Chinese researchers closely study samples of lunar soil brought by Chang’e-5

Until recently, research by a Chinese geochronologist Lee Hsien-Hua were focused on terrestrial molten rocks. But when in December 2020 the Chinese spacecraft delivered the first soil samples from the moon to Earth, the scientist switched all his attention to studying them. As Lee says, “I’m a newbie working on extraterrestrial rocks.”

Li is one of many planetary scientists in China who have had the opportunity to study lunar rock samples for the first time. They were collected and delivered to Earth by an automatic interplanetary station “Chang’e-5“for the first time since the NASA program”Apollo“and the launch of the Soviet interplanetary station”Luna-16“.

The first studies of lunar samples are already beginning to yield exciting results. Over the past six months, about six scientific papers have been published. Six more were presented at the Lunar And Planetary Science Conference in Houston (USA) during a session on Chinese lunar missions.

University of Notre Dame (USA) geologist Clive Neal worked on the collected Chang’e-5 samples with colleagues in China. According to him, many young Chinese scientists are participating in these studies. Chinese graduate students and even undergraduates also presented data in Houston on their work on lunar samples. The samples are exciting, Neal says, because they “represent a window into a completely different era of lunar magmatism” compared to previously collected samples.

The youngest breeds

“Chang’e-5” extracted 1.7 kg of loose basalt from the territory of a vast lava plain “Ocean of Storms» (Oceanus Procellarum), located in the northern part of the Moon. This choice of site is partly due to the fact that it could contain younger specimens than those brought in by the Apollo and Luna 16 missions. They can give insight into when the moon began to cool while being volcanically active.

Last July, the China National Space Administration (CNSA) donated samples to scientists. Between 31 scientific projects (out of 85 submitted), 1.75 g of fine-grained soil and hard rock were distributed. Several more rounds of applications to work with lunar samples soon followed.

The first thing the teams did was to date the samples. October 7 one of the projects appreciated the age of the rock is 1.96 Ga (± 57 Ma). Less than 2 weeks later, another team, including Lee, confirmed presented dates, estimating the age of the samples at 2 Ga (± 4 Ma). Thus, the Moon remained volcanically active for at least a billion years longer than was assumed after analysis of the Apollo samples.

According to one of the leading theories, based on satellite observations, the reason for the continued volcanic activity could be the heat-producing radioactive elements found in the lunar mantle, such as potassium (potassium) and thorium (thorium). But a team of researchers from IGG studied the submitted lunar samples and found that high levels of these elements were not actually the determining source of heat.

Another possible reason could be that the mantle contained enough water to lower the melting point of the materials and make it easier for the magma to erupt. But IGG planetary scientist Lin Yangting, along with his colleagues discoveredthat lunar rocks most likely originated from a relatively dry source.

Confused

The question of the heat source has baffled scientists. Lin, who has studied meteorite samples found on Earth, also does not know the answer to this question.

“This is a very big scientific problem,” says planetary geochemist Weibiao Hsu of Zijinshan Observatory (Purple Mountain Observatory) in China. The issue of the heat source shows how much people still have to learn about the evolution of the moon.

Hsu, who received two pieces of basalt to study, wondered if a closer look at these samples could show that they really come from a rich source of fuel elements. The recently published study by Lin and his colleagues was just carried out on soil samples containing many of the relevant materials. During the work, Hsu discovered that the rocks contain a high concentration of titanium. This suggests that they came from the depths of the lunar mantle.

According to Peking University geochemist Ming Tang, the researchers are taking every opportunity to study the samples. This is a great opportunity for Ming and other scientists interested in expanding knowledge in their field. Ming also received two tiny grains of basalt. He intends to analyze the samples to better understand the temperature level at which they formed. These are the first lunar grains in Tang’s life. Previously, he studied magma from volcanoes on Earth.

At the moment, theories about the source of heat on the Moon abound. But Hsu claims that there will be many groups trying to unravel this mystery and get other information about the moon. Many scientists have joined this field since the samples arrived on Earth.

Lin expects more researchers to join the study of the samples soon. Over the next ten years, China is planning a mission to obtain samples from the south polis of the moon and another mission to Mars. “Twenty or thirty years ago it was just a dream. Now it has come true,” says Lee.

doi.org/10.1038/d41586-022-00683-6

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