Primary Origin of Lunar Surface Water: Constraints from Observations of Chang'e-5

Water plays a crucial role in the Moon's evolution and holds significant implications for potential human activities on its surface. Previous studies, based on measurements of a limited number of lunar soil particles, have revealed evidence supporting various sources of lunar water, including its origin from the lunar interior, solar wind implantation, and impacts from comets or asteroids. Nevertheless, the limitation of these studies stems from the restricted number of particle samples, hindering the achievement of adequate statistical significance. As a result, the primary source of water on the Moon remains enigmatic. To address this critical question and advance our understanding of lunar water sources, we initiated new spectral measurements using lunar bulk soil collected by Chang'e-5 under controlled conditions. We observed variations in water content across different particle sizes. Our findings suggest that solar/ Earth wind implantation is likely the primary source of lunar surface water. The controlled experiments conducted on the lunar bulk soil samples provide valuable insights, offering statistical evidence for the origin of water in lunar soil. We also bridged the laboratory, in-situ, and orbital results, offering a cohesive understanding of lunar surface water characteristics as represented by Chang'e-5.