Findings from the first samples on the far side of the moon raise new questions about the history of the moon

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The moon has some new stories to tell.

Scientists have published the first detailed analyzes of the historic lunar soil and rock treasure that China recovered from the far side of the moon this year.

Chang’e-6, the first mission to retrieve soil from the far side of the moon, collected 1.9 kilograms (4.2 pounds) of lunar soil with a robotic probe in June before returning to Earth, a scientific feat that Consolidated China’s position as one of the world’s largest space powers.

The volcanic rock contained in the sample is 2.8 billion years old, suggesting that the unmanned mission’s landing site was volcanically active at the time, according to two papers published Friday in the journals Science and Nature. The eruption represented a relatively recent episode of volcanic activity on the moon that was not known from examining samples taken from the lunar far side as part of NASA’s Apollo program and Russia’s Luna missions, according to the new study resulted.

The age of the basalt rock on the far side is surprisingly young compared to previously studied samples on the far side of the moon, all of which were more than 3 billion years old, said Clive Neal, a professor at the University of Notre Dame and co-author of the Science paper. However, more recent close-up samples collected by China’s Chang’e-5 lunar mission in 2020 found them to be 2 billion years old.

The investigation also showed that the samples did not carry the signature of radioactive elements found in many Apollo-era samples.

“The relatively young age of the basalts (found from Chang’e-6) is surprising and the composition contains virtually no radioactive elements,” Neal said by email. This “raises the question of how and why these magmas were created.”

“That was the same question that is still being asked about the Chang’e 5 basalts,” he added.

“Unsolved Mystery”

The first soil samples from the moon, collected during the Apollo missions of the 1960s and 1970s, virtually rewrote science textbooks, revealing how the moon formed and that it was once covered by an ocean of magma.

“You know, one of the concerns is that we developed this detailed story (about the Moon) from all the Apollo results,” said Richard W. Carlson, scientist emeritus at the Earth & Planets Laboratory at the Carnegie Institution for Science in Washington, DC He was not involved in the new research.

“And one thing that’s always stuck in the back of my mind is whether this only applies to the Apollo region of the moon,” Carlson added.

NASA’s Apollo missions landed at six locations relatively close to the Moon’s equator between 1969 and 1972, while the Chang’e-5 spacecraft landed in the Moon’s northwest corner. The Chang’e-6 lunar probe landed at a site in the extensive South Pole-Aitken Basin, an impact crater formed about 4 billion years ago.

Now the Chang’e-6 samples can help scientists explore the differences between the near and far sides of the moon, previously discovered through remote sensing, by clarifying the volcanic history of the other side, Qiu-li Li said , corresponding author of the book natural scientist and research professor at the State Key Laboratory of Lithosphere Evolution at the Institute of Geology and Geophysics of the Chinese Academy of Sciences.

The side facing the Moon always faces the Earth – and was therefore easier to study – because the Moon takes the same time to orbit the Earth and rotate on its axis: about 27 days.

Previous remote sensing-based research found that the far side of the moon has different topography, a thicker crust, a different basalt distribution and different concentrations of thorium, a radioactive element found in the rock, Li said.

“The asymmetry between the front and back sides of the moon remains an unsolved mystery,” he said in an email.

Li and his team examined 108 basalt fragments contained in two small samples of soil on the far side of the moon. Most of the fragments were formed around 2.8 billion years ago, the researchers found by studying the decay of lead isotopes in the samples. However, according to the research, a fragment was formed around 4.2 billion years ago.

The basalt fragments examined in the Science article were also 2.8 billion years old. Taken together, the results of the two studies suggest that the moon was molten for a longer period of time than initially thought, Carlson said.

“We have no real idea why the moon has been melting for so long,” Carlson said in an email. “The moon is a pretty small body and would have had to cool down pretty quickly.”

Both papers found that the samples were not rich in KREEP, an acronym that stands for potassium (chemical symbol K), rare earth elements (REE) and phosphorus (P) and has been found in other Apollo-era lunar samples.

KREEP generates heat, Carlson said, and its existence would explain why volcanism on the moon lasted so long. He said it was interesting that the Chang’e-6 samples did not contain any radioactive elements.

Future Chang’e-6 sample research

These initial analyzes of lunar soil samples raise questions that will require more time and testing of additional samples to answer, Neal said.

China’s National Space Administration has said that scientists from outside China could apply to study the soil samples two years after the samples arrive on Earth, following a precedent set by NASA decades ago with the Apollo missions.

The Apollo moon flights ended in 1972, but NASA said it receives about 60 research requests for samples each year. According to the space agency, more than 2,500 scientific papers using Apollo data were published in 2015.

Li said foreign researchers like Neal are already able to work with their Chinese colleagues as part of a team.

Neal said he was “pleasantly surprised” that he was asked to take part in the project. However, he explained that he could only work on research “after hours” to avoid violating the Wolf Amendment, a 2011 US law that restricts NASA’s use of government funds for bilateral cooperation with China or its agencies without authorization from Congress or the United States.

NASA Administrator Bill Nelson suggested in July that research on the Chang’e-6 samples may not violate the Wolf Amendment.

The space agency declined to comment on the studies but said it was coordinating with U.S. researchers who have requested access to Chang’e-5 lunar samples.

“The agency is aware that CNSA interviewed applicants for international loans as part of the application process, but did not disclose its selection,” NASA said.

The two papers published Friday are not the first studies of the Chang’e-6 samples, Li said. A September paper characterized the samples but did not date them.

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