For over half a century, the Moon has been perceived as a largely ‘reduced’ world, where iron stubbornly resisted oxidation. But a groundbreaking discovery from China’s Chang’e-6 mission is rewriting the story of our celestial neighbor!
For years, scientists operated under the assumption that the Moon’s surface was too harsh, too devoid of oxygen, and too battered by solar radiation for minerals like hematite (rust) to naturally form. This view was largely based on samples from the Apollo missions, which seemed to confirm that the Moon’s environment simply wouldn’t allow for the development of these oxidized, or ‘rusty,’ minerals. The prevailing thought was that any hint of ferric iron phases found in the Apollo samples was merely contamination that occurred after the rocks returned to Earth.
However, the Chang’e-6 mission has thrown a wrench into this long-held belief. A recent study has unveiled the first confirmed presence of crystalline hematite and maghemite in lunar soil collected from the far side’s South Pole–Aitken Basin. This startling discovery suggests that oxygen-rich pockets did, in fact, exist on the Moon, likely created during massive impact events that briefly altered the local conditions. And this finding has the potential to explain some of the Moon’s most puzzling features.
A Paradigm Shift in Lunar Science
For decades, the scientific community largely agreed that the Moon originated from material from Earth’s mantle, following a violent collision with a Mars-sized body. The Moon’s internal chemistry seemed to support this narrative. But the surface environment, with its low oxygen levels and constant bombardment by solar particles, didn’t seem to fit the picture. Even orbital data hinting at the presence of hematite near the lunar poles sparked debate, with some scientists suggesting that oxygen drifting from Earth’s upper atmosphere might be responsible. But here’s where it gets controversial… despite these arguments, no one had found definitive, mineralogical proof of hematite formation on the Moon—until now.
The Chang’e-6 mission’s findings are particularly significant. The research team, comprised of scientists from the Institute of Geochemistry at the Chinese Academy of Sciences and Shandong University, identified micrometer-scale ferric iron particles in a mere three-gram soil sample. These tiny grains were confirmed using advanced techniques like Raman spectroscopy, transmission electron microscopy, and electron energy loss measurements.
What the Samples Reveal
Within the lunar soil, the researchers discovered nine minuscule grains containing ferric iron. One of these samples, encased in a breccia fragment, contained a hematite crystal only a few micrometers across. High-resolution images revealed it perched on a troilite grain. When the team examined a hair-thin slice of the region, they observed a layered structure: hematite on top of troilite, with magnetite and maghemite bridging the gap between the two. Energy-dispersive x-ray maps showed a clear separation between the minerals, proving that the ferric iron phases formed after the sulfide. The hematite grain also had a thin, glassy coating made of silicon and oxygen, which likely condensed from a vapor cloud. The lattice patterns in the hematite matched known crystal structures, and the iron’s oxidation state was consistent with pure Fe³⁺ in parts of the grain, with mixed valence states at the interface.
This level of detail leaves little room for doubt. These minerals formed on the Moon, not in a laboratory or during transport.
How Impacts Created Rust in a Low-Oxygen World
The most plausible explanation for this phenomenon points to large impacts. When a massive object slams into the Moon, temperatures can soar above 700 degrees Celsius. This causes minerals to break apart, releasing oxygen into a hot, turbulent plume. Even in a reduced environment, these violent events can briefly create oxidizing conditions. In this environment, troilite can lose sulfur and release iron, which then reacts with the newly freed oxygen. As the plume cools, iron condenses back onto nearby grains and forms ferric oxides. The Chang’e-6 samples were collected from a region shaped by countless large impacts over billions of years, making it an ideal location to capture minerals formed in these short-lived bursts.
The temperatures recorded in the sample suggest a sweet spot: hot enough to remove sulfur and oxidize iron, but not hot enough to break down nearby ilmenite. This aligns with the conditions expected at the edges of a large impact plume.
Why These Minerals Survived for Billions of Years
If impacts can create hematite, the next question is why earlier missions didn’t find it. The answer may lie in location and preservation. Most Apollo and Luna missions landed on the near side, where young lava flows cover much older impact deposits. The Chang’e-6 site, however, is on the lunar far side, within the South Pole–Aitken Basin. This area has fewer volcanic layers and better preserves ancient materials.
The site also experiences less solar wind than equatorial regions. Since solar wind particles can reduce Fe³⁺ back to Fe²⁺, a weaker flux helps ferric iron survive. Magnetic anomalies around the basin may offer even more shielding by redirecting charged particles. The presence of maghemite, a strongly magnetic mineral, may even help explain how those anomalies formed.
How Scientists Confirmed the Discovery
The team employed a suite of advanced tools to piece together the full story. Raman spectroscopy was used to identify grains with ferric signatures. Electron microscopes revealed crystal shapes and boundaries. Energy loss spectroscopy measured oxidation states with pinpoint accuracy. Thermodynamic modeling helped test whether impact conditions could produce the minerals found.
Each method converged on the same conclusion: The Moon’s surface has experienced brief periods of oxidation strong enough to produce hematite and maghemite, and the Chang’e-6 samples captured those traces.
Practical Implications of the Research
These findings reshape our understanding of lunar evolution. The presence of ferric minerals means the Moon’s surface chemistry is more dynamic than previously believed. The research provides a clearer view of how giant impacts influence planetary surfaces and offers new insights into the origin of lunar magnetic anomalies. It also guides future explorers in their search for oxidized resources that could support long-term missions.
More broadly, the research demonstrates that even airless bodies can undergo surprising chemical changes when impacts provide the right conditions.
What do you think? Does this discovery change your perception of the Moon? Are you surprised by the evidence of oxidation, or did you suspect that the Moon might be more complex than we previously thought? Share your thoughts in the comments below!
Research findings are available online in the journal Science Advances.