Saturn's moon Enceladus above Saturn's rings, Cassini image. The moon (centre, round) is 504 kilometres in diameter, and is the sixth-largest moon of Saturn. Enceladus has a surface of frozen water and reflects much of the sunlight that falls on it, producing a bright white colour. It orbits 180,000 kilometres above Saturn's uppermost clouds (brown, background), within the E ring region. The rings run horizontally across the image below the moon, and the shadow of the rings is seen on the planet at top left. Also visible on Saturn is the terminator (down centre), the region where day (left) gives way to night (right). Natural-colour image obtained on 18 January 2006 by the Cassini spacecraft's wide-angle camera.