Mercury’s Exosphere: Sputter Yields and Ion Flux

We present results from a comprehensive model of Mercury’s exosphere, constrained by detailed information on surface composition, source processes, and ion influx to the magnetospheric cusp regions. Our previous model (Burger et al. 2010), has been updated with surface composition maps from MESSENGER (Weider et al., 2015); ion influx onto the cusp regions from MESSEGER’s Fast Imaging Plasma Spectrometer (FIPS) instrument (Raines et al., 2014), and updated information on micrometeoritic influx. We will determine the sputter source rate for sodium using the measured ion precipitation data from FIPS along with sputter yields calculated by both SDTrim.SP and Molecular Dynamics codes. We have parsed the FIPS data to employ not only the proton influx but to use the angle of incidence of the protons, giving accurate sputter yields. The FIPS data also give us the cusp area for an average over MESSENGER orbits 2820-2845 and incident ion flux with energy per charge from 0.046 to 13.3 keV for protons.

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