H/C elemental ratio of the refractory organic matter in cometary particles of 67P/Churyumov-Gerasimenko

¹ Laboratoire Interuniversitaire des Systèmes Atmosphériques, UMR CNRS 7583, Université Paris Est Créteil (UPEC) et Université Paris Diderot (UPD), Créteil, France
e-mail: robin.isnard@lisa.u-pec.fr
² Laboratoire de Physique et Chimie de l’Environnement et de l’Espace, UMR CNRS 7328, Université d’Orléans et du CNES, Orléans, France
³ DTM, Carnegie Institution of Washington, Washington, DC, USA
⁴ MPS, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
⁵ Institut d’Astrophysique Spatiale, CNRS/Université Paris-Sud, Université Paris-Saclay, bâtiment 121, Université Paris-Sud, 91405 Orsay Cedex, France
⁶ CSNSM, CNRS-IN2P3, Université Paris-Sud, Université Paris-Saclay, BAtiment 104, 91405 Orsay Campus, France
⁷ Univ. Grenoble Alpes, CNRS, CNES, IPAG, 38000 Grenoble, France
⁸ Bioscience and Materials / Chemistry and Materials, RISE Research Institutes of Sweden, Stockholm, Sweden
⁹ Institute of Statistics and Mathematical Methods in Economics, Vienna University of Technology, Wiedner Hauptstrasse 7/105-6, 1040 Vienna, Austria

Received: 7 December 2018
Accepted: 5 March 2019

Abstract

Context. Because comets are part of the most primitive bodies of our solar system, establishing their chemical composition and comparing them to other astrophysical bodies gives new constraints on the formation and evolution of organic matter throughout the solar system. For two years, the time-of-flight secondary ion mass spectrometer COmetary Secondary Ion Mass Analyzer (COSIMA) on board the Rosetta orbiter performed in situ analyses of the dust particles ejected from comet 67P/Churyumov-Gerasimenko (67P).

Aims. The aim is to determine the H/C elemental ratio of the refractory organic component contained in cometary particles of 67P.

Methods. We analyzed terrestrial and extraterrestrial calibration samples using the COSIMA ground-reference model. Exploiting these calibration samples, we provide calibration lines in both positive and negative ion registration modes. Thus, we are now able to measure the cometary H/C elemental ratio.

Results. The mean H/C value is 1.04 ± 0.16 based on 33 different cometary particles. Consequently, the H/C atomic ratio is on average higher in cometary particles of 67P than in even the most primitive insoluble organic matter extracted from meteorites.

Conclusions. These results imply that the refractory organic matter detected in dust particles of 67P is less unsaturated than the material in meteorites.