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. Laboratory analysis of returned Chang'E-5 samples from the lunar surface show their hydroxyl contents to be on the weak end of lunar hydration features.

Automated summary

The distribution, characteristics, and sources of lunar water are still controversial. In this study, the Chang'E-5 mission conducted in-situ spectral observations and laboratory analysis of returned samples to investigate the hydroxyl contents in lunar soils. The results show that the hydroxyl contents in the Chang'E-5 landing site are relatively weak, consistent with predictions from remote sensing and ground-based telescopic data. The study also suggests that apatite may be an important source of excess hydroxyl observed in young mare regions.