Phoebe

Saturn IX

   Phoebe ("FEE bee") is the outermost of Saturn's known satellites. Phoebe is almost 4 times more distant from Saturn than its nearest neighbor (Iapetus).

        orbit:    12,952,000 km from Saturn
        diameter: 220 km
        mass:     4.0e18 kg

   Phoebe is the daughter of Uranus and Gaia; grandmother of Apollo and Artemis.

   Discovered by Pickering in 1898.

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

   It may be a captured asteroid or Kuiper Belt object.

   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.

Open Issues

• Why is Phoebe in such an odd orbit?
• Is it really the source of the dark material on Hyperion and the leading hemisphere of Iapetus?
• Phoebe's density is only 0.7 which is anomalously low. What is its composition?