SPUTTERING OF SURFACE MATTER FROM EUROPA

摘要

At the Jovian satellite Europa; the intense radiation bombardment of the surface produces a gas exosphere of sputtered molecules and volatile composition products. Only a couple of species in the exosphere have been identified: O_2 from water/ice, Na and K from decomposition of hydrated minerals, and likely, H_2O, SO_2 and CO_2. A detailed study of the Na/K ratio in Europa's exosphere will give a better understanding about the fractionation on freezing and up welling of subsurface ocean material. It is suggested that this exosphere must contain many other molecular species, which should be detectable, by a future space probe. This presents an exciting possibility of identifying surface constituents by detecting gas-phase products. Since the surface sputtering yields by heavy energetic ions like O or S are of order unity, we study if even heavy organic molecules imbedded in ice of Europa's surface can be ejected into the gas-phase and detected with a spacecraft orbiting Europa.