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Rhea (moon)

Discovered byGiovanni Cassini
Discovered in1672
Orbital characteristics
Semimajor axis527,040 km
Revolution period108h 25m 12s
Is a satellite ofSaturn
Physical characteristics
Equatorial diameter 1528 km
Surface area7,300,000 km2
Mass2.3166×1021 kg
Mean density1.24 g/cm3
Surface gravity0.26 m/s2
Rotation period108h 25m 12s
Axial tilt0.029°
Surface temp
53 K99 K

Rhea is the second largest moon of Saturn. It was discovered in 1672 by Giovanni Cassini. Rhea is an icy body with a density of about 1.24 gm/cm3. 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 kilometers in diameter, whereas the second area, in parts of the polar and equatorial regions, has craters under 40 kilometers in diameter. This suggests that a major resurfacing event occurred some time during its formation.

The leading hemisphere is heavily cratered and uniformly bright. Like 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.