Cassini has found evidence of possible ice volcanism on Enceladus, based on a warm spots in the “tiger stripes” (those blue surface features) around the moon’s south pole, and a tenuous atmosphere containing water vapor — especially concentrated at the south pole. All the signs point to a geologically active moon, kneaded and heated by Saturn’s gravitational influence, and constantly leaking heat and water to replenish its thin atmosphere and coat the surface with ice.
I remember that the spacecraft in Arthur C. Clarke’s 2061: Odyssey Three were driven by water-powered muon drives. If that science fiction technology ever becomes reality, worlds like Enceladus will be a dream come true. (Especially since Europa might be off-limits if the Monoliths have their way. ;-)
More Enceladus flyby photos from Cassini. Also check out The Planetary Society’s article on the flyby.