http://www.universetoday.com/am/publ...e.html?1882005

Saturn's Rings Have an Atmosphere of their Own

Summary - (Aug 18, 2005) Saturn's rings are separate from the planet they
circle, and then even have an atmosphere of their own. During several
flybys, Cassini has been able to detect very small amounts of molecular
oxygen floating around the rings. Molecules of water are broken apart by
ultraviolet light from the Sun; the hydrogen and some of the oxygen is lost
into space, and some of the oxygen is frozen back into the rings. But
there's enough of a cloud of these atoms around the rings that this process
must be ongoing and kept in a continual balance.