... A Star Where Photons Orbit . ... Enceladus orbits Saturn between the smaller Mimas and the larger Tethys. Enceladus is composed mostly of water ice and has the cleanest and purest ice surface in the Solar System. ... Saturn's Moon Tethys . ... Tethys is now known to be composed almost completely of water ice. ... The Crab Nebula resulted from a star that exploded - a supernova. ... The outer layers of the star were thrown violently into space, while the inner core collapsed to form a neutron star. ...