Evidence of water on the lunar surface from Chang'E-5 in-situ spectra and returned samples.

The distribution range, time-varying characteristics, and sources of lunar water are still controversial. Here we show the Chang'E-5 in-situ spectral observations of lunar water under Earth's magnetosphere shielding and relatively high temperatures. Our results show the hydroxyl contents of lunar soils in Chang'E-5 landing site are with a mean value of 28.5 ppm, which is on the weak end of lunar hydration features. This is consistent with the predictions from remote sensing and ground-based telescopic data. Laboratory analysis of the Chang'E-5 returned samples also provide critical clues to the possible sources of these hydroxyl contents. Much less agglutinate glass contents suggest a weak contribution of solar wind implantation. Besides, the apatite present in the samples can provide hydroxyl contents in the range of 0 to 179 ± 13 ppm, which shows compelling evidence that, the hydroxyl-containing apatite may be an important source for the excess hydroxyl observed at this young mare region.