The Moon has a smell. It has no air, but it has a smell. Each pair of Apollo astronauts to land on the Moon tramped lots of Moon dust back into the lunar module—it was deep gray, fine-grained and extremely clingy—and when they unsnapped their helmets, Neil Armstrong said, “We were aware of a new scent in the air of the cabin that clearly came from all the lunar material that had accumulated on and in our clothes.” To him, it was “the scent of wet ashes.” To his Apollo 11 crewmate Buzz Aldrin, it was “the smell in the air after a firecracker has gone off.”

All the astronauts who walked on the Moon noticed it, and many commented on it to Mission Control. Harrison Schmitt, the geologist who flew on Apollo 17, the last lunar landing, said after his second Moonwalk, “Smells like someone’s been firing a carbine in here.” Almost unaccountably, no one had warned lunar module pilot Jim Irwin about the dust. When he took off his helmet inside the cramped lunar module cabin, he said, “There’s a funny smell in here.” His Apollo 15 crewmate Dave Scott said: “Yeah, I think that’s the lunar dirt smell. Never smelled lunar dirt before, but we got most of it right here with us.”