In a groundbreaking discovery that promises to reshape our understanding of lunar geology and the early solar system, a team of planetary scientists has revealed new insights into the chemical state of the Moon’s mantle beneath one of its most enigmatic features, the South Pole–Aitken (SPA) basin. This immense impact basin, which is one of the largest and oldest impact structures in the solar system, has long been a subject of intrigue for scientists striving to decipher the Moon’s formation history and internal composition. The recent study, conducted by Zhang et al., uncovers that the mantle material beneath the SPA basin exhibits a more reduced chemical state than previously assumed, which has profound implications for models of lunar evolution.
The South Pole–Aitken basin, located on the lunar far side, spans roughly 2,500 kilometers in diameter and plunges up to 13 kilometers deep into the lunar crust and upper mantle. As one of the Moon’s oldest impact scars, it offers a unique geological window into the planet’s interior, potentially revealing preserved features from the primordial lunar mantle. Previous analyses based on lunar samples and remote sensing data have suggested various oxidation states across the lunar interior, but the new research breaks new ground by applying state-of-the-art spectroscopic and geochemical modeling techniques to high-resolution remote sensing data from recent lunar missions.
Zhang and colleagues focused on examining the mantle’s redox state—the balance between oxidized and reduced conditions—which critically governs the physical and chemical behavior of magmas, mantle melting processes, and volatile element retention. The research team utilized advanced algorithms to interpret spectral data, focusing on specific mineralogical proxies sensitive to oxidation states such as iron-bearing silicates and oxides. Their analyses were complemented by experimental petrology simulations aimed at reproducing potential mantle conditions under varying redox scenarios, thereby providing a robust cross-validation of observational data and theoretical models.
The central revelation from this study is that the lunar mantle beneath the SPA basin is significantly more reduced, meaning it contains a higher proportion of reduced iron and other elements, compared to the generally more oxidized mantle composition inferred from samples collected during the Apollo missions. This finding challenges long-held assumptions regarding the uniformity of the Moon’s mantle oxidation state and supports a more heterogeneous interior, shaped by complex processes both during and after lunar formation. The reduced state implies different thermal and chemical evolution pathways, affecting how we understand mantle convection, volcanism, and the genesis of lunar mare basalts.
One of the key implications of a more reduced lunar mantle is its impact on the nature and behavior of lunar magmatism. Reduced conditions enhance the presence of metallic iron and decrease the oxygen fugacity, which in turn influences melting temperatures and magma viscosities. Consequently, volcanic activity within the SPA basin region may have differed substantially from that in other lunar regions, possibly contributing to the distinct compositional signatures observed in remote sensing and sample return data. This provides a better framework to interpret the compositional diversity of lunar volcanic rocks and the timing of volcanic episodes in the Moon’s history.
Furthermore, the study offers fresh perspectives on the volatile inventory of the lunar interior. A more reduced mantle can retain higher concentrations of volatile components such as hydrogen, carbon, and sulfur in forms different from those found in more oxidized settings. This suggests that the lunar interior, or at least the portion beneath the SPA basin, might have preserved primordial volatiles from the Moon’s accretion or from late-stage volatiles delivered by impacts. Such insights are pivotal to unraveling the long-standing debate about the origin and distribution of lunar water, which has far-reaching implications for both planetary science and future human exploration.
The methodology employed by Zhang et al. is particularly notable for its integration of multispectral datasets and high-fidelity simulations. High-resolution data from instruments aboard NASA’s Lunar Reconnaissance Orbiter (LRO), China’s Chang’e missions, and other recent spacecraft provided the empirical foundation, while thermodynamic modeling established the chemical context. This multi-disciplinary approach underscores the increasing sophistication in planetary exploration, where remote sensing, petrological experiments, and computational simulations converge to produce nuanced views of extraterrestrial interiors inaccessible by direct sampling.
