In a blow to the search for extraterrestrial life, astronomers have been forced to discard a chemical compound previously thought to be a reliable indicator of biological activity.

In a paper published in Nature Astronomy, the researchers report the detection of a compound comprising methyl chloride and chloromethane (dubbed freon-40) around an infant star system called IRAS 16293-2422, and in the vicinity of the much-studied comet 67P/Churyumov-Gerasimenko.

The detections were made using data from the ESO's ALMA telescope in Chile and the ROSINA instrument onboard the observatory's Rosetta probe, which is currently orbiting the comet.

In both cases, the origins of the freon-40 must predate the origins of life, thereby ruling it out as an indicator of biology.