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Protostellar and cometary detections of organohalogens


Organohalogens, a class of molecules that contain at least one halogen atom bonded to carbon, are abundant on the Earth where they are mainly produced through industrial and biological processes1. Consequently, they have been proposed as biomarkers in the search for life on exoplanets2. Simple halogen hydrides have been detected in interstellar sources and in comets, but the presence and possible incorporation of more complex halogen-containing molecules such as organohalogens into planet-forming regions is uncertain3,4. Here we report the interstellar detection of two isotopologues of the organohalogen CH3Cl and put some constraints on CH3F in the gas surrounding the low-mass protostar IRAS 16293–2422, using the Atacama Large Millimeter/submillimeter Array (ALMA). We also find CH3Cl in the coma of comet 67P/Churyumov–Gerasimenko (67P/C-G) by using the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument. The detections reveal an efficient pre-planetary formation pathway of organohalogens. Cometary impacts may deliver these species to young planets and should thus be included as a potential abiotical production source when interpreting future organohalogen detections in atmospheres of rocky planets.

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Fig. 1: Methyl halide transitions in a spectrum extracted around protostar IRAS 16293B.
Fig. 2: Spatial emission of CH3 35Cl compared with that of CH3OCHO around protostar IRAS 16293B.
Fig. 3: Mass spectrum of the coma of comet 67P/C-G for molecular fragments around mass/charge equal to 50 u/e.


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This work is based on observations from ALMA, a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), NSC and ASIAA (Taiwan), and KASI (Republic of Korea), in co-operation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. Data from ROSINA, an instrument part of Rosetta mission, were used in this work. Rosetta is a European Space Agency (ESA) mission with contributions from its member states and NASA, and we acknowledge herewith the work of the whole ESA Rosetta team. E.C.F. and K.I.O. acknowledge financial support from the Simons Foundation (SCOL award 321183, KO) and to Northrop Grumman Corporation. The group of J.K.J. acknowledges support from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 646908) through ERC Consolidator Grant S4F. Research at the Centre for Star and Planet Formation is funded by the Danish National Research Foundation. Work at the University of Bern was funded by the State of Bern, the Swiss National Science Foundation, and the ESA PRODEX programme (Programme de Développement d’Expériences scientifiques). E.F.v.D. acknowledges A-ERC grant CHEMPLAN 291141. M.N.D. acknowledges the financial support of the Center for Space and Habitability (CSH) Fellowship and the IAU Gruber Foundation Fellowship. S.F.W. acknowledges financial support from a CSH fellowship.

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E.C.F. initiated the project, and identified and analysed the newly detected species in the protostar spectra. E.C.F. and K.I.O. wrote the manuscript together. The Principal Investigator of the PILS survey, J.K.J, together with H.C. and M.H.D.v.d.W. generated the datacubes from the ALMA observations and assisted with the column density determinations. H.S.P.M. computed the CH3F line catalogue and assisted with the CH3Cl spectroscopy interpretations. R.T.G contributed the text on the formation pathways to organohalogens under interstellar medium conditions. The Principal Investigator of the ROSINA programme, K.A., together with M.R. reduced the DFMS data, and identified and provided the CH3Cl abundance ratios. The ALMA-PILS and ROSINA-DFMS collaboration was initiated by E.F.v.D., M.N.D. and S.F.W. J.K.J., H.S.P.M. and E.F.v.D. provided extensive input on the text. All the authors contributed to discussions of the results and commented on the manuscript.

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Correspondence to Edith C. Fayolle.

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Fayolle, E.C., Öberg, K.I., Jørgensen, J.K. et al. Protostellar and cometary detections of organohalogens. Nat Astron 1, 703–708 (2017).

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