Formation of lunar surface water associated with high-energy electrons in Earth’s magnetotail

Solar wind implantation is thought to be one of the primary mechanisms in the formation of water (OH/H 2 O) on the surface of the Moon and possibly on the surface of other airless bodies. The lunar nearside spends ~27% of its daytime in Earth’s magnetotail where the solar wind flux is reduced by as much as ~99%. However, no correlated decrease in surficial water content has yet been seen on the lunar nearside. Here we report abundance observations of lunar surficial water on the nearside at different stages during the Moon’s passage through Earth’s magnetotail. We find that the water abundance at lunar mid-latitudes substantially increases in the dusk and dawn magnetosheath when the solar wind flux increases, yet remains nearly constant across the central magnetotail. We suggest that although we have confirmed the importance of the solar wind as a major source of fast water production on the Moon, hitherto unobserved properties of the plasma sheet properties may also play an important role.