Despite their inability to remove their helmets while on a walkabout, astronauts still say space stinks. So how's that even possible? Spacesuits are designed to protect astronauts from extreme temperatures and radiation while providing a constant supply of oxygen, keeping the suit pressurized, and filtering out any possible "smell" there might be in space.

Still, when the spacewalkers return to their craft, remove their helmets, and go through the airlock, they describe smelling a myriad of things from a Nascar race to barbeque, burning metal, brake pads, gunpowder, and even burnt almond cookies. Astronaut Don Pettit said it was hard to describe the smell exactly but likened it to "pleasant sweet smelling welding fumes.”

While it's still not known for sure where the scent is coming from, there are a few theories that might help explain the source. One idea blames it on dying stars releasing malodorous compounds called polycyclic aromatic hydrocarbons that float around forever and are found throughout the universe, while another explanation is a chemical reaction called oxidization.

The Australian Academy of Science says during an astronaut's time in space, single atoms of atomic oxygen accumulate on everything, from the suit to tools to equipment. It might just be that while pressurizing the airlock, those single atoms of atomic oxygen combine with O₂ to make ozone, and that's what astronauts are getting a whiff of.