The Moon is rusting: How is it possible?

15th Dec 2022
The Moon is rusting: How is it possible?

It’s no secret that Mars is called the Red Planet because of its reddish-orange hue. This hue is caused by rust that appeared when Mars still had an atmosphere, and the iron on its surface was oxidized due to contact with oxygen and water. And now imagine how surprised the scientists were to discover rust on an atmosphere-less Moon! Let’s find out why is the Moon rusting, and how to explain this phenomenon.

Why is the Moon rusting?

The reason is hematite; its presence on the Moon was detected in 2020 thanks to data collected by the Indian orbital lunar probe Chandrayaan-1. NASA’s Moon Mineralogy Mapper (M3) program uses images from the spacecraft to get an idea of the Moon’s surface mineral composition. The basis of hematite is iron oxide Fe2O3. This element is the main component of rust. The discovery of moon rust baffled scientists, as iron requires at least oxygen or water to oxidize. The first one is non-existent on the Moon because it does not have any atmosphere, while water exists in extremely small quantities and only in the form of ice. In addition, the Moon is constantly bombarded by solar wind proton streams. Protons are the nuclei of the hydrogen atom. By attaching electrons, they turn into atoms that can participate in chemical reactions. Oxidation occurs due to the loss of electrons, so even if all the necessary elements for this process were present on the Moon, the solar wind would have to neutralize it, acting as a reducing agent. That is why no one was ever surprised by the abundance of unoxidized iron in the samples collected by the Apollo crews. In other words, the natural satellite of the Earth is one of the most unsuitable places for rust formation.

But the Moon is really rusting, which is already a confirmed fact. How to explain this phenomenon? Scientists believe that the reason is Earth. More precisely, the Earth’s atmosphere and magnetosphere. And it’s not a joke.

Terrestrial oxygen

In 2007, the Japanese Kaguya orbiter discovered traces of terrestrial oxygen on the Moon. How did he get there? The carrier turned out to be the Earth’s magnetic field. Shaped like a comet with a tail, it extends far enough to capture the Moon. During a full moon, our satellite is in the magnetic tail of the Earth, far from the Sun. During this period, more than 99% of the solar wind is blocked, which means that hydrogen does not interfere with oxidation.

Polar Ice

But water plays its part, too. Scientists have found that hematite is distributed over the surface of the Moon mainly in asteroid impact sites, namely in the polar regions. That is, the heat generated from the collisions caused the ice to melt, and the dust particles mixed the resulting water molecules with iron.

ice at the Moon's poles
Blue areas show the location of ice at the Moon’s poles

How fast is the Moon rusting?

We found out that the Moon has water molecules and oxygen, while on a full moon, the Earth’s magnetic field is ideal protection from the effects of the solar wind. The combination of these three ingredients creates a suitable environment for the formation of Moon rusting. But the amount of water and oxygen is so scarce that this process is very slow and takes billions of years. Take a look at the map below — the amount of discovered hematite proves this statement.

hematite on the Moon - Map
Map of hematite on the Moon — red means more hematite.


By the way, a long time ago, the Moon was closer to the Earth than it is now. This means that it could obtain more oxygen. This hypothesis is strengthened by the fact the side of the Moon facing the Earth has more hematite than its back hemisphere.

Is the Moon rusting a bad thing?

Rust is the result of a common chemical reaction for nails, gates, the red rocks of the Grand Canyon, and even Mars. There is much more rust on Earth and Mars than on the Moon, but it does not threaten anything. Of course, one can recall Moon rusting bible verse about the blood moon prophecy:

“And I beheld when he had opened the sixth seal, and, lo, there was a great earthquake; and the sun became black as sackcloth of hair, and the moon became as blood.”

Book of Revelation, Chapter 6, Verses 11–13

But let’s be guided by scientific language. After all, if the scientists’ hypothesis about the origin of hematite on the Moon is confirmed, its delivered samples will be able to tell a lot about the evolution of the Earth’s atmosphere. The researchers hope that NASA’s new ARTEMIS lunar program will be able to provide these samples. And then we will surely know the reason for Moon rusting.

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