Tiny iron oxide grains found in lunar soil samples brought by the Chinese Chang’e-6 mission upend what was known about the Moon’s surface and magnetic properties, scientists revealed in a new study.
Until now, the Moon has been thought to have an environment that did not favour the oxidation of elements, and iron oxides were thought to be virtually absent.
Consistent with this, iron on the Moon has been found mostly in its reduced forms, without any added oxygen.
Recent exploration missions have hinted at the widespread presence of the magnetic iron-oxide mineral hematite in the Moon's high-latitude regions.
However, these minerals found in the Moon samples, including those collected during Nasa’s Apollo missions, were thought to be unstable compounds on the lunar surface.
Samples retrieved by the previous Chang'e-5 mission revealed evidence of some oxidised forms of iron within glass formed on lunar soil from meteorite impact's intense heat and pressure.
These results suggested that localised metal oxidation on the Moon existed during processes driven by external meteorite impacts.
But conclusive mineral evidence for strongly oxidising minerals like hematite on the Moon had remained elusive.
Now, Chang’e-6 lunar samples brought to Earth in June last year by China reveal tiny grains of the iron oxide mineral hematite, marking the first such discovery on the Moon.
These minerals were found mainly in grains of special Moon rocks made up of fragments fused by the intense heat and pressure of meteorite impacts, according to a new study published in the journal Science Advances.
“This finding provides credible evidence for the presence of Fe2O3 on the lunar surface, challenging the traditional understanding of the lunar surface,” scientists wrote in the study.
Researchers now theorise that these minerals were formed during large-scale meteorite impacts similar to the ones previously discovered in the lunar South Pole’s Aitken (SPA) basin, and the Apollo crater on the far side of the Moon.
During such meteorite impacts, scientists suspect oxygen-rich minerals like troilite and other sulphides on the Moon released their oxygen into the surroundings, which then reacted with the iron minerals, causing them to “rust”.
The findings were possible thanks to the successful return of soil samples from the SPA Basin by the 2024 Chang'e-6 mission, providing an opportunity to search for highly oxidised substances on the Moon, researchers say.
They could also help explain the origin of strange magnetic anomalies on the lunar surface, including those in the northwestern SPA Basin, which remain poorly understood, scientists say.
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