The first detection of an organohalogen molecule in space, discovered simultaneously in two different extraterrestrial locations, is reported in a paper published online this week in Nature Astronomy. The study identifies chloromethane (CH3Cl) from the comet 67P/Churyumov-Gerasimenko and around a young binary protostar - two contracting masses of gas and dust in the early stages of forming a binary star system.
Although nearly 200 chemical species have been detected in space, Edith Fayolle and colleagues’ discovery of chloromethane represents the first molecule to combine an organic methyl group with a halogen. It was detected by the ROSINA instrument on board the Rosetta spacecraft, which visited the comet 67P three years ago. Finding chloromethane on the comet may have implications for chemistry on Earth, as the authors calculate that comets such as 67P could have delivered up to 50 gigatonnes of chlorine to the early Earth through impacts. The accompanying detection of chloromethane in a young protostellar system (IRAS 16293-2422), using the Atacama Large Millimeter/Submillimeter Array (ALMA), indicates that chloromethane forms efficiently under pre-planetary conditions, and, when incorporated in comets, can survive the formation of a planetary system. The authors find a hint that another organohalogen, fluoromethane (CH3F), might also be present in IRAS 16293-2422.
Previous studies on exoplanets have considered chloromethane to be a biomarker molecule, as it can be emitted by tropical plants and peat bogs on Earth, but the findings presented here show that chloromethane can also form abiotically.