Rhea
Moon· orbits Saturn
Rhea is Saturn's second-largest moon — a heavily cratered ball of water ice and rock with a tenuous oxygen–carbon-dioxide exosphere.
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Key facts
Mass
2.31 × 10²¹ kg
0.0314 Moon masses
Radius
764 km
44% of our Moon's radius
Surface gravity
0.264 m/s²
3% of Earth's
Day length
4.5 days
Orbit around Saturn
4.52 Earth days
Science
Physical
- Mass
- 2.31 × 10²¹ kg · 0.0314 Moon masses
- Radius
- 764 km · 44% of our Moon's radius
- Density
- 1,237 kg/m³ · 1.2× water
- Surface gravity
- 0.264 m/s² · 3% of Earth's
- Escape velocity
- 635 m/s · 6% of Earth's
Orbit around Saturn
- Distance from Saturn
- 4,669,124 km
- Orbital period
- 4.5 days
- Eccentricity
- 0.001
- Inclination
- 0.30 °
Rotation
- Rotation period
- 4.5 days
- Tidal locking
- Tidally locked to its parent
Temperature
- Mean
- 76 K (-197 °C)
Composition
- Bulk composition
- Mostly water ice with about a quarter rock, probably only weakly differentiated.
Radiation & temperature
- Insolation
- 0.0112 S⊕ · 1% of the sunlight Earth receives
- Bond albedo
- 0.50 · reflects 50% of incoming sunlight
- Equilibrium temperature
- 76 K (-197 °C)
- Measured mean temperature
- 76 K (-197 °C)
Discovery & history
- Discovered
- December 23, 1672
- By
- Giovanni Domenico Cassini
- Method
- Visual discovery (telescopic)
- Name
- Rhea, the Titaness mother of the gods in Greek myth.
Cassini discovered Rhea, Saturn's second-largest moon, in 1672. A heavily cratered ball of ice and rock, it briefly seemed to possess a faint ring of its own — which would have been the only ring known around a moon, though later observations cast doubt on it.
Images
Images from open archives · credit shown per image