Using data gathered by the Atacama Large Millimeter/submillimeter Array (ALMA) and the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument on ESA’s Rosetta spacecraft, astronomers have found traces of the organohalogen Freon-40 (CH3Cl), also known as methyl chloride and chloromethane, around the binary protostellar system IRAS 16293-2422 and in the thin atmosphere of the famous comet 67P/Churyumov-Gerasimenko.
Freon-40 discovered by ALMA around the infant stars in the IRAS 16293-2422 system. Image credit: B. Saxton / NRAO / AUI / NSF / NASA / JPL-Caltech / UCLA.
Organohalogens are a class of molecules that contain at least one halogen atom bonded to carbon.
They are well known for their use in industry and for their detrimental effect on the ozone layer. Some organohalogens are also produced naturally, through different geological and biological (in organisms ranging from humans to fungi) processes.
The ALMA observation of Freon-40 is the first detection ever of a stable organohalogen in interstellar space.
However, this discovery is disappointing news for astrobiologists, who previously suggested searching for Freon-40 in the atmospheres of alien worlds as a possible indicator of life.
It indicates that Freon-40 forms naturally in interstellar clouds and endures long enough to become part of a forming solar system.
“IRAS 16293-2422 is a system of two protostars, each about the same mass as our Sun. It is located 391 light-years away in the Rho Ophiuchi star-forming region and is surrounded by a cloud of dust and gas. Finding Freon-40 near these young, Sun-like stars was surprising,” said Dr. Edith Fayolle, an astronomer with the Harvard-Smithsonian Center for Astrophysics.
“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.”
“ALMA’s discovery of organohalogens in the interstellar medium also tells us something about the starting conditions for organic chemistry on planets. Such chemistry is an important step toward the origins of life,” added Dr. Karin Öberg, also from the Harvard-Smithsonian Center for Astrophysics.
“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.”
Approximate location of 67P/Churyumov–Gerasimenko when the ROSINA instrument on ESA’s Rosetta spacecraft discovered traces of Freon-40, the same molecule detected by ALMA around IRAS 16293-2422. Image credit: B. Saxton / NRAO / AUI / NSF.
Rosetta was able to detect Freon-40 in the atmosphere of 67P/Churyumov-Gerasimenko using the onboard instrument known as the ROSINA.
“ROSINA was able to capture some of the molecules around the comet, separate them by mass, and count them with an exquisite precision,” said Dr. Kathrin Altwegg, a researcher at the University of Bern in Switzerland and principal investigator of ROSINA.
“This highly sensitive instrument enabled us to detect a host of chemicals around the comet, including the one also discovered by ALMA far from our Solar System.”
In addition, both ALMA and Rosetta detected Freon-40 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.
“This does, however, raise the question: ‘How much of the comet’s organic content is directly inherited from the early stages of star formation?’ Additional searches for organohalogens around other protostars and comets need to be undertaken to help find the answer,” Dr. Fayolle said.
The research is published in the journal Nature Astronomy.
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Edith C. Fayolle et al. 2017. Protostellar and cometary detections of organohalogens. Nature Astronomy 1: 703-708; doi: 10.1038/s41550-017-0237-7
