High energy electron irradiation promotes the space weathering process on the nearside of the Moon

Abstract

Space weathering occurs extensively on the surfaces of airless bodies, altering the optical properties of surface materials. Micrometeorite impacts and solar wind ion implantation are considered as two key driving mechanisms of space weathering on the lunar surface, leading to spectral reddening (an increase in spectral slope) and darkening (a reduction in overall reflectance). Their effects have been extensively studied, whereas the role of electron irradiation and its fundamental mechanisms remain less understood. This issue is particularly relevant when the Moon is within Earth’s magnetotail plasma sheet, where the flux of high-energy electron is significantly elevated. Therefore, here we investigate the space weathering effects induced by electron irradiation via simulated experiments. Our results demonstrate that electron irradiation induces significant reddening and darkening in the reflectance spectra of olivine and pyroxene. More importantly, these spectral changes are reduced after thermal annealing. Such spectral alterations are attributed to the formation of color centers during electron irradiation, which is fundamentally different from the production of nanophase iron induced by the bombardments of micrometeorites and solar wind. This provides a potential explanation for the differences in space weathering processes on the near and far sides of the Moon.