Poppe, Andrew - LADEE/LDEX Observations of Pick-up Ion Variability in the Lunar Exosphere

The lunar neutral exosphere is generated by a variety of sources, including thermal and photon-stimulated desorption, micrometeoroid impact vaporization, and charged particle sputtering. The relative importance of each of these production mechanisms should vary by species, location, and external conditions; however, definitive measurements have only been made for some production mechanisms for specific species. The Lunar Dust EXperiment onboard the LADEE mission was designed to investigate the micron and sub-micron sized dust environment around the Moon. Additionally, the instrument has also recorded extensive signatures of the total pick-up ion current around the Moon, originating from photo-ionization and charge exchange ionization of the lunar neutral exosphere. We have compared these measurements to a model of lunar pick-up ion fluxes from the exosphere that includes the presence of neutral species generated by thermal desorption, photon-stimulated desorption, sputtering, and impact vaporization. We present trends identified in the data and discuss implications for our understanding of the lunar exosphere as well as exospheres around other airless bodies throughout the solar system.