Actually, the Apollo astronauts did notice that the Moon had an odor, and they described it as “spent gunpowder.”
But if astronauts have to wear protective space suits and helmets to avoid fatal exposure to the vacuum of space, how would they smell the Moon? Could they just put their noses to the surface and sniff? No. But if they could just sniff the ground, would they be able to smell anything? No–there is no air on the Moon to carry odors.
So how could they smell the Moon? The Moon is covered with a very fine dust called regolith, dust made from the impacts of meteoroids (rocks in space) slamming into the Moon’s surface and breaking things up. This dust was so fine and clingy that it stuck to the astronauts’ space suits. They couldn’t get it all off before re-entering the lunar lander, so once they were safely back inside the lander, after removing helmets and gloves, they could feel the moondust, smell it, and taste it.
A recent Gizmodo article talks about the American Museum of Natural History’s “Beyond Planet Earth” exhibition in which there is a machine which allows you to sniff what the Moon smells like. Author Jesus Diaz describes the machine and his experience with it:
It was… weird. The machine is very simple. Put your nose next to the opening, click the button and the Moon smell air would flow for about 10 seconds. […] It’s true. It smells a bit like that, [“like spent gunpowder…like someone just fired a carbine”]. A bit metallic. Once you smell it, you can taste the metal in the middle part of your tongue. Which is weird, because even while regolith dust looks like gunpowder, its chemical composition is nothing like gunpowder.
While moondust may smell like gunpowder, the two substances are not similar, and moondust is not explosive. According to a NASA Science News article on “The Mysterious Smell of Moondust,” modern smokeless gunpowder is a mixture of nitrocellulose (C6H8(NO2)2O5) and nitroglycerin (C3H5N3O9). These flammable organic molecules are not found in lunar soil. Moondust is almost half silicon dioxide glass created by meteoroids hitting the moon, and it is also rich in iron, calcium and magnesium bound up in minerals such as olivine and pyroxene. So why the two smell similar, no one knows. A few theories–solar wind, chemical reactions, or oxidation–are discussed in that NASA article.
If you want to see a cool space exhibition and smell what the moon smells like, “Beyond Planet Earth” runs through August 12, 2012. If it’s not likely you can go (it’s not likely that I can go, either), you can still check out the info and video tours on the exhibit’s web site.