As the European Space Agency prepares to land the Rosetta space probe on the comet 67P/Churyumov-Gerasimenko, the team has discovered one unpleasant fact about the comet: it stinks.

The Rosetta probe was launched in March 2004 and reached the comet this August in preparation for landing on the comet next month. According to a CNET report, the Rosetta Orbiter Sensor for Ion and Neutral Analysis (ROSINA) has been using a pair of mass spectrometers to determine the chemical makeup of the material surrounding the comet, and has found that aroma to be closer to rotten eggs and pee.

ROSINA had been able to detect the chemical makeup of the comet’s halo of surrounding material — called the “coma” — which will continue to increase as the comet gets closer to the sun and starts to heat up. It currently stands at about 250 million miles from the sun.

The Rosetta team expected the coma to contain carbon dioxide and carbon monoxide almost exclusively, but soon found a much richer array of chemicals, including gaseous water, methane, ammonia, and methanol in additional to carbon dioxide and carbon monoxide. Further measurements revealed the presence of hydrogen sulphide, formaldehyde, hydrogen cyanide, sulphur dioxide and carbon disulphide, althoug in fairly low levels.

ROSINA principal investigator Kathrin Altwegg said the smell that would accompany such a mixture of substances would include the smell of rotten eggs from hydrogen sulphide; an almond-like bitter aroma from hydrogen cyanide; a “suffocating” odor from formaldehyde; the scent of a horse stable from the ammonia; and the smell of alcohol from the methanol to top it all off.

As the comet continues to get closer to the sun, it will release even more molecules, allowing scientists to better understand what it is made of.