Voyager 2 photograph of Iapetus, the outermost of the large icy moons of Saturn. With a diameter of 1460 kilometres, it is Saturn's third largest satellite after Titan & Rhea. It orbits Saturn once every 79 days. It is unusual in that most of its surface is bright & apparently consists of ordinary water ice, but the leading face is as black as tar or asphalt - as can be seen at lower left in this image. Since there are no bright rayed craters in the dark region, it is thought that the dark material is either thick or is renewed to cover bright meteor impact ejecta.