The rings consist of minute particles of ice and rock. At Saturn, some are as large as a small house, and concentrate in orbits only a few kilometers thick. Within the rings, the particles are widely separated. The origin of such rings is still uncertain, but opinion favors disruption of earlier satellites. The planets may have captured some from asteroid-like belts or from passing comets and other space debris.
Ice is often the dominant material at the surface.
The surfaces of many satellites show varying, often heavy, cratering that may be preserved states from soon after they formed. Some satellites have unusual, patchwork-like multityped terrains that suggest they were reassembled from pieces torn apart from a collision. Indications of later, partial melting are present in a few.