Rhea has a ring?

[mmcirvin]

Via james_nicoll: Cassini finds evidence of a debris disk and ring orbiting Saturn's moon Rhea. This would be the first known moon ring, and, as far as I know, the first evidence of natural material orbiting a moon.

Rhea is Saturn's second largest moon after Titan, but it never got much exciting press because it just sort of looks like a larger and less spectacular version of Dione. But this is something new, and further proves that the Saturn system is the solar system's premier home for weird orbital mechanics.

Comments

[pentomino.livejournal.com]

I'm more surprised that we haven't found moons with their own moons yet. Or have we?

[mmcirvin.livejournal.com]

No, but in many cases they would be unstable because of planetary tides (with our Moon there's also the problem of lumps in the mass distribution making low orbits unstable over the long haul). Evidently this isn't one of those cases, at least for dust-sized moons.

[beamjockey.livejournal.com]

Or it is unstable, but there's a fresh supply of dust coming from somewhere.

[mmcirvin.livejournal.com]

I was going by the article's statement that the ring had been theoretically modeled as stable for "a long time", but that's pretty vague, come to think of it.

[mmcirvin.livejournal.com]

...however, some moons of Saturn do have smaller moons bobbing around their L4 and L5 points, and Janus and Epimetheus are in a weird horseshoe-orbit arrangement with each other.

obligatory

[jvandenberg.livejournal.com]

that's no moon.