Saturn's moon Rhea is one of the 4 moons discovered by Giovanni Cassini in 1671-1684. It's the 3rd furthest large moon from Saturn, and the 19th most distant moon over all. Rhea measures 1529 km across, and orbits at an altitude of 527,000 km above the center of Saturn. It's the second largest moon orbiting Saturn It has a density of 1.2 grams per cubic centimeter. Since water is 1 g/cm3, this means that Rhea is mostly made of water ice, with about 25% rocks. As with most of Saturn's moons, Rhea is tidally locked to Saturn, so it always faces the same hemisphere towards the planet. As it orbits around Saturn, one hemisphere is leading and the other is trailing. The leading hemisphere of Rhea is heavily cratered and bright, while the trailing hemisphere has a network of bright streaks on a dark background. The trailing hemisphere also has much fewer craters. NASA reported in 2006 that Rhea might have a tenuous ring system, making this the first time a ring has been discovered around a moon. Here's an article from Universe Today about the discovery of rings around Rhea, and a nice image of Rhea captured by Cassini. Want even more info about Rhea. Two great resources are Solar Views and the Nine Planets. LINK: