Dione's thin oxygen exosphere

2 March 2012



When energetic (millions of degrees C) charged particles hit the icy surface of Dione they kick of molecules of water - this is called sputtering. Other energetic particles can then split up the hydrogen and oxygen in these water molecules in a process known as radiolysis. The hydrogen can escape from Dione but some of the molecular oxygen is trapped near to Dione forming the exosphere - and oxygen can be recycled via the surface, continuously replenishing the exosphere.

We know that this process also happens at Saturn's moon Rhea and also at Saturn's rings, where these charged particles sputter water molecules from the surfaces of the ring particles. Saturn isn't alone in this, however. Jupiter's icy moons Ganymede, Europa and Callisto, the targets of ESA's proposed JUICE mission for launch in 2022, also have exospheres produced by sputtering. This may therefore be a universal process, wherever an icy moon is bathed in a strong radiation environment, possibly even occuring in exoplanetary systems around other stars.

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Page last modified on 02 mar 12 13:10