You’d think space would smell like nothing. It’s a vacuum, no air, no sound, and surely no
smell. Yet astronauts from multiple space agencies, across decades of missions, keep coming
back with the same bizarre report: space has a distinct odour. The smell of space, if you will.
But do astronauts even have a sense of smell in space to detect these odours? It seems
impossible to smell anything when you’re all sealed up in a spacesuit, floating in the vacuum
of space. And technically, space is a vacuum, so no one has ever “smelled” it directly in the
traditional sense. If they tried, they wouldn’t live to tell the tale!
That said, astronauts have described smells associated with space. After returning from
spacewalks, they’ve reported unique odours clinging to their spacesuits or lingering in the
airlock once it’s re-pressurised. Smells that weren’t there before.
Smell is such an important part of our everyday lives. The ability to detect something
dangerous or toxic in the air could quite literally save your life. So when astronauts detect a
strange smell, they pay attention. When returning from a spacewalk, after being surrounded
by the emptiness of space, there’s a lingering trace of something. Metallic. Sharp. Gunpowder
and even, burnt steak.
British astronaut Tim Peake says it’s “weird, very hard to describe, and I think no two
astronauts can quite agree on what it smells like, but it’s a bit like burnt barbecue to me, if
you left the beef steaks on the barbecue on a bit too long, you get that metallic burnt smell.”
During the Apollo 11 mission, Buzz Aldrin, the second person to walk on the Moon after
Neil Armstrong, commented that his suit smelled like “burnt charcoal” when it was coated
with lunar dust. And on board Apollo 17, Harrison Schmitt stated that, “all I can say is that
everyone’s instant impression of the smell was that of spent gunpowder.” Tim Peake notes
that whenever experiments come back through the airlock, “you open it up and you get that
distinctive burnt metal smell.”
In an interview with Places & Faces, astrophysicist and cosmologist Dr Brad Tucker from the
Australian National University explained that everything shifts up there. “Your sense of touch
is massively different with microgravity, and your vision is very different – as your eye
changes due to microgravity and pressure in your head. Even your tongue is a bit different.
So I think many senses change in space, and it would definitely have an effect on the nose.”
“The source of these unpleasant fragrances is not fully understood,” Brad Tucker says. While
we are not 100% certain, there are a few theories.
The first, and more widely accepted theory is that it might be atomic oxygen causing an
ozone effect. Despite being in the vacuum of space, there are tiny traces of atomic oxygen up
around 400km where the space station orbits. When we re-pressurise the airlock, that atomic
oxygen mixes with O2 from the atmosphere.
Helen Sharman, the UK’s first astronaut, explains this theory to the BBC: “The atmosphere,
the environment, just around the space station, is pretty much a vacuum, but not completely
at that height. What we have in the residual atmosphere is atomic oxygen.”
Atomic oxygen, single atoms of oxygen, can cling to an astronaut’s spacesuit or tools. On
re-entering the space station, these single oxygen atoms combine with O2 present in the
cabin, making ozone (O3). Sharman says, “as soon as it reacts, you get that ozone smell.”
And we humans down here on Earth can experience the smell of ozone too. Have you ever
noticed the metallic smell of static electricity just after a thunderstorm? That’s ozone.
Another idea within this theory is that the vacuum of space actually pulls trace chemicals out
of the metal walls of the ship. These tiny particles are never noticeable under normal air
pressure, which holds them inside the metal. But once in space, they slowly off-gas and
collect in the airlock, releasing smells that would otherwise never reach your nose. So maybe
it’s not really the smell of space at all, but space’s effect on our ship.
The second, and far more exciting theory, is that it’s the smell of dying stars. Space is filled
with molecules called polycyclic aromatic hydrocarbons, or PAHs. These are byproducts of
dying stars, formed during stellar explosions and then scattered into the universe. PAHs
contain 20 to 25% of all carbon in the cosmos. When these molecules attach onto a spacesuit
and get brought inside to the airlock, astronauts are essentially smelling the chemical
remnants of dead stars.
PAHs are the same compounds you find in charred or burnt food. They are what makes
grilled meat smell grilled. So at your next family barbecue, you can smell the same
compounds that drift around between the stars and planets in space.
So what happens when astronauts come back down to Earth and catch a whiff of something
familiar? Dr Brad Tucker says it might just take them right back. “While I haven’t heard of
astronauts smelling those similar smells on Earth and thinking of space, I think some would.
Especially for those who spend multiple stints on the space station.” He explains that many
astronauts experience something called the overview effect – “a new profound outlook on
Earth and its fragility, and a new heightened connection to humanity and the environment.
So, I imagine those smells might also trigger that as well.”
NASA actually commissioned a perfume maker to recreate the smell of space in 2008 for
training purposes. Now there’s a company that sells this originally NASA commissioned
perfume: Eau de Space and Eau de Luna. After all, an astronaut needs to be able to
distinguish between the smell of PAHs on their spacesuit and a dangerous chemical leak on board the space station. For us down on Earth, it’s mostly just a fun conversation starter for
why your perfume smells a bit off.
Maybe our very own 2026 Australian of the Year, and only Aussie astronaut, Katherine
Bennell-Pegg, is preparing her nose by smelling Eau de Space. She’s yet to go to space, but
she’s already making history as the first person to train as an astronaut under the Australian
flag with the Australian Space Agency. We’ll have to wait and see what Katherine’s verdict is
on the smell of space.
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