As Comet 67P/Churyumov-Gerasimenko moves closer to the Sun, it becomes more "active," as gases escape from its nucleus through cracks and pores. The Rosetta spacecraft's mass spectrometers have identified the chemical composition of these emissions. If you could smell them, you'd probably wish you hadn't.

As of September 11th, the Rosetta Orbiter Sensor for Ion and Neutral Analysis (ROSINA) had detected:

  • Water (H2O)
  • Carbon monoxide (CO)
  • Carbon dioxide (CO2)
  • Ammonia (NH3)
  • Methane (CH4)
  • Methanol (CH3OH)

As of today, it's also found:

  • Formaldehyde (CH2O)
  • Hydrogen sulfide (H2S)
  • Hydrogen cyanide (HCN)
  • Sulfur dioxide (SO2)
  • Carbon disulfide (CS2)

As Kathrin Altwegg, the principal investigator for ROSINA, describes it:

"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 sulfer dioxide and a hint of the sweet aromatic scent of carbon disulfide, and you arrive at the 'perfume' of our comet."