Confirmation of tetrataenite in lunar soil returned from the South Pole–Aitken Basin sheds light on how space weathering shapes strong magnetic minerals on the Moon, offering fresh insights into the farside magnetic anomalies.
For decades, scientists have puzzled over the patchwork of magnetic anomalies scattered across the Moon’s surface, particularly on its elusive farside. Unlike Earth, the Moon today lacks a global magnetic field, yet orbital surveys have consistently detected localized regions of magnetized crust whose origins remain hotly debated. Recently, a team of researchers led by Professor Yang Li from the Institute of Geochemistry, Chinese Academy of Sciences, has uncovered compelling evidence hidden within the first-ever soil samples returned from the lunar farside. As detailed in their paper "Newly discovered tetrataenite in Chang’E-6 lunar soil: a space weathering-induced magnetic carrier," published in the international journal Planet (Volume2, Issue 1, 2026), the discovery of tetrataenite—a hard magnetic mineral with exceptional remanence carrying capacity— providing a new perspective on the formation and evolution of magnetic anomalies on the lunar surface.
The Chang’E-6 mission made history in 2024 by retrieving 1,935.3 grams of regolith from the Apollo basin, located within the vast South Pole-Aitken (SPA) basin, which is one of the largest and oldest impact basins in the solar system, characterized by strong magnetic anomalies. However, direct sample evidence of the mineral carriers responsible for these “magnetic memories” has been lacking. Employing focused ion beam sample preparation and high-resolution transmission electron microscopy, the team conducted detailed mineralogical and magnetic structural analyses on these precious samples.
Among tens of thousands of lunar soil particles, a particular troilite grain caught the researchers' attention. Hemispherical in shape with a porous texture and accompanied by curved metallic iron whiskers, the grain’s morphological features suggest it experienced intense thermal events—likely from multiple impact events. Crucially, within this grain, the team identified a metallic particle approximately 500 nanometers in diameter, exhibiting a gradient in nickel distribution. High-resolution imaging and electron diffraction analysis revealed that the region with roughly 50% nickel content displayed an ordered crystal structure, perfectly matching the tetrataenite phase. Tetrataenite is an ordered iron-nickel alloy previously found primarily in meteorites but never confirmed in lunar samples. Unlike soft magnetic pure iron, which is easily magnetized but also readily demagnetized, tetrataenite is a hard magnetic mineral capable of stably retaining remanent magnetism over billions of years. Using Lorentz transmission electron microscopy, the team directly observed that both the tetrataenite and the surrounding pure iron particles exhibited characteristic vortex magnetic structures—direct evidence of magnetic stability.
Regarding the formation mechanism of tetrataenite, the study suggests that the precursor material likely originated from nickel-rich chondritic meteorites that remained on the lunar surface following an impact event. Subsequent impacts heated and melted the troilite surrounding the iron-nickel metal, forming molten droplets that were ejected from the parent material and eventually deposited in the Apollo Basin. During cooling, when nickel content reached approximately 50%, the face-centered cubic taenite underwent an ordering reaction at temperatures below 350°C, with atoms rearranging into a body-centered tetragonal tetrataenite structure while simultaneously exsolving submicron-scale pure iron particles. The study also found that certain trace elements may play a key catalytic role in this process. The team observed that regions enriched in phosphorus were often associated with localized nickel enrichment, suggesting that phosphorus may facilitate the diffusion of iron and nickel atoms, thereby accelerating tetrataenite formation. While this hypothesis requires further verification, it opens new research avenues into the chemical controls on the evolution of magnetic minerals on airless body surfaces.
This discovery has profound implications for understanding how space weathering modifies and shapes magnetic signatures on the lunar surface. Impact-generated thermal events can effectively “manufacture” minerals with strong magnetic memory on the Moon. The coexistence of tetrataenite, nanophase pure iron particles, and iron whiskers suggests a complex assemblage of magnetic minerals on the lunar surface, whose collective behavior may be a significant source of the magnetic anomalies mapped by orbital instruments. As new lunar exploration campaigns—including Artemis and the Chang’E program—move forward, understanding the magnetic properties of lunar materials has become more than an academic pursuit. Magnetic anomalies can influence local space environments, potentially affecting future lunar surface operations and in-situ resource utilization. The identification of tetrataenite in the Chang’E-6 samples provides crucial mineralogical grounding for future far-side magnetic field measurements.
The Chang’E-5 and Chang’E-6 samples used in this study were provided by the China National Space Administration. The research was supported by the National Natural Science Foundation of China, the Frontier Science Key Research Program of the Chinese Academy of Sciences, and the Guizhou Provincial Basic Research Program, among others. The study represents a collaborative effort involving the Institute of Geochemistry, Chinese Academy of Sciences, Yunnan University, Anhui University, and the Deep Space Exploration Laboratory.
DOI: 10.15302/planet.2026.26009