Energetic neutral atom occultation: New remote sensing technique to study the lunar exosphere

摘要

We propose a new technique to investigate the lunar exosphere by measuring energetic neutral atoms (ENAs). The lunar exosphere is a typical exosphere of celestial bodies without a dense atmosphere and without a global magnetosphere, but our knowledge of it is incomplete because of a very limited number of observations. In this paper, we present a feasibility study for detecting the charge exchange solar wind ENAs in the vicinity of the Moon by developing a numerical model that simulates the interaction between the solar wind and the lunar exosphere. The calculated ENA flux reaches 107 cm?2 s?1, which corresponds to ～3% of the solar wind flux. The flux is high enough to be measured by existing ENA sensors. We also conducted many runs with different exospheric parameters. The charge exchange ENA flux is then found to depend both on the positions of the satellite and on the exosphere parameters. This result indicates that inversion techniques can in principle be applied in the future to reconstruct the exosphere profile from the obtained ENA flux data.