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From China:The Institute of Geology and Earth used electron microscopy to analyze the weathering mechanism of chang ‘e-5 samples

For billions of years, the moon’s surface has been subjected to intense space weathering, including micrometeorite impacts, solar winds and radiation from galactic cosmic rays. These processes have greatly altered the microscopic morphology, crystal structure and chemical composition of lunar surface materials, and thus changed the spectral characteristics of the moon, resulting in multiple solutions of geological analysis. Therefore, the in-depth study of the interaction process and mechanism between impact and solar wind radiation and matter is the key to understand the evolution of lunar surface matter and space environment, and provides an irreplaceable role for the planet’s habitable environment and its evolution. However, due to the small size and complex microstructure of lunar soil particles, it is difficult to distinguish the characteristics of micrometeorite impact and solar wind irradiation, resulting in a lack of understanding of the mechanism of space weathering. In addition, meteorite impacts may be random events, but solar wind exposure depends on latitude. Samples collected by the U.S. Apollo mission and the Soviet Luna mission were in the moon’s lower latitudes. Chang ‘e-5 sampling site is located at the mid-latitude (43.06°N), providing a unique perspective for the study of lunar space weathering at different latitudes.

Based on this scientific question, Gu Lixin, senior engineer of the Electron Microscope Laboratory of the Institute of Geology and Geophysics, Lin Yangting and Li Jinhua, researchers of the Key Laboratory of Earth and Planetary Physics of the Chinese Academy of Sciences, together with the Beijing High Pressure Science Center and the National Space Science Center of the Chinese Academy of Sciences, LABS in the electron microscope samples of single particle manipulation – sem morphology observation – fine machining of focused ion beam – tem structure analytic series analysis methods, such as the chang ‘e no. 5 samples of single particle surface multiphase material (, phosphate and silicate, oxide sulfide) by the same under the space environment of different microstructure response (figure 1).

The analysis results show that all the mineral phases exposed on the surface of basaltic debris have a redeposition layer rich in Si/O elements, and the solar wind damage layer is below. However, the structure and chemical composition of the solar wind damage layer are related to the types of matrix minerals (FIG. 2). Nanocrystalline iron (npFe0), amorphous and vesicle structures are the most common features of space weathering. It is found that the lamellar structure of the damaged layer of pyroxene irradiated by solar wind is consistent with that of pyroxene matrix, which provides conclusive evidence of solar wind reduction of nanocrystalline iron. The surface damage layer is amorphous, and the iron nanoparticles in the amorphous layer are spherical, but the grain size (~ 3-5 nm) is related to the iron content in the substrate layer. The crystal structure of ilmenite was maintained by solar wind irradiation, but fe-Ti element migration occurred, and the reduced iron nanoparticles were elongated (~ 20 nm). The surface of sulfide shows a serrated structure, and there is no obvious solar wind action area. The main reason is that the sulfide is desulfurized by solar wind ion erosion and forms iron whiskers (tens of nm ~ 300 nm). No iron nanoparticles were found on the surface of iron-poor white phospho-calcium ore. In addition, the damaged layers of ilmenite and white phosphocalciite have vesicle structures, but their morphology is different, which may be related to their crystal structures and surface tension.

Based on the analysis of surface morphology and internal structure of single-particle multiphase materials, it can be seen that space weathering of lunar soil is mainly caused by micrometeorite impact, solar wind and cosmic ray irradiation, etc., and their contributions can only be distinguished by means of fine morphology and structure characterization (FIG. 3). Compared with the analysis results of The Apollo samples, the surface microstructure characteristics and formation mechanism of the lunar samples do not show great differences, which provides support for remote sensing spectral correction of different dimensions. However, the similarity of microstructure does not mean that there are no differences in the solar wind-injected water preserved on the lunar soil surface. In addition, due to the diversity of space weathering effects, it is necessary to consider the complexity of the composition and space environment of the moon when extending the space weathering model to other non-atmospheric planets.

The study was recently published in Geophysical Research Letters. The research work was supported by the National Natural Science Foundation of China, the Key Deployment Project of the Chinese Academy of Sciences, the Civil Space Technology Advance Research Project of the China National Space Administration, and the Key deployment project of the Institute of Geology and Geophysics, Chinese Academy of Sciences.

