This animation depicts the presence of an extremely tenuous atmosphere of molecular oxygen around Jupiter's moon, Europa. It's icy surface is exposed to sunlight and is impacted by dust and charged particles trapped within Jupiter's intense magnetic field. Combined, these processes cause the frozen water ice on the surface to produce water vapor as well as gaseous fragments of water molecules. After the gas molecules are produced, they undergo a series of chemical reactions that ultimately form molecular hydrogen and oxygen. The relatively lightweight hydrogen gas escapes into space, while the heavier oxygen molecules accumulate to form an atmosphere which may extend 125 miles (200 kilometers) above the surface. The oxygen gas slowly leaks into space and must be replenished continuously.
Credit: Walter Feimer/STScI