Figure 7-19 RIVUXG Details of Saturn’s Rings and Orbiting Moons From edge to edge, Saturn’s enormous ring system would not even fit in the distance between Earth and the Moon. Composed primarily of water ice, the seven main rings are labeled in the order in which they were discovered. From the planet outward, the main rings are labeled, in the order of discovery, D, C, B, A, F, G, and E. The Cassini division is the largest gap in the rings and separates the B ring from the A ring. Just outside the A ring is the narrow F ring, shepherded by the tiny moons Pandora and Prometheus. One moon, Pan, actually orbits inside the A ring in the Encke Gap. Beyond that are two much fainter G and E rings, which extend from Mimas’s orbit to Titan’s orbit.