It's a Gas Gas Gas

The Cassini satellite probe found oxygen in the atmosphere on Rhea, one of Saturn's moons.

Not a lot -- Rhea is a relatively small body that is able to keep only a very thin atmosphere. But both oxygen and carbon dioxide showed up in small amounts when scientists steered Cassini through Rhea's atmosphere to "sniff" it and see what it's made of. Scientists believe that the oxygen replenishes itself as the O2 molecules are carried into Rhea's surface by its magnetic field, breaking apart water molecules found there in ice into hydrogen and oxygen. The continuing impact of gas molecules with the moon's surface sort of splashes these newly freed oxygen molecules back into its atmosphere.

Rhea was discovered in 1672, along with Tethys, Dione and Iapetus, by Italian astronomer and probe namesake Giovanni Domenico Cassini. Rhea is the name of the Titan in Greek mythology who wed her brother Kronos, or Saturn, and gave birth to several of the later Olympian gods and goddesses like Poseidon, Hades, Hera and Zeus. Since Kronos was afraid one of his children would overthrow him, based on a prophecy he had heard, he swallowed each of them whole when they were born. But Rhea conspired to hide their last child, Zeus, until he could grow and free his sisters and brothers. He did so -- the story is iffy as to whether or not he made Kronos throw up or he cut him open, but out sprang fully-grown gods and goddesses who then took over as rulers of the cosmos. Zeus followed one of his father's customs and marred Hera, his own sister.

I sometimes wonder if astronomy is too PG-13 to teach to kids.