Guest Author - Lea Terry

Icy and rugged, Rhea is Saturn's largest airless satellite. And now, it may be the first moon to have been discovered to have rings.

Rhea's Rings?

Rhea was discovered in 1672 by Giovanni Cassini; now the Cassini spacecraft has spotted evidence of at least one ring around the moon. The spacecraft has not taken images of the ring yet, but its instruments detected a debris disk around Rhea measuring several thousand miles. The discovery stems from a Cassini flyby of Rhea in November 2005, after which scientists began simulations to determine if the moon could support rings. These models suggest that the combination of Rhea's gravity field and orbit around Saturn could help rings stay in place around the moon for quite some time. Scientists belive the particles making up the disc and any rings are probably pebble- to boulder-sized, and there's also evidence of a dust cloud extending up to
3,000 miles from Rhea's center.

About Rhea

Rhea has a low density -- just 1.33 gm/cm3 -- which suggests that it has a rocky core that accounts for less than one-third of its mass, with water-ice making up the rest. Its heavily cratered surface has two distinct areas: one with craters larger than 25 miles in diameter, and another area in the polar and equatorial regions with craters less than 25 miles in diameter.