Saturn's fifth largest moon is thought to be mostly composed of water ice. It has a 250-mile-wide (400 km) impact crater called Odysseus, which is huge when compared with the moon's 659-mile (1,060km) diameter.
Tethys also has a large canyon called Ithaca Chasma that is several miles deep and extends around much of the moon.
Photo: Tethys with Saturn's rings taken by the Cassini probe (NASA/JPL/Space Science Institute)
Voyager 2 showed the world Saturn's intricate rings up-close for the first time. Strange features like shepherd moons and spokes gave researchers plenty to think about. The Voyager probes were launched in 1977.
Sir Patrick Moore looks at Cassini-Huygens's first images of some of Saturn's moons.
Sir Patrick Moore has a look at the Cassini-Huygens probe's first images of some of Saturn's icy moons - Phoebe, Mimas, Tethys and Iapetus - and discusses the mission with his guests.
Tethys or Saturn III is a mid-sized moon of Saturn about 1,060 km (660 mi) across. It was discovered by G. D. Cassini in 1684 and is named after titan Tethys of Greek mythology.
Tethys has a low density of 0.98 g/cm³ indicating that it is made of water ice with just a small fraction of rock. This is confirmed by the spectroscopy of its surface, which identified water ice as the dominant surface material. A small amount of an unidentified dark material is present as well. The surface of Tethys is very bright, being second brightest among the moons of Saturn after Enceladus, and neutral in color.
Tethys is heavily cratered and cut by a number of large scale faults/graben. The largest impact crater—Odysseus is about 400 km in diameter, while the largest graben—Ithaca Chasma is about 100 km wide and more than 2000 km long. These two largest surface features may be related. A small part of the surface is covered by smooth plains that may be cryovolcanic in origin. Like all other regular moons of Saturn Tethys formed from the Saturnian sub-nebula—a disk of gas and dust that surrounded Saturn soon after its formation.
Tethys has been approached by several space probes including Pioneer 11 (1979), Voyager 1 (1980), Voyager 2 (1981), and Cassini since 2004.
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