Why Is The Moon Rusting? Even Scientists Are Stumped

Here’s a bit of news guaranteed to surprise you: the Moon is rusting!

Seriously.

New research from ISRO’s Chandrayaan-1 lunar mission published evidence of a compound called hematite found at the Moon’s higher latitudes. Hematite — or Fe2O3 — is an oxide of iron that turns red when it begins to rust.

Rust, also known as iron oxide, is a reddish compound that forms when iron is exposed to water and oxygen. It’s a common chemical reaction observed in nails, gates, the iconic red rocks of the Grand Canyon — and yes, even Mars. The ‘Red Planet’ is nicknamed after its rosy colour that comes from the rust it acquired billions of years ago when iron on its surface combined with oxygen and flowing water that was once there on Mars (and might still be today. Or not. We’re still figuring it out!).

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 ice on the moon, but there’s been no evidence of the presence of  liquid water on the moon. We know there’s plenty of iron, but the moon has no oxygen or air. For the moon’s iron to turn rusty red, it needs what’s called an oxidizer — a molecule such as oxygen that removes electrons from a material such as iron. But the sun’s solar wind,  a stream of charged particles that constantly hits the moon with hydrogen, has the opposite effect. Hydrogen is a reducer or a molecule that donates electrons to other molecules. Without protection from solar wind, and without oxygen, there should be no way for rust to form on the moon. 

But evidence shows that it does! So, what on the Moon happened!

Where’s the oxygen coming from?

This baffling discovery led scientists on an intriguing search for the answer to how this seemingly impossible rust-formation was happening on the oxygen-less Moon. 

The sci-fi fans among you, as well as various imaginative minds would love the answer to be that an alien expedition — Kryptonians, anyone? — has been staying there while studying Earth. The likely explanation is far more simple, but by no means less impressive: the oxygen is coming from us!

The Answer

The moon doesn’t have an atmosphere of its own to provide sufficient oxygen, but scientists discovered that the parts of the moon most affected by rusting are the ones facing our planet. The scientists theorised that the oxygen from earth could be making the 2,39,000 mile journey all the way to the moon.

How Is The Moon Rusting?

The answer stems from Earth’s magnetic field. Now, remember when we talked about the solar wind that is constantly bombarding the moon and doesn’t allow rust to form? The same solar wind also hits our earth all the time but our protective magnetic field in the ionosphere saves us from it. Our planet’s magnetic field is compacted and streamlined by the solar wind and forms a tail (called the magnetotail). The oxygen from Earth’s upper atmosphere can be blown to the near side of the moon through this magnetotail. Scientists believe that the earth’s oxygen has hitched a ride to the moon for over two billion years!

What’s more? At every full moon, when the Earth is between the Sun and the Moon, the earth’s magnetotail blocks 99% of solar wind from blasting the moon. Think of this as a temporary curtain over the moon’s surface, allowing for brief periods of time for rust to form. 

Okay, so now we know where the oxygen is coming from. We also know how the Earth is saving the moon from all the solar wind. But there’s still one extra ingredient that’s needed for rust to form: water.

The moon mostly doesn’t have water, except for frozen water found in craters on the moon’s far side — far from where most of the rust was found. But the scientists propose that fast-moving space dust particles that bombard the moon might free water molecules locked into the moon’s surface layer. These freed water molecules then mix with the iron to form rust. These dust particles might even be carrying water molecules themselves, and their impact might create heat that could increase the oxidation rate.

Voila! We have all the ingredients to form rust: Oxygen blowing from earth’s atmosphere, frozen water getting freed by space dust particles and earth’s magnetic field saving the moon from the solar wind. 

That’s a truly exciting explanation, isn’t it? It should be noted that these are still hypotheses and more data is needed to understand exactly why the moon is rusting. But this is the best explanation the scientific community has for now. 

What do you think? Does the “Earth wind” theory seem believable enough to explain the phenomenon? Perhaps rust on the Moon can best be seen as a reminder of how much we still don’t know about our closest neighbour. Tell us in the comments section below. 

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