Methyl chloride (CH₃), a well-known organohalogen molecule, was detected simultaneously in both the low-mass protostar IRAS 16293-2422 and in comet 67P-Churyumov-Gerasimenko, as reported in 2017 by Fayolle et al. The interstellar detection was made with the ALMA observatory. Both the ³⁵Cl and ³⁷Cl isomers were detected for 13_K–12_K with K=0–4 and other rotational transitions. The cometary detection was made with the ROSINA-DFMS instrument on Rosetta.

News stories about the detection often connected it to one of the terrestrial use of methyl chloride (or chloromethane), as the refrigerant Freon-40 or R-40. In addition to industrial production and use, chloromethane is produced naturally as well. It is toxic.