Phoebe also stands out because it orbits in the opposite direction to the other major moons and is very dark in colour. All of these characteristics lead many astronomers to think that Phoebe did not form around Saturn but was an object - possibly from the Kuiper Belt - captured by Saturn's strong gravity.
Photo: Phoebe taken by the Cassini probe (Cassini Imaging Team, SSI, JPL, ESA, NASA)
An oddball moon orbits Saturn.
A flyby of Phoebe yields clues about the moon's origins.
The Cassini-Huygens probe, launched in 1997, made a close flyby of Saturn's moon Phoebe and answered a fundamental question about this unusual moon's origins. It turned out that Phoebe offers scientists a chance to learn more about the distant, icy outer Solar System.
Sir Patrick Moore looks at Cassini-Huygens's first images of some of Saturn's moons.
Sir Patrick Moore has a look at the Cassini-Huygens probe's first images of some of Saturn's icy moons - Phoebe, Mimas, Tethys and Iapetus - and discusses the mission with his guests.
Phoebe (//; Greek: Ancient Greek: Φοίβη Phoíbē) is an irregular satellite of Saturn with a mean diameter of 213 km. It was discovered by William Henry Pickering on 17 March 1899 from photographic plates that had been taken starting on 16 August 1898 at the Boyden Observatory near Arequipa, Peru, by DeLisle Stewart. It was the first satellite to be discovered photographically.
Phoebe was the first target encountered upon the arrival of the Cassini spacecraft in the Saturn system in 2004, and is thus unusually well-studied for an irregular satellite of its size. Cassini's trajectory to Saturn and time of arrival were specifically chosen to permit this flyby. After the encounter and its insertion into orbit, Cassini did not go much beyond the orbit of Iapetus.
Phoebe is roughly spherical and has a differentiated interior. It was spherical and hot early in its history and was battered out of roundness by repeated impacts. It is thought to be a captured planetesimal from the Kuiper belt.