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Orbit: 12,952,000 km from Saturn
Orbital period: 550 days
Gravity: 0.038 m/s²
Diameter: 220 km
Mass: 4.0e18 kg

 Discovered by Pickering in 1898. Phoebe is an irregular satellite of Saturn. It is thought to be a captured planetesimal from the Kuiper belt

On June 11, 2004 Cassini passed close to Phoebe on its way into the Saturn system, giving us our first  real look at it since Voyager and at much higher resolution.

Most of Saturn’s moons are bright but Phoebe’s albedo is very low (.05), as  dark as lampblack.

All of Saturn’s moons except for Phoebe and  Iapetus orbit very nearly in the plane of Saturn’s       equator.  Phoebe’s orbit is inclined almost 175° (its north pole is in  the opposite direction to Saturn’s).

Phoebe’s eccentric, retrograde orbit    and unusual albedo indicates that it may be a captured   comet or  Kuiper Belt object.  Data from Cassini’s 2004  flyby  reinforces this idea with the detection of CO2 trapped within its rocks. This rules out the earlier idea that it might have been a captured asteroid. It  appears that Phoebe is chemically similar to Pluto and  Triton. It is  probably very similar to the chemical  composition of the outer solar system at the very beginning.

Phoebe is also unusual in that it does not rotate synchronously as do all  the other moons of Saturn except Hyperion.

Material knocked off of Phoebe’s surface by microscopic meteor impacts   may be responsible for the dark  surfaces of Hyperion and the leading hemisphere of Iapetus.


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