Astronauts have described some unusual smells in space, which isn’t surprising considering that the chemistry there is very different from that on Earth. What does space smell like, and what are the cosmic sources of these smells?
Space is an airless vacuum, so technically you can’t smell anything in space. If you tried, you’d be dead. However, space is not a complete vacuum. It is full of all kinds of molecules, some of which have their own strong odor when we smell them Soil. Learning what different parts of space might smell like is a really cool way to gain a better understanding of cosmic chemistry.
Related: The International Space Station has a ‘peculiar smell,’ says astronaut
What do astronauts smell?
During the Apollo astronauts would do moon landings often comment on a gunpowder-like odor Once they climbed back into the airlock, entered the confines of their lunar lander, and removed their helmets. Similarly, astronauts returning to the confines of the International Space Station after a spacewalk report the smell of gunpowder, but also ozone and burnt steak.
So what’s going on? Where does the smell come from?
Scientists have two good theories. One of them is that, while an astronaut is doing a spacewalk, individual oxygen atoms can attach to their spacesuit, and when they reenter the airlock and become pressurized again, molecular oxygen – O2, or two oxygen atoms – flows into the airlock and combines with the individual oxygen atoms to form ozone, or O3. This would explain the sour, metallic smell.
What about the other scents? There’s probably something else going on. Polycyclic aromatic hydrocarbons (PAHs), found in charred foods such as burnt toast and grilled meat, are also routinely found in space. In fact, most interstellar carbon is locked up in PAHs. They are also plentiful in the solar systemso they can be easily picked up by astronauts and brought into the space station or a space capsule – and they are likely the source of the burnt flesh smell that astronauts report.
Indeed, NASA considers the smells of space to be more than just a curiosity. In 2008, the agency commissioned Steven Pearce – a chemist at Omega Ingredients who specializes in fragrances and flavors – to recreate the smells of space for astronauts in training. After all, an astronaut must be able to distinguish between the smell of PAHs on his space suit and a dangerous chemical leak on board the space station.
Stinky comets
So we have an idea of what space near Earth smells like. But what about further afield?
Other places in the universe also have unique scents – if only we could travel so far to smell them.
When the European Space Agency’s Rosetta spacecraft encountered each other comet 67P/Churyumov-Gerasimenko in 2014, it discovered a rich variety of molecules in the comet’s coma, the gaseous halo surrounding the comet’s solid nucleus. Among these molecules was hydrogen sulfide, which gives rotting eggs their unappetizing stench; ammonia, reminiscent of the disgusting smell of urine; hydrogen cyanide, which, despite its famously toxic nature, has a more attractive almond-like odor; sweet-smelling carbon disulfide; and the pickled aroma of formaldehyde.
You would probably turn your nose up at this combination of scents. But if there were an odor, it would probably be quite faint, since the vast majority of a comet’s coma is made up of water vapor and carbon dioxide.
The Gasoline Moon
There is one place where there is an atmosphere in which an odor can be retained Saturn‘s largest moon, Titan. However, the atmosphere doesn’t really help us smell anything. There’s no oxygen and it’s cold — minus 292 degrees Fahrenheit (minus 179.6 degrees Celsius) – so taking off our spacesuit helmet and taking a deep breath isn’t really an option. However, if we could do that, we would discover that Titan smells like gasoline.
Maybe we shouldn’t be surprised. After all, gasoline, or petrol, is made from crude oil that is rich in hydrocarbons, which are molecules formed from hydrogen and carbon atoms, such as methane and ethane. Titan’s atmosphere contains a dense smog of hydrocarbons, and on the surface of the moon, liquid hydrocarbons form oily lakes and rivers. But methane, the dominant hydrocarbon on Titan, doesn’t smell like anything. So what causes the moon’s stink?
NASA’s Cassini spacecraft identified an unknown chemical in Titan’s hazy atmosphere That NASA laboratory experiments on Earth it was determined to be a molecule containing nitrogen, methane and benzene and belonged to a family of molecules called polycyclic aromatic nitrogen heterocycles (PANHs). In particular, it is the benzene in the PANHs that gives Titan its petroleum stench, as benzene also occurs naturally in gasoline.
A drunken cloud of gas
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So the solar system is a pretty tantalizing place, but what about the rest of the universe?
Sagittarius B2, a giant interstellar molecular cloud of star-forming gas and dust less than 400 light-years from Earth’s center. Milky Way, there are all kinds of aromatic chemistry involved. For one thing, it contains a lot of alcoholincluding vinyl alcohol, methanol and ethanol, the type of alcohol in beer.
In 2009 also astronomers discovered the molecule ethyl formate in Sagittarius B2. Ethyl formate is the chemical that gives raspberries and rum their sweet scents, so even if the center of our galaxy smells like a brewery, it will at least be pleasant.