Saturn's second-largest moon Rhea has a wispy atmosphere with lots of oxygen and carbon dioxide, a new study has found.
NASA's Cassini spacecraft detected Rhea's atmosphere during a close flyby of the frozen moon in March. The discovery marks the first time an oxygen-rich atmosphere has been found on a Saturn satellite. [Photo of the Saturn moon Rhea.]
Oxygen atmospheres are known to exist on other natural satellites in our solar system. For example, Europa and Ganymede — two frigid moons of Jupiter — are also rich in oxygen.