Can The Spin Rates Of Irregular Satellites Provide Constraints To Their Formation Histories?

Irregular satellites are moons that revolve on distant eccentric and inclined orbits, with most orbiting retrograde. Unlike their regular counterparts, they are believed to have been captured from the protoplanetary disk in the early Solar System. Recently published data of Saturn's irregular satellites from the Cassini-Huygens mission cataloged their respective spin-rates and other physical properties. The distribution of satellite spin-rates may be a byproduct of their collisional history, which should also be reflected in their orbital architecture. The additional similarities between Phoebe and Himalia's orbital parameters may imply that Jupiter and Saturn started with different ratios of prograde and retrograde orbiting satellites. We are investigating this connection in greater detail and will report on our findings.