A laboratory study of water ice erosion by low-energy ions

Water ice covers the surface of various objects in the outer Solar system. Within the heliopause, surface ice is constantly bombarded and sputtered by energetic particles from the solar wind and magnetospheres. We report a laboratory investigation of the sputtering yield of water ice when irradiated at 10 K by 4 keV singly (C-13(+), N+, O+, Ar+) and doubly charged ions (C-13(2+), N2+, O2+). The experimental values for the sputtering yields are in good agreement with the prediction of a theoretical model. There is no significant difference in the yield for singly and doubly charged ions. Using these yields, we estimate the rate of water ice erosion in the outer Solar system objects due to solar wind sputtering. Temperature-programmed desorption of the ice after irradiation with C-13(+) and C-13(2+) demonstrated the formation of (CO)-C-13 and (CO2)-C-13, with (CO)-C-13 being the dominant formed species.