The recent anniversary of Apollo 11 reminded me of this article about how the astronauts said moondust smelled like spent gunpowder. There’s nothing in the moon regolith remotely similar to gunpowder in composition, but nevertheless, several of the astronauts agreed that was the closest in odor.
ISS astronaut Don Pettit, who has never been to the moon but has an interest in space smells, offers one possibility:
“Picture yourself in a desert on Earth,” he says. “What do you smell? Nothing, until it rains. The air is suddenly filled with sweet, peaty odors.” Water evaporating from the ground carries molecules to your nose that have been trapped in dry soil for months.
Maybe something similar happens on the moon.
“The moon is like a 4-billion-year-old desert,” he says. “It’s incredibly dry. When moondust comes in contact with moist air in a lunar module, you get the ‘desert rain’ effect–and some lovely odors.” (For the record, he counts gunpowder as a lovely odor.)
Don Pettit also wrote about the smell of the airlock after a spacewalk – metallic, like welding fumes. Sometimes there was the smell of ozone, which would be from the atomic oxygen in low Earth orbit reacting with the spacesuit materials.
One more thing a robotic explorer would not be able to tell us.