Simulation of micrometeorite bombardment and its implications for regolith evolution in a Hermean context

Abstract

Surficial regolith layers of atmosphere-free planetary surfaces are altered by a multitude of processes summarized as space weathering. Minerals comprising such altered surfaces can differ significantly (in terms of structure and resulting alteration products) from their terrestrial laboratory counterparts. These changes, when altered vs. unaltered materials are compared, can also be observed in the associated optical spectra (e.g., darkening and reddening in the near infrared range, and shifts, attenuation and broadening of characteristic bands in the mid infrared range). Understanding these changes is essential for interpreting optical remote sensing data. In order to better understand the damage imparted by micrometeorite bombardment into a planetary surface, we investigated the effects of vacuum ablation on powdered analog material with a ns-pulsed infrared laser and analyzed the run products with a Zeiss Libra transmission electron (TEM) microscope. We comminuted a single crystal of pure synthetic forsterite and pressed the powder (≤ 280 µm) into a pellet and irradiated it with the laser. The run products, e.g., ballistically relocated grains and melt sprinkles, were caught on TEM grids, which were positioned near the impact sites. Here, we report our findings on nanometer-sized modifications that were induced in the relocated grains, sputtered off plasma material and melt sprinkles that condensed on the TEM grid and discuss the implications of our results in the light of the Hermean surface.