Nature: China's first lunar rocks sparked a research boom

The British magazine Nature website pointed out on March 16 that in December 2020, China's Chang'e-5 returner brought back nearly 2 kilograms of lunar samples, and these lunar rocks have triggered a research boom by Chinese scientists, who are studying them to reveal the evolutionary history of the moon.

Sparked a research boom

Li Xianhua, a researcher at the Institute of Geology and Geophysics (IGG) of the Chinese Academy of Sciences, previously focused on molten rocks on Earth. But when Chang'e-5 brought China's first lunar rocks back to Earth, Li Xianhua turned to studying them.

Li Xianhua is one of many scientists in China who have had the first opportunity to study lunar rocks. The rock samples are the first lunar samples brought back by humans since NASA's Apollo mission and the Soviet Union's lunar mission more than 40 years ago.

At present, many Chinese scientists are studying the Chang'e-5 sample to understand the evolution of the moon. The early findings excited the scientists. In the past 6 months, they have published 6 papers on the Chang'e 5 sample. Last week, at the Lunar and Planetary Science Conference in Houston, Texas, USA, there was a forum on China's lunar mission, and scientists submitted about a dozen research results.

Cliff Neal, a professor of civil engineering and geological sciences at the University of Notre Dame who worked with Chinese scientists on the Chang'e-5 sample, said: "There are a lot of young Chinese researchers involved, and these lunar rocks are exciting because they are a window for scientists to study lunar magmatic activity at different times." ”

The youngest lunar rock

The Chang'e-5 mission collected about 1,731 grams of lunar samples from the basalt region in the northeastern corner of the storm ocean north of the moon. The site was chosen in part because it could contain younger volcanic material than the areas visited by the Soviet lunar and Apollo missions. Scientists hope that younger sites will give them an idea of what the moon "looks like" when it begins to cool but still has volcanic activity.

The latest research results of the Chang'e-5 lunar scientific research sample released by the Chinese Academy of Sciences prove that the Chang'e-5 lunar sample is a new type of lunar sea basalt, filling the "gap" in the lunar sampling missions of the United States and the Soviet Union. Studies have shown that the Moon still had magmatic activity until 2 billion years ago, and the source area of the lunar mantle for late magmatic activity is not rich in radioactive thermogenic elements and is very "dry". A number of breakthroughs have given a new understanding of the evolution of the moon, and put forward new directions for future lunar exploration and research, which have been highly praised by international experts.

Last July, the China National Space Administration distributed the first samples to chinese scientists. They selected 31 scientific projects from 85 applications and distributed about 17.5 grams of fine-grained powder and solid rock. Next, there were several more rounds of applications to study lunar samples.

The first research team determined the age of the lunar rocks. On October 7 last year, a research team reported that the basalt was 1.96 billion years old (an error of no more than 57 million years). Less than two weeks later, another team of researchers, including Li Xianhua, confirmed the date, estimating the age of the basalt to be 2 billion years (the error does not exceed 4 million years).

The findings confirm that the Moon was still volcanically active at the time, nearly 1 billion years later than the peak of volcanic activity shown by rocks retrieved by the Apollo mission.

Lunar volcanic activity is confusing

What caused these volcanic activities?

One theory based on satellite observations suggests that thermogenic radioactive elements found in the lunar mantle, such as potassium and thorium, may have been the driving force behind volcanic activity. But when another team at IGG examined the lunar basalt, they denied it.

Another explanation given by the scientists is that the mantle contains enough water to lower the temperature at which the material melts, making it easier for the magma to erupt. But IGG's planetary scientist Yang Ting Lin and colleagues have found that the lunar rocks may have come from relatively dry places.

The question of the heat source of the moon's volcanic activity has also puzzled scientists. In this regard, Lin Yangting said: "I have not found the answer."

Xu Weibiao, a researcher at the Nanjing Purple Mountain Observatory of the Chinese Academy of Sciences, said: "This is a very big scientific problem, and to figure this out, we need to further understand the evolutionary history of the moon." Xu Weibiao received two small lunar samples and is currently trying to figure this out.

Tang Ming, a geochemist at Peking University, said: "We are exploring all possibilities." Tang ming also received two tiny basalt particles and will analyze them to better understand the pressure and temperature at which they are produced. Tang Ming, who has previously studied the magma of Volcanoes on Earth, said: "Lunar samples are a great opportunity for me and many other Chinese scientists interested in expanding their research fields."

Currently, theories about the source of volcanic heat on the moon abound. But Xu weibiao said there will be many groups trying to solve the mystery and get more information about the moon. Since the Chang'e-5 sample arrived on Earth, he has seen many researchers join the field. This year, his lab received many requests to join their research topics, exceeding their expectations and "never before."

Lin Yangting hopes that more researchers will participate. Over the next decade, China plans to return a lunar south pole sample and another Mars sample return mission.

"Twenty or thirty years ago, it was just a dream, and now it has come true," Li Xianhua said.

Source: Science and Technology Daily