Rust has been detected on the Moon, and surprisingly, Earth may be the source of this chemical transformation. Recent research finds that oxygen escaping from Earth likely drives the oxidation of lunar iron into hematite near the poles.
Hematite, a common rust mineral on Earth, forms when iron oxidizes. Until recently, its presence on the Moon was puzzling. The Moon has no atmosphere, only a thin exosphere, and its surface constantly faces hydrogen from the solar wind, which should prevent oxidation.
Even if iron and oxygen were present, hydrogen in the solar wind normally cancels oxidation, making rust formation highly unlikely on the Moon.
Earth’s magnetotail and oxygen bombardment
Scientists propose that Earth’s magnetotail delivers oxygen ions to the Moon during full moons, while blocking 99 percent of the solar wind. This creates a rare window of reduced hydrogen bombardment combined with oxygen exposure, which can trigger hematite formation on lunar iron.
Xiandi Zeng and the team at Macau University of Science and Technologytested this hypothesis using laboratory simulations of lunar surface processes.
Laboratory simulations confirm the theory
The researchers fired oxygen ions at iron-rich minerals found on the Moon, including metallic iron, ilmenite, and troilite, to mimic Earth’s wind effects.
They also tested silicates like pyroxene and olivine, which did not form hematite, showing the oxidation process is selective for certain iron-bearing minerals. The experiments confirmed that oxygen ions from Earth could oxidize metallic iron into hematite, supporting the idea that Earth wind drives lunar rusting.
Hydrogen and hematite reduction
To see if solar wind could reverse oxidation, the team fired hydrogen ions at hematite. Low-energy beams failed, while high-energy beams mimicking Earth wind partially reduced hematite.
This explains why rust persists on the Moon. Hematite is concentrated near the poles. This is where Earth’s magnetotail channels oxygen ions effectively.
Interestingly, water detected near lunar hematite might be a by-product of hematite reduction. It forms when oxygen from hematite reacts with hydrogen.
Implications for lunar science
The formation of hematite on the Moon shows a chemical exchange between Earth and the Moon over billions of years. It potentially traces oxygen in Earth’s atmosphere.
The findings may help explain the history of the Great Oxidation Event on Earth. They offer insight into how planetary processes affect satellite surfaces.
Upcoming lunar missions like Chandrayaan-3 and Chang’E-7 targeting the south pole could provide further opportunities to study Earth-Moon interactions directly.
Conclusion
This discovery highlights how Earth’s oxygen affects the Moon, creating hematite near its poles despite a lack of atmosphere.
Laboratory simulations confirm selective oxidation of iron-bearing minerals, while hydrogen from the solar wind cannot fully reverse the rusting process.
Understanding these processes expands knowledge of lunar surface chemistry, long-term Earth-Moon interactions, and the complex dynamics of space weathering.