Saturn's F ring. Cassini spacecraft image of part of Saturn's 'F' ring. The F ring is a faint, narrow ring towards the outer edge of the ring system. The rings are mainly made of particles of water ice, ranging from microns to metres in diameter. This image was taken by the wide angle camera on the Cassini spacecraft after its entry into Saturn orbit on 1 July 2004. The spacecraft will spend four years collecting data about Saturn, its rings and its moons. For a closer view of part of the F ring, see R396/121.