What does space smell like?

Space is a near-perfect vacuum, so the idea of it having a smell sounds like a trick question. You cannot sniff nothing. And yet astronauts who have done spacewalks keep reporting the same thing: when they come back inside, there is a distinctive odour hanging around their gear. They are oddly specific about what it smells like, too.

The short answer

Astronauts have described the smell of space as something like seared steak, hot metal and welding fumes. Strictly speaking, they are not smelling space itself. During a spacewalk they are sealed inside their suits, which smell rather plastic. The odour appears afterwards, clinging to suits, helmets, gloves and tools, once the airlock has been repressurised and the helmets come off.

The real story

The descriptions come straight from people who have been there. The NASA astronaut Don Pettit, writing about his 2003 mission to the International Space Station, said the best description he could come up with was metallic, a rather pleasant sweet metallic sensation. Another NASA astronaut, Kevin Ford, said in 2009 that it was like something he had never smelled before, but would never forget.

So what is actually being smelled? The leading suggestion is that particles cling to the outside of suits and equipment during a spacewalk and are carried back inside. Atomic oxygen is thought to be among them. The chemist Steven Pearce, who was hired by NASA to recreate the smell on Earth so astronauts could get used to it during training, has suggested the metallic note may come from high-energy vibrations of ions.

That is the delightful twist: the answer that space smells of nothing is technically true in the vacuum itself, and practically wrong for anyone who has actually been out there. Space leaves a calling card, and astronauts bring it home on their sleeves.

And the station itself? Pettit described the inside of the ISS as smelling like a mix of machine shop, engine room and laboratory, with a hint of roast beef when someone opened a pouch of stew. Anyone who has lived in a shared house will understand.

Why people get it wrong

The logic seems watertight. Smell needs molecules to reach your nose, a vacuum has almost no molecules, so space must be odourless. The catch is that astronauts never smell space directly. They smell what space leaves on everything it touches. Low Earth orbit is not perfectly empty, and the materials exposed to it come back changed. It is a bit like asking what the beach smells like and being told sand has no smell, while your towel says otherwise.

The Sole’s final word: “Space smells like a barbecue next to a welding shop. Which, to be fair, is also most of Australia in December.”