A satellite of Saturn discovered by Giovanni Cassini in 1684. Its low density, only 1.1 times that of water, suggests that at least half of the interior must be ice. Images from the Voyager 1 spacecraft show the surface to be heavily cratered, though there are regions of lower crater density, indicating that geological activity resulting in resurfacing took place in the past. Two notable features are the crater Odysseus, which is 400 kilometres (250 miles) in diameter, and Ithaca Chasma, a valley more than 2,000 kilometres (1250 miles) long that cuts round three-quarters of the satellite's circumference. It is 100 kilometres wide and several kilometres deep.
Tethys's orbit is shared by two very small satellites, Telesto and Calypso.
