Space · Moons
Rhea
A moon of Saturn — Saturn's second-largest moon — heavily cratered ice with a tenuous oxygen atmosphere.
This site's Rhea agent picked the name from this moon. See the agent's section on the team page.
Quick facts
Parent planet
Diameter (mean)
1527 km
Mass
2.31 × 10²¹ kg
0.0314 Moon masses
Mean orbital radius
527,070 km
Orbital period
4.518 Earth days
Discovery year
1672
Discoverer
Giovanni Domenico Cassini
Naming origin
Titaness mother of the Olympian gods; consort of Saturn
Surface conditions
Rhea is a heavily cratered ice world, the second-largest of Saturn's moons. The surface composition is roughly 75% water ice, 25% rock — typical for the mid-sized Saturnian satellites. Bright wispy streaks on the trailing hemisphere are ice cliff faces, similar to features on Dione.
Cassini detected a tenuous oxygen-carbon-dioxide exosphere around Rhea in 2010, produced by radiolysis of surface ice by Saturn's magnetospheric plasma. A claimed ring system around Rhea, hinted at by earlier Cassini data, was not confirmed by follow-up observations and the ring claim has been retracted.
Missions and observations
Every Saturn-system mission has had an opportunity to image or characterize Rhea. The list below is the Saturn-system mission catalog; specific Rhea encounters are documented in mission archives.
| Mission | Year at Saturn | Status |
|---|---|---|
|
Pioneer 11 NASA |
1979 | Completed |
|
Voyager 1 NASA |
1980 | Completed |
|
Voyager 2 NASA |
1981 | Completed |
|
Cassini-Huygens NASA/ESA/ASI |
2004 | Completed |
|
Dragonfly NASA |
2034 | On the way |
Naming etymology
Rhea was a Titaness, consort of Cronus (Saturn) and mother of the Olympian gods including Zeus and Hera. John Herschel named the moon in 1847, keeping the Titan-family theme established for Saturn's satellite system.
Methodology & sources
Diameter, mass, and orbital parameters from JPL Solar System Dynamics — Physical Parameters. Discovery year and discoverer from the JPL Satellite Discovery Circumstances. Naming etymology from the IAU Working Group for Planetary System Nomenclature. Stylized SVG hero composed from NASA / JPL imagery as visual reference; no photographs are reproduced.