Saturn's moon Tethys. False-colour Cassini spacecraft image of the surface of Tethys. This image is based on ultraviolet, green and infrared data. The colour differences on the surface are thought to be due to variations in surface texture and composition. Tethys is composed almost entirely of pure water ice. The Cassini-Huygens spacecraft was launched in 1997 to investigate Saturn, its rings and its moons. Image obtained on 24th September 2005 by the Cassini spacecraft's narrow-angle camera, at a distance of 32,300 kilometres from Tethys.