Moreover, the identification of heterogeneity in the lunar mantle redox state aligns with recent findings suggesting complex mantle dynamics and possible ancient mantle overturn events following the Moon’s early differentiation. If parts of the lunar interior retained a significantly reduced signature, this could indicate that not all mantle domains mixed efficiently, preserving chemically distinct reservoirs over billions of years. This challenges simpler models of lunar mantle convection and necessitates more detailed geodynamic modeling to reconcile such chemical heterogeneity with the Moon’s thermal and structural evolution.
The insights from this research also enhance our understanding of the broader processes that governed terrestrial planet formation in the early solar system. The Moon is widely regarded as a natural laboratory for studying planetary differentiation and evolution due to its relatively accessible surface and lack of subsequent plate tectonics. Discovering a more reduced mantle domain beneath the SPA basin provides clues about the oxidation conditions prevalent in the inner solar system during the epoch of planetary accretion and helps constrain models of volatile delivery and retention in planetary bodies.
In addition to their geological significance, these findings carry implications for future lunar exploration goals, especially those targeting the South Pole–Aitken basin. As international space agencies and private enterprises develop plans for robotic missions and eventual crewed bases in this region, understanding the mantle composition is critical for resource utilization, such as extraction of volatiles or potential energy sources. A reduced mantle environment might support different mineral resources or influence in-situ resource utilization strategies, directly affecting mission planning and scientific priorities.
Critically, this study also highlights the importance of revisiting and refining lunar theories in light of new datasets and analytical techniques. For decades, much of lunar science rested upon the relatively limited suite of surface samples returned by Apollo missions, which, while invaluable, represent only specific locales and may not capture the full complexity of the lunar interior. By leveraging remote spectral data and integrating experimental petrology, Zhang and colleagues demonstrate how novel approaches can uncover previously hidden aspects of lunar geology, encouraging a re-examination of other lunar regions with similarly advanced methods.
As the Moon continues to be a focal point for planetary science and human exploration alike, understanding its interior chemical state is a foundational piece in the puzzle. The discovery of a more reduced mantle beneath the South Pole–Aitken basin can serve as a catalyst for new hypotheses concerning the Moon’s formation, its internal differentiation processes, and the volatile history of terrestrial planets more broadly. It challenges scientists to rethink models of lunar evolution and encourages the incorporation of variable oxidation states into future studies.
Looking ahead, the research community anticipates that upcoming missions equipped with landers and rovers targeting the SPA basin, such as those planned in China’s Cháng’é lunar program and NASA’s Artemis initiative, will provide critical ground truth for these remote sensing discoveries. Direct sampling and in-situ analysis of mantle-derived materials would allow for precision measurements of oxidation conditions and volatile contents, validating or refining the reduced mantle hypothesis and expanding our knowledge far beyond what is currently possible.
The implications of this study also underline the interconnectedness of planetary bodies within our solar system, showing how comparative planetology benefits from integrating data across different missions and scientific disciplines. By fostering collaboration between spectroscopists, petrologists, geochemists, and planetary modelers, this holistic approach is setting a new standard for unraveling planetary interiors and the histories written into their chemical fingerprints.
In conclusion, Zhang et al.’s revelation of a more reduced mantle beneath the lunar South Pole–Aitken basin represents a significant leap forward in lunar science. It opens new avenues for investigating the Moon’s thermal and chemical evolution, informs our understanding of volatile retention in planetary mantles, and provides crucial context for future exploration endeavors. As we stand on the cusp of a renewed era of lunar exploration, insights into the Moon’s interior composition will help unlock the mysteries of our closest celestial neighbor and enrich our understanding of planetary formation dynamics across the cosmos.
Subject of Research: Chemical state and redox conditions of the lunar mantle beneath the South Pole–Aitken basin.
Article Title: A more reduced mantle beneath the lunar South Pole–Aitken basin.
Article References:
Zhang, H., Yang, W., Zhang, D. et al. A more reduced mantle beneath the lunar South Pole–Aitken basin. Nat Commun 16, 6985 (2025). https://doi.org/10.1038/s41467-025-62341-5
Image Credits: AI Generated
