出典:Wiktionary
出典:Wikipedia
出典:『Wikipedia』 (2011/06/12 15:19 UTC 版)
A planetary ring is a ring of cosmic dust and other small particles orbiting around a planet in a flat disc-shaped region. The most spectacular planetary rings known are those around Saturn, but the other three gas giants of the solar system (Jupiter, Uranus and Neptune) possess ring systems of their own.