Dione is composed primarily of water ice, but as the third densest of Saturn’s moons (after Enceladus and Titan, whose density is increased by gravitational compression) it has a considerable fraction (~ 46%) of silicate rock in its interior.
Though somewhat smaller and denser, Dione is otherwise very similar to Rhea. They both have similar albedo features and varied terrain, and both have dissimilar leading and trailing hemispheres. Dione’s leading hemisphere is heavily cratered and is uniformly bright. Its trailing hemisphere, meanwhile, contains an unusual and distinctive surface feature: a network of bright ice cliffs.
Dione’s icy surface includes heavily cratered terrain, moderately cratered plains, lightly cratered plains, and areas of tectonic fractures. The heavily cratered terrain has numerous craters greater than 60 miles in diameter. The plains areas tends to have craters less than 20 miles in diameter. Some of the plains are more heavily cratered than others. Much of the heavily cratered terrain is located on the trailing hemisphere, with the less cratered plains areas present on the leading hemisphere.