"Natural products" of the moon are too precious, scientists "eat more than one soil" to squeeze the greatest value
How to use the 1731 grams of precious lunar soil sample, which has condensed the hard work and wisdom of countless astronauts, and in which fields can it be used to give full play to its value have always been people's concerns.
In the early morning of December 17, the Chang'e-5 returner, which had been on a business trip for 23 days, landed in Siziwangqi, Inner Mongolia, and the Chang'e-5 "earth-digging" mission was successfully completed.
The mission brought back about 1,731 grams of lunar soil samples. After that, these precious lunar soil samples will enter the field of scientific research, providing important references for mankind to understand the moon and explore more distant deep space.
However, why must the lunar soil samples brought back by Chang'e 5 to be "authentic" and how to do it?
How do scientists plan to conduct analysis and research on these samples that use a little less?
A reporter from Science and Technology Daily interviewed relevant experts.
The analysis results have been affected
In the entire process of sampling, packaging, transportation, opening, and handing over, how to ensure that the lunar soil samples brought back by Chang'e 5 are not contaminated is an issue of great concern to the designers, which is directly related to the subsequent analysis and research work. Whether it can be carried out smoothly and whether the results of lunar soil sample analysis can be trusted.
"Oxygen and moisture in the earth's atmosphere, and even various microorganisms in the earth's environment, may contaminate samples." According to Peng Jing, deputy chief designer of the Chang'e-5 probe system, during the Apollo Moon landing era Two cases can prove this point well.
"After analyzing the lunar soil samples brought back by Apollo, some scientists once declared that the lunar soil contained water, but this was questioned by many people because it was impossible to ensure that it was not contacted during the transportation and processing of the Apollo samples. The atmosphere of the earth, and according to our observations of the moon from the earth, there is no water ice in most areas on the front of the moon. Even if there is, it will quickly volatilize under environmental conditions such as the moon’s vacuum and direct solar radiation. Dropped. Therefore, the relevant conclusions have not been recognized by the academic community."
"In 1969, after Apollo 12 landed on the moon, astronauts visited Prospector 3, which landed on the moon in 1967, and retrieved some equipment from the probe that had landed for more than two years to study long-term exposure to the moon. Whether the equipment on the device will be affected by moon dust, high and low temperature changes, space radiation, etc. But surprisingly, some researchers later detected a kind of Streptococcus bacteria on the earth inside the equipment. Two possible explanations are proposed. One is that this microorganism does exist on the moon, and the other is that this microorganism was brought from the earth by Prospector 3 and survived on the moon for two years without being killed by the harsh space environment. These two explanations, no matter which one is trusted, are shocking and caused a lot of controversy at the time. Later, until 2000, some researchers engaged in planetary protection analyzed the video of the process at that time and found that they were involved in the research. The clothes of the researchers are short-sleeved, and it is likely that the microbes on their exposed skin contaminated the sample, which led to such a wrong conclusion. Therefore, the National Aeronautics and Space Administration (NASA) later improved the extraterrestrial object The sample analysis process avoids such mistakes from happening again.” Peng Jing said.
"Double insurance" to ensure that samples are not contaminated
The protection of lunar soil samples this time mainly relies on two layers of protection.
The first is to use a sealed package device with extremely low leakage rate.
"When the lunar soil samples have not returned to the earth, whether it is the sampling process on the lunar surface, or the rendezvous and docking and sample transfer processes in space, the vacuum environment can be guaranteed. What needs to be worried about is the impact of temperature changes on the samples. For this reason, the researchers kept the temperature of the sealed package device in the return device at -25°C—55°C. Compared with the temperature range of the moon itself (-180°C—130°C), the temperature changed very little. No effect. Especially when the returner enters the earth's atmosphere, although the surface temperature of the returner is as high as 2000℃-3000℃, the temperature in the sealed package device can still be maintained within this range." Peng Jing said.
At the same time, the leak rate of the hermetically sealed device used on Chang'e 5 is extremely low, which can ensure that after returning to the earth, even if it stays in the earth’s atmosphere for about 72 hours, no other substances will enter the device to contaminate the lunar soil samples.
The second layer of protection is related measures in the process of handover, transportation and handling after returning to the earth.
When the sealed package device is handed over to the scientists, they will use a special protective device to store the sealed package device, which is filled with protective nitrogen.
"Nitrogen is an inert gas. With reference to past processing experience, scientists believe that it will not react with lunar soil samples, so the lunar soil samples in the sealed package device can be protected to the greatest extent during sample transfer and transportation. Follow-up In the process of opening the sealed package device in the ground laboratory, researchers also need to wear gloves to handle the sealed container and lunar soil samples in a special nitrogen-filled device, so as to maintain the original shape of the lunar soil samples as much as possible.” Peng Jing said .
