Lunar rocks brought back by China’s Chang’e-6 mission contain the first clear physical evidence of hematite and maghemite formed by asteroid impacts. This discovery, published on November 14 in Science Advances, challenges what scientists thought they knew about how oxidation can happen on the Moon’s airless surface.
The minerals were found in samples collected from the South Pole–Aitken (SPA) Basin, one of the Moon’s oldest and biggest impact craters. A team from the Institute of Geochemistry at the Chinese Academy of Sciences and Shandong University used cutting-edge techniques to confirm the presence of crystalline hematite and maghemite.
Until now, the Moon has been considered a place where oxidation doesn’t really occur, mainly because of its lack of atmosphere and overall low oxygen levels. But this sample-based proof shows that, under the right conditions, even the Moon can host highly oxidized minerals.
Digging Through Ancient Lunar Ground
The SPA Basin, where the Chang’e-6 mission landed, is a huge scar on the Moon’s far side, created billions of years ago by a massive impact. For the study, the researchers used electron microscopy, electron energy loss spectroscopy, and Raman spectroscopy to study the samples. The minerals they found were small, just microns across, but their structure clearly showed they were native to the Moon, not brought in from Earth.
This marks the first time that hematite and maghemite, in crystalline form, have been directly identified in lunar material returned to Earth. Their unique features prove that they were created by lunar processes, specifically during violent surface events in the Moon’s past.
Asteroid Strikes Turned Lunar Iron Into Rust
The team believes the minerals formed when large asteroid impacts generated intense heat, vaporizing material on the surface. In that brief moment, a high-oxygen vapor cloud could form, enough to trigger oxidation. As Phys.org reports:
“The extreme temperatures generated by large impacts would have vaporized surface materials, creating a transient high-oxygen-fugacity vapor-phase environment.”
During this window, iron from lunar minerals like troilite would have been released, oxidized, and deposited as hematite and maghemite. These minerals were found alongside magnetite, showing a range of oxidation states, all connected to the same process.
Rusty Minerals Hint At Moon’s Magnetic Secrets
The study also highlights a possible link between these oxidized iron minerals and long-standing magnetic anomalies observed on the Moon. Regions such as the northwestern SPA Basin exhibit unexplained magnetic signatures. Since hematite and maghemite are known magnetic carriers, their formation may help account for these anomalies. As noted by the research team:
The findings provide “key sample-based evidence to clarify the carriers and evolutionary history of these lunar magnetic anomalies.”
By associating oxidation processes with ancient impact events, the study adds a new dimension to the understanding of lunar geological evolution. The direct observation of hematite in returned samples bridges the gap between remote sensing data and ground truth.