When astronauts return from space walks and remove their helmets, they are welcomed back with a peculiar smell. An odor that is distinct and weird: something, as astronauts have described it, like "seared steak." And also: "hot metal." And also: "welding fumes."

Our space explorers are remarkably consistent in describing Space Scent in meaty-metallic terms. "Space definitely has a smell that's different than anything else," astronaut Tony Antonelli has said. As three-time spacewalker Thomas Jones notes has put it, space "carries a distinct odor of ozone, a faint acrid smell."

Space, Jones elaborated, smells a little like gunpowder. It is "sulfurous."

Add to all those anecdotal assessments the recent discovery, in a vast dust cloud at the center of our galaxy, of ethyl formate — and the fact that the ester is, among other things, the chemical responsible for the flavor of raspberries. Add to that the fact that ethyl formate itself smells like rum. Put all that together, and one thing becomes clear: The final frontier sort of stinks.

But ... how does it stink, exactly? It turns out that we, and more specifically our atmosphere, are the ones who give space its special spice. According to one researcher, the aroma astronauts inhale as they move their mass from space to station is the result of "high-energy vibrations in particles brought back inside which mix with the air."

So NASA is now trying to reproduce that smell for training purposes — the better to help preemptively acclimate astronauts to the odors of the extra-atmospheric environment. And the better to help minimize the sensory surprises they'll encounter once they're there. The agency has hired the scent chemist Steve Pearce to recreate space stench, as much as possible, here on earth.

Pearce came to NASA's attention after he recreated, for an art installation on "Impossible Smells," the scents of the Mir space station. (He notes that this was a feat made more complicated by the fact that cosmonauts tend to bring vodka with them into space — which affects not only the scent of their breath, but also the odor of their perspiration.) The result of Pearce's efforts? "Just imagine sweaty feet and stale body odor, mix that odor with nail polish remover and gasoline... then you get close!"

As for Pearce's NASA-commissioned eau de vacuum, he's working on the project in his spare time. And the wonderfully poetic descriptions provided by astronauts themselves are helping him as he goes along. Such as, for example, this sweet-smelling stuff from wonder-astronaut Don Pettit:

"Each time, when I repressed the airlock, opened the hatch and welcomed two tired workers inside, a peculiar odor tickled my olfactory senses," Pettit recalled. "At first I couldn't quite place it. It must have come from the air ducts that re-pressed the compartment. Then I noticed that this smell was on their suit, helmet, gloves, and tools. It was more pronounced on fabrics than on metal or plastic surfaces."

He concluded:

"It is hard to describe this smell; it is definitely not the olfactory equivalent to describing the palette sensations of some new food as "tastes like chicken." The best description I can come up with is metallic; a rather pleasant sweet metallic sensation. It reminded me of my college summers where I labored for many hours with an arc welding torch repairing heavy equipment for a small logging outfit. It reminded me of pleasant sweet smelling welding fumes. That is the smell of space." Image courtesy of NASA Kennedy Space Center Photo Archive

This article originally published at The Atlantic here