Tethys

Tethys (Greek: Τηθύς, Hebrew: טתיס, Russian: Тефия) is one of the moons of Saturn, discovered in 1898 by astronomer Edward Emerson Barnard. It is named after the Titaness Tethys of Greek mythology, a sister and wife of Oceanus. Tethys is composed mostly of water ice with a small fraction of rock. At 1,062 kilometers in diameter, it is the 16th-largest moon in the Solar System. It is also known for its large impact crater, Odysseus, which is about 400 kilometers in diameter, and its vast system of icy cliffs and troughs called Ithaca Chasma, which is up to 100 kilometers wide and 3 to 5 kilometers deep. Tethys orbits Saturn at a distance of about 295,000 kilometers, taking around 1.89 Earth days to complete one orbit. The moon is in a 4:3 mean motion resonance with the larger moon Dione, which stabilizes its orbit. Tethys is also notable for its low density, suggesting a high water ice content, and its relatively high albedo, indicating a clean, fresh surface.