Rhea, discovered by Giovanni Domenico Cassini in 1672, is the largest of the midsized icy satellites of Saturn. Its distance to Saturn is 527,000 km (or 8.7 Saturnian radii). Its diameter is 1,528 km and its density is 1.24 g/cm3, typical of a water-ice body. Rhea was first observed by Voyager 1 in 1980 and then more extensively explored since 2005 by the Cassini orbiter. The surface of Rhea is heavily cratered with little differentiation, with the exception of Izanagi crater, which is 250 km in diameter. Rhea has no orbital resonance with any other satellite, which accounts for the lack of tidal heating and hence of geological activity.