It turned out that the moon is covered with rust. Perhaps the Earth is "to blame" for this

Iron reacts very actively with oxygen, forming a reddish rust, usually seen on

Earth. However, the surface and interior of the moon are practically devoid of oxygen, so pure metallic iron predominates there. Strongly oxidized iron has not been confirmed in samples obtained from the Apollo missions. In addition, hydrogen in the solar wind erodes the surface of the moon, which inhibits oxidation. So, the presence of highly oxidized iron-bearing minerals such as hematite on the Moon is an unexpected discovery.

Our hypothesis is that lunar hematiteis formed by the oxidation of iron on the lunar surface with oxygen from the upper layers of the Earth's atmosphere, which has been continuously blown out onto the lunar surface by the solar wind when the moon has been in the tail of the earth's magnetosphere for the past several billion years.

Shuai Li, Associate Research Fellow, Hawaii Institute of Geophysics and Planetology (HIGP)

To make this discovery, Lee, professor at HIGPPaul Lucy and colleagues at NASA's Jet Propulsion Laboratory (JPL) analyzed hyperspectral reflection data from NASA's JPL Moon Mineralogy Mapper (M3) program aboard India's Chandrayaan-1 mission.

Moon Hematite Map - Red means more hematite. Credit: Shuai Li

This new study was inspired by Lee's previous discovery of water ice in the moon's polar regions in 2018.

“When I examined the M3 data in polarregions, I found that some spectral features and patterns differ from those that we see at lower latitudes or in the Apollo samples, Lee said. - I was curious if it was possible that there is a reaction of water and rock on the moon. After several months of research, I realized that I was seeing a trace of hematite. "

The team found that places where hematite is present correlate strongly with water content at high latitudes and are more concentrated on the near side, which is always facing Earth.

“More hematite on this side suggeststhat it might be related to Earth, ”Lee said. “It reminded me of the Japanese Kaguya Mission's discovery that oxygen from the Earth's upper atmosphere can be brought to the surface of the Moon by the solar wind when the Moon is in the tail of the Earth's magnetosphere. Thus, Earth's atmospheric oxygen can be the main oxidant for the production of hematite. The impact of water and interplanetary dust could also play a decisive role.

The blue areas in this composite imageobtained with the Moon Mineralogy Mapper (M3) aboard the Indian Space Research Organization's Chandrayaan-1 orbiter, show the concentration of water at the moon's poles. While on the spectrum of rocks, the researcher discovered traces of hematite, a form of rust. Credit: ISRO / NASA / JPL-Caltech / Brown University / USGS

“Interestingly, hematite is not entirely absent atthe far side of the moon, where Earth's oxygen may never have reached, ”Lee said. “The tiny amount of water (<~ 0.1 wt%) seen at high lunar latitudes may have been heavily involved in the formation of hematite on the far side of the moon, with important implications for the interpretation of observed hematite on some water-poor asteroids class S ".

Spectral class S - the class of asteroids, which includes objects with silicon (stone) composition. Therefore, asteroids of this class are also called stone. They make up 17% of all known asteroids, thus forming the second most common class of asteroids, after carbon ones.

Improved map of hematite (red) on the Moon using spherical projection (near side only). Credit: Shuai Li

“This discovery will change the way we think about the polar regions of the moon,” Lee concludes. "The earth could have played an important role in the evolution of the lunar surface."

The research team hopes the missionsNASA ARTEMIS will be able to return hematite samples from the polar regions. The chemical signatures of these samples could support their hypothesis about whether lunar hematite is oxidized by Earth's oxygen, and could help reveal the evolution of Earth's atmosphere over the past billions of years.

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