Chinese scholars have made progress in the latitude of the lunar surface and the formation of solar wind water

Fig.
1 Hydrogen content depth profile of Chang'e-5 lunar soil particles and their space regolith layer thickness

Fig.
2 Numerical simulation
of hydrogen content depth profile in silicate glass and minerals.
(A, B) the process of diffusion loss of hydrogen after burial; (C, D) Dynamic processes of solar wind hydrogen injection and heating diffusion loss

With the support of the National Natural Science Foundation of China (grant numbers: 41973064, 42103035, 42230206), Xu Yuchen, associate researcher of the National Space Science Center of the Chinese Academy of Sciences, and researcher Lin Yangting, associate researcher of the Institute of Geology and Geophysics, Chinese Academy of Sciences, have made progress
in the formation of solar wind in latitudes and latitudes on the lunar surface 。 The research results, titled "Chang'e-5 lunar soil reveals high abundance of solar wind-derived water in lunar soils from the middle latitude", were published in the Proceedings of the National Academy of Sciences on December 13, 2022 Sciences
).
Link to the paper: _istranslated="1">.

Through the study of remote sensing spectroscopy, it was found that the content of OH/_H2Oon the lunar surface may have a positive correlation with latitude, that is, from the equator to the poles, the water content gradually increases with the increase of latitude, reaching the highest in the
polar region.
In addition, the study also found that the water content in the same area of the lunar surface also changed significantly, with daily variations of up to 200 ppm, presumably due to
the higher rate of water loss on the lunar surface caused by the solar wind.
Lunar samples collected by the American Apollo and Soviet lunar spacecraft are located in the low latitude region (8.
9°S-26.
1°N), making it difficult to study the possible effects
of latitude (and the associated lunar surface temperature) on lunar surface water content.
China's Chang'e-5 successfully landed on the moon at the end of 2020 and collected and returned 1.
731 kg of lunar soil samples
.
The landing site of Chang'e-5 is located at 43.
06° north latitude, which is higher than the 9 landing zones
of Apollo and Luna.
In addition, the basalt in the Chang'e-5 landing area is the youngest, about 2 billion years old
.
Such young, mid-latitude lunar soil samples give us the opportunity to study
the evolution of the solar wind, the lunar surface water cycle and transport.

The research team used nano-ion probe-transmission electron microscopy analysis to analyze the hydrogen content and isotope and microstructure of 17 particles selected from two parts of lunar soil
.
The results show that the very top layer of the Chang'e-5 lunar soil grain (~100 nm) has a high hydrogen content (meaning it has a high water content) (Figure 1), which is higher
than previously thought.
Combined with its extremely low D/H isotope ratio, it proves that the hydrogen was injected
by the solar wind.
Based on the measured hydrogen content and the particle size distribution of lunar soil samples, the solar wind source water content in the Chang'e-5 landing area was estimated to be 46 ppm, which was consistent
with the results of remote sensing data.
In addition, the researchers performed heating experiments on some of the particles, and then performed nanoion probe analysis
.
The results showed that the hydrogen injected by the solar wind was well preserved on the surface of the particles
.
Based on the Chang'e-5 data and the existing experimental data of Apollo, the joint team constructed a dynamic equilibrium model of solar wind injection and diffusion loss (Figure 2).

The model predicts that lunar soil particles at high latitudes may contain higher solar wind-induced water, which can be easily extracted and utilized
by particle size sorting and heating.