To the surprise of many planetary scientists, hematite , an oxidized iron ore , has been discovered at high latitudes on the Moon. Oxygen from Earth may have influenced their presence.
It is the conclusion of a study led by Shuai Li, assistant researcher at the Hawaii Institute of Geophysics and Planetology (HIGP), at the UH Manoa School of Ocean and Terrestrial Sciences and Technology (SOEST), and published in the journal ‘ Science Advances ‘.
Iron is highly reactive with oxygen, forming the reddish rust commonly seen on Earth. The surface and interior of the Moon, however, are virtually devoid of oxygen, so pristine metallic iron is prevalent on the Moon and highly oxidized iron has not been confirmed in samples returned from the Apollo missions.
Also, hydrogen from the solar wind hits the lunar surface, which acts in opposition to oxidation. Therefore, the presence of highly oxidized iron-containing minerals, such as hematite, on the Moon is an unexpected discovery.
‘Our hypothesis is that lunar hematite is formed through the oxidation of iron on the lunar surface by oxygen in the Earth’s upper atmosphere which has been continuously drawn to the lunar surface by the solar wind when the Moon is in the Earth’s magnetic tail for the past billions of years, ”explains Li.
To make this discovery, Li, HIGP professor Paul Lucey, and co-authors from NASA’s Jet Propulsion Laboratory (JPL) analyzed hyperspectral reflectance data acquired by NASA’s JPL-designed Moon Mineralogy Mapper (M3). aboard India’s Chandrayaan-1 mission.
This new research was inspired by Li’s earlier discovery of water ice in the Moon’s polar regions in 2018. “When I examined the M3 data in the polar regions, I found some spectral features and patterns that are different from what we see. in the lower latitudes or the Apollo samples – Li details. I was curious to know if it is possible that there are reactions of water and rock on the Moon. After months of research, I discovered that I was seeing the signature of the hematite.
The team found that the places where hematite is present are strongly correlated with the water content at high latitude and others previously found and are more concentrated on the near side, which is always facing the Earth.
“More hematite on the lunar near side suggested that it could be related to Earth,” Li deduces. This reminded me of a discovery by the Japanese Kaguya mission that oxygen from Earth’s upper atmosphere can be carried to the lunar surface by the solar wind when the Moon is on the Earth’s magnetic tail. Therefore, atmospheric oxygen on Earth could be the main oxidant to produce hematite. Water and the impact of interplanetary dust may also have played a role. ‘
“Interestingly, hematite is not absolutely absent from the far side of the Moon, where the Earth’s oxygen may never have reached, although far fewer exposures were observed,” Li admits. The miniscule amount of water (<0.1% by weight) observed at high lunar latitudes may have been substantially involved in the hematite formation process on the far side of the moon, which has important implications for the interpretation of the hematite observed in some water-poor S-type asteroids. ‘
Li assures that “this discovery will reshape our knowledge about the polar regions of the Moon. The Earth may have played an important role in the evolution of the Moon’s surface. ‘
The research team hopes that NASA ARTEMIS missions will be able to return samples of hematite from the polar regions. The chemical signatures of those samples can confirm your hypothesis that lunar hematite is oxidized by Earth’s oxygen and can help reveal the evolution of Earth’s atmosphere over the past billions of years.
