  Outer satellites of the planets have distant, eccentric orbits that can be
highly inclined or even retrograde relative to the equatorial planes of their
planets. These irregular orbits cannot have formed by circumplanetary accretion
and are likely products of early capture from heliocentric orbit. The irregular
satellites may be the only small bodies remaining which are still relatively
near their formation locations within the giant planet region. The study of the
irregular satellites provides a unique window on processes operating in the
young solar system and allows us to probe possible planet formation mechanisms
and the composition of the solar nebula between the rocky objects in the main
asteroid belt and the very volatile rich objects in the Kuiper Belt. The gas
and ice giant planets all appear to have very similar irregular satellite
systems irrespective of their mass or formation timescales and mechanisms.
Water ice has been detected on some of the outer satellites of Saturn and
Neptune whereas none has been observed on Jupiter's outer satellites.
