Rhea

Wife of Chronus

Rhea [REE-a] is the fourteenth of Saturn's known moons and is the second largest. It is the largest airless moon in the Saturnian system. Rhea was named after the sister and wife of Chronus in Greek mythology (Saturn in Roman). She was also the mother of Demeter, Hades (Pluto), Hera, Hestia, Poseidon (Neptune), and Zeus (Jupiter). Rhea was discovered by Giovanni Cassini in 1672. Nearly everything we now know about Rhea was discovered during the two Voyager missions.

Cassini close-up image of Rhea showing numerous craters (NASA/JPL/Space Science Institute)		Cassini close-up image revealing ridges on the rim of a crater (NASA/JPL/Space Science Institute)		Voyager 1 close-up photo of Rhea's north polar region (NASA/JPL)

Another Icy World

Rhea is an icy body very similar to Dione, although slightly larger in size. It has a very low density, which indicates that it is composed mainly of water ice with rocky material making up less than one third of its total mass. The temperature on Rhea ranges from -281° F (-174° C) in the sunlight to -364° F (-220° C in the shade.

Features of Rhea

Rhea is one of the most heavily cratered satellites in the Solar System. The surface features of this moon can be divided into two different geological areas based on the density of the craters. The first area contains craters that are larger than 25 miles (40 km) in diameter. The largest of these craters is Izanagi. It has a diameter of 140 miles (225 km). Craters in the second area are smaller than 25 miles in diameter. The difference in these areas indicates that some great event served to resurface parts of this moon at some point in the past. Similar differences in crater size can be found on Mimas and Dione. Like Jupiter's moon Callisto, Rhea's craters lack the high surface features found in craters on Mercury and the Moon. Line Dione, Rhea orbit around Saturn is synchronous, meaning that it always keeps the same face toward Saturn. On the trailing hemisphere of Rhea can be found several bright, wispy lines. These linear features are believed to be fractures, and may indicate that Rhea has expanded and contracted due to internal heating and cooling. Similar linear features are found on Dione. Rhea has no detectable atmosphere.