Halogens as tracers of protosolar nebula material in comet 67P/Churyumov-Gerasimenko

Frederik Dhooghe (1) , Johan de Keyser (2, 1) , Kathrin Altwegg (3, 4) , Christelle Briois (5) , Hans Balsiger (3) , Jean-Jacques Berthelier (6) , Ursina Calmonte (3) , Gaël Cessateur (1) , Michael R. Combi (7) , Eddy Equeter (1) , Björn Fiethe (8) , Nicolas Fray (9) , Stephen Fuselier (10, 11) , Sébastien Gasc (3) , Andrew Gibbons (1, 12) , Tamas I. Gombosi (13) , Herbert Gunell (1) , Myrtha Hässig (3, 10) , Martin Hilchenbach (14) , Léna Le Roy (4) , Romain Maggiolo (1) , Urs Mall (14) , Bernard Marty (15) , Eddy Neefs (1) , Henri Rème (16) , Martin Rubin (3) , Thierry Sémon (3) , Chia-Yu Tzou (3) , Peter Wurz (3, 4)

1 BIRA-IASB - Belgian Institute for Space Aeronomy / Institut d'Aéronomie Spatiale de Belgique
2 CmPA - Centre for Mathematical Plasma-Astrophysics [Leuven]
3 Physikalisches Institut [Bern]
4 CSH - Center for Space and Habitability
5 LPC2E - Laboratoire de Physique et Chimie de l'Environnement et de l'Espace
6 PLANETO - LATMOS
7 CLaSP - Department of Climate and Space Sciences and Engineering
8 IDA - Institute of Computer and Network Engineering [Braunschweig]
9 LISA (UMR_7583) - Laboratoire Interuniversitaire des Systèmes Atmosphériques
10 Space Science and Engineering Division [San Antonio]
11 UTSA - The University of Texas at San Antonio
12 Spectroscopie de l'atmosphère, Service de Chimie Quantique et Photophysique
13 AOSS - Department of Atmospheric, Oceanic, and Space Sciences [Ann Arbor]
14 MPS - Max-Planck-Institut für Sonnensystemforschung
15 CRPG - Centre de Recherches Pétrographiques et Géochimiques
16 IRAP - Institut de recherche en astrophysique et planétologie

We report the first in situ detection of halogens in a cometary coma, that of 67P/Churyumov-Gerasimenko. Neutral gas mass spectra collected by the European Space Agencys Rosetta spacecraft during four periods of interest from the first comet encounter up to perihelion indicate that the main halogen-bearing compounds are HF, HCl and HBr. The bulk elemental abundances relative to oxygen are ∼8.9 × 10⁻⁵ for F/O, ∼1.2 × 10⁻⁴ for Cl/O, and ∼2.5 × 10⁻⁶ for Br/O, for the volatile fraction of the comet. The cometary isotopic ratios for ³⁷Cl/³⁵Cl and ⁸¹Br/⁷⁹Br match the solar system values within the error margins. The observations point to an origin of the hydrogen halides in molecular cloud chemistry, with frozen hydrogen halides on dust grains, and a subsequent incorporation into comets as the cloud condensed and the solar system formed.

Domains: Earth and Planetary Astrophysics [astro-ph.EP]; Solar and Stellar Astrophysics [astro-ph.SR]

Frederik Dhooghe, Johan de Keyser, Kathrin Altwegg, Christelle Briois, Hans Balsiger, et al.. Halogens as tracers of protosolar nebula material in comet 67P/Churyumov-Gerasimenko. Monthly Notices of the Royal Astronomical Society, 2017, 472 (2), pp.1336-1345. ⟨10.1093/mnras/stx1911⟩. ⟨insu-01575014⟩