A new analysis of lunar soil from China’s Chang’e-6 mission has revealed something scientists didn’t expect to find on the moon – tiny grains of iron rust.
Until now, the moon was believed to lack the oxygen conditions needed for iron oxidation, so the discovery challenges long-standing views of lunar surface chemistry and may help explain mysterious magnetic anomalies detected in several regions.
The findings, published in the peer-reviewed journal Science Advances, come from a research team led by Shandong University with support from the Institute of Geochemistry of the Chinese Academy of Sciences and Yunnan University.
The team identified micrometre-scale crystals of hematite and maghemite, both forms of iron oxide, within the Chang’e-6 samples – a discovery that suggests previously unknown surface processes may have been shaping the moon for billions of years.
Discovery challenges decades-old assumption
For decades, scientists believed the moon lacked the conditions needed for iron oxidation, making iron oxides virtually nonexistent on its surface. Even though the Apollo missions detected some ferric iron–bearing materials, such as magnetite and iron hydroxides, the discovery was quickly dismissed.
A landmark study in 1971 argued that these compounds could not remain stable on the lunar surface and were most likely the result of contamination after the samples returned to Earth. This view shaped scientific thinking for more than half a century, reinforcing the idea that the moon was a dry, highly reduced environment with no natural pathway for iron to rust, the South China Morning Post reported.
That assumption began to crumble in recent years as remote sensing data and lunar samples suggested that iron oxidation may be more common on the moon than once believed. Since 2020, observations from the Moon Mineralogy Mapper have shown widespread hematite – a highly oxidised mineral – at high lunar latitudes.
Then in 2022, advanced microscopic analysis of Chang’e-5 samples revealed traces of nanophase magnetite, adding further evidence that oxidation can occur on the lunar surface.
Samples show rust is intrinsic to the moon’s geology
By studying the Chang’e-6 samples returned in June last year, Chinese scientists identified micron-scale hematite grains for the first time, demonstrating that these iron oxides are a natural part of the moon’s geology. To understand how ferric iron forms on the moon, the researchers examined several possible mechanisms and ruled out some alternatives.
They found that oxidised iron minerals appeared mainly in lunar soil breccias – rocks made of fragments fused by the extreme heat and pressure of meteorite impacts – while such minerals were absent in untouched fragments of ancient volcanic rock. The researchers suggest that the hematite grains were produced by massive impact events, like those that created the South Pole–Aitken basin and the Apollo crater on the moon’s far side.
The South Pole–Aitken basin, home to the Chang’e-6 landing site, is one of the oldest and largest impact basins in the solar system; it has experienced multiple major collisions and remained untouched by later volcanic lava flows, making it an ideal location for preserving minerals created by ancient impacts.