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, ice-covered moon is more than 932 million miles from Earth. For another, the average surface temperature is -292 degrees Fahrenheit. Still, the discovery implies that worlds with oxygen-filled air may not be so unusual in the cosmos.
And at less than 62 miles 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. At about 327,000 miles from Saturn, Rhea orbits inside the planet's magnetic field. Rhea's oxygen atmosphere is believed to be maintained by the ongoing chemical breakdown of water ice on the moon's surface, driven by radiation from Saturn's magnetosphere.