Distribution and Abundance of Solar Wind-Derived Water in Chang'E-5 Core Samples and Its Implications

Knowledge regarding the abundance and distribution of solar wind (SW)-sourced water (OH/H2O) on the Moon in the shallow subsurface remains limited. Here, we report the NanoSIMS measurements of H abundances and D/H ratios on soil grains from three deepest sections of the Chang'E-5 drill core sampled at depths of 0.45-0.8 m. High water contents of 0.13-1.3 wt.% are present on approximately half of the grain surfaces (topmost similar to 100 nm), comparable to the values of Chang'E-5 scooped soils. The extremely low delta D values (as low as -995 parts per thousand) and negative correlations between delta D and water contents indicate that SW implantation is an important source of water beneath the lunar surface. The results are indicative of homogeneous distribution of SW-derived water in the vertical direction, providing compelling evidence for the well-mixed nature of the lunar regolith. Moreover, the findings demonstrate that the shallow subsurface regolith of the Moon contains a considerable amount of water.