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Faint Ring Thread, Saturn's D, E and G rings
Guest_BruceMoomaw_*
post Apr 27 2006, 07:20 PM
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It may be simply that Enceladus' south-polar plumes are spitting particles out at high speed in an out-of-plane direction. It may also be that the E Ring particles -- being both very small, and made of low-density water ice (unlike the very fine but rocky particles in the F and G Rings) are more susceptible to being pushed around by Saturn's magnetospheric processes. (For instance, water ice will sputter far more than rock when it's hit by charged-particle radiation.)
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Rob Pinnegar
post Jun 7 2006, 05:04 PM
Post #32


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In the past week or so some new G Ring images have been posted to the main website.

Some of the ones taken on May 28th appear to show an object near the inner edge of the G Ring; in most such images, it's near the top of the frame and next to the "left arc" of the G Ring. I'll try to add one of them here.
Attached Image


It really looks like a moon. I'm guessing maybe it's Epimetheus? It appears to be too close to the G Ring to be Epimetheus, but that might just be a perspective effect. Epimetheus does have a bit of orbital inclination which might contribute to its apparent closeness to the G Ring as well.
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jsheff
post Jun 9 2006, 05:02 PM
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And, lest we forget, there's the ring that Cassini discovered shortly after SOI: S/2004 1R. I know it was announced to be 138,000 km out from Saturn's center. That would put it between Atlas and Prometheus, and between the outer edge of the A ring but interior to the F ring. I haven't heard much more about it since. Does anyone know if this is still considerd a distinct ring?
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Rob Pinnegar
post Aug 1 2006, 10:48 PM
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Well, here we go again.

There are some nice new shots of the D, E and G rings that have gone up in the last few days. Here are a couple of them: a D Ring shot, showing a nice panorama of the whole region (and a big chunk of the C Ring for scale)...

Attached Image


... and a G Ring shot, apparently showing some structure that was commented on earlier in this thread. We've GOTTA figure out what those resonances are.

Attached Image


We should be getting a lot more like this in the future, with Cassini now out of the ring plane.
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Ian R
post Aug 2 2006, 02:57 AM
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Thanks to Rob's earlier research, I've picked out the C and D rings in the latest Cassini image:

Attached Image


C is rendered in green, while D is rendered in yellow.

Ian.


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Rob Pinnegar
post Sep 15 2006, 07:08 AM
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A lot of new ring images have gone up in the past few days. Quite a few of these target the D Ring specifically, but these all seem to be washed out. There are however two non-targeted ones under the "Saturn-Rings" general heading that turned out very nicely.

Here's one that shows D72 and D73:
Attached Image


And a shot of D68:
Attached Image


The image of D72 and D73 seems to show some structure in the gap between the two rings that wasn't so prominent earlier. Hard to say if this is an actual change in ring structure, or just a better image (or a different viewing angle, given that these are dust rings).

[Edit: Incidentally, today (Sept.15th) is the big day for C and D ring observations, according to the "Cassini At Saturn" section of the Cassini mission website. Quoting from that:

"Sep. 15, 2006: Cassini views the Sun as is (sic) passes behind Saturn and the rings. The rate of passage through the rings is very slow and the view will yield information on the D and C rings that is impossible at any other time in the tour."

I'm guessing that at least some of this will involve stellar occultation data, so we won't see all of it, but with any luck we will get the best shots of the entire mission coming down the pipeline in the next couple of days. We'll see.]
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Ian R
post Sep 21 2006, 10:50 AM
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Here are two great recent Cassini pictures of the D Ring:

http://saturn.jpl.nasa.gov/multimedia/imag...3/N00066088.jpg

http://saturn.jpl.nasa.gov/multimedia/imag...3/N00066089.jpg

I've merged these two images to produce the following version that preserves faint and dusty areas, without washing out the brighter ringlets:

Attached Image


Ian.


