Scientists just found out that this comet smells like rotten eggs and horse crap

The awful-smelling comet 67P/C-G. (ESA/Rosetta/NAVCAM)

The Rosetta space probe is about to make history.

In August, it arrived within miles of the comet 67P/C-G. Next month, if all goes to plan, it'll send the first-ever spacecraft to make a controlled landing on a comet's surface.

In the meantime, it's discovered something truly important: the comet smells absolutely terrible.

As Kathrin Altwegg — the researcher who runs the craft's instrument that detects particles given off by the comet — told the European Space Agency, "The perfume of 67P/C-G is quite strong, with the odor of rotten eggs (hydrogen sulphide), horse stable (ammonia), and the pungent, suffocating odor of formaldehyde."

Video taken by the Rosetta probe as it neared the comet. (ESA/Rosetta/Navcam)

NPR science reporter Geoff Brumfiel puts it more bluntly: "Taking a whiff of this comet would be like sharing a horse barn with a drunk and a dozen rotten eggs."

The terrible smell is simply the result of the chemicals naturally given off by the 2.5 mile-wide chunk of rock, dust, and ice as it begins to vaporize as it nears the sun. Of course, anyone actually standing next to it would be wearing a spacesuit and inhaling a self-contained air supply, but studying these chemicals is interesting for researchers, because of what it tells them about the comet's composition and the way it originally formed.

It also brings up an interesting question: do all comets smell this awful? In truth, we still don't know, because we've never sent a spectrometer (the instrument that detects these chemicals) so close to one before.

Hat tip to Geoff Brumfiel/NPR.

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