Astronomers have discovered surprising hematite deposits across the surface of the Moon. The deposits are found at high-latitude and predominantly on the near side of our satellite. This led researchers to suggest an unexpected culprit. They believe that Earth’s oxygen is flying to the Moon and forming the mineral.

Hematite is a type of oxidized iron, chemically akin to rust that forms when iron reacts with oxygen on Earth. Unlike our planet, the Moon is completely devoid of oxygen, so it was unsurprising all the iron discovered both in remote observations and in the Apollo lunar samples were pristine. The discovery of hematite, however, challenges this. Reporting in Science Advances, researchers have an idea of how the Earth might be responsible for the Moon's rust.

"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," lead author Dr Shuai Li, from the Hawai'i Institute of Geophysics and Planetology, said in a statement.

These observations were taken by the NASA-developed Moon Mineralogy Mapper (M3) onboard India's Chandrayaan-1 mission. M3 was previously used by Li in the discovery of water ice deposits in the Moon’s polar regions, and this new discovery comes from that work too.

"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," Li explained. "I was curious whether it is possible that there are water-rock reactions on the Moon. After months of investigation, I figured out I was seeing the signature of hematite."

The team connected these observations to the discovery made by the Japanese Kaguya mission of how oxygen from Earth’s upper atmosphere can be blown onto the surface of the Moon by the solar wind. The presence of some hematite on the far side suggests that ice water might also have played a role.

"This discovery will reshape our knowledge about the Moon's polar regions," concluded Li. "Earth may have played an important role in the evolution of the Moon's surface."

The team hopes that one of the Artemis missions, which will mark humanity's return to the Moon, will collect rocks in the polar regions to be analyzed in detail and hopefully confirm these findings.