The Cassini spacecraft captures this dual portrait of an apparently dead moon and one that is very much alive. Tethys, in the foreground, shows no signs of recent geologic activity. Enceladus, however, is covered in fractures and faults -- near its south pole in particular -- and spews icy particles into space from active vents. Tethys' giant crater Odysseus lurks in the dark just west of the terminator. North on the moons is up.