Meat, metal, raspberries, rum ...

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, astronauts have described it, like "seared steak." And also: "hot metal." And also: "welding fumes." 

Our extraterrestrial explorers are remarkably consistent in describing Space Scent in meaty-metallic terms. "Space," astronaut Tony Antonelli has said, "definitely has a smell that's different than anything else." Space, three-time spacewalker Thomas Jones has put it, "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." 

In the past, NASA has been interested in reproducing 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, in 2008, talked with the scent chemist Steve Pearce about the possibility of recreating 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. (This was, he noted, 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 that 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!"

Those efforts, alas, did not move forward. But had Pearce continued in creating a NASA-commissioned eau de vacuum, he would have had the aid of wonderfully poetic descriptions provided by astronauts themselves. 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.

*Update: I've changed some of the wording in this and the next two paragraphs to reflect the age of NASA's scent-recreation efforts. Those efforts were going strong in 2008, but seem to have stalled at present, and Pearce was not finally hired for the project. Thanks to MIT's Charlie Petit for pointing that out. 

Hat tip Brian Fung