Lunar water cycle and D/H fractionation driven by solar wind implantation and micrometeorite impacts

The mechanisms governing the lunar water cycle and hydrogen isotope (D/H) fractionation driven by solar wind implantation and micrometeorite impacts remain poorly understood. Here, using synergistic simulation experiments, we show that micrometeorite impacts not only enhance the formation of solar wind-derived water through impact-induced mineral damage, but also enable the formed solar wind-derived water to be partially retained within the impact melt. Micrometeorite impacts also induce significant hydrogen isotope fractionation, resulting in the preferential retention of isotopically lighter water within the melt, while leaving the residual water isotopically heavier in the region surrounding the impact area due to thermally driven escape. We estimate that H₂O released from minerals can migrate across the surface and ultimately contribute 4.34 × 10 9 – 2.39 × 10 10 kg of water ice to the polar regions within 10 5 years. This study elucidates the solar wind and micrometeorites impact-driven water cycle and D/H fractionation on the Moon – processes that might also occur on other airless bodies such as Mercury and asteroids, and provides crucial insights into the origin of water in the terrestrial planets.