This article first appeared in Issue 18 of our digital magazine CURIOUS.
When it comes to astronomy, sight is the sense that we as a species mostly rely on. Contrary to popular belief there is some sound in space – the sonification of many cosmic events can deliver intriguing insights – and a lucky few can actually touch space material, but what about smell?
Can we smell space or do space objects have a smell? Futurama had a running gag with the Smell-O-Scope, a telescope that can smell through cosmic distance. We are not quite there yet, but between astronauts’ experience and the chemical analysis of distant objects, we have identified many “smells” of places and objects in the cosmos.
Outer space is like a seared steak?
Astronauts have reported that the International Space Station (ISS) doesn’t smell too good. It is usually home to about seven astronauts (but it can get more crowded). European astronaut, former commander of the ISS, and all-round legend Samantha Cristoforetti described it as a persistent “peculiar odor” in the ISS that it takes a few days to get used to it.
But that is still about the inside of a spacecraft, what about the outside? Upon returning from space walks or when the hatch is open, there is a strange smell in the air. Astronauts have described it in different ways: metallic, like welding fumes, like gunpowder, and even like the smell of a seared steak. After all, the rays of the Sun are quite unforgiving when it comes to being in low-Earth orbit.
Moon dust and Moon allergies
The smell of gunpowder, specifically acrid gunpowder, has also been reported from the surface of the Moon. The 12 men who walked on its surface brought dust back into the lunar module, which they could smell. That’s what you get when your surface is bombarded by sunlight with no atmosphere to act as a filter for 14 days a month over 4.5 billion years.
The Moon’s smell might not be exactly offensive, but you have a risk of being severely allergic to it.
“All I can say is that everyone’s instant impression of the smell was that of spent gunpowder, not that it was ‘metallic’ or ‘acrid’. Spent gunpowder smell probably was much more implanted in our memories than other comparable odors,” Apollo 17’s Harrison Schmitt, who Moon walked in December 1972, told Space.com.
Schmitt didn’t just not enjoy the smell, he had an allergic reaction to the sharp, abrasive, and possibly toxic Moondust; his nose became swollen at first contact with the dust, and even when brought back to Earth, it continued to cause reactions. Schmitt recalled in 2019 that a flight surgeon had such a strong allergic reaction while taking suits out of the command module that they couldn’t continue working on it.
So, the Moon’s smell might not be exactly offensive, but you have a risk of being severely allergic to it. You have been warned.
The stinking Solar System
But let’s extend our reach a bit beyond our cozy corner of the universe. What kind of molecules are found elsewhere in the Solar System? Seven out of the eight planets have substantial enough atmospheres for us to smell something; only one won’t kill you if smell its air: Earth.
Many gases that are found in abundance in the atmospheres of planets are odorless, such as hydrogen, helium, carbon dioxide, and methane. So what we are looking at are the minor components of these worlds – and none of them are a bouquet of roses. A chief molecule that is commonly found is ammonia; both Jupiter and Uranus have it in their atmospheres. Ammonia famously smells like urine or sweat, so not exactly a pleasant smell, but there’s worse.
It seems that the Earth is not just the most habitable planet in the Solar System by far, but it is also the one that smells the best.
Venus, Mars, and Uranus have in common the presence of hydrogen sulfide, which is also known as sewer gas, stink damp, and manure gas. It’s the smell of rotten eggs and farts, at least at low concentrations, so you need to be careful about not encountering pockets of it because it then gets sickeningly sweet. And then it kills you, like roughly everything else on those planets. Mars might have some sweet, chalky undertones, but if you like something more intriguing and dangerous, we can either go back to Jupiter or take on the comets.
Similar molecules have been found in the icy travelers of the Solar System, with the addition of delicious (and highly poisonous) hydrogen cyanide. As popularized by Agatha Christie, cyanide has a bitter almond smell. It is found on comets and in the atmosphere of Jupiter.
It seems that the Earth is not just the most habitable planet in the Solar System by far, but it is also the one that smells the best – hey, maybe that’s a solution to the Fermi Paradox, aliens have not contacted us because they think we stink.
Cocktails at your local giant molecular cloud
When it comes to interstellar molecules that are fun to smell, there is no better than ethyl formate, which was discovered in molecular cloud Sagittarius B2. You might not be familiar with ethyl formate as a molecule, but we are pretty certain that you have experienced it: the substance is what we normally associate with the characteristic smell of rum. That is not all: it is partially responsible for the flavor of raspberries.
There is some fascinating chemistry happening over eons in the space between stars and where stars are being born.
Now, a giant nebula that smells of rum and tastes of raspberries sounds delicious, and is definitely an improved sensory experience compared to the rather stinky Solar System. Unfortunately, molecular clouds have an extremely low density, and while there is a lot of alcohol present (sounds like a great party nebula) it also contains Butyronitrile, the smell of which is described as suffocating, as well as cyanide, so more bitter almonds. Do not go sniffing Sagittarius B2.
Acetic acid has also been discovered in Sagittarius B2 and other molecular clouds. The name might not tell you much, but it is a substance that gives vinegar its characteristic odor. So all in all, Sagittarius B2 is a bit vinegary, a bit rummy, a bit almondy, and a whole lot pungent.
Researchers have found all sorts of interesting molecules in interstellar space. There is some fascinating chemistry happening over eons in the space between stars and where stars are being born. Many of these molecules are odorless but there are a bunch with distinct smells, many of which are just strong and sharp such as methyl isocyanate or the aforementioned Butyronitrile.
Another interesting molecule that is commonly used on Earth and also found in the depths of space is formaldehyde, an important ingredient in embalming fluid renowned for its characteristic pungent smell.
So, the universe is a mixed bag of odorous molecules, some delicious and some revolting. The ability to discover these molecules from such a long distance away is phenomenal. The most distant of such molecules, also found in abundance closer to home, are Polycyclic Aromatic Hydrocarbons (PAHs), which have been detected by JWST in a galaxy whose light had to travel 12.5 billion years to reach us. PAHs smell like car tires or asphalt.
Among the fumes, the choking hazards, and the titillating scents, these molecules offer a window into how the Earth came to be and also how life had the building blocks to form on our planet. From foul-smelling interstellar molecules to the scent of a rose, there is a giant leap, but by studying the chemistry of the universe we can find out all the necessary steps to go from one to the other.
CURIOUS magazine is a digital magazine from IFLScience featuring interviews, experts, deep dives, fun facts, news, book excerpts, and much more. Issue 21 is out now.
Source Link: What Does The Universe Smell Like?