Solar Wind Sputtering of Secondary Ions from Water-ice-covered Regolith Analogs

The surfaces of airless bodies in space are constantly bombarded by solar wind and magnetospheric ions that sputter regolith grains and eject secondary particles into the exosphere. Refractory elements, water, and other volatile species can potentially be detected using secondary ion mass spectrometry (SIMS). This manuscript characterizes the sputtered secondary ions produced by solar wind energy ions from (i) silica, (ii) iron oxide, and (iii) pyrite. The samples were exposed to 5 keV H 2 + primary ions, and SIMS spectra were collected (i) from bare samples at room temperature, (ii) after cooling to 100 K and depositing ∼20–50 monolayers of D 2 O, and (iii) after rewarming to room temperature. Sputtering the bare samples produced abundant refractory ions that were representative of the measured sample compositions but whose relative intensities differed from the bulk. Depositing water completely obscured the mineral substrates, and the observed intensity of water-group ions passed through a maximum as the substrate was exposed. This behavior was observed for all three samples and can be understood by changes in the surface structure or morphology for thin (<10 monolayers) ice coverages. Additionally, the deposited D 2 O was seen to chemically react with the substrate surfaces, and deuterated molecular ions were seen in several of the postdeposition room-temperature spectra. Future work will determine the total secondary ion yields for water in contact with various regolith materials and their dependence on the underlying substrate composition, temperature, and incident ion type and energy.