Rhea (moon)

Rhea

Discovery
Discovered by	Giovanni Cassini
Discovered in	1672
Orbital characteristics
Semimajor axis	527,040 km
Eccentricity	0.001
Revolution period	108 h 25 min 12 s
Inclination	0.35 °
Is a satellite of	Saturn
Physical characteristics
Mean diameter	1528 km
Surface area	7,300,000 km2
Mass	2.3166×1021 kg
Mean density	1.24 g/cm3
Surface gravity	0.26 m/s2
Rotation period	108 h 25 min 12 s (synchronous)
Axial tilt	0.029 °
Albedo	0.65
Surface temp.	min mean max 53 K 99 K
Atmosphere	none

Rhea is the second largest moon of Saturn and was discovered in 1672 by Giovanni Cassini. It is named after the titan Rhea of Greek mythology. It is also designated Saturn V.

The name "Rhea" and the names of all seven satellites of Saturn then known were suggested by John Herschel in his 1847 publication Results of Astronomical Observations made at the Cape of Good Hope. [1]

Physical characteristics

Rhea is an icy body with a density of about 1,240 kg/m³. This low density indicates that it has a rocky core taking up less than one-third of the moon's mass with the rest composed of water-ice. Rhea's features resemble those of Dione, with dissimilar leading and trailing hemispheres, suggesting similar composition and histories. The temperature on Rhea is −174 °C in direct sunlight and between −200 °C and −220 °C in the shade.

Rhea is heavily cratered and has bright wispy markings on its surface. Its surface can be divided into two geologically different areas based on crater density; the first area contains craters which are larger than 40 km in diameter, whereas the second area, in parts of the polar and equatorial regions, has craters under 40 km in diameter. This suggests that a major resurfacing event occurred some time during its formation.

The leading hemisphere is heavily cratered and uniformly bright. As on Callisto, the craters lack the high relief features seen on the Moon and Mercury. On the trailing hemisphere there is a network of bright swaths on a dark background and few visible craters. It is thought that these bright swaths may be material ejected from ice volcanoes early in Rhea's history when it was still liquid inside.

See also: List of geological features on Rhea

The Cassini-Huygens orbiter is due to perform a flyby of Rhea on November 25, 2005.

Helene | Rhea | Titan