Chinese researchers have detected micrometer-sized grains of iron oxides – essentially “iron rust” – in lunar soil from the Chang’e‑6 mission, overturning long‑held assumptions that the Moon’s surface is almost entirely non‑oxidizing and chemically “reduced.”
Rust on a World With No Air
A joint Chinese team has announced the first confirmed discovery of crystalline hematite and maghemite – both iron oxides commonly known on Earth as forms of rust – in samples returned from the Moon’s far side by the Chang’e‑6 probe.
The findings challenge the traditional view that, without free oxygen and liquid water, the lunar surface should not host significant oxidation products such as Fe₂O₃, the chemical formula for hematite.
The research, led by scientists from Shandong University, the Institute of Geochemistry of the Chinese Academy of Sciences and Yunnan University, analyzed just a few grams of regolith collected from the South Pole–Aitken (SPA) Basin, the largest and one of the oldest known impact basins in the solar system.
Within this tiny sample, the team identified micrometer‑scale grains of hematite (α‑Fe₂O₃) and maghemite (γ‑Fe₂O₃), providing direct, sample‑based evidence that oxidized iron minerals can form and survive on the Moon.
How the Discovery Was Made
To confirm the grains were genuinely lunar and not contamination from Earth, researchers combined a suite of high‑precision techniques, including micro‑area electron microscopy, electron energy loss spectroscopy and Raman spectroscopy.
These methods allowed them to map crystal structures, measure oxidation states at nanometer scales and show that the iron oxides are embedded in native lunar breccias rather than introduced later.
High‑resolution imaging revealed hematite crystals perched directly on troilite (iron sulfide) grains, with magnetite and maghemite forming transitional layers at the boundary, a structure consistent with in‑situ transformation rather than terrestrial rusting after sample return.
Energy‑dispersive X‑ray maps showed sharp chemical separations between sulfide, intermediate oxides and fully oxidized hematite, reinforcing the interpretation that these minerals formed through a multi‑step process on the Moon itself.
A New Oxidation Mechanism for the Moon
The presence of rust raises the immediate question: where did the necessary oxygen come from on an airless world?
The new study argues that large impact events over lunar history briefly created localized, oxygen‑rich vapor plumes capable of stripping sulfur from troilite and oxidizing iron to higher valence states.
According to the analysis, when an asteroid or comet slams into the SPA Basin, it generates extreme temperatures and pressures, vaporizing rock and producing short‑lived pockets with elevated oxygen fugacity.
In this environment, iron in sulfide minerals can lose sulfur and react with available oxygen, later condensing as ferric oxides – hematite and maghemite – that coat or replace earlier minerals as the plume cools.
Links to Lunar Magnetic Anomalies
One of the most intriguing aspects of the finding is its potential connection to long‑mysterious magnetic patches around the South Pole–Aitken Basin.
Magnetite and maghemite, two intermediate iron oxides identified alongside hematite, are strongly magnetic and could serve as the mineral carriers for these localized anomalies.
Until now, explanations for SPA’s magnetic signatures relied largely on indirect models and remote sensing data, without physical samples to tie the magnetism to specific minerals.
The new work offers the first sample‑based evidence that impact‑driven oxidation not only produced rust but also created magnetic iron oxides that may record the Moon’s ancient impact and thermal history.
Challenging Long‑Held Moon Theories
For decades, lunar science has been built on the notion that the Moon’s surface is overwhelmingly in a “reduced” chemical state, with very limited oxidative processes.
The confirmed presence of Fe³⁺‑bearing minerals such as hematite shows that, at least in some regions and epochs, oxidation was far more significant than models predicted.
This discovery complements earlier orbital detections of hematite at the Moon’s poles and suggestions that oxygen ions from Earth’s magnetosphere – sometimes called “Earth wind” – could slowly rust the lunar surface over billions of years.
Together, these lines of evidence are forcing scientists to revisit assumptions about how oxygen, water molecules and solar‑wind chemistry have interacted with lunar rocks through deep time.
Wider Implications for Lunar Evolution
By tying rust formation to specific impact processes in one of the oldest basins, the Chang’e‑6 samples provide a new tool for reconstructing the Moon’s environmental conditions billions of years ago.
The oxidation state recorded in these tiny grains could indirectly preserve information about impact plume temperatures, volatile content and the availability of oxygen‑bearing species in the early inner solar system.
The findings also have implications for future resource use and exploration planning at the lunar south pole and far side.
Iron oxides and associated magnetic minerals might influence regolith properties, drilling behavior and in‑situ resource utilization strategies, while also marking regions where past impacts concentrated useful materials.
What Comes Next for Lunar Science
The study, published in the journal Science Advances, is being hailed by Chinese officials and planetary scientists as a key milestone that opens a new chapter in understanding lunar oxidation.
Researchers expect that continued analysis of the Chang’e‑6 collection – along with future samples from upcoming missions – will uncover more examples of oxidized minerals and refine models of how they formed.
Follow‑up work will focus on mapping where similar rust‑bearing deposits might exist across the Moon and comparing their signatures with orbital magnetic and spectral data.
As more nations prepare sample‑return missions and human expeditions to the lunar south pole, these microscopic grains of “iron rust” are set to play an outsized role in rewriting what is known about Earth’s closest neighbor.
