The atmospheric carbon dioxide was thought to be the result of the oxidation of oxygen molecules in the exosphere. As a consequence of this discovery, Rhea became the first Saturnian moon, and only ...

Add Yahoo as a preferred source to see more of our stories on Google. On Dec. 23, 1672, Italian astronomer Giovanni Cassini discovered Rhea, Saturn’s second-largest moon. Rhea is made up of rock and ...

Looking for a sky event this week? Check out our full Sky This Week column. January 25: Aries' Hoofprint Saturn's four brightest moons are lined up for ideal viewing this evening. You can catch the ...