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Tethys (moon)
Moon of Saturn / From Wikipedia, the free encyclopedia
Tethys (/ˈtiːθɪs, ˈtɛθɪs/), or Saturn III, is the fifth-largest moon of Saturn, measuring about 1,060 km (660 mi) across. It was discovered by Giovanni Domenico Cassini in 1684, and is named after the titan Tethys of Greek mythology.
![]() Tethys imaged by the Cassini orbiter, April 2015 | |
Discovery | |
---|---|
Discovered by | G. D. Cassini |
Discovery date | 11 March 1684 |
Designations | |
Designation | Saturn III |
Pronunciation | /ˈtɛθəs/[1] or /ˈtiːθəs/[2] |
Named after | Τηθύς Tēthys |
Adjectives | Tethyan[3] /ˈtɛθiən, ˈtiː-/[1][2] |
Orbital characteristics | |
294619 km | |
Eccentricity | 0.0001[4] |
1.887802 d[5] | |
Average orbital speed | 11.35 km/s |
Inclination | 1.12° (to Saturn's equator) |
Satellite of | Saturn |
Physical characteristics | |
Dimensions | 1076.8 × 1057.4 × 1052.6 km[6] |
531.1±0.6 km[6][7] | |
Mass | 6.1749×1020 kg[7] (1.03×10−4 Earths) |
Mean density | 0.9840±0.0033 g/cm3[7] |
0.146 m/s2 [lower-alpha 1] | |
0.394 km/s[lower-alpha 2] | |
synchronous[8] | |
zero | |
Albedo | |
Temperature | 86±1 K[12] |
10.2[13] |
Tethys has a low density of 0.98 g/cm3, the lowest of all the major moons in the solar system, indicating that it is made of water ice with just a small fraction of rock. This was confirmed by the spectroscopy of its surface, which identified water ice as the dominant surface material. A further, smaller amount of an unidentified dark material is present as well. The surface of Tethys is very bright, being the second-brightest of the moons of Saturn after Enceladus, and neutral in color.
Tethys is heavily cratered and cut by a number of large faults and trench-like graben. The largest impact crater, Odysseus, is about 400 km in diameter, whereas the largest graben, Ithaca Chasma, is about 100 km wide and more than 2,000 km long; the two surface features may be related. A small part of the surface is covered by smooth plains that may be cryovolcanic in origin. Like the 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 and observed by several space probes, including Pioneer 11 (1979), Voyager 1 (1980) and Voyager 2 (1981), with Cassini-Huygens observing the moon the most, and in greatest detail, during its extensive mission to the Saturnian system (2004-2017).