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 (H₂O) have been reported to be scarce on the Moon. We propose a potential method for obtaining water on the Moon through H₂O formation via endogenous reactions in lunar regolith (LR), specifically through the reaction FeO/Fe₂O₃ + H → Fe + H₂O. This process is demonstrated using LR samples brought back by the Chang'E-5 mission. FeO and Fe₂O₃ 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 H₂O 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 H₂O on the Moon. Among the five primary minerals in LR returned by the Chang'E-5 mission, FeTiO₃ ilmenite contains the highest amount of H, owing to its unique lattice structure with sub-nanometer tunnels. For the first time, in situ heating experiments using a transmission electron microscope reveal the concurrent formation of Fe crystals and H₂O 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 H₂O on the Moon, which is helpful for establishing a scientific research station on the Moon.