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MOON

Phoebe

The captured Centaur — a retrograde, distant outer moon that supplies the dust painting Iapetus.

Orbits Saturn

Retrograde orbit u2014 almost certainly a captured Centaur or Kuiper Belt object.
Source of the enormous, tenuous Phoebe ring discovered in 2009.
Dust from Phoebe falls onto Iapetus's leading hemisphere, producing its dark side.

Physical Properties

Mean radius107 km

Mass8.292e18 kg

Density1.638 g/cm³

Rotation period9.27 h

Bond albedo0.081

Orbit

OrbitsSaturn

Semi-major axis12,947,780 km

Eccentricity0.1635

Inclination173.04°

Orbital period550.3 d

Missions to Phoebe

1 spacecraft tracked on Space Launch Live.

Sources & Further Reading

Numerical values (radius, mass, orbital elements, temperatures) are drawn from NASA NSSDC Planetary Fact Sheets, JPL Horizons, and the JPL Small-Body Database. Last refreshed: 2026-04-18 18:19:24.

Phoebe is one of Saturn’s outer, irregular moons and the largest of them. Its retrograde, highly inclined orbit and C- to B-type spectral properties strongly suggest it was captured from the Centaur or Kuiper Belt population early in Saturn’s history. In 2009 NASA’s Spitzer Space Telescope discovered the enormous, tenuous Phoebe ring — by far the largest known planetary ring — dust ejected from Phoebe that slowly spirals inward and coats one hemisphere of the synchronously-rotating Iapetus.