This is a schematic diagram of magma and thermal evolution in different periods of the moon (drawn on October 20, 2022). Xinhua News Agency ( Photo provided by , Institute of Geology and Geophysics, Chinese Academy of Sciences)
Chinese scientists have proposed a new lunar thermal evolution model based on the study of Chang'e-5 lunar soil, revealing a major mystery that plagues the academic community: why the moon still has volcanic activity 2 billion years ago.
Chen Yi, a researcher at the Institute of Geology and Geophysics, Chinese Academy of Sciences, introduced that the moon was formed about 4.5 billion years ago, with a mass of only about 1% of the earth. For such a small celestial body, should theoretically cool down quickly, stop volcanic activities very early, and become a "death" planet.
The return of Chang'e-5 lunar soil samples has triggered a new round of lunar research. In October 2021, Chinese scientists published three articles in the journal Nature, revealing that lunar volcanic activity can last until 2 billion years ago, refreshing human cognition of lunar magma activity and thermal evolution history.
Experts introduced that lunar basalt is a rock formed by partially melting the lunar mantle (equivalent to the earth's mantle) and formed by cooling and crystallization by volcanoes erupting to the surface of the moon. International scholars have proposed two hypotheses about partial melting of lunar mantle that is continuously cooled: one is that radioactive element generates heat to cause the lunar mantle to heat up; the other hypothesis is that if the water content is high, it will reduce the melting point of the lunar mantle.
However, Chinese scientists' research on Chang'e-5 basalt revealed that the lunar mantle source region is not rich in radioactive heat generation elements and is very "dry", which excludes the above two hypotheses. Therefore, why lunar volcanic activities have lasted for so long has become an unsolved mystery in the new round of lunar research.
期0期平台方3期 and electronic probe laboratory engineer at the Institute of Geology and Geophysics, Chinese Academy of Sciences is analyzing the composition of Chang'e-5 lunar soil (photo taken on October 14, 2022). Xinhua News Agency (Photo provided by the Institute of Geology and Geophysics, Chinese Academy of Sciences)
In response to this problem, Chen Yi led a scientific research team to select 27 representative Chang'e-5 basalt cuttings, and used the latest developed scanning electron microscopy quantitative scanning technology to analyze the main components of the whole rock of the rock. Combined with a series of petrology and thermodynamics simulation calculations, the initial magma composition of Chang'e-5 basalt was successfully restored, and compared it with the initial magma of the Apollo sample to calculate their origin depth and temperature.
study found that compared with Apollo samples, the initial magma of young Chang'e-5 basalt contains more calcium and titanium, which indicates that more calcium-rich titanium-rich substances are added in the lunar mantle source region of Chang'e-5 basalt. This part of the material is precisely the product of late crystallization of the lunar magma ocean, and has the characteristics of fusibility. Its addition will significantly reduce the melting point of the lunar mantle and induce partial melting of the lunar mantle to form young lunar basalt. Further simulation calculations show that the interior of the moon has undergone more than one billion years of continuous cooling, and the temperature has only dropped by about 80 degrees Celsius.
Chen Yi said that the study shows that although the moon's interior is continuously cooling slowly, the meltable components crystallized in the late magma ocean of the lunar magma are constantly added to the deep lunar mantle, not only "replenish calcium and titanium" to the lunar mantle, but also reduce the melting point of the lunar mantle, thus overcoming the slow cooling internal environment of the lunar mantle and triggering a long-term and continuous lunar volcanic effect.
This result was published in the latest issue of the American journal "Science Advances".
Source: Xinhua News Agency (Reporters Liu Yiwei and Yu Fei)
Producer: Jingke
Supervision and audit: Dong Xiao
Editor: Zhou Wenjing
Proofreading: Jia Yutao
