Massive water production from lunar ilmenite through reaction with endogenous hydrogen

Finding water resources is a crucial objective of lunar missions. However, both hydroxyl (OH) and natural water (HO) have been reported to be scarce on the Moon. We propose a potential method for obtaining water on the Moon through HO formation via endogenous reactions in lunar regolith (LR), specifically through the reaction FeO/FeO + H → Fe + HO. This process is demonstrated using LR samples brought back by the Chang’E-5 mission. FeO and FeO are lunar minerals containing Fe oxides. Hydrogen (H) retained in lunar minerals from the solar wind can be used to produce water. The results of this study reveal that 51–76 mg of HO can be generated from 1 g of LR after melting at temperatures above 1,200 K. This amount is ∼10,000 times the naturally occurring OH and HO on the Moon. Among the five primary minerals in LR returned by the Chang’E-5 mission, FeTiO ilmenite contains the highest amount of H, owing to its unique lattice structure with sub-nanometer tunnels. For the first time, heating experiments using a transmission electron microscope reveal the concurrent formation of Fe crystals and HO bubbles. Electron irradiation promotes the endogenous redox reaction, which is helpful for understanding the distribution of OH on the Moon. Our findings suggest that the hydrogen retained in LR is a significant resource for obtaining HO on the Moon, which is helpful for establishing a scientific research station on the Moon.