Improved map of hematite (red color) on the moon using a sphere projection (only close by). Photo credit: Shuai Li
To the surprise of many planetary scientists, the oxidized iron mineral hematite was discovered at high latitudes on the moon. This is evident from a study published today Advances in science Led by Shuai Li, research fellow at the Hawaii Institute for Geophysics and Planetary Studies (HIGP) at the UH Mānoa School of Ocean and Earth Science and Technology (SOEST).
Iron reacts very quickly with oxygen and forms reddish rust, which is often found on earth. However, the lunar surface and interior are virtually oxygen free, so pristine metallic iron predominates on the moon and highly oxidized iron has not been confirmed in samples returned from the Apollo missions. In addition, hydrogen bursts the surface of the moon in the solar wind, which counteracts oxidation. The presence on the moon of highly oxidized ferrous minerals such as hematite is therefore an unexpected discovery.
“Our hypothesis is that lunar hematite is formed by the oxidation of iron on the lunar surface by the oxygen from the Earth’s upper atmosphere, which has been continuously blown onto the lunar surface by the solar wind when the moon has been in the Earth’s magnetic tail for the last several billion years. ” said Li.
Map of hematite on the moon – more reddish color means more hematite. Photo credit: Shuai Li
To make this discovery, Li, HIGP Professor Paul Lucey and co-authors of NASAJet Propulsion Laboratory (JPL) and elsewhere, they analyzed the hyperspectral reflectance data collected by the Moon Mineralogy Mapper (M3), developed by NASA JPL on board India’s Chandrayaan-1 mission.
This new research was inspired by Li’s earlier discovery of water ice in the polar regions of the moon in 2018.
“When I examined the M3 data in the polar regions, I found that some spectral features and patterns were different from what we see in the lower latitudes or in the Apollo samples,” said Li. “I was curious to see whether it is possible that there are water-stone reactions on the moon. After months of research, I found that I was seeing the signature of hematite. ”
The team found that the places where hematite is present correlate strongly with the water content in high latitude Li and others previously found, and are more focused on the near side that is always facing the earth.
“More hematite near the moon suggested that it was earth-related,” said Li. “This reminded me of a discovery by the Japanese Kaguya mission that oxygen from the upper atmosphere of the earth could be blown onto the surface of the moon by solar wind when the moon is in the magnetic tail of the earth. So the atmospheric oxygen on earth could be the main oxidant for the production of hematite. The influence of water and interplanetary dust could also have played a crucial role. ”
“Interestingly, on the other side of the moon, where Earth’s oxygen may never have been reached, hematite is not absolutely absent, although much fewer exposures have been observed,” said Li. “The tiny amount of water (<~ 0.1 wt%) , which was observed at high latitudes of the moon, may have been significantly involved in the hematite formation process on the far side of the moon, which has important implications for the interpretation of the observed hematite in some arid S asteroids. "
"This discovery will change our knowledge of the polar regions of the moon," said Li. "The earth may have played an important role in the evolution of the moon's surface."
The research team hopes that NASA's ARTEMIS missions can return hematite samples from the polar regions. The chemical signatures of these samples can confirm their hypothesis as to whether the lunar hematite is being oxidized by the earth's oxygen and can help reveal the evolution of the earth's atmosphere over the past billions of years.
Read The Moon Is Rusting, Puzzling Scientists to learn more about this study.
Reference: “Widespread hematite in the high latitudes of the moon” by Shuai Li, Paul G. Lucey, Abigail A. Fraeman, Andrew R. Poppe, Vivian Z. Sun, Dana M. Hurley and Peter H. Schultz, September 2, 2020 , Advances in science.
DOI: 10.1126 / sciadv.aba1940
