The surprising reason scientists say comets would smell absolutely terrible

Comets may look beautiful as they travel through space, but scientists say one of them would have an unpleasant smell if humans could get close enough to experience it.

The European Space Agency’s Rosetta spacecraft studied Comet 67P/Churyumov–Gerasimenko and found that its surrounding coma contained a mix of chemicals associated with some of the most recognizable unpleasant odours on Earth.

Why Comet 67P smells so bad

The answer lies in the gases released by the comet. ROSINA, an instrument aboard Rosetta, detected molecules including hydrogen sulphide, ammonia, formaldehyde, hydrogen cyanide, methanol, sulphur dioxide and carbon disulphide, as per The Christian Science Monitor report.


Each chemical would contribute a different smell to the comet’s overall “perfume.”

Hydrogen sulphide is associated with the smell of rotten eggs, while ammonia can bring to mind a horse stable or urine. Formaldehyde adds a pungent, suffocating odour, and hydrogen cyanide has a faint, bitter, almond-like aroma.

The mixture would also contain methanol, associated with alcohol, sulphur dioxide with a vinegar-like smell, and carbon disulphide, which has a sweet aromatic scent.

Scientists used the comet’s chemical makeup to recreate its smell

The comet’s main constituents included odourless water vapour, carbon dioxide and carbon monoxide. However, traces of the particularly pungent and toxic chemicals helped scientists create a picture of what the comet might smell like.

The result was an unusual combination of rotten eggs, horse stable, formaldehyde, bitter almonds, alcohol, vinegar and a hint of sweetness.

The smell could become stronger near the Sun

Scientists said the comet’s aroma would become stronger as it moved closer to the Sun. As the comet released more gas, its coma, the fuzzy cloud surrounding its nucleus, would become more active, as per a CBS News report.

That changing chemical mixture gave researchers an opportunity to study the comet in greater detail.

What Comet 67P can reveal about the early Solar System

The research was about far more than discovering what a comet might smell like.

By analysing the chemicals released by Comet 67P/Churyumov–Gerasimenko, scientists hoped to understand its chemical makeup and compare it with other comets.

The broader goal was to learn more about the solar nebula from which the Solar System, and ultimately life itself, emerged, as per the CBS News report.

Scientists even recreated the comet’s unpleasant scent

In 2016, Dr Colin Snodgrass of the Open University in the UK commissioned The Aroma Company to recreate the unpleasant scent and impregnate it into promotional postcards, as reported by BBC.