96.3% Hydrogen, 3.25% Helium
Pan, Atlas, Prometheus, Pandora, Epimetheus, Janus, Mimas, Encedalus, Tethys, Telesto, Calypso, Dione, Helene, Rhea, Titan, Hyperion, Iapetus, Phoebe, plus 16 other unnamed moons
10-11 hours/29.5 Earth years
Saturn is the sixth planet in the Sol system, between Jupiter and Uranus. Is is most famous for its rings, and has as many as 61 moons, although most of them continue to be unnamed. It is a gas giant.
In Roman mythology, Saturn was the god of agriculture and harvest, often appearing with a sickle. Sailor Saturn carries a similar staff instrument in her glaive, and harvest can be loosely associated with destruction, or the ending of things, as Sailor Saturn's powers pertain to.
More information about Saturn can be found on its wikipedia page.