Rhea (moon)

Giovanni Cassini

Rhea, Earth & Moon size comparison

PIA18310-SaturnMoon-Rhea-20150210

Rhea at approximately 2,348 miles (3,778 kilometers) away

Rhea ice cliffs

PIA08148 (Rhea-Splat)

Rhea is the second-largest moon of Saturn and the ninth-largest moon in the Solar System. Discovered in 1672 by Giovanni Domenico Cassini, it was named after Rhea, a Titaness and the mother of the gods in Greek mythology. Rhea is primarily composed of water ice and a smaller fraction of rocky material, making it an intriguing subject of study in planetary science.

Physical characteristics

Rhea has a mean radius of about 763.8 km and follows a nearly circular orbit around Saturn at a distance of approximately 527,108 kilometers. Its low density suggests that it is composed largely of water ice with a rocky core, which is typical for bodies in the outer Solar System. The moon's surface is heavily cratered and features several large impact basins, indicative of a long history of collisions. Bright wispy markings, believed to be ice cliffs created by tectonic fractures, are also visible on its surface.

Orbit and rotation

Rhea orbits Saturn in about 4.5 Earth days and is in a synchronous rotation with the planet, meaning the same side always faces Saturn. This synchronous rotation is common among the major moons of the gas giants in the Solar System. Rhea's orbit lies within Saturn's magnetosphere, which protects it from the solar wind, but also subjects it to bombardment by energetic particles.

Exploration

Rhea has been visited by several spacecraft, most notably the Voyager 1 and Voyager 2 missions in the 1980s and later by the Cassini–Huygens mission, which provided detailed images and data about the moon's surface and environment. These missions have increased our understanding of Rhea, including its geology, surface composition, and the potential for an extremely thin atmosphere, or exosphere.

Scientific interest

Scientific interest in Rhea revolves around its composition and history. As a body dominated by water ice, Rhea could provide insights into the processes that govern the outer Solar System's icy bodies. Additionally, understanding Rhea's geological history, including its cratering record, can offer clues about the conditions in the Saturn system over time. There is also interest in the possibility of a subsurface ocean, similar to those suspected on other moons like Enceladus and Europa, though evidence for such an ocean on Rhea is currently more speculative.

See also

• Moons of Saturn
• List of natural satellites
• Planetary science