The moon probably shouldn’t have rust. 

Rust, an iron oxide, requires both oxygen and water to occur naturally, so you’d think the moon — a celestial body that is mostly dry and completely absent of oxygen — wouldn’t have any rust whatsoever. But it turns out it does. And scientists are trying to figure out why.

A new study published in Science Advances took data from Indian Space Research Organization’s Chandrayaan-1 orbiter and discovered that the rock at the moon’s poles had a different composition compared with other areas of the moon. Upon closer inspection Shuai Li, the lead author on the study, discovered hematite, a common iron oxide — rust, essentially. 

He reached out to scientists and NASA Jet Propulsion Laboratory to confirm the find. 

“At first, I totally didn’t believe it. It shouldn’t exist based on the conditions present on the moon,” said JPL scientist Abigail Fraeman, one of the scientists Li contacted. “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.”

So why does rust currently exist on the moon? There are a number of factors, but Earth is partly to blame.

To begin with, water exists on the moon in small quantities. Ice water exists in lunar craters, but that water exists on the far side of the moon, far from where the rust occurred. The current theory is that dust particles that often hit the moon are helping release water molecules, mixing those water molecules with iron on the surface.

Then there’s the oxygen part. That’s where Earth comes in.

Thanks to the fact it exists in such close proximity to Earth, the moon plays host to trace amounts of oxygen, traveling from Earth’s upper atmosphere all the way to the moon. Li found that the side of the moon that faces Earth has more rust than the areas that don’t face Earth. 

He believes this process has been occurring on the moon for billions of years. Moon, please accept our most sincere apologies for the rust.