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Enceladus Plume Search, Nov. 27
David
post Nov 28 2005, 11:54 PM
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QUOTE (ElkGroveDan @ Nov 27 2005, 12:15 AM)
Looks like they need to use the serendipity filter.
*


Hurrah for a remarkably effective use of the "serendipity filter"! biggrin.gif

Maybe they can name Enceladus' south pole "Serendip"? smile.gif
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EccentricAnomaly
post Nov 29 2005, 12:44 AM
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The E-Ring is just such a donut of material around Enceladus' orbit, and is probably responsible for the light background as well. See here: http://saturn.jpl.nasa.gov/multimedia/imag...cfm?imageID=808 for a depiction of the E-ring.

QUOTE (akuo @ Nov 28 2005, 04:29 PM)
Looking at the raws I noticed that the whole background of the images is light, not just the plumes. This is especially evident on the overexposed images of encaladus:


Notice how the background space is lighter than the "dark side" of  Encaladus. Does this mean that plume material is all around, maybe making up a donut of the material around Encaladus's orbit?
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edstrick
post Nov 29 2005, 07:50 AM
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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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ugordan
post Nov 29 2005, 08:07 AM
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QUOTE (volcanopele @ Nov 28 2005, 11:59 PM)
Fountains of Enceladus
http://ciclops.org/view.php?id=1688
In perhaps the fastest image release ever, this release shows the new jets found near in the south polar region of Enceladus.
*

That really was fast! I would have expected at least a week's worth of sleep-overs before you guys would come up with something wink.gif


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Guest_BruceMoomaw_*
post Nov 29 2005, 08:23 AM
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Crowing about one's foresight is bad manners, Ed. I should know; I do enough of it.
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edstrick
post Nov 29 2005, 08:39 AM
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(grins a bit toothily at Bruce Moomaw, canary feathers in one corner of the mouth)

Agreed, I'm being a bit prickly, but I made specific points in my posting that were never addressed, and I felt the whole discussion including those points was rather summarily dismissed.

I think I asked somewhat later (maybe in another thread) for some other moons' high-phase images with non-pume features that were a good counter example as evidence that the Enceladus pics were just scattered light (so I could run comparison enhancements on them), but never got pointed toward any.
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Gsnorgathon
post Nov 29 2005, 10:52 AM
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Good for you, Ed! Crow all you like! (Actually, from where I sit it doesn't sound much like crowing, mostly just "On date X I made statement Y and provided evidence Z." I suppose there's maybe a bit of neener-neener in there, but the fact-to-neener ratio seems plenty high.)

But to return to our regularly scheduled topic: How tightly is it possible to constrain the origin of those plumes? Among other things, I'm wondering if they're coming from multiple tiger stripes or just one.
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edstrick
post Nov 29 2005, 11:55 AM
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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.
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ugordan
post Nov 29 2005, 12:16 PM
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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.


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jmknapp
post Nov 29 2005, 02:18 PM
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We're set for a Christmas rerun:



The above is oriented with north pointing straight up.


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ugordan
post Nov 29 2005, 02:33 PM
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QUOTE (jmknapp @ Nov 29 2005, 03:18 PM)
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...


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jmknapp
post Nov 29 2005, 03:40 PM
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QUOTE (ugordan @ Nov 29 2005, 10:33 AM)
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.


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The Messenger
post Nov 29 2005, 05:18 PM
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QUOTE (ugordan @ Nov 29 2005, 05:16 AM)
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.
*

NO! No! Nooo!

There is no question that there is outgassing, no question about the source. If we want to know the reason there is a hot spot, we must establish more constraints, and the gravity data is an absolutely essential step. We know the energy is not solar - Enceladus is too reflective. We must learn how the mass of Enceladus is internally distributed in order to assess geological stress and other potential sources of heat.

By all means, more imaging passes should be scheduled into the extended mission, but no one knows when this mission will end, and we will never solve the puzzle without gravitational constraints.
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Omega
post Nov 29 2005, 05:53 PM
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Regarding possible artifact--

QUOTE
Images of other moons, such as Tethys and Mimas, taken in the last 10 months from similar lighting and viewing geometries, and with identical camera parameters, were closely examined to demonstrate that the plume towering above Enceladus' south pole is real and not a camera artifact.
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volcanopele
post Nov 29 2005, 07:30 PM
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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.


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