Observations made with the Atacama Large Millimeter/submillimeter Array (ALMA) and ESA’s Rosetta mission have revealed the presence of the organohalogen Freon-40 (CH3Cl) in gas around both an infant star and a comet. Organohalogens are formed by organic processes on Earth, but this is the first ever detection of them in interstellar space. This discovery suggests that organohalogens may not be as good markers of life as had been hoped, but that they may be significant components of the material from which planets form.
Results will be published in the journal Nature Astronomy on October 2nd (Fayolle and colleagues). The team of researchers includes Dutch astronomers Matthijs van der Wiel (ASTRON), Niels Ligterink, and Ewine van Dishoeck (Leiden Observatory). This result underscores the challenge of finding molecules that could indicate the presence of life beyond Earth.
Published by the editorial team, 2 October 2017
Using data captured by ALMA in Chile and from the ROSINA instrument on ESA’s Rosetta mission, a team of astronomers has found faint traces of the chemical compound Freon-40, also known as methyl chloride and chloromethane, around both the infant star system IRAS 16293-2422 , about 400 light-years away, and the famous comet 67P/Churyumov-Gerasimenko (67P/C-G) in our own Solar System. The new ALMA observation is the first detection ever of a saturated organohalogen in interstellar space .
Organohalogens consist of halogens, such as chlorine and fluorine, bonded with carbon and sometimes other elements. On Earth, these compounds are created by some biological processes — in organisms ranging from humans to fungi — as well as by industrial processes such as the production of dyes and medical drugs .
This new discovery of one of these compounds, Freon-40, in places that must predate the origin of life, can be seen as a disappointment, as earlier research had suggested that these molecules could indicate the presence of life.
“Finding the organohalogen Freon-40 near these young, Sun-like stars was surprising,” said Edith Fayolle, a researcher with the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts in the USA, and lead author of the new paper. “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.”
Exoplanet research has gone beyond the point of finding planets — more than 3000 exoplanets are now known — to looking for chemical markers that might indicate the potential presence of life. A vital step is determining which molecules could indicate life, but establishing reliable markers remains a tricky process.
“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,” adds Karin Öberg, a co-author on 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 nascent rocky exoplanets.”
Co-author Jes Jørgensen from the Niels Bohr Institute at University of Copenhagen adds: “This result shows the power of ALMA to detect molecules of astrobiological interest in solar systems in the making. Using ALMA we have previously found simple sugars and precursors to amino acids around different stars.” Ewine van Dishoeck confirms: “The additional discovery of Freon-40 around Comet 67P/C-G strengthens the links between the pre-biological chemistry of distant protostars and our own Solar System.”
The astronomers also compared the relative amounts of Freon-40 that contain different isotopes of carbon in the infant star system and the comet — and found similar abundances. This supports the idea that a young planetary system can inherit the chemical composition of its parent star-forming cloud and opens up the possibility that organohalogens could arrive on planets in young systems during planet formation or via comet impacts.
 This protostar is a binary star system surrounded by a molecular cloud in the Rho Ophiuchi star-forming region, which makes it an excellent target for ALMA’s millimetre/submillimetre view.
 The data used were from the ALMA Protostellar Interferometric Line Survey (PILS). The aim of this survey is to chart the chemical complexity of IRAS 16293-2422 by imaging the full wavelength range covered by ALMA's band 7 on very small scales, equivalent to the size of the Solar System.
The species CF+, which could be considered as an organohalogen, had already been detected, but is not stable.
 Freon was widely used as a refrigerant (hence the name) but is now banned as it has a destructive effect on the Earth’s protective ozone layer.
Image credit:B. Saxton (NRAO/AUI/NSF); NASA/JPL-Caltech/UCLA.The background image of the Rho Ophiuchi cloud complex is from NASA's Wide-field Infrared Survey Explorer (WISE).
Article: ‘Protostellar and Cometary Detections of Organohalogens’, E. Fayolle et al., 2 oktober 2017, Nature Astronomy. https://www.nature.com/articles/s41550-017-0237-7