Saturn's moon Tethys. False-coloured Cassini image of Tethys, one of the moons of Saturn. This is the side of Tethys that faces away from Saturn. Tethys is primarily composed of water ice, and is around 1070 kilometres in diameter. Two of the large craters visible on its surface are Penelope (centre left) and Melanthius (lower centre). At upper right, the flattened limb (rim) of the moon is due to the massive impact crater Odysseus. This false-colour image is based on ultraviolet, green and infrared data. The colour differences are thought to be due to variations in surface texture and composition. Image data obtained by Cassini's narrow-angle camera on 31 December 2006, at a distance of 414,000 kilometres.