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

[dilo]

Great work Rob! Due to the general lack of information on the internet with regards to the D-ring, this thread has been a joy to read. 

agree!

[alan]

Nice views of the G-ring. Anyone know why it has such a sharp inner edge?
http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=52733
and the E-ring, it appears to have a narrow core at the edge of the frame.
http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=52722

[pat]

Nice views of the G-ring. Anyone know why it has such a sharp inner edge?
http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=52733
and the E-ring, it appears to have a narrow core at the edge of the frame.
http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=52722

dare I say, inner edge defined by a (n undiscovered) satellite?

[Rob Pinnegar]

dare I say, inner edge defined by a (n undiscovered) satellite?

Does anybody have a Cassini-determined value for the radius of the inner edge of the G Ring? Without that, it's hard to figure out whether that sharp edge is due to a resonance.

[Edit: It seems pretty close to Enceladus 5:3, though.]

This is just a hunch, but the material in the G Ring almost looks like it's being "piled up" against that inner boundary. It'd be neat if its mass density turned out to be an exponential. (But given that this ring shows arcs, things probably aren't that simple, I guess.)

[Guest_BruceMoomaw_*]

Since the G Ring is located between Mimas and the Coorbital Moons, I'd like to know whether its relatively sharp inner boundary is at an orbital resonance point with the latter.

[Rob Pinnegar]

Since the G Ring is located between Mimas and the Coorbital Moons, I'd like to know whether its relatively sharp inner boundary is at an orbital resonance point with the latter.

Well, just running through this on my calculator, and using 151472 km as the semimajor axis for Janus, Janus 6:5 should be at a=171048 km, and Janus 7:6 should be at a=167866 km. So the G Ring's inner boundary could be the 7:6 resonance.

The 6:5 resonance is probably too far away from Saturn. It should still fall inside the G Ring, though. I wonder if its effects will be visible?

[SigurRosFan]

PIA07643: G Ring Aglow

http://photojournal.jpl.nasa.gov/catalog/PIA07643

[Rob Pinnegar]

Hmmm. Can anyone else besides me see two "boundaries" within the G Ring, in the image referenced in the above post?

If those really are discontinuities in ring density, I wonder if they are associated with some of the resonances mentioned in previous posts?...

[alan]

Is the glow above and below the rings real or an artifact?
http://saturn.jpl.nasa.gov/multimedia/imag...6/W00012426.jpg

[Rob Pinnegar]

Is the glow above and below the rings real or an artifact?

My guess is that it's glare from the main rings. If it was due to the E Ring, it would extend all the way from the top of the image to the bottom.

Also, exposure times that are long enough to bring out the E Ring usually seem to massively overexpose the main rings. That has been the case in the past, at least.

[Rob Pinnegar]

By the way, since I'm here... just as a follow up to some of the D Ring material that I posted a few months back in this thread:

I had been wondering why the inner edge of the C Ring was defined the way it was. One possible explanation, which I didn't think of at the time, is that those four little ringlets at the outer edge of the D Ring ("D++" for want of a better term) simply didn't show up in the Voyager images. Looking at some of the old Voyager shots of the rings, those ringlets aren't really visible.

The D++ ringlets also have a lower density than the C Ring, so they may not really have showed up very well in the occultation data. I have tried to confirm this by looking at the occultation data, but unfortunately I've been having trouble figuring out how to work with it.

[dilo]

Elaboration of G ring image W00012790

Attached thumbnail(s)

 

[Rob Pinnegar]

There are quite a few new images of the D Ring now up on the Cassini website. Since we're so close to the ring plane at the moment, the rings have a very "foreshortened" appearance. However, D68 and D73 are quite visible, as are the fuzzed-out remains of D72.

One of the interesting things about these new images is that, if you look at some of them closely (particularly the ones for which parts of the rings are hidden by Saturn's shadow) you can see vertical "bands" outside the main rings that look very much as if they might be the E and G rings. These could of course be artifacts, and it wouldn't surprise me at all if they turned out to be just that... but if they really are rings E and G, this would probably be the first time we've seen all seven main rings in the same image. I hope this isn't wishful thinking on my part.

Since Cassini's first images of the D Ring came back from Saturn more than a year ago, these new images may give some idea of whether there have been further changes in the D Ring during the Cassini mission. (Hopefully, at least.)

[alan]

The Enceladus Ring

An interesting feature of note in this image is the double-banded appearance of the E-ring, which is created because the ring is somewhat fainter in the ringplane than it is 500-1,000 kilometers (300-600 miles) above and below the ringplane. This appearance implies that the particles in this part of the ring have nonzero inclinations (a similar affect is seen in Jupiter's gossamer ring). An object with a nonzero inclination does not orbit exactly at Saturn¿s ringplane. Instead, its orbit takes it above and below the ringplane. Scientists are not entirely sure why the particles should have such inclinations, but they are fairly certain that the reason involves Enceladus.

http://saturn.jpl.nasa.gov/multimedia/imag...fm?imageID=2092

[Rob Pinnegar]

Interesting.

IIRC, a similar phenomenon occurs in dust in the main asteroid belt, with concentrations 9 degrees above and below the plane of the solar system. This is an old, hazy memory, probably dating to my undergraduate days (back in the Proterozoic) but the theory is that this is the result of a recent asteroid-asteroid collision. The dust particles are on elliptical, inclined orbits, and statistically they spend more time at aphelion, which leads to this weird effect.

In unrelated news (here we go again) there was some mention a while back of some targeted D Ring observations slated for this September -- occultation data this time, not images. They're scheduled for when Cassini is at aphelion, so that its motion relative to Saturn is very slow -- this ought to give good resolution. Be interesting to see what that turns up.