A planetary ring is a ring of dust and other small particles orbiting around a planet in a flat disc-shaped region. The most spectacular and famous planetary rings are those around Saturn, but all four of the solar system's gas giant planets (Jupiter, Saturn, Uranus, Neptune) posess ring systems of their own.
The origin of planetary rings is not precicely known, but they are thought to be unstable and dissipate over the course of tens or hundreds of millions of years. As a result, modern ring systems must be of modern origin, possibly formed of debris from a moon that suffered a large impact or was disrupted by the parent planet's gravity when it passed within the Roche limit.
The composition of ring particles varies, and can be either silicate or icy dust.