Rhea (moon)
Mosaic of Rhea, assembled from Cassini imagery taken on 26 November 2005 | |||||||||
| Discovery | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Discovered by | G. D. Cassini | ||||||||
| Discovery date | December 23, 1672 | ||||||||
| Designations | |||||||||
Designation | Saturn V | ||||||||
| Pronunciation | /ˈreɪ.ə/ | ||||||||
Named after | Ῥέᾱ Rheā | ||||||||
| Adjectives | Rhean /ˈreɪ.ən/ | ||||||||
| Orbital characteristics | |||||||||
| Periapsis | 526512 km | ||||||||
| Apoapsis | 527567 km | ||||||||
| 527040 km | |||||||||
| Eccentricity | 0.001 | ||||||||
| 4.518212 d | |||||||||
Average orbital speed | 8.48 km/s | ||||||||
| Inclination | 0.35° | ||||||||
| Satellite of | Saturn | ||||||||
| Physical characteristics | |||||||||
| Dimensions | 1532.4 × 1525.6 × 1524.4 km | ||||||||
| 763.5±0.5 km | |||||||||
| 7325342 km2 | |||||||||
| Mass | (2.3064854±0.0000522)×1021 kg (~3.9×10−4 Earths) | ||||||||
Mean density | 1.2372±0.0029 g/cm3 | ||||||||
| 0.26 m/s2 | |||||||||
| 0.3911±0.0045 (disputed/unclear) | |||||||||
| 0.635 km/s | |||||||||
| 4.518212 d (synchronous) | |||||||||
| 0° | |||||||||
| Albedo | 0.949±0.003 (geometric) | ||||||||
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| 10 | |||||||||
Rhea (/ˈreɪ.ə/) is the second-largest natural satellite of Saturn and the ninth-largest moon in the Solar System, with a diameter of 1,528 kilometers (949 miles). Rhea is the smallest body in the Solar System that is confirmed to be in hydrostatic equilibrium. It has a nearly circular orbit around Saturn, but it is also tidally locked, like Saturn's other major moons. It rotates with the same period it revolves or orbits. Thus, one hemisphere always faces towards the planet.
The moon has a fairly low density, composed of roughly three-quarters ice and only one-quarter rock. The surface of Rhea is heavily cratered, with distinct leading and trailing hemispheres. Like the moon Dione, it has high-albedo ice cliffs that appear as bright wispy streaks visible from space. The surface temperature varies between −174 °C and −220 °C.
Rhea was discovered in 1672 by Giovanni Domenico Cassini. Since then, it has been visited by both Voyager probes and was the subject of close targeted flybys by the Cassini orbiter in 2005, 2007, 2010, 2011, and once more in 2013.