Chemical found around star deals blow to search for aliens

Scientists have found traces of methyl chloride around an infant star system and a comet, disproving astrobiologists who previously suggested that searching for the chemical in the atmospheres of alien worlds is an indicator of life.

Using the Atacama Large Millimeter/submillimeter Array (ALMA) telescope in Chile, researchers 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 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," said Edith Fayolle, a researcher at Harvard-Smithsonian Center for Astrophysics (CfA) in the US.

"We simply didn't predict its formation and were surprised to find it in such significant concentrations," said Fayolle.

"It's clear now that these molecules form readily in stellar nurseries, providing insights into the chemical evolution of solar systems, including our own," she said.

"ALMA's discovery of organohalogens in the interstellar medium also tells us something about the starting conditions for organic chemistry on planets," said Karin Oberg, an astrochemist at CfA.

"Such chemistry is an important step toward the origins of life," said Oberg, co-author of the study.

"Based on our discovery, organohalogens are likely to be a constituent of the so-called 'primordial soup', both on the young Earth and on newly formed rocky exoplanets," she said.

The researchers also note that abundant organohalogens around a young Sun-like analogue demonstrate that the organic chemicals present in the interstellar medium involves halogens, which was previously not known.

In addition, both ALMA and Rosetta detected this molecule in similar abundance ratios. Since comets are a remnant of the formation of our solar system and retain a chemical fingerprint of that era, the new observations support the idea that a young solar system can inherit the chemical make-up of its parent star-forming cloud.