Fifty years ago, NASA and the Soviet space program conducted the first sample-return missions from the Moon. This included moon rocks brought back to Earth by the Apollo Astronauts and those obtained by robotic missions as part of the Soviet Luna program. Analysis of these rocks has revealed a great deal about the Moon’s composition, formation, and geological history. In particular, scientists have concluded that the rocks were formed from volcanic eruptions more than three billion years ago.
In recent years, there has been a resurgence in lunar exploration as NASA and other space agencies have sent robotic missions to the Moon (in preparation for crewed missions). For example, China has sent several orbiters, landers and rovers to the Moon under the Chang’e program, including sample return missions. A new study led by planetary scientists from chinese academy of sciences (CAS) analyzed samples obtained by the Chang’e-5 rover dating back two billion years. Their research could provide valuable insight into how young volcanism shaped the lunar surface.
The research was carried out by a team from Institute of Geology and Geophysics of the Chinese Academy of Sciences (IGGCAS), led by Dr. Su Bin, Dr. Yuan Jiangyan and Dr. Chen Yi – members of the IGGCAS Laboratory of Lithospheric Evolution and Terrestrial and Planetary Physics. They were joined by researchers from Nanjing University’s Lunar and Planetary Science Institute (LPSI) and the CAS Center for Excellence in Comparative Planetology. An article describing their findings appeared in the journal Scientists progress October 21.
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Based on samples returned from Apollo and Luna missions, scientists speculated that the Moon had been geologically dead for three billion years. However, new lunar rock samples obtained by the Chang’e-5 mission (and returned to Earth in 2021) were only 2 billion years old, indicating that volcanic activity occurred at least a billion years older than expected. As a small rocky body, the heat that fueled volcanism on the Moon should have been lost long before these eruptions occurred.
Previously, scientists have speculated that late-stage volcanism may have been driven by high water content or the decay of radioactive elements in the lunar mantle. However, the numerous analyzes carried out on the samples obtained by the Chang’e-5 rover have dismissed this consensus. Based on their analysis, CAS researchers found that low-melting minerals in the mantle could have allowed for compression, leading to young volcanism. Professor Chen Explain in a recent CAS statement:
“The recent melting of the lunar mantle can be achieved either by raising the temperature or by lowering the melting point,” he said. “To better understand this problem, we should estimate the temperature and pressure in which the young volcanism was created.”
For their analysis, the CAS team conducted a series of fractional crystallization and lunar mantle melting simulations that compared 27 basalt clasts obtained by the Chang’e-5 mission to those returned by the Apollo missions. They found that young magma samples had higher concentrations of calcium oxide and titanium oxide than older Apollo magma samples. The presence of these minerals, which melt more readily than previous mineral accumulations in the lunar mantle, means that the volcanism would have been driven by gravity and caused the mantle materials to overturn.
Their analysis revealed that mantle compression could have occurred at similar depths but at cooler temperatures that would still have produced volcanoes. This research is no different from what planetary scientists have learned about Mars in recent years. Billions of years agothe red planet had thousands of eruptions on its surface, some of which have given rise to the largest volcanoes in the solar system (such as Olympus Mons). Scientists suspect that Mars became geologically dead when its interior cooled. But recent findings indicate that he may still experience limited volcanic activity.
This study presents the first viable explanation for young volcanism on the Moon that is consistent with samples returned from the Chang’e-5 rover. This study could inform future planetary studies of the thermal and geological evolution of the Moon. Like Dr. Su noted:
“This is a fascinating result, indicating a significant contribution of oceanic accumulations of late-stage lunar magma to the Chang’e-5 volcanic formation. We found that Chang’e-5 magma was produced at similar depths but 80 degrees Celsius cooler than older Apollo magmas This means that the lunar mantle experienced a slow and sustained cooling from 80 degrees Celsius around 3 billion to 2 billion years ago.