Comet 67P/Churyumov-Gerasimenko (67P/C-G) is emitting vast quantities of hydrogen sulfide, the gas normally associated with the smell of rotten eggs. This odor was detected by a pair of mass spectrometers aboard the Rosetta spacecraft, managed by the European Space Agency (ESA).
The comet is still more than 250 million miles away from the Sun, a distance at which some astronomers believed only carbon dioxide and carbon monoxide would be released from the frozen body.
"The perfume of 67P/C-G is quite strong, with the odor of rotten eggs (hydrogen sulfide), horse stable (ammonia), and the pungent, suffocating odor 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" Kathrin Altwegg, principal investigator for the team managing the Rosina flight mass spectrometer, said.
Comets can be thought of as "dirty snowballs," composed of frozen water, along with dry ice (sold carbon dioxide), along with a range of other constituent chemicals. As they approach the Sun, comets heat, slowly releasing gases from their surface. These are pushed back by the solar wind, forming the tails that make comets so distinctive. These gases are what Rosetta is detecting with its instruments. As is the case with most comets, the vast majority of gases released by 67P/C-G are carbon monoxide and dioxide.
"ROSINA has made the surprising observation that the ratio between these species varies quite significantly, depending on where in the coma Rosetta is. Sometimes carbon monoxide is almost as abundant as water; sometimes it's only around 10 percent," the Rosina team reported.
The Rosina spectrometer has taken more than 40,000 spectral readings of the comet, in order to determine its makeup.
Comets represent some of the oldest material in the Solar System, left nearly unchanged since the formation of our family of planets. By carefully studying the chemical makeup of comets, astronomers believe they can answer long-standing mysteries of how our Sun and its retinue of planets formed, well over four billion years ago. The icy bodies could also reveal how life first started on Earth. Some biologists believe the building blocks of life may have been brought to our planet long ago from comets, journeying from the outer reaches of the Solar System.
"Further work will show how 67P/C-G compares with other comets, for example by revealing differences between comets originating from the Kuiper Belt (like 67P/C-G) and comets that hail from the distant Oort cloud (like Comet Siding Spring, which recently flew past Mars)," ESA officials wrote on a Web page announcing detection of the gases from the comet.
