LUNAR-SURFACE COMPOSITION AND SOLAR WIND-INDUCED SECONDARY ION MASS-SPECTROMETRY

The Moon has no strong global magnetic field and only a tenuous atmosphere, so solar wind ions (approximately 95% H+, 5% He++) directly bombard the lunar surface, sputtering atoms and secondary ions from the exposed grains of the regolith. The secondary ions potentially provide surface composition information through secondary ion mass spectrometry (SIMS), a standard laboratory surface composition analysis technique. In this paper we report the results of laboratory SIMS experiments on lunar soil simulants using solar wind-like ions. We find that H+ and He++, while not efficient sputterers, nevertheless produce significant fluxes of secondary lunar ions, including Na+, Mg+, Al+, Si+, K+, Ca+, Ti+, Mn+ and Fe+. We predict that lunar surface secondary-ion fluxes range between approximately 10 and 10(4) ions cm-2 s-1, depending on the species.