http://www.sci-news.com/space/hematite-moon-08809.html
Map of hematite (redder color) on the Moon.
Image credit: Li et al, doi: 10.1126/sciadv.aba1940.
The lunar surface and interior, 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.
In addition, hydrogen in solar wind blasts the lunar surface, which acts in opposition to 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 hematite is formed through oxidation of lunar surface iron by the oxygen from the Earth’s upper atmosphere that has been continuously blown to the lunar surface by solar wind when the Moon is in Earth’s magnetotail during the past several billion years,” said Dr. Shuai Li, a researcher in the Hawai’i Institute of Geophysics and Planetology at the University of Hawaii.
To make this discovery, Dr. Li and colleagues analyzed hyperspectral reflectance data acquired by the M3 instrument.
“When I examined the M3 data at the polar regions, I found some spectral features and patterns are different from those we see at the lower latitudes or the Apollo samples,” Dr. Li said.
“I was curious whether it is possible that there are water-rock reactions on the Moon. After months investigation, I figured out I was seeing the signature of hematite.”
The researchers found the locations where hematite is present are strongly correlated with water content at high latitudes and are more concentrated on the nearside, which always faces the Earth.
“More hematite on the lunar nearside suggested that it may be related to Earth,” Dr. Li said.
“This reminded me the discovery by JAXA’s Kaguya mission that oxygen from the Earth’s upper atmosphere can be blown to the lunar surface by solar wind when the Moon is in the Earth’s magnetotail.”
“So, Earth’s atmospheric oxygen could be the major oxidant to produce hematite. Water and interplanetary dust impact may also have played critical roles.”
“Interestingly, hematite is not absolutely absent from the farside of the Moon where Earth’s oxygen may have never reached, although much fewer exposures were seen.”
“The tiny amount of water (< 0.1 wt.%) observed at lunar high latitudes may have been substantially involved in the hematite formation process on the lunar farside, which has important implications for interpreting the observed hematite on some water poor S-type asteroids.”
“This discovery will reshape our knowledge about the Moon’s polar regions.”
“Earth may have played an important role on the evolution of the Moon’s surface.”
The discovery is reported in a paper published today in the journal Science Advances.
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