Hopes for cosmic 'biomarker' dashed

The organohalogic chemical, methyl chloride, has been found by ALMA and Rosetta in interstellar space for the first time. The discovery dashes hopes of using the chemical for detecting life remotely around other worlds, but could be an important step to understanding how life evolved in the first place. 


Methyl chloride has been found in the nebula surrounding the infant stars in IRAS 16293-2422.
Credit: B. Saxton (NRAO/AUI/NSF); NASA/JPL-Caltech/UCLA


The organic chemical methyl chloride has been found in interstellar space using data captured by the Atacama Large Millimeter/submillimeter Array (ALMA) and the Rosetta mission.

This is the first time an organohalogen – containing carbon and hydrogen bonded with a halogen; in this case chlorine – has been observed in interstellar space.

It had been hoped that the molecule could be used as a biomarker; a compound whose detection would indicate the presence of life. But the discovery suggests it can occur without the intervention of biology.

The news has served to underscore how difficult the hunt for life beyond our planet will be.

On Earth methyl chloride, otherwise known as Freon-40, is created by living organisms – from human to fungi and everything in between.

The ALMA observations uncovered the chemical around an infant star, IRAS 16293-2422.

“Finding the organohalogen Freon-40 near these young, Sun-like stars was surprising,” says Edith Fayolle, a researcher with Harvard-Smithsonian Centre for Astrophysics who led the study.

“We simply didn’t predict its formation and were surprised to find it in such significant concentrations. It’s clear now that these molecules form readily in stellar nurseries, providing insights into the chemical evolution of planetary systems, including our own.”

The chemical was also found in the thin atmosphere of comet 67P/Churyumov-Gerasimenko by the Rosetta orbiter.


An image of Comet 67P/Churyumov-Gerasimenko taken in May 2015 by the Rosetta orbiter, the same month the orbiter made the first detection of the organohalogen methyl chloride, CH3CL with its ROSINA instrument.
Credit: ESA/Rosetta/NavCam , CC BY-SA 3.0 IGO


The discovery suggests that rather than methyl chloride being created by life, it is instead an integral part of planetary formation.

“ALMA’s discovery of organohalogens in the interstellar medium also tells us something about the starting conditions for organic chemistry on planets," says Karin Öberg, also from the Harvard-Smithsonian Centre for Astrophysics and co-author of the study.

"Such chemistry is an important step toward the origins of life. Based on our discovery, organohalogens are likely to be a constituent of the so-called ‘primordial soup’, both on the young Earth and on nascent rocky exoplanets.”

Rather than a sign of life already existing, methyl chloride could be a necessary precursor to life, without which none can evolve.

“Our results shows that we still have more to learn about the formation of organohalogens. Additional searches for organohalogens around other protostars and comets need to be undertaken to help find the answer,” says Fayolle.


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