Chinese scientists published three new papers in nature, a top scientific journal,[1][2][3] analyzing samples taken from the moon by Chang'e-5. The results show that the most recent lunar sample brought back the youngest lunar soil and rock, only 2 billion years old, revealing the moon's unknown past.
Before our country, both the United States and the Soviet Union had collected lunar samples. During the American Apollo manned lunar landing, the astronauts brought back 380 kilograms of lunar rock six times (later sent 1 gram to China). In the 1970s, the Soviet Union launched an unmanned probe to land on the moon, bringing back lunar samples three times, totaling 301 grams.
After nearly 50 years, China launched Chang'e 5 to the moon, an unmanned probe that landed on the front of the moon, collected 1731 grams of lunar samples, and successfully returned to the earth. Previously, the first lunar samples of Chang'e-5 have been distributed to a number of scientific research institutions. Now, the study of lunar samples of Chang'e-5 has finally come to fruition.
The analysis shows that the lunar samples brought back by the United States and the Soviet Union are very old, more than 3 billion years old, and the oldest is even more than 4.4 billion years old. Previous research has shown that the moon's interior cooled down quickly, stopping volcanic activity as late as 2.8 billion years ago, and the surface became silent.
However, the results of Chang'e-5's lunar sample analysis showed that the moon actually had volcanic activity 2 billion years ago, a result that surprised astronomers. The lunar volcanoes of the time spewed magma onto the surface, which then solidified into basalt, eventually being brought back to Earth by Chang'e-5.
On the other hand, the moon's last driving force for volcanic activity is not the radioactive elements potassium, uranium and thorium, as previously thought. Theoretically, the heat generated by the decay of these radioactive elements could help melt the rock in the lunar mantle, forming a large amount of magma that would eventually trigger a volcanic eruption. However, the scientists did not detect these radioactive elements in the basalt brought back by Chang'e 5.
In these new studies, the scientists also analyzed moisture in lunar samples. Previous studies have suggested that the lunar mantle has a higher water content because water can lower the melting point of rocks, allowing the moon's volcanic activity to last longer. But the new study shows that the samples are unusually dry, with a moisture content of only one to five parts per million.
For a smaller body like the Moon, the internal cooling rate is very fast, and volcanic activity should soon stop. Without large amounts of radioactive elements or water, how could the moon's volcanic activity have lasted until 2 billion years ago?
Astronomers don't know the exact reason for this. Several hypotheses have been proposed, such as tidal heating of the Earth, the thick soil on the lunar surface acting as a warming, or the impact of large asteroids and comets. The mystery of the evolutionary history of the Moon requires further sample analysis.
The lunar soil and rocks brought back by Chang'e 5 contain not only the history of lunar evolution, but also various natural resources that human beings need. According to statistics, there are more than 100 known minerals on the moon, of which 5 are unique to the moon and do not exist on the earth.
Some metal resources on the moon are very rich, such as titanium, whose reserves are estimated to be more than 100 trillion tons, and the reserves of titanium ore on Earth are estimated at 2 billion tons. Titanium has very excellent corrosion resistance, its strength - density ratio is the highest of metals, so it is widely used in the field of navigation and aerospace. It is conceivable that in the future "great space age", human beings will mine titanium ore in large quantities on the moon.
In addition, there is a large number of extremely scarce resources on the moon - helium-3. Controlled nuclear fusion is the key to humanity's progress to a higher level of civilization, and scientists are currently testing nuclear fusion reactions in deuterium and tritium, but this reaction will create neutron radiation problems and also lose some energy. Helium-3, on the other hand, can achieve perfect nuclear fusion without radioactive contamination and at a lower cost.
Helium-3 is mostly derived from the solar wind, but due to the existence of the Earth's atmosphere and magnetic field, the solar wind is basically unable to reach the Earth's surface directly, so helium-3 is very rare on Earth. The Moon has no atmosphere and magnetic field, and the solar wind directly bombards the lunar surface, so a large amount of helium-3 has accumulated on the Moon.
It is conservatively estimated that more than 1.1 million tons of helium-3 exist on the lunar surface. Only 100 tons of helium-3 is needed to generate electricity, which can meet the global human consumption of 1 year. Although helium-3 on the moon is limited and seems to have only been used by humans for more than 10,000 years, this is crucial for the further development of human civilization. Even if helium-3 is exhausted on the moon, there are still more helium-3s on Jupiter, Mercury and other celestial bodies to be mined.
Helium-3 has extremely high application prospects and value, up to $3 billion per ton, equivalent to 19.1 billion yuan. At present, the Beijing Geological Research Institute of the Nuclear Industry, which obtained 50 mg of chang'e-5 lunar samples, is studying helium-3 in the lunar soil and exploring technologies for extracting helium-3 from it.
Next, China will further explore the moon, launch a number of unmanned probes to the moon, and collect samples from different regions of the moon to bring back to the earth. Exciting manned lunar landings are also in the works, and we hope to see Chinese astronauts personally set foot on the lunar surface in the near future (perhaps a decade or so).
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[1] Qiu-Li Li, Qin Zhou, Yu Liu, Zhiyong Xiao, et al. Two billion-year-old volcanism on the Moon from Chang’E-5 basalts, Nature, 2021, DOI: 10.1038/s41586-021-04100-2.
[2] Heng-Ci Tian, Hao Wang, Yi Chen, Wei Yang, et al. Non-KREEP origin for Chang’E-5 basalts in the Procellarum KREEP Terrane, Nature, 2021, DOI: 10.1038/s41586-021-04119-5.
[3] Sen Hu, Huicun He, Jianglong Ji, Yangting Lin, et al. A dry lunar mantle reservoir for young mare basalts of Chang’E-5, Nature, 2021, DOI: 10.1038/s41586-021-04107-9.