... Cassini reveals oxygen atmosphere of Saturn's moon Rhea . ... The Cassini-Huygens mission has discovered a tenuous atmosphere infused with oxygen and carbon dioxide at Saturnт??s moon Rhea т?? the first time a spacecraft has captured direct evidence of an oxygen atmosphere at a world other than Earth. ... Completing the picture of Rhea's atmosphere, Cassini's ion and neutral mass spectrometer detected neutral particles when Cassini swept within 60 miles (100 km) of the moon's surface in March 2010. ...