While in orbit, astronauts protect themselves inside vehicles, suits, and space stations, "because direct exposure would certainly kill them." As such, no one has directly smelled the scent of space. However, upon returning to Earth, astronauts often describe unexpected odors reminiscent of burnt steak and used gunpowder. Astronauts regularly catch a whiff of a unique smell when they remove their helmets, and their compatriots also notice this smell emerging when opening the doors of the pressure equalization chamber.
NASA astronaut Dominic Antonelli noted after a "spacewalk" (exiting the International Space Station) in 2009, "Space definitely has a smell different from anything else." In general, astronauts often compare the smell of space to that of "hot metal, burnt meat, burnt cookies, spent gunpowder, and welding metal," according to Steve Pearce, a biochemist and CEO of Omega Ingredients, who was contracted by NASA in 2008 to recreate the smell of space in the lab, based on interviews with astronauts to assist him in the industry.
Where might this smell come from? There are several possible explanations for this odor, relating to the oxygen that floats around the International Space Station. Ultraviolet rays from the sun can break down oxygen molecules (O2), which consist of two oxygen atoms, into individual oxygen atoms. Miranda Nelson, a mission control flight controller for spacewalks at NASA's Johnson Space Center in Houston, stated to Live Science that "this atomic oxygen may cling to spacesuits and the walls of the pressure equalization chamber, and other objects exposed to space, leading to chemical reactions that could explain the smell, such as the formation of ozone."
Nelson added, "The other, more fun theory is that the smell is related to stellar explosions, dying stars." She indicated that "these explosions produce smelly particles known as polycyclic aromatic hydrocarbons, which are found in coal, food, oil, and other materials." However, Nelson affirmed that "both ideas lack data from formal studies."
