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On planet Earth it is common to find rusty metals. This occurs when these elements come into contact with oxygen in the atmosphere. Therefore, finding oxidized materials in environments without air and, therefore, in the absence of oxygen, seems impossible..
This is precisely what is happening on the Moon, according to a study, published in the journal Science Advances, which describes the presence, in several places on the surface of the only natural Earth satellite, of hematite, a form of oxide that , requires oxygen and water to form.
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The research reviewed data from the Indian Space Research Organization’s Chandrayaan-1 orbiter, which discovered water ice and mapped a variety of minerals while studying the Moon’s surface in 2008.
The lead author of the research, Shuai Li, from the University of Hawaii, studied data from the Moon Mineralogy Mapper instrument of Chandrayaan-1, or M3, which was built by the Jet Propulsion Laboratory (JPL). ) of NASA.
Li focused on the data on the lunar poles. While the surface of the Moon is littered with iron-rich rocks, she was surprised to find a close match to the spectral signature of hematite.
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“The mystery begins with the solar wind, a stream of charged particles that flows from the Sun, bombarding the Earth and the Moon with hydrogen. Hydrogen hinders the formation of hematite. It is a reducer, that is, it adds electrons to the materials with which it interacts. That is the opposite of what is needed to produce hematite, “says the expert.
And he continues: “for iron to oxidize, an oxidant is required, which eliminates electrons. And while the Earth has a magnetic field that protects it from this hydrogen, the Moon does not,” explains NASA in a statement.
“It is very disconcerting, because the Moon is a terrible environment for hematite to form”said Li, who reached out to JPL scientists Abigail Fraeman and Vivian Sun to help analyze the M3 data and confirm her discovery of hematite.
“At first, I didn’t fully believe it. It shouldn’t exist under the conditions present on the Moon, ”Fraeman said. “But ever since we discovered water on the moon, people have been speculating that there might be a greater variety of minerals than we think if that water had reacted with the rocks,” he added.
Assembling the puzzle
After observing closely, Fraeman and Sun were convinced that the M3 data do indicate the presence of hematite at the lunar poles.
“In the end, the spectra contained hematite convincingly, and an explanation was needed as to why it is on the Moon,” Sun said.
The scientific paper offers a three-point model to explain how rust could form in such an environment. To get started, Although the Moon has no atmosphere, it harbors traces of oxygen, the source of which is planet Earth.
“Earth’s magnetic field creeps behind the planet like a windsock. In 2007, the Japanese orbiter Kaguya discovered that oxygen from Earth’s upper atmosphere can travel in this magnetic tail, as it is officially known, traveling the 385,000 kilometers to the Moon, ”the researchers note.
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That finding fits with the M3 data, which found more hematite on the near side of the Moon facing Earth than on the far side. “This suggested that oxygen from the Earth might be driving the formation of hematite,” Li said.
The Moon has drifted slowly away from Earth for billions of years, so it is also possible that more oxygen passed through this rift when the two were closer together in the ancient past.
Then there is all the hydrogen that is delivered by the solar wind. As a reducing agent, hydrogen should prevent oxidation from occurring. But the Earth’s magnetic tail has a mediating effect.
“In addition to transporting oxygen to the Moon from our planet, it also blocks more than 99% of the solar wind during certain periods of the Moon’s orbit (specifically, when it is in the full moon phase).
That opens occasional windows during the lunar cycle when rust can form.
The third piece of the puzzle is water. While most of the Moon is completely dry, water ice can be found in the shaded lunar craters on the opposite side of the Moon. But the hematite was detected far from that ice. Instead, the article focuses on the water molecules found on the lunar surface.
Li proposes that fast-moving dust particles that regularly hit the Moon could release these surface-borne water molecules, mixing them with iron in the lunar soil.
The heat from these impacts could increase the rate of oxidation; the dust particles themselves may also be transporting water molecules, implanting them on the surface to mix with the iron.
At the right times, that is, when the Moon is protected from the solar wind and there is oxygen present, a chemical reaction could occur that induces oxidation.
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