ROSINA ion zoo at Comet 67P

¹ Department of Physics, Imperial College London, Prince Consort Road, London SW7 2AZ, UK
e-mail: arnaud.beth@gmail.com
² Department of Physics, Umeå University, 901 87 Umeå, Sweden
³ Physikalisches Institut, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland
⁴ Center for Space and Habitability, University of Bern, Gesellschaftsstrasse 6, 3012 Bern, Switzerland
⁵ LATMOS, 4 Avenue de Neptune, 94100 Saint-Maur, France
⁶ Department of Climate and Space Sciences and Engineering, University of Michigan, 2455 Hayward, Ann Arbor, MI 48109, USA
⁷ Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Ringlaan 3, 1180 Brussels, Belgium
⁸ Institute of Computer and Network Engineering (IDA), TU Braunschweig, Hans-Sommer-StraSSe 66, 38106 Braunschweig, Germany
⁹ Space Science Division, Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78228, USA
¹⁰ University of Texas at San Antonio, San Antonio, TX, USA

Received: 24 September 2019
Accepted: 7 July 2020

Abstract

Context. The Rosetta spacecraft escorted Comet 67P/Churyumov-Gerasimenko for 2 yr along its journey through the Solar System between 3.8 and 1.24 au. Thanks to the high resolution mass spectrometer on board Rosetta, the detailed ion composition within a coma has been accurately assessed in situ for the very first time.

Aims. Previous cometary missions, such as Giotto, did not have the instrumental capabilities to identify the exact nature of the plasma in a coma because the mass resolution of the spectrometers onboard was too low to separate ion species with similar masses. In contrast, the Double Focusing Mass Spectrometer (DFMS), part of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis on board Rosetta (ROSINA), with its high mass resolution mode, outperformed all of them, revealing the diversity of cometary ions.

Methods. We calibrated and analysed the set of spectra acquired by DFMS in ion mode from October 2014 to April 2016. In particular, we focused on the range from 13–39 u q⁻¹. The high mass resolution of DFMS allows for accurate identifications of ions with quasi-similar masses, separating ¹³C⁺ from CH⁺, for instance.

Results. We confirm the presence in situ of predicted cations at comets, such as CH_m⁺ (m = 1−4), H_nO⁺ (n = 1−3), O⁺, Na⁺, and several ionised and protonated molecules. Prior to Rosetta, only a fraction of them had been confirmed from Earth-based observations. In addition, we report for the first time the unambiguous presence of a molecular dication in the gas envelope of a Solar System body, namely CO₂⁺⁺.