Data streaming home from NASA's Cassini probe suggests that one of Saturn's largest moons, Dione, has a thin glaze of oxygen in its upper atmosphere.
In April of 2011, the probe did a close pass of Dione to confirm scientists' suspicions that the gelid moon had an atmosphere. The layer of oxygen ions is inconceivably thin, detectable only by Cassini's sensitive equipment. You'd have to travel 300 miles above the Earth's surface to find such scarce levels. (By comparison, world records in parachuting are from about 20 miles up.)
The lorn surface of Dione is pocked with craters and ancient tectonic scarring. A third the size of our own moon, Dione is an orb of frozen water compacted around a rock core. As it swings around the ringed gas giant, it is bombarded by charged particles from Saturn's bustling magnetic field. These spry particles crash into Dione's surface, upheaving ionized molecular oxygen into its thin atmosphere. Scientists call this process "sputtering."
Cassini team leader Robert Tokar of Los Alamos labs recently said in a statement that the Cassini data demonstrates that oxygen "can come from a process that doesn't involve life."
This might require scientists to rethink how oxygen ends up in an atmosphere.