Nanoscale reservoirs store solar wind-derived water on the lunar surface

Abstract

• Solar wind hydrogen and water measured in lunar grains via novel coordinated analyses. • Solar wind hydrogen and water are retained in space weathered rims of lunar grains. • Hydrogen and water are stored in higher concentrations in nanoscale vesicles. • We propose a mechanism to form molecular water within defects in space weathered rims. • Variability of water in rims may influence the behavior of water on the lunar surface. Observations of widespread hydration across the lunar surface could be attributed to water formed via the implantation of solar wind hydrogen ions into minerals at the surface. Solar wind irradiation produces a defect-rich outer rim in lunar regolith grains which can trap implanted hydrogen to form and store water. However, the ability of hydrogen and water to be retained in space weathered regolith at the lunar surface is not well-understood. Here, we present results of novel and coordinated high-resolution analyses using transmission electron microscopy and atom probe tomography to measure hydrogen and water within space weathered lunar grains. We find that hydrogen and water are present in the solar wind-damaged rims of lunar grains and that these species are stored in higher concentrations in the vesicles that are formed by solar wind irradiation. These vesicles may serve as reservoirs that store water over diurnal and possibly geologic timescales. Solar wind-derived water trapped in space weathered rims is likely a major contributor to observations of the widespread presence, variability, and behavior of the water across the lunar surface.

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