comet landing sites
Still image of Philae separating from Rosetta and descending to the surface of comet 67P/Churyumov-Gerasimenko ESA

A space probe by the European Space Agency (ESA) has discovered that comets smell like rotten eggs and horse manure.

The ESA's Rosetta space mission found that Comet 67P/C-G has the foul aroma due to a mix of gases, including ammonia, formaldehyde, sulphur dioxide, and methane – a gas produced by flatulent cows.

The smell was uncovered by the Rosetta Orbiter Sensor for Ion and Neutral Analysis (Rosina), which consists of two mass spectrometers that study the comet's coma – a nebulous envelope that surrounds its nucleus.

Kathrin Altwegg, principal investigator at Rosina said the stench of Comet 67P/C-G is "quite strong" thanks to its potent cocktail of gases, including the "pungent, suffocating odour of formaldehyde".

"This is mixed with the faint, bitter, almond-like aroma of hydrogen cyanide," she said.

ESA short film Ambition
ESA's six-minute film Ambition stars Aidan Gillen and actress Aisling Franciosi, and was directed by Tomek Baginski. The film aims to promote the work of the Rosetta probe ESA

"Add [a] whiff of alcohol (methanol) to this mixture, paired with the vinegar-like aroma of sulphur dioxide, and a hint of the sweet aromatic scent of carbon disulphide, and you arrive at the 'perfume' of our comet."

Altwegg added however, that the density of these pungent molecules is very low, and the main part of the coma is made up of water and carbon dioxide mixed with carbon monoxide.

Next month, the Rosetta spacecraft will drop a small robot on the surface of Comet 67P/C-G's 4km-wide ice body in order to closely analyse its chemistry.

Professor Mark McCaughrean, chief scientific advisor of ESA, told the BBC: "We are trying something supremely ambitious. Rosetta is a first; it's unique."

Earlier this week, the ESA released a short sci-fi film to promote its Rosetta comet mission. The seven-minute film, aptly called Ambition, stars Game of Thrones actor Aidan Gillen and actress Aisling Franciosi as a master and apprentice on an alien world.

Shot on location in Iceland, Ambition was directed by Poland's Tomek Bagiński, who was nominated for an Oscar in 2003 for his animated short Katedra.