Saturn Moon Has Oxygen Atmosphere

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.')

At about 327,000 miles (527,000 kilometers) 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.

The Hubble Space Telescope and NASA's Galileo probe found in 1995 that a similar process creates tenuous oxygen atmospheres on Jupiter's ice moons Europa and Ganymede."