Outermost relatively large moon of Saturn. A dark large irregular moon, thought to be a planetesimal from the Kuiper Belt. It was likely spherical in its past, is about the same density as Pluto, and has a denser core. Its composition and density are more similar to KBOs than objects of the Saturnian system. Has water ice on its surface and probably liquid water in its interior at some point in its history. First satellite discovered using photography. First moon targeted by Cassini. Source of dark hemisphere of Iapetus. Smaller fragments land on Hyperion and Titan.