Astronauts can’t just pull off their helmets and take a big whiff to discover what space smells like, but they have discovered that space has a distinct odor when they return to the safety of their space vehicle. They’ve reported that the smell is something similar to seared steak, burning metal, or welding fumes.
The smell becomes coated on the astronauts helmet, suit, and gloves after they come back inside from the vacuum of space, and is so peculiar that no one can quite agree on what it really smells like. What is the cause of this unique smell then?
It seems the smell stems from materials that float in space and throughout the universe called polycyclic aromatic hydrocarbons. These same compounds can even be found in oil and coal. The ability for the astronauts to smell the odor may come about because of oxidation and the hydrocarbons reaction to the oxygen-rich interior of the spacecraft.
Another distinct smell astronauts have reported from space came from walks on the moon. Astronauts have said that the moon, and more specifically moondust, smell like spent gunpowder. The same oxidation process may have occurred when the particles reacted with oxygen in the lunar lander. Curiously, moondust and moon rocks brought back to Earth have no smell. Astronauts actually tried to bring back moondust in special containers that were vacuum sealed, but jagged portions of the moondust damaged the inside of the container thus letting in oxygen or water vapor which effectively neutralized the moondust. Moon dust, incidentally, doesn’t have the same properties as gunpowder and isn’t flammable like gunpowder is.
Moondust is composed of iron, magnesium, and calcium, and half of it is silicon dioxide glass. The fine dust coated the suits and tools of the astronauts that walked on the moon and was almost impossible to get off before they reentered. The astronauts would bring much of it into the lunar lander where they would smell the distinctive odor. Though the astronauts that visited the moon agreed that moondust smelled like spent gunpowder, it is still a mystery exactly why.
Knowing the smell of space or the moon might seem like a trivial thing but knowing what to expect and what smells an astronaut might experience is rather important. The smell of seared steak or spent gunpowder while in space could be a little disconcerting.