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

Irregular satellites are believed to have been captured from the circumstellar disk during planetary formation, and were once probably the most collisionally active population in the Solar System. The resulting orbital architectures at Jupiter and Saturn, especially the similarities between their largest moons Himalia and Phoebe, may provide clues to the origin of the systems. The spin-rates of several of Saturn’s irregular satellites have been recently published; we are investigating whether the spin-rate distribution can significantly constrain their collisional histories. If Phoebe and Himalia share similar histories, then the satellites’ spin-rates may indicate that Jupiter and Saturn captured different numbers of prograde and retrograde orbiting satellites.