Iapetus (/aɪˈæpᵻtəs/; Greek:Ιαπετός), or occasionally Japetus /ˈdʒæpᵻtəs/, is the third-largest natural satellite of Saturn, eleventh-largest in the Solar System, and the largest body in the Solar System known not to be in hydrostatic equilibrium. Iapetus is best known for its dramatic 'two-tone' coloration. Discoveries by the Cassini mission in 2007 revealed several other unusual features, such as a massive equatorial ridge running three-quarters of the way around the moon.