Phoebe
Moon· orbits Saturn
Phoebe is a dark, irregular outer moon of Saturn on a retrograde orbit — most likely a captured Kuiper-belt object or centaur rather than a body that formed at Saturn.
Open in 3D viewSee Phoebe in the live, interactive 3D map
Key facts
Mass
8.29 × 10¹⁸ kg
0.000113 Moon masses
Radius
106 km
6% of our Moon's radius
Surface gravity
0.0488 m/s²
0% of Earth's
Day length
9.27 hours
Orbit around Saturn
550 Earth days
1.51 Earth years
Science
Physical
- Mass
- 8.29 × 10¹⁸ kg · 0.000113 Moon masses
- Radius
- 106 km · 6% of our Moon's radius
- Density
- 1,639 kg/m³ · 1.6× water
- Surface gravity
- 0.0488 m/s² · 0% of Earth's
- Escape velocity
- 102 m/s · 1% of Earth's
Orbit around Saturn
- Distance from Saturn
- 14,759,748 km
- Orbital period
- 550.3 days
- Eccentricity
- 0.164
- Inclination
- 175.20 °
Rotation
- Rotation period
- 9.27 hours
- Rotation
- Spins once every ~9.3 hours — NOT tidally locked, unlike Saturn's regular moons (Cassini). Its short spin is unrelated to its ~1.5-year retrograde orbit.
Temperature
- Mean
- 110 K (-163 °C)
Composition
- Bulk composition
- A dark mix of water ice, rock and carbon-rich material, resembling an outer Solar System body.
Radiation & temperature
- Insolation
- 0.011 S⊕ · 1% of the sunlight Earth receives
- Geometric albedo
- 0.06
- Equilibrium temperature
- 89 K (-184 °C)
- Measured mean temperature
- 110 K (-163 °C)
- Greenhouse warming
- +21 K
Discovery & history
- By
- William Henry Pickering
- Method
- Photographic plates
- Name
- Phoebe, a Titaness of Greek myth.
Phoebe was the first moon discovered photographically, found by William Pickering in 1899 on plates from Harvard's southern station. It circles Saturn backwards, far out and steeply tilted — a captured visitor from the outer Solar System that Cassini revealed as a battered, primitive body.
Images
Images from open archives · credit shown per image