Solar Wind Access to Grains in the Upper Layer of Regolith

Abstract

AbstractThe surface of the Moon is exposed to the solar wind and the particles can reach a few average grains deep into the regolith. This work examines the depth of penetration of solar wind particles in lunar regolith using equations derived from analytical, Monte Carlo, and ray tracing techniques and discrete element method simulations. It is shown that the process can be approximately described using an exponential distribution function starting from some small depth with parameters depending on void ratio, solar wind incidence angle, and regolith grain size distribution. The proton implantation rate into the regolith as a function of depth is proposed with the coefficients computationally derived from Monte Carlo simulations of proton implantation process.