The Smell of Moon Dust

[By Samud Shetty, Edited by Roshan Samuel]

We (humans) landed on the Moon 50 years ago. Specifically, Neil Armstrong and Buzz Aldrin landed the Apollo Lunar Module Eagle on July 20, 1969, at 20:17 UTC, as part of Apollo 11, which also involved Michael Collins, who flew the command module Columbia in lunar orbit.

Pictured above: The (very real) Moon Landing
Pictured above: The (very real) Moon Landing

But you already knew that.

3 guys went to the moon,

2 landed,

1 said something famous about small steps and giant leaps, etcetera…

Let’s talk about something a bit unusual : The Smell of Moon Dust.

No, it doesn’t smell like cheese. However, it does smell like burnt gunpowder. Moondust was notoriously clingy, and after anywhere between the 2.5 hours of moonwalk on Apollo 11 to the mammoth 22 hours worth on Apollo 17, astronauts were repeatedly exposed to the smell of lunar dust in their modules when they repressurized. Here’s what some astronauts have to say:

“It smells like spent gunpowder,” says Gene Cernan from Apollo 17.

“All I can say is that everyone’s instant impression of the smell was that of spent gunpowder, not that it was ‘metallic’ or ‘acrid’.” says Harrison “Jack” Schmitt of Apollo 17. (This man is the first person to get hay fever from moon dust, by the way).

“It smells like charcoal, or fireplace ashes sprinkled with water,” says Buzz Aldrin (remember him?) of Apollo 11.

“It has that taste — to me, [of] gunpowder — and the smell of gunpowder, too.” radioed Charlie Duke from Apollo 16.

You get the point. In total, 12 people have walked on the moon, and their accounts of the smell are fairly consistent. In the words of Jack Schmitt, “All of the Apollo astronauts were used to handling guns”, so they knew what they were talking about (not to mention that they were American, but that’s a different story). But gunpowder and moondust aren’t chemically similar at all. Modern smokeless gunpowder is a mixture of nitrocellulose (C6H8(NO2)2O5) and nitroglycerin (C3H5N3O9), while moondust is mostly silicon dioxide glass from meteorite impacts, and various minerals made up of iron, calcium, and magnesium. So why the smell?

It’s all about chemistry

Here’s the most widely accepted theory: Moondust is formed when meteorites hit the surface of the moon, reducing rocks to jagged dust. As a result of the smashing process, broken molecules in the dust have “dangling bonds”–unsatisfied electrical connections that need atomic partners . Lunar rock and soil is roughly 43-percent oxygen (the dioxide part of silicon dioxide), therefore most of these unsatisfied bonds are from oxygen. When these molecules get in astronauts’ noses, these dangling oxygen bonds find partners in their mucous membranes, leading to the sensation of smell. As those dangling oxygen bonds are usually associated with burnt gunpowder (burnt gunpowder smells distinctly different from its uncombusted counterpart), the astronauts put two and two together, et voila!

The reason this distinct smell vanishes on Earth is because of our lovely, life-sustaining atmosphere. Moondust comes into contact with moist, oxygen-rich air, which pacifies the dangling bonds, in a similar way that the astronauts’ mucous membranes did. However, if you shatter a Moon rock on Earth, the same burnt gunpowder smell should linger in the air for a while.

NASA plans to send people back to the moon in 2024, and they’ll stay much longer than Apollo astronauts did, with better equipment. Maybe they’ll be able to solve the mystery of the smell of moon dust.

After all, we’ve just begun smelling the moon.

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