Space Smells Like Seared Steak and Metal

While you can't directly smell space due to its vacuum, astronauts consistently report a distinct odor that clings to their suits and equipment after a spacewalk. This cosmic scent is often described as a mix of seared steak, hot metal, and welding fumes. Apollo 17 astronaut Harrison Schmitt, a geologist who walked on the Moon, noted that the lunar dust in his cabin smelled like spent gunpowder. These descriptions, while varied, all point to a "burnt" aroma.

The leading scientific explanation for this otherworldly smell points to polycyclic aromatic hydrocarbons (PAHs). These are carbon-containing compounds that are abundant throughout the universe and are byproducts of the combustion that occurs in dying stars. PAHs are also found on Earth in substances like coal, oil, and even in some foods. When astronauts return from a spacewalk, these molecules, which have attached to their suits, are brought into the oxygen-rich environment of the spacecraft, where they can be detected by the human nose.

Another contributing factor to the smell is believed to be the process of oxidation that occurs when the airlock is repressurized. In the vacuum of space, single atoms of oxygen can adhere to the fabric of a spacesuit. When these atoms are reintroduced to the molecular oxygen inside the spacecraft, they can combine to form ozone, which has a sharp, acrid smell similar to burnt metal. This combination of ancient stardust and chemical reactions creates the unique and memorable scent of space reported by those who have ventured into the final frontier.