Abstract The speciation, inventory, and dynamic changes of water (OH/H 2 O) on the lunar surface remain poorly constrained. The Chang’e-6 (CE-6) mission conducted in situ spectroscopic measurements of lunar water over time intervals shorter than one lunar local hour (10:00–11:00 a.m.). By integrating spectral analysis with quantitative water content estimation, we provide compelling evidence for two distinct water reservoirs: adsorbed molecular water (H 2 O) on the surfaces of soil grains, and hydroxyl (OH) groups incorporated within the crystal lattices of minerals. The in situ observations further document the gradual loss of water molecules (up to 48 ppm) until near exhaustion over an hourly time scale on the lunar surface. For the first time, we calculated the apparent desorption activation energy ( E d = 1.23–1.26 eV) of water molecules based on in situ measurements, which is consistent with observations from the Lyman Alpha Mapping Project spectrometer and results from laboratory experiments. These water molecules are inferred to originate from solar wind proton (H + ) implantation, forming via recombinative desorption of chemically bound OH in lunar minerals and glasses. This study constitutes a significant advance toward elucidating lunar water dynamics and provides critical parameters for modeling the lunar water cycle.
Chi et al. (Tue,) studied this question.