Figure 1. Surface morphology of lunar soil particles

FIG. 2. Microstructure of different mineral phases

Figure 3. Space weathering process and response models of different mineral phases

For billions of years, the moon’s surface has been subjected to intense space weathering, including micrometeorite impacts, solar winds and radiation from galactic cosmic rays. These processes have greatly altered the microscopic morphology, crystal structure and chemical composition of lunar surface materials, and thus changed the spectral characteristics of the moon, resulting in multiple solutions of geological analysis. Therefore, the in-depth study of the interaction process and mechanism between impact and solar wind radiation and matter is the key to understand the evolution of lunar surface matter and space environment, and provides an irreplaceable role for the planet’s habitable environment and its evolution. However, due to the small size and complex microstructure of lunar soil particles, it is difficult to distinguish the characteristics of micrometeorite impact and solar wind irradiation, resulting in a lack of understanding of the mechanism of space weathering. In addition, meteorite impacts may be random events, but solar wind exposure depends on latitude. Samples collected by the U.S. Apollo mission and the Soviet Luna mission were in the moon’s lower latitudes. Chang ‘e-5 sampling site is located at the mid-latitude (43.06°N), providing a unique perspective for the study of lunar space weathering at different latitudes.

Based on this scientific question, Gu Lixin, senior engineer of the Electron Microscope Laboratory of the Institute of Geology and Geophysics, Lin Yangting and Li Jinhua, researchers of the Key Laboratory of Earth and Planetary Physics of the Chinese Academy of Sciences, together with the Beijing High Pressure Science Center and the National Space Science Center of the Chinese Academy of Sciences, LABS in the electron microscope samples of single particle manipulation – sem morphology observation – fine machining of focused ion beam – tem structure analytic series analysis methods, such as the chang ‘e no. 5 samples of single particle surface multiphase material (, phosphate and silicate, oxide sulfide) by the same under the space environment of different microstructure response (figure 1).

The analysis results show that all the mineral phases exposed on the surface of basaltic debris have a redeposition layer rich in Si/O elements, and the solar wind damage layer is below. However, the structure and chemical composition of the solar wind damage layer are related to the types of matrix minerals (FIG. 2). Nanocrystalline iron (npFe0), amorphous and vesicle structures are the most common features of space weathering. It is found that the lamellar structure of the damaged layer of pyroxene irradiated by solar wind is consistent with that of pyroxene matrix, which provides conclusive evidence of solar wind reduction of nanocrystalline iron. The surface damage layer is amorphous, and the iron nanoparticles in the amorphous layer are spherical, but the grain size (~ 3-5 nm) is related to the iron content in the substrate layer. The crystal structure of ilmenite was maintained by solar wind irradiation, but fe-Ti element migration occurred, and the reduced iron nanoparticles were elongated (~ 20 nm). The surface of sulfide shows a serrated structure, and there is no obvious solar wind action area. The main reason is that the sulfide is desulfurized by solar wind ion erosion and forms iron whiskers (tens of nm ~ 300 nm). No iron nanoparticles were found on the surface of iron-poor white phospho-calcium ore. In addition, the damaged layers of ilmenite and white phosphocalciite have vesicle structures, but their morphology is different, which may be related to their crystal structures and surface tension.

Based on the analysis of surface morphology and internal structure of single-particle multiphase materials, it can be seen that space weathering of lunar soil is mainly caused by micrometeorite impact, solar wind and cosmic ray irradiation, etc., and their contributions can only be distinguished by means of fine morphology and structure characterization (FIG. 3). Compared with the analysis results of The Apollo samples, the surface microstructure characteristics and formation mechanism of the lunar samples do not show great differences, which provides support for remote sensing spectral correction of different dimensions. However, the similarity of microstructure does not mean that there are no differences in the solar wind-injected water preserved on the lunar soil surface. In addition, due to the diversity of space weathering effects, it is necessary to consider the complexity of the composition and space environment of the moon when extending the space weathering model to other non-atmospheric planets.

The study was recently published in Geophysical Research Letters. The research work was supported by the National Natural Science Foundation of China, the Key Deployment Project of the Chinese Academy of Sciences, the Civil Space Technology Advance Research Project of the China National Space Administration, and the Key deployment project of the Institute of Geology and Geophysics, Chinese Academy of Sciences.

Figure 1. Surface morphology of lunar soil particles

FIG. 2. Microstructure of different mineral phases

Figure 3. Space weathering process and response models of different mineral phases

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