After a spacewalk, astronauts returning to the ISS often describe an unexpected smell. They compare it to burnt steak, spent gunpowder, or hot metal. Why does space smell like that?
Outside the spacecraft, astronauts are protected by the vehicle’s hull and by their spacesuits; otherwise they wouldn’t survive, says Ofek Birnholz, an astrophysicist at Bar-Ilan University in Israel. So no one can smell the vacuum of space directly.
Still, after coming back from a spacewalk, astronauts regularly notice a distinct odor when they take off their suits. Their colleagues on the station notice it too, Live Science reports.
“Space definitely has a smell,” said Dominic Anthony Antonelli, a NASA astronaut who did a spacewalk in 2009.
Astronauts frequently describe the scent as “hot metal, burnt meat, or pastries, along with burnt gunpowder and welding metal,” said Steve Pearce, a biochemist and CEO of Omega Ingredients.
Former astronaut Thomas Jones compared the smell to ozone. His colleague Don Pettit described it on NASA’s blog as “pleasant, sweet, metallic.” “It reminded me of a summer spent in college, where I worked for many hours with an arc welding torch, repairing heavy equipment for a small logging company. The pleasant welding smoke had a sweet smell. That is the smell of space,” Pettit wrote.
Where is this smell coming from?
Space isn’t a perfect vacuum. “We’re not talking about a space completely devoid of particles,” says Miranda Nelson, a spacewalk dispatcher at NASA’s Johnson Space Center in Houston.
There are a few possible explanations for the odor. One involves oxygen around the International Space Station. Ultraviolet rays from the Sun can break oxygen molecules (O2) into individual atoms. Nelson says that atomic oxygen can cling to spacesuits, airlock walls, and other objects in space and trigger chemical reactions that produce ozone and other scents.
Nelson also mentions a wilder idea: the smell could come from dying stars. Emissions from supernovae produce molecules called polycyclic aromatic hydrocarbons, which are also found in coal, grilled food, and oil. Nelson says neither of these explanations has official confirmation yet.
Extraterrestrial scent
In 2008, to give astronauts more realistic training, NASA asked Steve Pearce to recreate the smell of space based on astronauts’ descriptions. The goal was to reduce surprises for future spacefarers they might encounter in orbit.
Pearce didn’t fly into space or sniff spacesuits. Instead, he combined safe, available aromatic materials that evoked what astronauts described.
With Pearce’s help, a perfume called Eau de Space debuted in 2020 and became a bestseller.
