 1465 Joined: 9-February 04 From: Columbus OH USA Member No.: 13 |
One thing that strikes me in the CICLOPS press release:
"...it is not clear if the plume emanating from the south pole arises because of water vapor escaping from warm ice that is exposed to the surface, or because at some depth beneath the surface, the temperatures are hot enough for water to become liquid which then, under pressure, escapes to the surface like a cold Yellowstone geyser." http://ciclops.org/view.php?id=1652 If it was water vapor escaping from exposed ice, wouldn't it be a diffuse cloud over the area, rather than concentrated in fountains or jets? And would the water molecules or other material have the escape velocity needed to join the e-ring? Are the linear features in images like that below then rays of sunlight shining through a diffuse cloud (like sunbeams through clouds or forest cover on Earth) rather than the representing the fountains themselves? And yet they are using the term fountains, which would imply some sort of pressurized spray, no? -------------------- |
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