Tuesday, June 24, 2008
Monthly moon round-up - Dione
Size: 1,120 kilometers - 4th largest moon of Saturn
Orbital radius: 377,400 kilometers - 6.26 Saturn radii - within the E ring
Orbital period: 2.737 days - about 1/6 of Titan's
Discovery: 1684 by Giovanni Domenico Cassini
Dione's globe is dominated by a star-like pattern of bright "wispy terrain" -- or so it appeared from the Voyagers' distant views. It was long speculated that the wispy terrain represented relatively fresh volcanic flows of icy material. Close views from Cassini have revealed that the wisps are not volcanic features at all. They are exposed cliff faces, a terrain created by the fracturing and faulting of Dione's surface. In fact, there are fractures to be seen everywhere on Dione, representing multiple generations of tectonic events. Some slice up craters, while others have craters superimposed on them.
Features on Dione are named for people and places from Virgil's Aeneid, which complements similar Tethys' naming scheme (the Odyssey).
Like Tethys, Dione has little rocks keeping it company in its Lagrange points: Helene occupies the same orbit as Dione, 60 degrees ahead, while Polydeuces occupies the same orbit, 60 degrees behind.