Dione has oxygen exosphere
27 Apr 2012 by hjdhbqddhb.d hjdhbqddhb.d
Saturn’s moon Dione has a weak exosphere which includes molecules of oxygen suggests new findings from Cassini.
In a pass of Dione in April 2010, the Cassini Plasma Spectrometer (CAPS) detected molecular oxygen ions – O2+ – near the moon’s icy surface due to the bombardment by particles trapped in Saturn’s strong magnetic field. This is the first in situ detection of a neutral exosphere surrounding an icy moon.
“It now looks like oxygen production is a universal process wherever an icy moon is bathed in a strong trapped radiation and plasma environment,” said Professor Andrew Coates of the UCL Mullard Space Science Laboratory (MSSL), and an author of the paper published in Geophysical Research Letters.
“Energetic particles hit the icy surface, the hydrogen is lost and molecular oxygen remains as an exosphere. We now know that this happens at Saturn’s moons as well as Jupiter’s – and it may well occur in extrasolar planetary systems too.”
Scientists from the Los Alamos National Laboratory in the US – led by Robert Tokar – used the measurements from CAPS to estimate the density of the molecular oxygen ions to be in the range of 0.01 to 0.09 ions per cubic centimetre. The O2+ ionsare produced when neutral molecules are ionised and the measurements confirm a neutral exosphere surrounds Dione.
Electron measurements from UCL’s electron spectrometer (ELS) – which forms part of CAPS – played a key role in reaching this conclusion, and data showed the plasma wake due to Dione and characterised changes in Saturn’s magnetosphere during the flyby.
“Dione’s exosphere is very thin – compared to Earth’s atmosphere the density is about a million billionth,” said Dr Geraint Jones. “The exciting thing is that there is oxygen – and the oxygen may be being recycled via the surface.”
Dione joins Rhea and Saturn’s main rings as having an oxygen rich exosphere. Jupiter’s moons Ganymede, Europa and Callisto – the target for the European Space Agency’s proposed JUICE (Jupiter ICy moons Explorer) mission for launch in 2022 – are also icy moons.
