ten smells from outer space

Earth’s moon is a dead and desolate place. Covered in grey dust and with no atmosphere to diffuse odours it is not a place you would go looking for the smell of anything. But the men who have stepped foot on the Moon have revealed that the fine dust which coats its surface offers a complex sensory experience. It is soft and crisp as freshly fallen snow and reflects the sun in a shimmering sparkle. The real surprise came when the lunar explorers returned to their pod. Their suits were loaded with clinging motes of moon dust. It got everywhere. Astronaut John Young said the taste was “not half bad,” while Gene Cernan likened the smell of the Moon to spent gunpowder.

Titan, Saturn’s largest satellite, is the only moon to have a thick atmosphere and the only place besides Earth we know has surface liquid. Those expecting a gentle day’s splashing in Titan’s waterways are in for a disappointment. The lakes and oceans of Titan are not pleasant pools of water but oily hydrocarbon soups. These hydrocarbons make the yellow haze of Titan’s air smell just like a garage where someone has knocked over a tank of petrol. Benzene, a chemical which smells sickly sweet with hints of petrol, falls from the sky in snowflakes.

In the constellation Aquila there is a reservoir of booze beyond the dreams of even the most giddy socialite. The nebula, an enormous cloud of gas and dust, contains enough ethyl alcohol to make 400 trillion trillion pints of beer. Other nebulae contain methanol which is the poisonous cousin of the deliciously drinkable ethyl alcohol. The human nose cannot easily tell the two chemicals apart. Those looking for a way to experience the thrill of space would therefore be justified in filling a perfume spritzer with vodka and spraying it in their face. That is not something the next nebula of our list lends itself to.

The Calabash Nebula is a gas cloud over one quadrillion metres in length that looks beautiful through a telescope. Once you find out how Calabash smells you would not want to approach closer than the end of telescope. Astronomers have given Calabash the evocative name of Rotten Egg Nebula. It has many of the sulphur compounds you would find in both rotten eggs and stinks bombs. The sulphurous molecules have been forced out by a red giant star undergoing an energetic transformation. Some astrophysicists have poetically termed this a “star fart.” The gas is being ejected into the depths of space at almost a million kilometres per hour.

The Rosetta mission to land a probe on a comet as it sped through the Solar System was one of space exploration’s greatest successes. Among the remarkable discoveries Rosetta made about Churyumov-Gerasimenko Comet 67P is what it smells like. The results are not likely to invite return visitors. Researchers detected ammonia (found in cat urine and cleaning products), hydrogen cyanide (bitter almonds), and hydrogen sulphide (produced by rotten eggs). To help people imagine the conditions on Comet 67P a reproduction of this atmosphere was made that anyone interested was invited to give a sniff. The scientists who made this faux-cometary fragrance had to replace several of the ingredients however to avoid murdering the inquisitive.

We don’t tend to think of the other planets as active in the same way Earth is. They look unchanging and eternal. In fact the most volcanically active spot in the Solar System is Jupiter’s moon Io. Io is crushed and stretched by Jupiter’s intense gravity and this powers volcanoes that spew gases over the moon. Io’s atmosphere is made of these outgassings and the result is not one likely to be forgotten. Sulphur dioxide, the main component of the atmosphere, is a pungent and toxic gas that smells like a burning match. Other sulphur compounds found in trace amounts would give Io a rotten egg odour.

Aromatic compounds, those containing rings of carbon atoms, are well named as their complex shapes lead to many of them having strong aromas. It is a double edge blade however as their intriguing scents can mask toxic effects. Polycyclic aromatic hydrocarbons (PAHs) are a type of aromatic compound found everywhere in space. When a star dies it ejects massive clouds of matter an in these hot vapours PAHs are able to form. These large molecules can smell of anything from sweet barbeque to burning coals to petrol. They may also have the scent of life itself. Some researchers believe that PAHs from space were involved in the development of life on Earth.

Jupiter is by far the largest planet in the Solar System. A gas giant, its atmosphere comes in defined layers. A descent through them would present an olfactory adventurer with quite the tale to tell - if they survived. The fluffy outer clouds of Jupiter would have the tang of a freshly cleaned toilet as they are composed of ammonia. Delving deeper you would reach an eggy layer of sulphurous clouds. Sulphur is common element in the universe which explains why its rotten essence can be detected wherever we seem to look. The last smell you would get on Jupiter is one familiar to readers of murder mysteries; the bitter almond scent of deadly hydrogen cyanide.

Sagittarius B2 is a vast cloud of gas and dust near the core of our galaxy. Scientists that turned their telescopes on it made an exciting discovery. Sagittarius B2 contains a chemical called ethyl formate. This is important because it is a key precursor to amino acids, compounds vital to life on Earth. For our purposes however it is interesting because this means that the cloud, if we could reach it, would smell heavily of rum. Ethyl formate is both part of the smell of rum and the taste of raspberries. If we could mix Sagittarius B2 with one of the vast clouds of alcohol out there we could make a cosmic cocktail.

Astronauts all seem to agree that space has a distinctive aroma but few agree as to exactly what it is space smells like. Is it steak sizzling in a frying pan? Metal being welded together? A pile of wet clothes? Walnuts? All of these have been likened to the smell experienced by astronauts when they step back into the air-lock after a spacewalk. You might think that a mostly empty vacuum would have no odour at all but it seems what few molecules there are in space have a potent nasal kick. It may also be that the charged ions carried on the Solar wind react with the air once the astronauts return to their ship creating a unique and unplaceable perfume.