Saturn and its moon Tethys Cassini spacecraft image Tethys is some kilometres in diameter and it orbits just less than kilometres from Saturn It is primarily composed of water ice Two large craters are visible on its surface Odysseus upper right and Melanthius bottom centre Saturn itself is a gas giant planet some kilometres in diameter It is composed almost entirely of hydrogen with a rocky core and traces of other gases The extreme temperatures and pressures inside Saturn mean that the hydrogen in its interior is in a metallic state This image was taken on rd December while Cassini was around million kilometres from Saturn
