Tethys is Saturn's fifth largest satellite with a diameter of 1060 km. It is located at a distance of 294,619 km from the center of the planet and its orbital period is 45.43 hours, the same as its rotation. It was discovered in 1684 by Giovanni Cassini. It has the lowest density among the largest satellites in the Solar System, indicating that it is made up of water ice with a very small fraction of rock. Confirmation came from spectroscopic results that identified water ice as the dominant substance on the surface. A small amount of an unidentified dark material also appeared. The surface of Tethys is very bright, occupying the second position in brightness of Saturnian satellites after Enceladus.
