High-speed hydrogen ions injected from the solar surface into the lunar surface and enhanced on the surface of lunar soil particles are shown in a schematic representation. Credit: Prof. Lin Yangting's group
Due to its crucial role in future space exploration, a lot of attention has been paid to the quantity, distribution, and origin of lunar surface water.
The grain rims of the soil samples collected by the Chang'e-5 mission have high hydrogen and a low hydrogen ratio, consistent with the assumption that lunar water originates from the solar wind.
The findings have been published in the National Academy of Sciences' Proceedings.
Researchers performed simulations to assess hydrogen preservation in lunar soils at different temperatures. They found that SW-originated water might be readily preserved in the middle and high-latitude areas of the lunar surface, according to Professor Lin Yangting of IGG, the corresponding author of the study.
Previous investigations have demonstrated that water (OH/H2O) on the lunar surface changes with latitude and day (up to 200 ppm) and implies a rapid desorption rate from the lunar surface.
The Chang'e-5 mission collected soil samples from the youngest known lunar basalts (2.0 Ga) and the most driest basaltic basement. Therefore, Chang'e-5 samples are crucial to studying the spatial-temporal distribution and retention of SW-derived water in the lunar regolith.
Researchers used NanoSIMS depth-profiling measurements to determine hydrogen abundance and calculated deuterium/hydrogen ratios on 17 lunar soil grains returned by the Chang'e-5 mission.
Results demonstrated that the majority of grain rims (topmost 100 nm) had extremely high hydrogen concentrations (1,116—2,516 ppm) with extremely low D values (908 to-992), suggesting that the Chang'e-5 lunar soils contain water that is SW-derived.
Researchers used this knowledge to develop a model of the dynamic equilibrium between the implantation and outgassing of SW-hydrogen in lunar soil grains. Temperature (latitude) plays a crucial role in the implantation and migration of hydrogen in lunar soils.
Professor Lin believes that hydrogen would be found even greater in the lunar polar regions thanks to particle sorting and heating.
Yuchen Xu, Heng-Ci Tian, Chi Zhang, Marc Chaussidon, Jialong Hao, Ruiying Li, Lixin Gu, Wei Yang, Liying Huang, Jun Du, Yazhou Yang, Yang Liu, Huaiyu He, Yongliao Zou, Fuyuan Wu, and Yuchen Xu, 12 December 2022, Proceedings of the National Academy of Sciences. DOI: 10.1073/pnas.2214395119