A recent paper by Science Advances reviewed the data given by Indian Space Research Organization's very own Chandrayaan-1 orbiter that previously discovered water ice and also mapped out a significant variety of minerals while it was surveying the Moon's very own surface back in 2008.
Lead author Shuai Li known from the University of Hawaii extensively studied the data and was very much surprised to find out that there is a close match with a certain spectral signature of hematite. This is the mineral that is a kind of iron oxide, otherwise known as rust. The big question is, if the moon does not have oxygen or even liquid water, how on Earth can it rust?
Why is there rust on the moon
The mystery all started with the solar wind and a stream of charged particles that actually flew out from the Sun shooting hydrogen to both the Earth and the Moon. Hydrogen also makes it difficult for the formation of hematite. In fact, this is quite the opposite.
In order for rust to be formed from iron, it still requires an oxidizer capable of removing electrons. Although Earth already has a magnetic field that is shielding it from this actual hydrogen, the Moon, however, does not.
Li admitted that it was completely unbelievable at first but with the finding of water on the Moon, speculations have grown regarding the possibility of a larger variety of minerals if the water actually reacted with rocks.
After close observation, it was decided that the spectra were actually hematite-bearing, and there also needed to be an explanation for its presence on the Moon.
Three hypotheses on how rust formed:
The first theory is that although the Moon does not have an atmosphere, it is actually home to a trace amount of oxygen that is actually coming from Earth. This works by Earth's magnetic field trailing behind the Moon just like a windsock. Back in 2007, Japanese orbiter Kaguya found that Earth's upper atmosphere can latch onto the trailing magnetotail travelling at 239.000 miles towards the Moon.
Another theory is that hydrogen could actually be delivered by the known solar wind. Although hydrogen is a reducer, Earth's magnetotail serves as a mediating effect. Besides just sending oxygen to the Moon coming from Earth, it is said to also block about 99% of the known solar wind on certain periods of the Moon's orbit especially during a full Moon since this opens certain occasional windows when rust can form.
The third theory is that although the shell of the Moon is dry, Moon water ice was found in lunar craters. The theory expresses that the hematite was actually detected away from the ice. The paper, however, focuses on water molecules discovered on the Moon's surface. Li actually proposes that certain fast-moving dust particles could, in fact, release certain surface borne molecules mixing with natural iron in the Moon's soil. The heat could also affect the oxidation rate and dust particles themselves might already be carrying water molecules.
JPL scientist Vivian Sun noted that the results show that there are even more complex chemical processes that are happening within the solar system. It was also stated that future missions to the Moon are needed to test these hypotheses.