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.

[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?