The ninth of Saturn's known satellites. It it 1060 km across and orbits at a mean distance of 294,660 km from Saturn. It has a rotational period of 1.89 days that equals its orbital period. Tethys is thought to be composed almost entirely of water-ice because of its low density (1.21 gm/cm3). The western hemisphere of Tethys is dominated by a huge impact crater called Odysseus, whose 400 km diameter is nearly 2/5 of that of Tethys itself. Tethys has two moons named Telesto and Calypso. It was discovered by J.-D. Cassini in 1684.
In Gk. mythology Tethys was a Titaness and sea goddess who was both sister and wife of Oceanus.