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Rev 16 - Oct 2-21, 2005 - Telesto, Tethys, Dione D1, Dione-Telesto-Enceladus
Ian R
post Oct 16 2005, 02:05 AM
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Great shot of Tethys:

Attached Image


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Decepticon
post Oct 16 2005, 02:51 AM
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Is that Melanthius or Antinous at south pole?
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edstrick
post Oct 16 2005, 05:41 AM
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Bill Harris:
"My take on Telesto? It looks like a snow-covered rubble pile. By chance or design, some rubble has parked at the L4 point, and there is a source of fine material (water ice?) that drifts onto this rubble pile."

That's more or less my take on it. Post Voyager models suggested all the mid and smaller inner sats except maybe Rhea had a significant chance of being impact disrupted and re-accreted long after the formation of the Saturn system, and it's was plausible at the time that the lagrangian moons and the like were fragments that escaped capture. I don't know the current status of the idea, though.
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SigurRosFan
post Oct 16 2005, 10:36 AM
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Decepticon: It's Melanthius at the pole.


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helvick
post Oct 16 2005, 11:00 AM
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QUOTE (edstrick @ Oct 16 2005, 06:41 AM)
Bill Harris:
".. or design, some rubble has parked at the L4 point..."
*

"Yo Zeus, where'd you put all the ice dude?" laugh.gif
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Decepticon
post Oct 18 2005, 12:11 AM
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Dione update!

http://ciclops.org/view_event.php?id=39
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tfisher
post Oct 18 2005, 01:20 AM
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One of the new Dione products (Dione in Full View) includes a false-color image of that moon produced using IR, Greeen, and UV data. It has a conspicuous yellowish-green stripe down the middle from top to bottom. Does anyone (for instance volcanopele/Jason, who shows as the leading name on the image credit) know what this indicates? Surely not a compositional difference. And I would have expected an illumination effect (like a specular point) to be more localised. Is it just an artifact of the method of producing the coloration?
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JRehling
post Oct 18 2005, 01:42 AM
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QUOTE (tfisher @ Oct 17 2005, 06:20 PM)
One of the new Dione products (Dione in Full View) includes a false-color image of that moon produced using IR, Greeen, and UV data.  It has a conspicuous yellowish-green stripe down the middle from top to bottom.  Does anyone (for instance volcanopele/Jason, who shows as the leading name on the image credit) know what this indicates?  Surely not a compositional difference.  And I would have expected an illumination effect (like a specular point) to be more localised.  Is it just an artifact of the method of producing the coloration?
*


My first guess would be that this is a demonstration that the reflectance function of Dione varies with wavelength and that if the spacecraft were fixed and we watched Dione rotate, the stripe would stay fixed in the image -- slide longitudes on Dione's surface.
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Phil Stooke
post Oct 18 2005, 02:31 AM
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A thought or two on Telesto...

First those 'creases' noted by edstrick... frost polygons? I can't quite get my mind around that. You get the freezing but how would you get any thawing? I am more inclined to think they are merely the places where talus aprons (for want of a better term... debris shaken downslope by successive impacts) meet. Start with an irregular surface shedding debris, and it moves outwards from the high points until it meets another apron coming from another direction. If you draw expanding boundaries around a set of points they meet and form linear troughs... called thiessen polygons, if I recall correctly, in geometry.

Second... where's the debris coming from? Telesto looks more like Deimos, to me, than any other object we've seen. The best explanation for Deimos's thick debris layer is that it's ejecta from a VERY large crater, either just deposited directly from the impact or reaccreted after a period spent orbiting Mars. Remember the last phase of ejecta dispersal is slow, low energy, forming high rims on lunar craters... it doesn't have to get blown off even a small object, but it can also get reaccreted.

Deimos doesn't have a very large crater? Yes, it does, the big saddle at the south pole, nearly the same diameter as Deimos itself.

These ideas about Deimos are from Peter Thomas, not me, but I agree with him.

Phil


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Bill Harris
post Oct 18 2005, 10:19 AM
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Telesto in an oddball, the classic "bunny in the clouds" for visual appearance. Although it does have the appearance of a snow-covered clod with frost polygons, that ain't likely. biggrin.gif I like your interpretation.

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volcanopele
post Oct 18 2005, 05:47 PM
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QUOTE (tfisher @ Oct 17 2005, 06:20 PM)
One of the new Dione products (Dione in Full View) includes a false-color image of that moon produced using IR, Greeen, and UV data.  It has a conspicuous yellowish-green stripe down the middle from top to bottom.  Does anyone (for instance volcanopele/Jason, who shows as the leading name on the image credit) know what this indicates?  Surely not a compositional difference.  And I would have expected an illumination effect (like a specular point) to be more localised.  Is it just an artifact of the method of producing the coloration?
*

I'm not quite sure what happened to the color in that mosaic. The yellow stripe is real, but the right half of the mosaic should be same color but it wouldn't come out that way...very odd.


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JRehling
post Oct 18 2005, 07:14 PM
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QUOTE (Phil Stooke @ Oct 17 2005, 07:31 PM)
A thought or two on Telesto...

Second... where's the debris coming from? Telesto looks more like Deimos, to me, than any other object we've seen.  The best explanation for Deimos's thick debris layer is that it's ejecta from a VERY large crater, either just deposited directly from the impact or reaccreted after a period spent orbiting Mars.  Remember the last phase of ejecta dispersal is slow, low energy, forming high rims on lunar craters... it doesn't have to get blown off even a small object, but it can also get reaccreted.
Phil
*


Maybe the answer to the question is the same as: Where did Telesto come from? To put that another radical way: Did these L4 and shepherd moons grow -- recently? If a point in space is an attractor for debris, and the Saturn system has lots of it "snowing" around, maybe Telesto, et al, are what you get.

If so, then the stuff on top of Telesto's craters could be just more of the stuff that snowed in over time to make Telesto in the first place.
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Phil Stooke
post Oct 18 2005, 07:40 PM
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All very true, I guess. I prefer to think of something old that's been battered rather than something that's been assembled recently. But that's just my preference, and I admit there's no way for me to prove it. Though Telesto looks as if it has a lot of 'ghost craters' under that smooth surface, and it might be hard to reconcile that with a more recent formation.

Phil


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alan
post Oct 19 2005, 04:01 AM
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Titan, Dione and Prometheus in one shot
http://saturn.jpl.nasa.gov/multimedia/imag...5/N00041980.jpg
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pat
post Oct 19 2005, 05:23 PM
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QUOTE (alan @ Oct 19 2005, 05:01 AM)


and thats Telesto level with Titan about the same distance to the right of the rings (in the image) as Titan is to the left. A nice family portrait.


Incidently if the limb of Dione and the edges of the rings look odd/pixelated its because you are looking at the image scaled and not at its full 1024x1024 resolution.
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