A new study by a Chinese research team has shed new light on the presence and formation of ferric iron (Fe3+), a version of iron that contains oxygen, on the lunar surface.
Surprisingly abundant traces of the compound were discovered in glassy agglutinates — rock and mineral mixed with melted glasses — present in lunar soil brought to Earth by China’s Chang’e-5 mission in 2020. Scientists assumed then that ferric iron would be rare on the Moon since its surface is known to be chemically “reductive,” an environment that makes forming oxidized compounds difficult. The mission sourced the 1,700 grams (approximately 60 ounces) of lunar soil from the Mons Rümker volcanic complex, a previously unexplored region on the Moon. According to the new research based on the Chang’e-5 samples published in Nature Astronomy on Monday, there may be more ferric iron on the moon than previously believed, as the compound can be formed from the constant barrage of tiny rocks called micrometeorites on the lunar terrain.
“The occurrence of Fe3+ in lunar materials has been discussed for decades,” the Chinese research team, led by professors Xu Yigang and He Hongping from the Guangzhou Institute of Geochemistry of the Chinese Academy of Sciences, noted in the study. “How Fe3+ forms, accumulates and evolves in the reductive environment of the Moon surface is still under debate.”
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“Here we present robust evidence from a lunar sample for the formation of a large amount of lunar Fe3+ during micrometeoroid impacts on the airless lunar surface,” the team added.
The scientists concluded that since the Moon does not have an atmosphere like Earth, it is more vulnerable to impacts from micrometeorites.
Lunar samples brought to Earth by NASA astronauts of the Apollo program in the late ‘60s to early ‘70s similarly contained amounts of Fe3+ that were only faintly detected at the time.
Scientific analyses of the Apollo samples conducted with better instruments in recent years actually showed higher concentrations of the compound.
In 2020, researchers from the University of Hawaii detected the presence of hematite (a form of iron oxide or rust) on the lunar surface after studying data from the Indian Space Research Organization’s Chandrayaan-1 orbiter, which surveyed the Moon in 2008.
The scientists posited that the oxygen in the iron compounds may have originated from lunar ice deposits or Earth due to the atmospheric gas that leaks into space.