Date: September 12, 2020 Source: University of Hawaii at Manoa Summary: A surprising finding of rust, the oxidized iron mineral hematite, has been discovered at high latitudes on the Moon.
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To the surprise of many planetary scientists, a study published recently in Science Advances led by Shuai Li, assistant researcher at the Hawai’i Institute of Geophysics and Planetology (HIGP) at the UH Mānoa School of Ocean and Earth Science and Technology (SOEST) finds the oxidized iron (rust) mineral hematite at high latitudes on the Moon.
Iron is highly reactive to oxygen — which causes reddish rust commonly found on Earth. However, the lunar surface and interior are completely oxygen-free, so there is plenty of pure metal iron on the Moon and strongly oxidized iron is not confirmed in samples returned from the Apollo missions. In addition, hydrogen blast the lunar surface in solar waves. Hydrogen protects against oxidation and now it is an exciting discovery to discover minerals, such as hematite, with heavily oxidized iron on the Moon.
“Our hypothesis is that lunar rust 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 Li.
In order to make this discovery, Li, HIGP professor Paul Lucey and co-authors of NASA’s Jet Propulsion Laboratory ( JPL) and elsewhere analyzed the hyperspectral reflectance data acquired by the Moon Mineralogy Mapper (M3) engineered by NASA JPL onboard the Chandrayaan-1 mission in India.
This new research was motivated by Li ‘s earlier 2018 discovery of water ice in the polar regions of the Moon..
“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,” said Li. “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 team found that the positions where hematite is present are closely associated with water content at high latitude Li and others found earlier and are more oriented on the nearside, which is often facing the Earth.
“More hematite on the lunar nearside suggested that it may be related to Earth,” said Li. “This reminded me a discovery by the Japanese 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 far-side of the Moon where Earth’s oxygen may have never reached, although much fewer exposures were seen,” said Li. “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 far-side, 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,” said Li. “Earth may have played an important role on the evolution of the Moon’s surface.”
The research team hopes NASA’s ARTEMIS missions will be able to return samples of hematite from the polar regions. These samples’ chemical signatures can validate their theory as to whether the lunar hematite rust is oxidized by Earth’s oxygen and can help understand the evolution of the Earth’s atmosphere over the last billions of years.
University of Hawaii at Manoa. (2020, September 2). Has Earth’s oxygen rusted the Moon for billions of years?. ScienceDaily. Retrieved September 9, 2020 from www.sciencedaily.com/releases/2020/09/200902152152.htm
- Shuai Li, Paul G. Lucey, Abigail A. Fraeman, Andrew R. Poppe, Vivian Z. Sun, Dana M. Hurley and Peter H. Schultz. Widespread hematite at high latitudes of the Moon. Science Advances, 2020 DOI: 10.1126/sciadv.aba1940