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Chinese scientists have discovered that lunar volcanism was occurring about 800 million to 900 million years later than previously thought, after analysing lunar samples returned by the Chang’e 5 missie, suggesting the moon cooled down much more slowly.
Researchers at the Chinese Academy of Sciences’ Institute of Geology and Geophysics presented their results in three papers published in Nature on 19 Oktober.
Their analysis of basalt, a type of rock formed during volcanic eruptions, not only indicated that the lunar samples were the youngest to be dated, but also provided new data on the composition and water content of the moon’s interior, offering new insights on the moon’s thermal evolution.
The Chang’e 5 lunar mission returned with 61 ounces of lunar samples on 17 December last year, meer as 40 years after the US Apollo and Soviet Union Luna missions retrieved their samples. The samples were then distributed to 13 research institutes on 12 Julie, with the research team at the Institute of Geology and Geophysics receiving about 0.18 ounce.
Volcanism is a sign that a celestial body is still dynamic, and studying planetary volcanism can reveal a planet’s deep composition and thermal evolution. Lunar volcanism was most active on the near side of the moon, covering about 17 per cent of the lunar surface.
Geochemist Li Xianhua, an academician at the Institute of Geology and Geophysics, said scientists have always been interested in figuring out exactly when lunar volcanism started and ended, as well as the mechanism of formation of the most recent volcanism.
Previous radioisotope dating of lunar samples brought back by the Apollo and Luna missions suggested that most lunar volcanic activities ceased by about 2.9 billion or 2.8 billion years ago. Those samples were collected within 30 degrees of the moon’s equator and could not represent the large lunar surface.
Chang’e 5 landed in the Oceanus Procellarum region, far from the Apollo and Luna sampling sites and believed to be one of the youngest mare basalt sites on the moon. Scientists had used crater-counting chronology, another dating method based on the number of craters, to predict that it might have seen lava flows between three billion and one billion years ago.
“But three to one billion years is a very long gap with many uncertainties, and because of the lack of young samples, the age and formation mechanism could not be determined,” Li said.
After studying the isotopes of the rocks, Li and his colleagues confirmed that the Chang’e 5 basalt came from the same eruption lava, which occurred about two billion years ago, delaying the end of the moon’s volcanic activity by 800 million to 900 million years. Their finding also helps create a benchmark to better calibrate crater-counting chronology models.
Yin Qingzhu, a cosmochemistry professor at the University of California, Davis, called the findings a “major achievement” that has been long awaited worldwide. “How the moon was able to maintain magmatic activity to two billion years ago under these very unfavourable conditions will be a new research topic in the future. It will lead to the next extensive discussion and in-depth research in the global planetary science community.”
Previously published on Chinadaily.com.cn