Space is, technically, a vacuum: no air, no suspended molecules, nothing to carry a scent from one point to another. And yet astronauts who have been on spacewalks come back describing, almost without exception, a very specific smell.
They don’t notice it while they’re outside. They notice it when they come back in.
When astronauts return from a spacewalk and remove their helmets, they’re immediately struck by the smell of cosmic molecules that clung to their suits during the walk. By their own accounts, the smell is anything but subtle.
Astronaut Don Pettit documented it in a NASA blog after a 2003 mission. He wrote that the best description he could offer was a metallic, sweet, and pleasant smell — comparable to the smell of arc welding he remembered from summers spent working in a machine shop.
Pettit completed several spacewalks over the course of his career, giving him plenty of opportunities to verify the observation firsthand.
Other astronauts have described the smell of space in slightly different terms: “burning metal,” “a sharp, ozone-like odor,” “walnuts and brake pads,” “gunpowder,” or “a singed almond cookie.” The words vary, but everyone agrees on one point: there is something scorched about it, something that brings to mind the smell of burning.
Astronaut Nicole Stott described the smell as “very distinctive, a kind of sweet metal” — comparable to the metallic tang of a freshly opened tin can or the smell of hot metal on a car engine.
Why It Smells That Way: The Theories Science Offers
No one has ever smelled space directly. The vacuum prevents molecules from reaching the nose — and venturing out without a suit would, of course, be fatal. What astronauts perceive is not space itself but what space leaves behind on materials.
One of the most compelling explanations points to the airlock repressurization process. When astronauts re-enter the International Space Station, atomic oxygen clings to their suits during the walk.
Upon returning to an oxygen-rich atmosphere, those reactive molecules trigger oxidation reactions — similar to combustion, but without flame or smoke. The result is the burnt smell that so many astronauts consistently describe.
NASA researcher Scott Sandford offered another perspective. The space station moves fast enough to pass through the thin residual atmosphere at that altitude, generating a halo of excited oxygen around it. This causes oxidation in the materials on the leading side of the station. Spacesuits, in that sense, act as passive collectors of those reactive compounds.
A second line of research points to polycyclic aromatic hydrocarbons — compounds produced by dying stars. These are toxic combustion byproducts found in coal, petroleum, and, in varying concentrations, in food. They are distributed throughout the solar system and can collect on suits during spacewalks.
They are, essentially, the ash of dead stars. And they smell like it.
The Moon Has a Smell, Too
Astronauts from the Apollo program had a similar experience — though with a twist.
During the Apollo 11 mission, Buzz Aldrin noted that his suit smelled like “burnt charcoal” after being coated in lunar dust. On Apollo 17, Harrison Schmitt said that when the crew smelled the Moon, their immediate impression was of freshly fired gunpowder.
Lunar dust has an extraordinarily fine, jagged structure, never worn smooth by wind or water erosion. When it comes into contact with the oxygen inside the lunar module, chemical reactions produce the characteristic burnt smell.
And the Center of the Galaxy Smells Like Raspberry and Rum
The question of what space smells like has, in reality, very different answers depending on where you look. While what’s closer to home smells of metal and welding, the center of the Milky Way holds something far more surprising.
In 2009, an international team of astronomers was searching for amino acids in Sagittarius B2, the largest star-forming molecular cloud near the galactic center. They didn’t find amino acids — but they did detect ethyl formate.
This molecule is the primary flavor compound in raspberries and one of the key contributors to the taste of rum, though other components are needed to fully replicate that aroma. The concentration is far too low to detect at any useful range, and the distance makes any visit impossible for rather more obvious reasons.
NASA once commissioned fragrance specialist Steven Pearce to recreate the smell of space for use in training simulations. Pearce blended several aromas to capture the qualities of “hot metal, seared meat, burnt cake, gunpowder, and welded metal.”
The resulting perfume, called Eau de Space, became a bestseller after its 2020 launch.
That the universe smells of gunpowder near Earth and of raspberries near the galactic center says a great deal about its chemical complexity — and about how many apparently simple questions still have no definitive answer, cosmic wonders that also inspire stargazers to chase Milky Way double arch.
