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.

[Ian R]

Hi Rob,

What's the best way to get a copy of this paper on the D-ring? Is there an internet source where it can be located?

Speaking of the faint Saturnian rings, this is probably one of the best images of the G-ring ever taken:

http://saturn.jpl.nasa.gov/multimedia/imag...7/W00004084.jpg

[Rob Pinnegar]

Hi Ian,

That's a really nice shot of the G Ring. It has a very well defined inner boundary; I assume this must be due to a satellite resonance, but am not sure which one. Also there is a hazy band outside it that looks suspiciously like the E Ring, assuming it's not a glare artifact from Saturn and the main rings.

As for the Icarus paper, I did a quick look round the Internet and didn't find it anywhere, except for the abstract of course. I can give you the reference though: Mark R. Showalter, "Saturn's D Ring in the Voyager Images", Icarus 124, pp. 677-689 (1996). It's a pretty thorough treatment of the subject.

Do you have access to the Web of Science? If you have a university library card, and if your university subscribes to that journal, you ought to be able to download it from there. But Web of Science is sadly not available to the general public.

There are two good images of the D Ring in the Voyager images. The one taken by Voyager 2 is the one you'll normally find in Google searches because it has less smear. The nice thing about the Voyager 1 image though is that it includes the innermost part of the C Ring which gives a better idea of scale. I've attempted to attach that image to this post below (sorry if it doesn't work -- this is the first time I've tried attaching an image). Comparison with the recent Cassini image I've cited above shows the apparent changes in the outer part of the D ring.

 C3494650.BMP ( 626.05K ) Number of downloads: 972


If I didn't know better, I'd be tempted to suggest that D72 has "migrated outward" and merged with D73. However, that just doesn't seem physically possible. We do have to keep in mind here that there are changes in apparent brightness of ring components due to viewing-angle effects. That's probably a contributing factor.

Cheers
Rob