Astronomers have identified widespread hematite deposits across the Moon's surface—a puzzling find, given the satellite's oxygen-free environment.
Hematite, a form of oxidized iron akin to rust, typically forms when iron reacts with oxygen. Yet the Moon lacks oxygen and faces a constant barrage of hydrogen from the solar wind, which donates electrons to surface materials. Oxidation, by contrast, involves electron loss—making the Moon an unlikely place for hematite formation.
Remote observations and Apollo mission samples previously revealed only pristine lunar iron. That changed with a recent study analyzing hyperspectral data from the Moon Mineralogy Mapper (M3) instrument aboard India's Chandrayaan-1 mission. Researchers detected hematite signatures at the lunar poles—an unexpected revelation.
“When I examined the M3 data from the polar regions, I noticed spectral patterns differing from those at lower latitudes or in Apollo samples,” says lead researcher Shuai Li from the Hawaii Institute of Geophysics and Planetology. “After months of analysis, I confirmed the presence of hematite.”
The hematite's distribution aligns closely with previously mapped water traces in these regions, offering a key clue.
Li's team connected this to findings from Japan's Kaguya mission in the late 2000s, which showed oxygen from Earth's upper atmosphere being swept onto the Moon by solar wind.
This mechanism likely drives hematite formation, particularly during full moons when the Moon sits in Earth's magnetotail, away from the Sun. Here, over 99% of solar wind is deflected for several hours, allowing oxidation to proceed unimpeded.
Over billions of years, trace water, imported oxygen, and these monthly windows have produced observable hematite. Upcoming NASA Artemis missions aim to sample polar hematite, with chemical analysis poised to validate this hypothesis.
