Earth Wind as a Possible Exogenous Source of Lunar Surface Hydration

Understanding the sources of lunar water is crucial for studying the history of lunar evolution, as well as the interaction of solar wind with the Moon and other airless bodies. Recent orbital spectral observations revealed that the solar wind is a significant exogenous driver of lunar surficial hydration. However, the solar wind is shielded over a period of 3–5 days per month as the Moon passes through the Earth's magnetosphere, during which a significant loss of hydration is expected. Here we report the temporal and spatial distribution of polar surficial OH/H2O abundance, using Chandrayaan-1 Moon Mineralogy Mapper (M3) data, which covers the regions inside/outside the Earth's magnetosphere. The data shows that polar surficial OH/H2O abundance increases with latitude, and that the probability of polar surficial OH/H2O abundance remains at the same level when in the solar wind and in the magnetosphere by controlling latitude, composition, and lunar local time. This indicates that the OH/H2O abundance in the polar regions may be saturated, or supplemented from other possible sources, such as Earth wind (particles from the magnetosphere, distinct from the solar wind), which may compensate for thermal diffusion losses while the Moon lies within the Earth's magnetosphere. This work provides some clues for studies of planet–moon systems, whereby the planetary wind serves as a bridge connecting the planet with its moons.