[Rockhounds] The Moon Is Rusting

[Kreigh Tomaszewski]

The Moon, our closest cosmic neighbour, and the only other body in the
Solar System on which humans have set foot, is fairly well known to us. We
know that there is practically no air. We know that there is water ice, but
no liquid water.

So you can understand why the detection of haematite on the Moon has
scientists baffled, since haematite is an oxidised form of iron that, here
on Earth, requires the presence of both air and water to form.

Especially since the Moon is constantly bombarded with a stream of hydrogen
from the solar wind, a reducing agent that 'donates' its electrons to the
materials it interacts with. Oxidisation occurs due to a loss of electrons
- so even if all of the right elements were present for oxidisation to
occur, the solar wind should cancel it out.

"It's very puzzling," said planetary scientist Shuai Li of the University
of Hawaii at Manoa. "The Moon is a terrible environment for haematite to
form in."
https://www.sciencealert.com/the-moon-is-rusting-despite-the-absence-of-liquid-water-and-oxygen