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The moon is rusting. Earth’s moon. It’s rusting. Scientists have discovered hematite, a common iron-oxide (rust) mineral, forming at the lunar poles. 

Rust is a common chemical reaction found on Earth and Mars, where liquid water and oxygen are, or were, present. For rusting to occur there need to be three ingredients: iron, water, and oxygen. Iron is plentiful on and under the moon’s surface, according to NASA, but you might think the other two aren’t present. However, in 2018 NASA confirmed water’s existence there in the form of ice, though only in the moon’s shadowed portions. 

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Therein lies the conundrum for scientists, because the moon doesn’t have an atmosphere to hold oxygen. But it turns out there are, in fact, trace amounts of oxygen on Earth’s little companion. More surprisingly, that oxygen supply comes from Earth’s own upper atmosphere, traveling along trails of its magnetic field, known as a magnetotail. This means that the moon has all the ingredients for rust to form — but the water was nowhere near the forming hematite. 

The current theory is that fast-moving dust particles collide with the moon, releasing water molecules from the surface to mix with the iron-rich soil. The dust particles themselves might even carry water molecules. Still, it’s just a theory for now. Researchers have plenty more to do before they have a definitive answer.

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Miguel J. Rodriguez Carrillo/Getty Images

There are a lot of factors on the moon that would seemingly prevent rust from forming. As previously mentioned, the ice isn’t anywhere near the hematite, but scientists believe they have the answer to that. Another complication is the hydrogen discovered in moon rocks, which poses a significant problem for rust. Rusting happens when electrons are being removed from the iron because of an oxidizer. Hydrogen adds electrons to anything it interacts with, making it more difficult for rust to form. 

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But Earth’s magnetotail might be doing more than sending oxygen to the moon. It blocks out the majority of solar winds, especially during the full moon. During this period, Earth’s magnetic field also blocks hydrogen from getting to the moon’s surface, creating ideal conditions for rust. 

“At first, I totally didn’t believe it,” Jet Propulsion Laboratory scientist Abigail Fraeman told NASA. “It shouldn’t exist based on the conditions present on the moon. But since we discovered water on the moon, people have been speculating that there could be a greater variety of minerals than we realize if that water had reacted with rocks.” 

NASA had planned a new moon-landing mission by 2024, but that was delayed and is now expected for mid-2027. In the meantime, the group studying this anomaly will have to settle for satellite images. The Jet Propulsion Laboratory is developing a new version of the Indian Space Research Organization’s Moon Mineralogy Mapper instrument, which is how it received the data originally.

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