The Moon is turning slightly red. The blame? Probably from Earth. A team of astronomers at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, has discovered striking deposits of hematite (Fe2O3) on the Moon’s surface that are found at high latitudes and predominantly on the near side of our satellite relative to us, according to data from the Moon Mineralogy Mapper (M3) aboard India’s Chandrayaan-1 mission. Hence, experts suggest that the atmosphere of our planet may be causing the Moon to rust. They believe that oxygen from the Earth is flying to the Moon and forming this mineral.
Iron is very reactive to oxygen
Iron oxide, or oxide of iron, is a reddish compound that forms when iron is exposed to water and oxygen . Rust is the result of a chemical reaction common for materials such as nails, doors, the red rocks of the Grand Canyon of the Colorado in the United States, and even for Mars. In fact, our neighboring red planet gets this nickname from the rust it acquired a long, long time ago, when iron on its surface combined with oxygen and water, the scientists explain in their study published in the journal Science Advances.
However, the Moon does not have this tendency to oxidation because it neither has an atmosphere nor does it have water . It is dry. So how is it possible that it is rusting? If there are highly oxidized minerals on the Moon, like hematite , what is the explanation?
“It’s very puzzling,” said Shuai Li, an assistant researcher at the Hawaii Institute of Geophysics and Planetology at the University of Hawaii at Mānoa and a leader on the paper. “The Moon is a terrible environment for rust to form.”
To elucidate this question, the scientists analyzed the hyperspectral reflectance data acquired by the M3 instrument.
“When I examined the M3 data in the polar regions, I found that some spectral features and patterns are different from what we see at lower latitudes or the Apollo samples,” Li clarified. “I was curious if it is possible that there are water-rock reactions on the Moon. After months of research, I discovered that I was seeing the hematite signature . “
Furthermore, the places where hematite was (and is) present are more concentrated on the near side, which always faces Earth.
Does the Earth have something to do with it?
” 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 that has been continuously drawn to the lunar surface by the solar wind ,” says Li. This terrestrial oxygen travels to the Moon along an elongated stretch of the planet’s magnetic field called the ‘magnetic tail’.
The Earth’s magnetic tail can reach the near side of the moon , where the greatest amount of hematite has been identified. In addition, at each full moon, the magnetic tail blocks 99% of the solar wind from hitting the Moon, drawing a temporary curtain on the surface and facilitating certain periods of time for rust to form. However, we still lack another ingredient for rust to form: water.
And the water?
According to the researchers, fast-moving dust particles bombarding the Moon could release water molecules trapped in the satellite’s surface layer, allowing the water to mix with the iron and ultimately obtaining the other necessary component that we were missing.
“This discovery will reshape our knowledge about the Moon’s polar regions, ” Li said.
It seems that our planet has played a more than relevant role in the evolution of the surface of our small satellite. Yes indeed; more data will be needed to verify this hypothesis. Fortunately, one of the future missions of NASA’s Artemis program, which will mark humanity’s return to the Moon in 2024, will collect rocks in the satellite’s polar regions to analyze in detail and hopefully confirm these findings.
Referencia: Shuai Li et al. 2020. Widespread hematite at high latitudes of the Moon. Science Advances 6 (36): eaba1940; doi: 10.1126/sciadv.aba1940
