New ring discovered around Saturn Options

[volcanopele]

not necessarily. As I pointed out before, for example, Janus and Epimetheus have a similar dust ring at their orbits made of micrometeorite ejecta and they have a prograde orbits around Saturn.

And adding to my list of "Moons with rings at their orbits", I should have also added Pan and Atlas.

[HughFromAlice]

News of the new Saturnian ring has travelled fast. Without being chauvinistic, I am glad to say I come from a forward looking scientifically literate country.......... our only quality national daily 'The Australian' has been quick to snaffle up this newsworthy item and give it a prominent place today. Who says we're behind the times down this way??????



Round here it's out with the delta Vs and albedo calculations and back to the good old trines and sesquiquadrates ! Perhaps I'll swallow national pride and keep checking the UMSF pages !

[mchan]

Unenviable that you have astrologers finding a giant ring around Saturn.

[djellison]

Would it be shorter to write a list of Saturnian moons that DON'T have associated dust rings? And would the same not be true of...er...anywhere with moons?

[brellis]

Unenviable that you have astrologers finding a giant ring around Saturn.

Would they be Australogers?

[Gsnorgathon]

not necessarily. As I pointed out before, for example, Janus and Epimetheus have a similar dust ring at their orbits made of micrometeorite ejecta and they have a prograde orbits around Saturn.

And adding to my list of "Moons with rings at their orbits", I should have also added Pan and Atlas.

I wasn't very clear there... what I meant was, "might Phoebe's retrograde orbit have something to do with how huge the ring is, by contributing to higher-velocity impacts that would produce more ejecta and/or more widely-scattered ejecta, when compared with the rings formed by impacts on other moons?" But I'm having a hard time figuring out how that might work, anyway.

If Phoebe's a captured TNO, maybe it's just got a higher volatiles concentration, and the ring's a toroidal comet tail.

[Hungry4info]

Back during the Cassini flyby of Phoebe, I recall them saying that Phoebe was confirmed not to be a captured body. Is my memory faulty? (It was a long time ago.

[nprev]

I don't know how they could have confirmed that, frankly. The retrograde orbit alone is practically a smoking gun; AFAIK, all other known retrograde satellites are thought to be captured.

[Anne Verbiscer]

Could it be that Phoebe is a captured burnt out comet!??

That is precisely one of the scenarios we considered when we wrote our proposal to search for a ring with Spitzer.

[nprev]

Interesting! Could you please describe some of the others, Anne?

[elakdawalla]

One idle thought led to another: I wondered if Cassini got whacked by any Phoebe ring particles as it passed through on its way in to SOI. Then I realized there's an instrument on Cassini designed to measure that, the CDA. Of course, that data's old enough that it's in the PDS. If I had time, I'd dig into it and see if I could understand or deal with the CDA data. I don't have time, though, so I just sent an email to the CDA team leader asking about it and hope I'll get a reply. But I thought I'd mention it here, just in case anybody else feels like attempting to dig into the PDS and see what CDA data looks like!

--Emily

[stevesliva]

Still an artist's impression. But the article said the discovery was made using Spitzer when it still had cryogen, and that the observations were of basically empty space.

Finally saw a "real" photo somewhere:
http://apod.nasa.gov/apod/ap091013.html

Original here:
http://www.spitzer.caltech.edu/Media/relea...c2009-19a.shtml

[Anne Verbiscer]

Interesting! Could you please describe some of the others, Anne?

Sorry to take so long to answer this!

Some of those 'other scenarios' explored the possibility that Phoebe at one time or another exhibited Chiron-like activity. The two objects have similar colors and perihelion distances; however, Phoebe appears to have more water on its surface (seen in near-infrared spectra) than Chiron does. Other possible sources of dust considered were collisional, from both major impacts and micrometeoritic erosion.