Oxygen‐Deficient Magnetite in Chang’e‐6 Sample as Evidence for Impact Induced Deoxygenation of the Moon

Abstract

The Moon’s highly reduced nature contrasts with recent findings of ferric iron (Fe ³⁺ )‐bearing phases, suggesting an active redox cycle on the Moon. While solar wind proton reduction and impact‐vaporization oxygen loss from minerals are proposed drivers for lunar reduction, direct nanometer‐scale evidence for impact‐driven deoxygenation has been lacking. Here we report the discovery of oxygen‐deficient magnetite within impact melt glass in Chang’e‐6 lunar farside samples from the South Pole‐Aitken basin. This subhedral magnetite grain (Length 2.5 μm; width 1.5 μm.) exhibits a non‐stoichiometric composition and crystal chemical formula [(Fe ²⁺ _1.158(7) Mg _0.070(5) ) _∑1.228 (Fe ³⁺ _1.534(9) Cr ³⁺ _0.137(14) Al _0.101(8) ) _∑1.772 ] _∑3.000 (O _3.886 □ _0.114 ) _∑4.000 , confirming significant oxygen vacancies (□). Magnetite heating experiments (1000°C, in Ar atmosphere) replicated these features, demonstrating thermal deoxygenation generates oxygen vacancies through O ₂ evolution and concurrent Fe ³⁺ reduction. Our findings provide the first mineral structural evidence that post‐shock heating drives deoxygenation in oxygen‐bearing minerals, establishing impact‐induced oxygen removal as a fundamental mechanism making the localized lunar surface chemically reduced.