Faint Ring Thread, Saturn's D, E and G rings Options

[Rob Pinnegar]

There are two new "Raw Images" up that give a good view of Saturn's D Ring. As of today (July 17th) they are on the first page of the Raw Images section. The better of the two is image number W00009347.

The very narrow inner ringlet is called D68 and it is the innermost well defined ringlet of the entire ring system -- it's only about 7250 kilometres above the cloud tops, about half-way from the planet to the inner edge of the C Ring. If you search the "Saturn-D Ring" section of Raw Images, there is a nice narrow angle view (N00035241) which I am pretty sure is a close-up of D68. D68 is an oddball, it really is sort of "in the middle of nowhere".

The brighter ringlet in the upper right is called D73. About a thousand kilometres inward from D73, there is a noticeable "dark zone". In the Voyager images, there was a third bright narrow ringlet inside this zone, D72, which seems to be gone now, strangely enough. The relevant Voyager images are Voyager 1 image 34946.50, and Voyager 2 image 44007.53. If the diffuse ringlet at the inner edge of the "dark zone" is what is left of D72, it looks to have migrated a bit closer to Saturn in addition to spreading out a lot. (By the way, I'm not making up these ringlet designations on the fly -- they are given in a paper by Mark Showalter that was published in Icarus in 1996, which is pretty much the only major paper on the D Ring.)

To give some idea of scale, the three bands of material in the far upper right corner are part of the innermost ringlet of the C Ring (this can also be seen on some images of the rings taken on May 3rd of this year).

Since it is so faint and doesn't appear in many images, the D Ring rarely attracts much attention. But it's kind of neat to look at if you haven't seen it before, particularly because of D68, which is sort of the "anti-F ring" in a way.

[alan]

This looks like a good opportunity to observe the d-ring:

http://space.jpl.nasa.gov/cgi-bin/wspace?t...=1&showsc=1

Any images planned at this time?

[bdunford]

What are we seeing in this image that was targeting the G-ring?

http://saturn.jpl.nasa.gov/multimedia/imag...iImageID=112363

If you turn your monitor brightness up, a 'goblet' shape is visible. Is that a camera artifact? Or the shadow of the planet and rings? Or something else?

[Rob Pinnegar]

Just as a news note:

There's a recent D-Ring paper in Icarus -- the first major paper on the subject since 1996, as far as I know.

"Saturn's dynamic D ring", by Hedman et al., Icarus 188 (2007), 89-107.

I've only had a chance to skim it, but it contains some interesting material.

[ugordan]

Two long exposure images of the G ring:

http://saturn.jpl.nasa.gov/multimedia/imag...iImageID=166193
http://saturn.jpl.nasa.gov/multimedia/imag...iImageID=166194

They show a streak right in the densest part of the ring that could be a solid object smeared by the long exposure. It's not in the direction of the stars and roughly follows the orbital motion of the ring (depends what point Cassini was exactly tracking so it makes it slightly sideways).

I know of denser clumps of icy particles isolated/theorized in the G ring, but has a more compact object (moonlet ?) ever been observed there?

[Floyd]

I agree that it looks like something very interesting. Tracks the ring perfectally.

[bdunford]

If confirmed, I vote they name the moonlet after you, Gordan.

[ugordan]

LOL!

[ilbasso]

Any chance that it's the Millennium Falcon trying to hide amidst the debris?

[jasedm]

Well spotted Gordan!
The fact that it appears in two separate frames increases the likelihood of it being a 'real' object rather than an artifact in the optics.
One of the frames cropped, enhanced and magnified:

Attached thumbnail(s)

 

[Ken90000]

Personally, I think it is awfully bright to be an undiscovered moon. It is brighter than the Op Nav shots of Pallene and Methone that we are used to seeing. Likewise, that is a lot of orbital motion for the relatively short exposure which looks to me to be a few second given the few stars included.

My vote is it is a clump of larger rocks that appear brighter at this phase angle.

[tedstryk]

During the ring plane crossing in the 1990s, Hubble spotted quite a few transient clumps in the rings. That may be what this is. It would be awesome if Cassini could get a closeup of one of them, although I realize how difficult that would be.

[Floyd]

Nice series of 10 G-Ring crossing images from August 22.

[Floyd]

Also two more pictures of the clump taken on August 22.


August 22 images:
http://saturn.jpl.nasa.gov/multimedia/imag...3/N00119215.jpg
http://saturn.jpl.nasa.gov/multimedia/imag...3/N00119214.jpg
August 15 images:
http://saturn.jpl.nasa.gov/multimedia/imag...3/N00118601.jpg
http://saturn.jpl.nasa.gov/multimedia/imag...3/N00118600.jpg

The pictures taken on the 22nd look exactly like those on the 15th, so clump or smeared object doesn't change much over a 7 day period.

[Floyd]

The team now has good orbital data on the G-Ring object(s) with the images 7 days apart. I would guess that these first two sets of images were taken to keep as much of the ring in focus as possible-but not worrying about smear along track. Over the next few orbits, they should be able to take images tracking the object(s), but smearing out more distant parts of ring. Cassini will be have 7 more revolutions in this 7-day orbit before the next Enceladus encounter.
I'm betting that it is a small moon.

[Rob Pinnegar]

This is very interesting.

The two ends of the smeared ring "event" seem quite abrupt, similar to the background starlines, which suggests a discrete object rather than a "clump". But for a compact enough clump maybe this wouldn't be an issue -- and, as has already been pointed out, if it's a moonlet why haven't we seen it already?

Maybe we're looking at the formative stages of a transient clump? That would be great. (If true.)