The study also shed new light on the complex chemical exchange between Earth and the Moon. “We conducted a series of experiments involving oxygen and hydrogen irradiation to simulate processes on the lunar surface. Our experiments demonstrated for the first time both the formation and reduction of hematite minerals,” wrote the team led by planetary scientist Xiandi Zhen.
The Recipe for Hematite Formation
Hematite forms as a result of iron oxidation, a process commonly known as rusting. This mineral is abundant on Earth. Meanwhile, the lacks an atmosphere, possessing only a thin exosphere that does not contain oxygen. Additionally, our planet’s natural satellite is constantly bombarded by a stream of hydrogen from the solar wind. Hydrogen acts as a reducer, donating its electrons to the materials it interacts with. Oxidation occurs through the loss of electrons. So even if all the necessary elements for oxidation were present on the Moon, the solar wind would neutralize them.
One possible explanation for the presence of hematite is linked to Earth. The solar wind, which affects Earth’s magnetosphere, causes its structure to stretch in the opposite direction of the Sun. This magnetospheric tail also contains particles that leak from Earth’s atmosphere, as reported by Science Alert.
During a full moon, ions of terrestrial oxygen reach Earth’s natural satellite as it passes through the tail of its magnetosphere. Being in Earth’s shadow means that 99 percent of the solar wind cannot reach the Moon.
This means that Earth’s satellite is bombarded by oxygen for about five days each month, while experiencing reduced bombardment by hydrogen. This is a potential recipe for hematite formation.
Diagram illustrating the configuration of Earth, the Moon, and the Sun that can create hematite.
What Did the Experiment Show?
During the laboratory experiment, researchers directed oxygen ions at iron-rich minerals to simulate the effect of Earth’s wind in the magnetospheric tail. For lunar iron mineral analogs, the scientists used pyroxene, olivine, ilmenite, troilite, and an iron meteorite. They also conducted experiments with magnetite (Fe3O4), confirming that this mineral is an intermediate stage between metallic iron and hematite.
The results showed that oxygen ions can oxidize metallic iron, ilmenite, and troilite. However, the effect was significantly stronger for metallic iron. At the same time, iron-bearing silicates like pyroxene and olivine did not form hematite at all, indicating the selectivity of the process.
“Our experimental results convincingly demonstrate that hematite can form on the Moon’s surface under the influence of oxygen ions. Earth’s wind—the primary source of energetic oxygen ions on the Moon—acts as an oxidizer, causing the oxidation of various minerals, such as metallic iron and iron-bearing oxides and sulfides, prevalent in the lunar regolith,” the researchers wrote in their report.
They believe that while these iron-bearing minerals occur as micro-particles or small crystals in the lunar regolith, they can undergo direct oxidation under the influence of Earth’s wind.
The scientists also noted that the solar wind cannot reverse the rusting process of lunar iron caused by the periodic influx of terrestrial oxygen. This also explains why hematite is concentrated near the lunar poles: Earth’s magnetospheric tail directs oxygen ions toward high latitudes while deflecting many hydrogen ions.
The findings of the study were published in the journal Geophysical Research Letters.
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