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remcook
post Sep 27 2006, 08:09 PM
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someone can't draw straight lines... (sorry, but I'm seeing al these interesting new raw images all of a sudden)

http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=84407
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ugordan
post Sep 27 2006, 08:39 PM
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QUOTE (remcook @ Sep 27 2006, 09:09 PM) *
someone can't draw straight lines... (sorry, but I'm seeing al these interesting new raw images all of a sudden)

http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=84407

That's probably the F ring, only seen at an oblique angle. Frames with a greater exposure expose two rings to its left and right. The disturbance could be due to Prometheus, which VP identified in one of the frames in this thread.

Wow, check this one out!


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Rob Pinnegar
post Oct 12 2006, 04:33 AM
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In the news today... some new theories about a possible recent collision between the D Ring and a Saturn-crossing interloper:

http://ciclops.org/view.php?id=2281&flash=1

There is one thing here that surprises me: namely, that the authors haven't tried to connect their postulated ~1984 impact with the atrophying of the D72 ring feature. To summarize some of the earlier posts in this thread, D72 was very bright when the Voyagers passed Saturn, but it has drastically faded since then, and what is left of it also seems to have moved a few hundred kilometres closer to Saturn. So there's been some radial movement of material since 1980/81.

Well, since the proposed impact date of 1984 is just an estimate, it stands to reason that it could be off by a few years. If that's true, it's very tempting to think of the D72 feature seen by Voyager as being the initial result of that collision. D72 could have been brand-new when the Voyagers passed by in 1980/81, maybe only a year or two old. A recent origin would help explain how it disappeared so fast... it was a transient feature that we just happened to catch at its brightest.

The changes in the spacing of the ringlets in the outer D Ring also seems to be connected to D72. The current spacing is 30 km, but apparently was 60 km in 1995 when Hubble took some observations of this region. In 1981, it was 130 km... and D72 clearly marked the demarcation between the outer D Ring and a longer-wavelength region in the inner D Ring. Showalter's 1996 paper in Icarus shows this. (It's odd that these three values of spacing are nearly in the ratio 1:2:4. This could be coincidence, but it makes me wonder whether the 1981 and 1996 estimates were limited by the resolution of Voyager and Hubble; perhaps these were picking up subharmonics of the main pattern?)

There's no way the authors aren't aware of these points. The Showalter paper is the only major D Ring paper out there, so it's *gotta* be one of the key references of their work. That means there has to be some good reason why they aren't making a connection with D72 in the press release. Presumably we'll find out what that reason is when the paper gets published.
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Rob Pinnegar
post Nov 12 2006, 06:29 PM
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A neat abstract regarding the G Ring and resonances:

http://adsabs.harvard.edu/abs/2006DPS....38.4704B
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Rob Pinnegar
post Mar 7 2007, 02:28 AM
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Yet another batch of D Ring shots are online today. These ones include some nice resolution of the dusty regions between the D68, D72, and D73 ringlets, regions which look blank in most images.

D Ring observations seem a lot more common in the past half year or so. Either the viewing angles have become more favourable, or the recently-discovered time-lapse changes in Saturn's innermost ring have piqued some people's interests. I'm guessing it's the latter.
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elakdawalla
post Mar 7 2007, 03:58 PM
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It probably has to do with the high-inclination orbits they've been doing -- top-down looks at the rings.

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ugordan
post Apr 8 2007, 03:12 PM
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What do you make of this image: http://saturn.jpl.nasa.gov/multimedia/imag...iImageID=106655?

It's apparently a long exposure, motion-compensated image targetting a section in the main rings, but I'm puzzled by that sharp gap in the star trail. The way I see it is there had to be an unusually discrete and opaque segment of the rings there, so opaque that there's virtually no starlight passing through. There's also a segment to the left where the starlight is faded a bit but there doesn't appear to be anything out of the ordinary there.

Weird.


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nprev
post Apr 8 2007, 03:23 PM
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Either that, or a one-in-a-million chance occultation by an embedded satellite was my first thought. Of course, the gap in the star trail is pretty big for that...


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