Rare lunar "soil": exploring the extraordinary value of lunar soil

Chang'e 6 returned triumphantly, bringing back rare "local specialties" from the far side of the moon! This is the first time that humans have returned samples from the far side of the moon. Every grain of soil carries the secrets and treasures of the deep moon. Why do the world's major space powers aim to take a handful of soil from the moon? What is the value of these gray soils?

1. The Origin of 1 Gram of Lunar Soil

In the 1960s and 1970s, the United States and the Soviet Union, which had rapidly developed into two superpowers after World War II, set their sights on competing for supremacy on the Earth's only satellite, the Moon, 380,000 kilometers away from the Earth. A series of black technologies for landing on this planet were invented and used in engineering practices to explore the Moon. Today, we see a large number of bulky spacecraft that were once used for landing on the Moon, which are the "masterpieces" of that era. In that lunar race, the United States brought back a total of 382 kilograms of lunar soil and rocks. In the Apollo 17 mission in 1972, astronauts brought back 110.5 kilograms of lunar samples at once.

Compared with the lively scene of American astronauts driving lunar rovers to collect samples on the lunar surface, the Soviet Union, which used two "bathtub-shaped" robots to accurately collect samples, seemed much more "polite". The Soviets, who relied entirely on automation to complete the sampling and return, contributed a total of 301 grams of lunar soil to the human "lunar return sample" family. To this day, the ability to independently explore extraterrestrial bodies is still regarded as the jewel in the crown of the world's technological power. With the shocking rocket launches time and time again, various detection equipment that integrates the wisdom of mankind has been sent to the extraterrestrial world.

In May 1978, Jimmy Carter, then the 39th President of the United States, sent National Security Advisor Zbigniew Brzezinski to visit China in an attempt to break the barriers between China and the United States at the time. In addition to a five-star red flag that was said to have been brought to the moon, Brzezinski also presented the Chinese government with a gram of lunar rock collected by the Apollo 17 astronauts. This precious sample was later divided into two parts, 0.5 grams of which was used for popular science and collected by the Beijing Planetarium, and the other 0.5 grams was used for scientific research by Chinese astrochemist Academician Ouyang Ziyuan, marking the beginning of Chinese lunar soil research.

2. The Origin of Lunar Soil

(This is Lunar Sample No. 001 photographed at the National Museum of China. Photographed by Xinhua News Agency reporter Jin Liangkuai)

As we all know, the moon, as the satellite of the earth, has played an indispensable role in protecting the earth from the threat of small celestial bodies in the universe. As a result, the surface of the moon has become uneven, forming many craters formed by meteorite impacts. According to the laboratory research results of lunar sampling and the interpretation of remote sensing data from orbiting probes around the moon, the average thickness of the lunar soil on the surface of the moon today is 4 to 5 meters. For such a thickness, researchers speculate that there are two main sources:

Loose sticky soil hypothesis Since there is no oxide film on the surface of dust particles under vacuum conditions, the stickiness of the dust particles at their contact points needs to be considered. The lunar soil on the surface of the moon has a loose structure. Under the influence of the gravity of the upper lunar soil and the frequent impact of meteorites, the deeper you go, the denser the lunar soil becomes.

Lunar soil is made up of large minerals . The lunar landscape is formed by meteorite impacts. During the meteorite impact, a large amount of debris material layer is formed. The thickness of this material layer near the lip of the impact crater is 10 meters to 100 meters, and the thickness in the area between the impact craters reaches 1 meter. In this case, the lunar soil surface is composed of loose and porous materials, which are produced by frequent meteorite impacts.

The lunar surface is not weathered or eroded by running water like on Earth. Without the protection of a dense atmosphere, the lunar surface materials are completely exposed to solar radiation. The constant impact of high-energy cosmic radiation and solar wind particles, as well as the huge temperature difference between day and night on the moon, have accelerated the fragmentation of rocks on the lunar surface. Along with the geological activities of the lunar crust, after billions of years of evolution, the lunar surface was covered with thick dust, thus forming lunar soil.

Unlike most of the " soil " on Earth that is rich in microorganisms and water , lunar soil is dry and powdery . According to the data analysis results obtained from the Apollo series of exploration missions, the lunar exploration mission, and the Chang'e lunar exploration program, the chemical composition of lunar soil and lunar rocks is mainly oxides of 14 elements such as silicon, magnesium, aluminum, calcium, iron, manganese, and nickel. The density of lunar soil is about 1.5 grams per cubic centimeter. The mineral fragments in the lunar soil are mainly olivine, plagioclase, pyroxene, ilmenite, spinel, basalt, anorthite, peridotite, sulphite, breccia fragments, molten rock, microbreccia, impact glass, igneous fragments, etc. Look! The seemingly simple lunar soil has very complex chemical composition, rock type and mineral composition .

3. The impact of lunar dust on lunar exploration

Moon dust is the main component of lunar soil . Moon dust is generally about 10 microns in diameter, but such small and rough dust can cause long-term and irreversible effects on the power supply and mechanical components of astronauts and deep space exploration equipment: due to the adhesion and viscosity of moon dust, astronauts may have difficulty in moving the joints of the space suits they wear; the power and mechanical arm connections of the lunar rover will fail due to the adhesion of a large amount of static moon dust; the solar panels of the orbiting probe flying around the moon will have a significant impact on their power due to long-term collision and friction with a large amount of moon dust.

Lunar dust affects the pace of human lunar exploration not only in microscopic but also in macroscopic ways. Moreover, lunar dust is also playing an important role as a "tracer" in lunar physical field and geological research. Due to the widespread and multi-layered distribution of lunar dust on the lunar surface , researchers are able to use these characteristics to construct " invisible " lunar physical field models such as lunar electrostatic field distribution , lunar local magnetic field characteristics , lunar atmospheric density and distribution .

4. Building a lunar base

Humans have made great efforts to understand the mysteries of the world outside the Earth. By building optical astronomical telescopes, radio telescopes and other telescopes to spy on the universe in various bands, the space around us is becoming three-dimensional and clear. By launching various probes, the mysteries of the planets and their satellites in the solar system are gradually being unveiled. On these planets, we will be able to conduct more exploratory experiments and observations more clearly and without human interference, and understand the surrounding universe more accurately. Looking back at the Earth from the Moon, the only satellite of the Earth, we can continuously monitor the near-space environment and atmosphere of our blue home.

As the cradle of life, the Earth not only shelters and nurtures Earth's creatures, but also gives us the opportunity to go far away. After 23 years of construction and operation, humans have fully mastered the ability to live and work in low-Earth orbit using the International Space Station. The Moon and Mars have become new continents for us to display our infrastructure skills. Before completely solving a series of problems that plague human survival on extraterrestrial bodies, such as cosmic radiation, self-sufficiency in food, and physiological limits, we need to use robots to continue to collect more scientific data for research and learn more about extraterrestrial survival. Perhaps we will continue to observe this world that is about to land in a "close-up" way by building a lunar space station. In order to manufacture building materials and even scientific instruments on the moon using local materials , researchers and engineers are jointly conducting unprecedented research on lunar soil . The goal is to use 3D printing technology to turn lunar soil into building components for manned lunar bases , thereby getting rid of the heavy and expensive labor of transporting building materials from the earth to the moon .

The seemingly inconspicuous gray lunar soil can not only protect us from the sun, wind and meteorite rain, but also provide us with clean energy and even water. Through the analysis of a large amount of lunar global spectrum data and lunar samples, the lunar soil is rich in helium-3 and other usable future energy sources. Of course, based on the current knowledge of mankind, it will take some time for us to fully master the technology to extract or efficiently utilize these resources on site.