Space smells like seared steak, hot metal, and welding fumes.

The unique scent of space is primarily attributed to polycyclic aromatic hydrocarbons (PAHs), which are organic molecules found throughout the universe. These molecules are produced by dying stars and are similar to the compounds found in charred food and coal. When astronauts perform extravehicular activities (EVAs), these particles cling to the fabric of their spacesuits and the surfaces of their equipment.NASA astronaut Don Pettit described the odor as a pleasant metallic sensation, comparing it to sweet-smelling welding fumes or seared steak. The smell is not noticeable while in the vacuum of space because the suits are pressurized and oxygen-sealed. It only becomes apparent during repressurization when the space particles mix with the cabin's atmosphere and undergo oxidation.Another contributing factor is atomic oxygen. In low Earth orbit, single atoms of oxygen can chemically bond to the suit's surface. When the airlock is repressurized, these atoms collide with O2 molecules to form ozone (O3), which has a sharp, acrid, and metallic scent. This chemical reaction further enhances the 'burnt' smell reported by crews on the International Space Station.To help train future explorers, NASA commissioned chemist Steve Pearce of Omega Ingredients in 2008 to recreate this scent for simulation purposes. Pearce used the accounts of astronauts to develop a fragrance that mimics the ozone and smoky metallic notes of the cosmos. Understanding these chemical interactions helps scientists study the composition of the interstellar medium and the effects of the space environment on materials.