Phoebe

Phoebe is an irregular satellite of Saturn with a mean diameter of 213 km (132 mi). It was discovered by William Henry Pickering on March 18, 1899 from photographic plates that had been taken starting on 16 August 1898 at the Boyden Station of the Carmen Alto 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 believed to be a captured centaur that originated in the Kuiper belt. Phoebe is the second largest retrograde satellite in the solar system after Triton.
== Phoebe ring ==
The Phoebe ring is one of the rings of Saturn. This ring is tilted 27 degrees from Saturn's equatorial plane (and the other rings). It extends from at least 128 to 207 times the radius of Saturn; Phoebe orbits the planet at an average distance of 215 Saturn radii. The ring is about 40 times as thick as the diameter of the planet. Because the ring's particles are presumed to have originated from micrometeoroid impacts on Phoebe, they should share its retrograde orbit, which is opposite to the orbital motion of the next inner moon, Iapetus. Inwardly migrating ring material would thus strike Iapetus's leading hemisphere, contributing to its two-tone coloration. Although very large, the ring is virtually invisible—it was discovered using NASA's infrared Spitzer Space Telescope.
Material displaced from Phoebe's surface by microscopic meteor impacts may be responsible for the dark areas on the surface of Hyperion. Debris from the biggest impacts may be the origin of the other moons of Phoebe's group (the Norse group)—all of which are less than 10 km in diameter.
Category:Moons
Category:Moons of Saturn
Category:Natural satellites