Comet blasts created Saturn's many moonsThe dozen small distant moons of Saturn discovered in 2000 are pieces of larger bodies shattered by cometary impacts, say planetary scientists. Researchers already knew that the new moons must have been captured as the planet formed because they have irregular orbits that keeps them 10 to 20 million kilometres from Saturn. But it now appears that the six to 32 km bodies are only fragments of the original objects... Two groups formed when comets demolished larger, captured moons. The other was formed when a one to three kilometre comet blasted chunks of Phoebe, a 220-km satellite of Saturn, into orbit... The idea of catastrophic cometary impacts on moons is not new. Earlier work indicated that some small inner moons, such as Miranda, reassembled themselves after being shattered by collisions... The Earth's lone Moon has probably survived destruction because comet impacts are much less common in the inner Solar System.
by Jeff Hecht
11 July 2001
Is Phoebe A Kuiper Belt Object?Phoebe is a 200 km scale irregular satellite of Saturn. With a retrograde orbit (inclination 178 deg), Phoebe cannot have formed in a Saturn-associated accretion disk and, instead, is inferred to have been captured from an independent orbit around the Sun... The two main possibilities are that... Phoebe was captured from heliocentric orbit near Saturn, probably in association with planet formation itself... OR... Phoebe was captured from a more distant reservoir, possibly the Kuiper Belt. We do not possess any way to decide clearly between these possibilities. Recently, Kuiper Belt capture has been widely publicised and two (not wholly convincing) strands of evidence have been supplied.
by David Jewitt
Last updated Jun 2006