Rotten eggs, horse urine, alcohol, and bitter almonds: this is the bouquet of odours you would smell if a comet in deep space could be brought back to Earth, European scientists say.

An instrument aboard the European Space Agency's Rosetta spacecraft has detected some intriguing chemical signatures from Comet 67P/Churyumov-Gerasimenko (67P/C-G) since their rendezvous in deep space in August, the scientists said.

Molecules detected include ammonia, methane, hydrogen sulphide, hydrogen cyanide and formaldehyde.

"If you could smell the comet, you [would] probably wish that you hadn't," said the team wryly in a blog posted on the European Space Agency (ESA) website.

The device, called Rosina-DFMS, is a mass spectrometer.

It has been analysing the signature of gas given off by the "coma" - the comet's head, as it heads towards the Sun.

"The perfume of 67P/C-G is quite strong," said Kathrin Altwegg, Rosina's chief scientist.

"With the odour of rotten eggs (hydrogen sulphide), horse stable (ammonia), and the pungent, suffocating odour of formaldehyde, this is mixed with the faint, bitter, almond-like aroma of hydrogen cyanide.

"Add some 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."

The detection of so many different molecules at this stage has been a surprise, the ESA said.

The Rosina team believed only the most volatile molecules, carbon dioxide and carbon monoxide, would be released as the comet's icy surface started slowly to warm.

On a six-and-a-half-year orbit, 67P/C-G is the target of an ambitious mission to shed light on the origins of comets, ancient travellers of the Solar System.

Rosetta caught up with it after a 6 billion kilometre trek that required four flybys of Earth and Mars, using the gravity of each planet as a slingshot to build up speed.

It is now in close orbit around the comet at a distance of around 400 million kilometres from the Sun.

The scout will send down a robot lander on November 12 to carry out on-the-spot scientific tests.

On August 13 next year the comet and Rosetta will be 185 million kilometres from the Sun, their closest approach to our star.