Lunar soil samples collected by the Chinese lunar probe Chang'e-5 are presented to the media at the University of Hong Kong on Aug 7, 2023. (CALVIN NG / CHINA DAILY)

BEIJING - Global experts have measured the maturity index of the lunar soil brought back by the Chang'e 5 mission by magnetic techniques for the first time after the return of samples, shedding light on the space weathering processes occurring on the Moon's surface.

The lunar soil maturity is an index to characterize the space weathering degree of the soil. It is quantified by a variety of indices such as mean grain size, agglutinate abundance and solar wind gases abundances.

Researchers used magnetic techniques to measure the maturity index of Chang'e 5 lunar soil and found that its Is/FeO value is between 4 and 20, one of the lowest Is/FeO values obtained so far, indicating that it is among the most immature soils on the Moon

Studying the maturity index can reveal the interaction between micrometeorites, solar wind and lunar surface, and reflect the geological process of lunar soil formation.

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The value of Is/FeO (the intensity of the characteristic ferromagnetic resonance normalized to total iron content) is regarded as the only golden standard of lunar soil maturity, according to the research paper published in the journal Icarus.

Researchers from the China University of Geosciences, Wuhan, Brown University and the University of Hawaii used magnetic techniques to measure the maturity index of Chang'e 5 lunar soil and found that its Is/FeO value is between 4 and 20, one of the lowest Is/FeO values obtained so far, indicating that it is among the most immature soils on the Moon.

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"This indicates that the lunar soil in the sampling area of the Chang'e 5 mission was exposed to the space environment for the shortest time after formation," said Xiao Long, a professor at the China University of Geosciences, Wuhan.

According to him, based on current studies of Chang'e 5 samples, its landing and sampling unit is much younger than all Apollo and Luna units, which may be the reason why the Chang'e 5 lunar soil is the most immature.

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The Chang'e 5 probe returned to Earth on Dec 17, 2020, retrieving a total of 1,731 grams of lunar samples, mainly rocks and soil from the Moon's surface.