Recently, the planetary science team at Shandong University conducted a Raman spectroscopic analysis of lunar soil samples returned by China’s Chang’e-6 mission. Their study provides the first mineralogical "ground truth" of the magnesium-rich pyroxene annulus of the South Pole–Aitken (SPA) basin on the lunar farside. This breakthrough fills a long-standing gap in our understanding of the lithological composition of this region, which until now has relied solely on remote sensing data. The findings offer crucial evidence for deciphering the crust–mantle evolution of the lunar farside. The study, titled "Impact-induced mixing generated the stratified soils of the Lunar South Pole–Aitken Basin", was published in Communications Earth & Environment, a high-impact journal under the Nature Portfolio (JCRQ1, Impact Factor 8.953). Dr. Cao Haijun, a postdoctoral researcher at Shandong University, is the first author of the paper, with Professor Ling Zongcheng serving as the corresponding author. Shandong University is credited as the leading institution for this work.

The SPA basin is thought to be the largest, deepest, and oldest impact basin on the Moon, and possibly across all terrestrial planets in the Solar System. Such a giant impact may have excavated the lunar crust and exposed deep-seated materials, possibly the mantle, making the SPA basin a site of exceptional scientific interest for investigating the early thermal evolutionof theMoon, impact history, and crust–mantle composition. Based on orbital remote sensing data, the SPA basin has been subdivided into four compositional zones (Figure 1). Among them, the internal “Mg-rich pyroxene annulus” at the basin floor is enriched in low-Ca pyroxene and exhibits distinctly Mg-rich characteristics compared to the surrounding regions. However, the mineralogy, lithology, and origin of this Mg-rich zone have long remained debated.

Figure 1 The four distinct compositional zones within the SPA basin

Due to the absence of returned samples, investigations of magnesium-rich annulus with the SPA basin have long relied on lunar remote sensing data, leading to considerable uncertainty and divergent interpretations. In 2024, China’s Chang’e-6 mission achieved a breakthrough by returning the first lunar soil samples from the Apollo basin within the SPA basin, providing direct mineralogical evidence for constraining the origin of materials in this region. Using laser confocal Raman micro-spectroscopy, the research team performed a comprehensive mineralogical survey of the Chang’e-6 soil. Sixteen mineral phases were identified, dominated by plagioclase, pyroxenes, and amorphous glass (Figure 2). The sample shows significant input from exogenous materials but contains notably lower abundances of olivine and ilmenite compared to Chang’e-5 soils from the lunar nearside. Approximately 31–40% of the sampled material is interpreted to derive from the ejecta of Chaffee S crater, which contains a magnesium-rich annulus with the SPA. This component is characterized by major element compositions of 46.0–46.3 wt% SiO2, 21.0–23.5 wt% Al₂O₃, 6.9–10.1 wt% FeO, 9.9–11.0 wt% MgO, 12.5 wt% CaO, along with Mg# values ranging from 63.7 to 74.0. Comprehensive geochemical and mineralogical analyses reveal that the magnesium-rich SPA annulus material mainly consists of ferroan norite, which is composed of approximately 63–67% plagioclase and about 25–27% low-calcium pyroxene. In contrast to the more mafic pristine plutonic rocks formed by the SPA impact melt (~25% plagioclase), the markedly higher plagioclase content in the magnesium-rich SPA annulus suggests substantial post-impact modification. This likely involved the incorporation of ~61–63% crustal material into the pristine noritic assemblage, including crater wall collapse or infilling by ejecta from other basins, resulting in the formation of a plagioclase-rich, Mg-enriched pyroxene annulus.

Figure 2 Mineralogical composition of the Chang’e-6 lunar soil

Based on the spectroscopic and mineralogical characteristics of the Chang’e-6lunar soil, the team propose an impact-induced mixing model for the regolith evolution at the Chang’e-6 landing site. The model delineates the formation and evolution history of young mare regolith on the lunar farside into five distinct stages (Figure 3): (1) formation of the Chang’e-6 basalt unit ~2.8 billion years ago, followed by development of an early ancient soil layer; (2) distal impacts (e.g., Chaffee S) emplaced Mg-rich noritic ejecta across the landing site; (3) repeated secondary impacts in the vicinity shattered the ejecta and facilitated the accumulation of amorphous glass; (4) continued micrometeoroid bombardment supplied coarse materials and induced low-temperature shock metamorphism, contributing to soil pulverization; and (5) prolonged space weathering enriched the regolith in fine-grained particles, agglutinitic glass, and metallic iron.

Figure 3 Evolutionary history of the Chang’e-6 lunar soil

In recent years, the planetary science team at Shandong University has made significant advances in response to national strategic goals in deep space exploration. Their research field spans planetary remote sensing and spectroscopy, planetary geology, meteoritics, and cosmochemistry etc. To date, the team has published over 200 SCI-indexed papers in journals including Science, Nature Astronomy, Nature Communications, Communications Earth & Environment, JGR, and Icarus. Since 2021, the team has applied Chang’e 5/6 lunar samples from the China National Space Administration for research. To date, 23research papers related to laboratory analysis of returned samples and remote sensing analysis of the Chang’e 5/6 landing sites have been published. The team has led several key programs supported by the National Natural Science Foundation of China (NSFC) and other institutes. This work has been funded by the National Key R&D Program of China, the NSFC, and the China Postdoctoral Science Foundation.