Analyses of samples from the Apollo missions suggest that the Moon formed devoid of native water. However, recent observations by Cassini, Deep Impact, Lunar Prospector and Chandrayaan-1 indicate the existence of an active water cycle on the Moon. Here we report observations of this water cycle, specifically detections of near-surface water released into the lunar exosphere by the Neutral Mass Spectrometer on the Lunar Atmosphere and Dust Environment Explorer. The timing of 29 water releases is associated with the Moon encountering known meteoroid streams. The intensities of these releases reflect the convoluted effects of the flux, velocity and impact location of the parent streams. We propose that four additional detected water releases represent the signature of previously undiscovered meteoroid streams. We show that water release from meteoroid impacts is indicative of a lunar surface that has a desiccated soil layer of several centimetres on top of uniformly hydrated soil. We infer that the Moon is currently in the process of losing water that was either delivered long ago or present at its formation.
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The NMS data supporting this Article are publicly available from the Planetary Data System (http://pds-atmospheres.nmsu.edu/data_and_services/atmospheres_data/LADEE/nms.html).
The Matlab scripts used for the analyses and modelling described in this study can be obtained from the corresponding author on reasonable request.
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The LADEE/NMS investigation was supported by NASA. Tests and calibrations were completed at the Planetary Environment Laboratory of NASA’s Goddard Space Flight Center. We thank R. R. Vondrak, W. M. Farrell, R. M. Killen and T. H. Morgan for insightful discussions and comments. We also thank E. Raaen for his calibration support, E. Zubritsky for editing and J. Friedlander for graphics assistance.
The authors declare no competing interests.
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Benna, M., Hurley, D.M., Stubbs, T.J. et al. Lunar soil hydration constrained by exospheric water liberated by meteoroid impacts. Nat. Geosci. 12, 333–338 (2019). https://doi.org/10.1038/s41561-019-0345-3
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