Help. National Geographic. Home. Saturn Moon Has Oxygen Atmosphere. An oxygen atmosphere has been found on Saturn's second largest moon, Rhea, astronomers announced Thursday—but don't hold your breath for colonization opportunities. For one thing, the 932-mile-wide (1,500-kilometer-wide), ice-covered moon is more than 932 million miles (1.5 billion kilometers) from Earth. For another, the average surface temperature is -292 degrees Fahrenheit (-180 degrees Celsius). And at less than 62 miles (100 kilometers) thick, the newfound oxygen layer is so thin that, at Earthlike temperatures and pressure, Rhea's entire atmosphere would fit in a single midsize building.
Still, the discovery implies that worlds with oxygen-filled air may not be so unusual in the cosmos. (Related: "Potentially Habitable Planets Are Common, Study Says. ") Hubble finds a star eating a planet.