Remote sensing data showed that water (OH/H2O) on the moon depends on latitude and likely varies from time to time. It suggests that a solar wind produced water with a high outgassing loss on the lunar surface.

However, it is still being determined whether or not the solar wind-derived water in the lunar soil grains can be stored below the surface. The abundance, distribution, and origin of surface water on the Moon has attracted much interest recently due to its critical importance to upcoming space exploration.

The Chang’e-5 lunar soil grain margins have high hydrogen concentrations and low deuterium/hydrogen (D/H) ratios, which are consistent with lunar water coming from the solar wind, according to a joint research team from the National Space Science Center (NSSC) and the Institute of Geology and Geophysics (IGG), both associated with the Chinese Academy of Sciences (CAS).

The researchers simulated the retention of hydrogen in lunar soils at different temperatures. They found that the lunar surface’s middle and high latitudes could effectively trap water emanating from the solar wind.

prof. IGG’s LIN Yangting, the study’s corresponding author, said: “The polar lunar soils may hold more water than Chang’e-5 samples.”

The Chang’e-5 mission returned soil samples from a mid-latitude (43.06° N) site, unlike the six Apollo and three Luna missions, which all landed at low latitudes (8.97° N). S – 26.13°N). . The Chang’e-5 samples were also taken from the driest basalt basement and the youngest known lunar basalt (2.0 Ga). To address the spatio-temporal distribution and retention of SW-derived water in the lunar regolith, Chang’e-5 samples are essential.

The researchers performed deuterium/hydrogen ratio calculations and NanoSIMS depth profiling measurements on 17 lunar soil grains recovered by the Chang’e-5 mission.

Most of the grain edges (upper 100 nm) had exceptionally low D values ​​(-908 to -992) and high hydrogen concentrations (1,116–2,516 ppm), suggesting a SW origin according to the results. The bulk SW-derived water content for the Chang’e-5 lunar soils was estimated to be 46 ppm, which is similar to the remote sensing result based on the grain size distribution of the lunar soils and their hydrogen content.

Heating tests on some of the grains showed that the hydrogen absorbed by the SW could be retained after burial. The researchers created a model of the dynamic equilibrium between the implantation and outgassing of SW hydrogen in lunar soil grains using this data and previous studies, demonstrating that temperature (latitude) is a critical factor in the implantation and migration of hydrogen in lunar soils .

prof. LIN said: “Using this model, they predicted an even greater amount of hydrogen in the grain margins in the polar regions of the moon. This discovery has great significance for the future use of water resources on the moon. By sorting and heating particles, it is also relatively easy to exploit and use the water in the lunar soil.”

Magazine reference:

  1. Yuchen Xu et al. High abundance of water from the solar wind in mid-latitude lunar soils. PNAS. DOI: 10.1073/pnas.2214395119