In order to preserve and process lunar soil samples, the scientists of the ground application system tried their best to build special storage facilities and sample processing and analysis laboratories, and formulated detailed operating procedures to ensure that lunar soil samples were not contaminated as much as possible. Obtain correct and credible scientific research results.
"Multi-pronged approach" to save precious samples
How to use the 1731 gram precious sample, which has condensed the hard work and wisdom of countless astronauts, and in which fields can it be used to give full play to its value have always been people's concerns.
The so-called non-destructive analysis is a method of inspecting and testing the internal and surface structure and state of the tested object without damaging or affecting the internal organization of the tested object.
"After the sample comes back, according to the normal procedure, it must go through a non-destructive-less-destructive-destructive analysis process to ensure maximum scientific output." said Long Xiao, a professor in the School of Earth Sciences, China University of Geosciences (Wuhan).
Non-destructive analysis can help researchers understand the basic situation of the sample.
Professor Zhao Yuyan of the School of Earth Exploration Science and Technology of Jilin University said: “Currently common non-destructive analysis such as X-ray fluorescence spectroscopy is to use the primary X-rays emitted by an X-ray tube to excite atoms in the sample, and generate results by analyzing different elements in the sample. Characteristic fluorescent X-ray wavelength (or energy) and intensity, to obtain the element composition and content information in the sample."
In order to save samples, researchers also tend to use microanalysis when they have to damage the samples. In this analysis method, the permitted amount of the tested substance is usually only about one percent of the constant, and the weight is about 1-15. Milligrams.
"For example, laser ablation inductively coupled plasma mass spectrometry technology, which focuses the laser beam on the surface of the sample to ablate and vaporize it, and load the sample particles into the plasma through a carrier gas for ionization, and then mass filter through the mass spectrometry system. Use receivers to detect ions with different mass-to-charge ratios. This technology directly abates solid samples, avoiding reagent contamination, incomplete sample decomposition, and loss of volatile elements, and also eliminates the interference of polyatomic ions caused by water and acid. In addition, micro-technology methods also include nano-ion probe technology, micro-laser Raman spectroscopy, Fourier transform infrared spectroscopy, etc." Zhao Yuyan said that the current analysis technology has begun to be intelligent, miniaturized, online and instrumental. The development of the combined use direction, but in view of the preciousness and particularity of lunar soil samples, it is necessary to further improve the analysis methods, improve the sensitivity and resolution of the corresponding instruments, and develop new technologies and methods.
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Lunar soil samples can tell us this
Through the analysis of lunar soil samples, the results of mathematical models established by researchers to estimate the age of celestial bodies can be corrected.
Xiao Long said: "The existing lunar age curve has been calibrated with the existing lunar samples of mankind. It basically covers from 3.9 billion years to 3 billion years, but the data from 3 billion years to more than one billion years cannot be due to lack of samples. Correction, the samples brought back by Chang'e-5 just made up for the gap in this period."
At the same time, the lunar soil obtained this time can also provide an important reference for people to understand the geological evolution of the moon.
The Chang'e-5 landing area is one of the largest late-stage basalts on the moon, and the basalt samples obtained are "younger" than those obtained by the US Apollo program and the Soviet Lunar 16th.
Professor Meng Zhiguo of the School of Earth Exploration Science and Technology of Jilin University said: “The younger the age of the basalt, the deeper the source area. The deep mantle material represented by these samples and the shallow moon represented by the Apollo Project basalt The mantle material must have differences in the content of ferro-titanium and the mineral composition. Researchers hope to obtain new knowledge of the geochemical and mineralogical properties of the late basalt source area and its isotopic and trace element characteristics; understand the radioactive element thorium (Th) Enrichment mechanism and its role in later volcanic activity; to improve the understanding of the late lunar internal thermal evolution history, to test and constrain the lunar thermal evolution model, and to interpret some outstanding issues in the late lunar volcanic activity."
Meng Zhiguo pointed out: "In addition to the field of astronomy, the lunar soil is also of great significance to the field of microorganisms and resources. For the former, the establishment of a permanent lunar base is one of the important development directions for future planetary exploration. To achieve this goal, research on microorganisms The suitability of the lunar surface, whether the lunar soil is suitable for the growth and reproduction of microorganisms, and whether it is suitable for agricultural development are all questions that cannot be avoided. In terms of lunar resources, the sample obtained this time is the lunar soil with the highest content of titanium and iron. The content of helium-3 will also be higher. We look forward to this sample analysis to have a higher level of understanding of the content, distribution characteristics and distribution rules of helium-3. At the same time, ilmenite itself is also an important lunar resource. The by-products extracted from titanium and iron are water necessary for human life, and the hydrogen and oxygen after water electrolysis are also necessary resources for humans to carry out scientific research activities on the moon."