Chang'e rock samples rewrite lunar history

Chinese scientists found that lunar volcanism was happening 800 to 900 million years later than believed after samples brought back by the Chang'e 5 mission suggested the Moon cooled down more slowly than previously thought.

The results of the analyses, conducted by researchers from Institute of Geology and Geophysics, a subsidiary of Chinese Academy of Sciences, are presented in three papers published by British scientific journal Nature on Tuesday.

Studies of the lunar basalt, a type of rock formed by volcanic eruptions, also provided new data on the composition and water content of the Moon, offering new insights into its thermal evolution.

Li Xianhua, academician in geochemistry at the Institute of Geology and Geophysics, said previous radioisotope dating of lunar samples brought back by US Apollo and Soviet Union Luna missions more than 40 years ago suggested that most volcanic activity ceased around 2.9 or 2.8 billion years ago.

The samples returned by Chang'e 5 in December last year were from the Oceanus Procellarum, a mid-latitude region and believed to be one of the youngest basalt sites on the Moon.

After studying the rock's isotopes, Li and his colleagues confirmed that the Chang'e 5 basalts came from an eruption that occurred roughly 2.030 billion (±0.004 billion) years ago, advancing the end of lunar volcanic activity by 800 to 900 million years.

Researchers in another study also discovered that the high content of heat-producing elements in the samples did not originate in the Moon's mantle, where lava would ordinarily have been formed. Yang Wei, a researcher at the institute, said this indicates that scientists need to explore new thermal models to explain why lunar volcanic activity continued for so long.

A third paper discussed the water content of the samples. Analysis showed that 2 billion years ago, the deep lunar mantle of the sampling area was much drier than samples taken from regions subject to older instances of volcanism.

"The results raise new questions about the study of the thermal evolution of the Moon. It is still unclear why the Moon cooled down so slowly, and a new theoretical framework and evolutionary model is needed to provide new directions for future lunar exploration and research," Li said.