Answer: Gunpowder

They might have differing opinions on the most magical part of space travel or who the best baseball player in U.S. history is, but there’s one thing that all the Apollo program astronauts that came in contact with the Moon seem to agree on: Moon dust, or lunar soil, smells like spent gunpowder.

Despite the fact that lunar soil, composed of shattered silicon dioxide glass created by meteorite impacts (approximately 50 percent), iron, calcium, and magnesium (bound up in olivine, pyroxene, etc.), has nothing in common (other than a rough color resemblance) to gunpowder, the Apollo astronauts described its smell as such. Apollo 16 astronaut Charlie Duke radioed home, “It has that taste — to me, [of] gunpowder — and the smell of gunpowder, too.” Next trip, Apollo 17 astronaut Gene Cernan described the smell inside the cabin of the lander as “smells like someone just fired a carbine in here”, then in a later interview described the fine gray powder by saying “it smells like spent gunpowder”.

Although we don’t have a concrete reason as to why the soil took on a gunpowder like smell when the astronauts encountered it within the lander, one theory is that the tens of thousands of years of lunar impacts created broken chemical bonds within the soil. When exposed to the oxygen rich environment of the lander cabin, a cascade of tiny chemical reactions ensued. Whatever the reaction was, it reminded the astronauts strongly of the after effects of rifle fire.