Saturn
Recent data from the Cassini spacecraft has shown that the rings have their own atmosphere, free from the planet's atmosphere. The rings' atmosphere is made of oxygen gas, and it is produced when the Sun's ultraviolet light breaks up the water ice in the rings. Chemical reactions also occur between the ultraviolet light and the water molecules, creating hydrogen gas. The oxygen and hydrogen atmospheres around the rings are very widely spaced. As well as oxygen and hydrogen gas, the rings have a thin atmosphere made of hydroxide (a combination of oxygen and hydrogen called an anion), which was discovered by the Hubble Space Telescope.