Hematite, a type of rust, requires both water and oxygen to form. But the moon lacks both oxygen and liquid water. Which is why scientists were so surprised when they discovered hematite in lunar water samples they were studying from India's 2008 Space Research Organization's Chandrayaan-1 mission.
"It's very puzzling," research leader Shuai Li from the University of Hawaii said in a statement reported by Newsweek. "The Moon is a terrible environment for hematite to form in."
So Li sent the samples to Abigail Fraeman and Vivian Sun from NASA's Jet Propulsion Laboratory for confirmation.
"At first, I totally didn't believe it," Fraeman told Newsweek. "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."
- Magnetism: Oxygen can travel from the Earth to the moon via the Earth's magnetic field. This explains why there is more rust on the side of the moon facing the Earth.
- Hydrogen Shield: Solar winds bombard the moon with hydrogen, which interferes with the oxidation process that forms rust. But the Earth's magnetic field also blocks the moon from solar winds when the moon is full, giving rust enough time to form.
- Water Ice: There is water ice present on the moon, as Li discovered in 2018. Li thinks that the water molecules in the ice could be freed by dust particles that strike the moon's surface, then mix with iron to form rust. The oxidation process would be sped as the particles became heated.
Li's two discoveries — of water ice and rust — were both located near the moon's poles.
"This discovery will reshape our knowledge about the Moon's polar regions," Li said in a University of Hawaii press release. "Earth may have played an important role on the evolution of the Moon's surface."
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