Europa
Europa, the fourth largest of Jupiter's moons, resembles Io in it's physical make-up. It is terrestrial, composed of molten silicate rock. Europa's surface is unique. Unlike the craterous Callisto, it is almost entirely smooth: only three large craters have been found on it's surface. There is speculation that beneath the icy surface of Io there is liquid water which would make it the only other body in the Solar System with large bodies of water.