Saturn's moon Enceladus has oxygen

Saturn's moon Dione has a thin oxygen atmosphere

Los Alamos (USA) - The fourth largest moon on the planet Saturn is surrounded by a thin atmosphere of molecular oxygen. This is shown by measurements from the American space probe Cassini, about which an international team of researchers reports in the journal "Geophysical Research Letters". The discovery shows that oxygen occurs frequently in the Saturn system and can also occur without biological processes, according to the scientists.

"Now we know that Dione - in addition to the Saturn rings and the small moon Rhea - is a source of oxygen molecules," says Robert Tokar of the Los Alamos National Laboratory in the USA, who led the scientific investigation. Dione is 1,120 kilometers in diameter and orbits Saturn every 2.7 days at a distance of 380,000 kilometers. The measurements now published are from April 7, 2010, when Cassini flew at an altitude of 500 kilometers above the surface of the moon.

However, the atmosphere discovered by the space probe is extremely thin. The air pressure on the surface of Dione corresponds roughly to the pressure that prevails in the earth's atmosphere at an altitude of 480 kilometers. For comparison: the International Space Station (ISS) orbits the earth at an altitude of 350 to 400 kilometers.

According to Tokar and his colleagues, possible causes for the atmosphere are high-energy radiation or particle streams from the sun, which release oxygen from the ice on the surface of Saturn's moon. The researchers also want to keep an eye out for geological processes that could release oxygen from inside Dione when the Cassini space probe passes by.