Astronomers discover traces of methyl chloride around infant stars and nearby comet

Organohalogen methyl chloride discovered by ALMA around the infant stars in IRAS 16293-2422. These same organic compounds were discovered in the thin atmosphere surrounding 67P/C-G by the Rosetta space probe. The background image of the Rho Ophiuchi cloud complex is from NASA’s Wide-field Infrared Explorer (WISE). Credit: B. Saxton (NRAO/AUI/NSF); NASA/JPL-Caltech/UCLA

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have detected the faint molecular fingerprint of methyl chloride – a chemical commonly produced by industrial and biological processes here on Earth – around an infant star system known as IRAS 16293-2422. Traces of this organic compound were also discovered in the thin atmosphere of comet 67P/Churyumov-Gerasimenko (67P/C-G) by the Rosetta space probe.


Methyl chloride (CH3Cl), also known as Freon-40, is one of a class of molecules known as organohalogens. This new ALMA observation is the first detection ever of a stable organohalogen in interstellar space. The results are published in the journal Nature Astronomy.

The cosmic discovery of this organic compound, however, is disappointing news for astrobiologists, who previously suggested searching for methyl chloride in the atmospheres of alien worlds as a possible indicator of life. The recent ALMA and Rosetta detections raise doubts about that proposal, however. They indicate that methyl chloride forms naturally in interstellar clouds and endures long enough to become part of a forming solar system.

IRAS 16293-2422 is a collection of several infant stars, or protostars, each about the same mass as our Sun. It is located about 400 light-years from Earth and is still surrounded by its natal cocoon of dust and gas.

“Finding organohalogens near these young, Sun-like stars was surprising,”…

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