NASA discovers a new Earth, NASA's Cassini spacecraft has "sniffed" oxygen ions around Saturn's icy moon Dione for the first time, confirming the presence of a very tenuous atmosphere. The oxygen ions are quite sparse showing that Dione has an extremely thin neutral atmosphere.At the Dione surface, this atmosphere would only be as dense as Earth's atmosphere 300 miles (480 kilometers) above the surface. The detection of this faint atmosphere, known as an exosphere, is described in a recent issue of the journal Geophysical Research Letters.
Dione's oxygen appears to derive from either solar photons or energetic particles from space bombarding the moon's water ice surface and liberating oxygen molecules. But scientists will be looking for other processes, including geological ones, that could also explain the oxygen.
Several solid solar system bodies – including Earth, Venus, Mars and Saturn's largest moon Titan – have atmospheres. But they tend to be typically much denser than what has been found around Dione, scientists suspected molecular oxygen would exist at Dione because NASA's Hubble Space Telescope detected ozone.
