Space Smells Like Steak

While you can't actually smell anything in the vacuum of space, astronauts consistently report a distinct odor upon returning to their spacecraft. After a spacewalk, once they are safely inside and remove their helmets, a sharp, acrid scent fills the air. Many have compared it to the smell of seared steak, hot metal, or even spent gunpowder. This lingering aroma isn't from the vacuum itself, but from compounds that have hitched a ride on their suits and equipment, outgassing once they are back in a pressurized environment.

The scientific explanation for this cosmic odor points to polycyclic aromatic hydrocarbons (PAHs). These carbon-based molecules are byproducts of combustion and are abundant throughout the universe, forming in the fiery death of stars and drifting through interstellar (Review) clouds. On Earth, we encounter PAHs in charred food, coal, and car exhaust, which explains the familiar 'burnt' quality of the scent. Interestingly, while the immediate smell of near-Earth space is metallic, other parts of the cosmos have different chemical profiles. A giant dust cloud at the center of our galaxy, for instance, is full of ethyl formate, the same chemical that gives raspberries their flavor.