Earth’s oxygen can cause the Moon to rust


It takes oxygen to rust iron. So when scientists spread hematite widely through lunar high latitudes, they were surprised. How did this happen?

A new study suggests that oxygen from Earth may play a role in rusting the moon.

Hematite, also known as hematite, is an iron oxide with the formula Fe2O3. It is common on Earth, and is the main iron ore extracted by mining. It is formed only in the presence of oxygen.

The formation of hematite on the moon is an unexpected event. There is no oxygen to speak of, so there is no way for iron oxidation and hematite. Not only that, but the lunar surface is completely exposed to hydrogen in the solar wind, which actively resists oxidation. So what’s happening?

“I was curious if it is possible that there are water-rock reactions on the moon.”

Shuai Li, Lead Writer, University of Hawaii

A new study reveals that the Earth’s atmosphere is the source of oxygen for lunar hematite. The paper is titled “Extensive Hematite at High Latitudes of the Moon.” The lead author is Shuai Li, an assistant researcher at the University of Hawaii and the Institute of Geology and Hawaii Sciences (HIGP) at the University of Hawaii at the Hawaii School of Onion and Earth Science and Technology (SOAST). The paper is published in the journal Science Advance.

“Our hypothesis is that lunar hematite is formed by oxidation of lunar surface iron by oxygen from the Earth’s upper atmosphere that has been continuously flown from the solar wind to the lunar surface when the moon is in the Earth’s magnetic core during the past several billion years. “Lee said in a press release.

“Earth may have played an important role on the development of the lunar surface.”

Shuai Li, Lead Writer, University of Hawaii

These results originated from a collaboration between the Indian Space Research Organization NASA and ISRO. In 2008, ISRO launched its Chandrayaan-1 lunar orbiter. The mission only lasted 10 months out of an expected two years, but it still collected a significant amount of scientific data. Along with all its Indian scientific instruments, the orbiter also carried out six other instruments from other organizations and countries.

NASA contributed Moon Mineralogy Mapper or M3. It was an imaging spectrometer designed for mineralogical maps of the lunar surface. It was the first device to provide high-resolution imagery of minerals on the lunar surface. This new research is largely based on that data.

“When I examined M3 data in the polar regions, I found that some spectral features and patterns are different from those we see in samples from lower latitudes or Apollo,” Lee said. “I was curious if it is possible that there are water-rock reactions on the moon. After months of investigation, I came to know that I was seeing the signature of the hematite. ”

Previous research of the Moon was also involved in this discovery. Back in 2018, Lee was a writer announcing the discovery of water ice on the moon. The research was based on M3 data, and the Lunar Reconnaissance Laser Olimator based on the Lunar Reconnaissance Laser Olimator.

An image from a 2018 research showing water ice deposits on the moon. Image courtesy: Li et al, 2020

In this new research, Li and his colleagues found that hematite concentrations strongly correlated with water ice deposits. The hematite also focuses more on the proximity of the Moon, which always faces the Earth.

This image from the study is a map of hematite on the moon.  The redder color means more hematite is present.  Sincerely: Shuai Li
This image from the study is a map of hematite on the moon. The redder color means more hematite is present. Sincerely: Shuai Li

“This discovery will reopen our knowledge of the Moon’s polar regions,” Lee said. “Earth may have played an important role on the development of the lunar surface.”

This is where some other previous research plays come into play. The Japanese (JAXA) Kaguya mission, also known as SELENE (Selenological and Engineering Explorer), was a lunar orbiter launched in 2007, and orbited the moon for a year and eight months.

Kagua’s mission was to study the geology of the Moon, its origin, its surface atmosphere and its gravitational field. But it also found evidence of oxygen transported from the Earth’s atmosphere to the Moon. For five days in each orbit of the Moon, it is protected from the solar wind by the Earth’s magnetosphere. During that time, oxygen is able to move from the Earth’s atmosphere to the lunar surface.

This data from the 2017 paper shows how the Earth's oxygen is transported to the Moon for five days in each lunar orbit.  The squares represent the position of the Kaguya spacecraft.  Image Credit: Terada et al, 2017
This data from the 2017 paper shows how the Earth’s oxygen is transported to the Moon for five days in each lunar orbit. The squares represent the position of the Kaguya spacecraft. Image Credit: Terada et al, 2017

“More hematite on the adjacent lunar suggested that it may be related to the Earth,” Lee said. “It reminded me of a discovery by the Japanese Kugya Mission that oxygen from the Earth’s upper atmosphere can be blown up by the solar wind to the lunar surface when the moon is in the Earth’s magnetotail. Therefore, the Earth’s atmospheric oxygen may be the major oxidant producing hematite. Water and interplanetary dust effects may also have played an important role. ”

Although hematite concentrations near the Moon were much more prevalent, there were few on the far side. The reasons for this are still unclear, although Lee says it may shed some light on hematite formation on asteroids.

Lee said, “Interestingly, the hematite is not at all absent from the end of the moon, where the Earth’s oxygen has never reached, although very little exposure has been observed.” “Small amounts of water (<~ 0.1 wt. Percent) have been observed at lunar high latitudes that may be largely involved in the hematite formation process at lunar distances, with some water poorly important to explain the hematite observed at S. The implications are. Type asteroids. "

This figure of study shows the spectra of hematite deposits.  The red and blue lines represent different ways of interpreting the data, while the black line is a laboratory measurement for comparison.  Image courtesy: Li et al, 2020
This figure of study shows the M3 spectra of hematite deposits. The red and blue lines represent different ways of interpreting the data, while the black line is a laboratory measurement for comparison. Image courtesy: Li et al, 2020

If this research is correct, it means that hematite deposits may be important clues to Earth’s history. If hematite is preserved in craters with varying ages of impact, those deposits will contain different isotopes of oxygen from different time periods in Earth’s geologic past. If future missions like Artemis can collect samples from those craters, scientists can learn a lot. Not only can this vindicate Lee’s hypothesis, it can shed new light on Earth’s history.

As the authors write in their paper, “Hematite formed on craters of different ages near the lunar can record the oxygen signatures of the Earth’s atmosphere over the last ~ 2.4 billion years. The measurements of isotopes in these hematite exposures can reveal the evolution of the Earth’s atmosphere over the past billions of years. ”

Lee and his colleagues also say that these hematite deposits may be important in-situ resources in the future. “It is suggested that the lunar polar regions are relatively iron-poor. Thus, our mapped hematite may be an important in situ resource for iron metal. ”

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