What does dust from the moon smell like?
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All 12 of the astronauts who walked on the moon reported that the dust smelled like gunpowder. For example, during Apollo 16, Charlie Duke reported
150:09:18 Duke: Houston, the lunar dust smells like gunpowder. (Pause)
150:09:27 England: We copy that, Charlie.
150:09:31 Duke: Really, really a strong odor to it.
This NASA article confirms that all 12 reported the gunpowder smell. The odor increased with proximity to the dust, but diminished over time. However, the same article reports that researchers who worked with the samples back on Earth never experienced such a smell.
This does raise the question why the astronauts observed that smell. The matter is still not fully resolved, but there are four potential hypotheses:
The dust chemically resembles gunpowder. Unlikely. The original formula for gunpowder was charcoal, sulfur, and nitrate. Modern gunpowders also contain carbon, sulfur, and nitrogen. However, these elements aren't found in substantial amounts in lunar rocks or dust. Nor would it explain why the researchers didn't experience the smell.
The odor actually came from the lunar module itself. Perhaps something was outgassing a smell, which became noticeable to the astronauts when they returned from their EVA. Duke at first expressed concern that he thought the smell was coming from the oxygen supply. However, this would not explain the association of the smell with the proximity of moon dust. Also, no one involved with the manufacturing, test articles, or simulations of the LM complained about such a smell.
The dust reacts with mucus in the nose. It's suggested by this article. However, that doesn't explain why researchers didn't experience the smell.
The dust chemically reacts with compounds in the LM air. I find this explanation most likely; it explains why others would not have experienced the smell, and why the effect diminished over time.
Regardless of the odor mechanism, the NASA article suggests that all of the dust samples were eventually inactivated by exposure to air.