Ion composition at comet 67P near perihelion: Rosetta observations and model-based interpretation

Kevin L. Heritier (1) , Kathrin Altwegg (2) , Hans Balsiger (2) , Jean-Jacques Berthelier (3) , Arnaud Beth (1) , André Bieler (2) , Nicolas Biver (4) , Ursina Calmonte (2) , Michael R. Combi (5) , Johan de Keyser (6) , Anders I. Eriksson (7) , Björn Fiethe (8) , Nicolas Fougere (5) , Stephen Fuselier (9, 10) , Marina Galand (1) , Sebastien Gasc (2) , Tamas I. Gombosi (5) , Kenneth C. Hansen (5) , Myrtha Hassig (2, 9) , Ernest Kopp (2) , Elias Odelstad (7) , Martin Rubin (2) , Chia-Yu Tzou (2) , Erik Vigren (7) , Véronique Vuitton (11)

1 Department of Physics [Imperial College London]
2 Physikalisches Institut [Bern]
3 PLANETO - LATMOS
4 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
5 AOSS - Department of Atmospheric, Oceanic, and Space Sciences [Ann Arbor]
6 BIRA-IASB - Belgian Institute for Space Aeronomy / Institut d'Aéronomie Spatiale de Belgique
7 IRF - Swedish Institute of Space Physics [Uppsala]
8 IDA - Institute of Computer and Network Engineering [Braunschweig]
9 Space Science and Engineering Division [San Antonio]
10 UTSA - The University of Texas at San Antonio
11 IPAG - Institut de Planétologie et d'Astrophysique de Grenoble

We present the ion composition in the coma of comet 67P with newly detected ion species over the 28 to 37 u mass range, probed by Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA)/Double Focusing Mass Spectrometer (DFMS). In summer 2015, the nucleus reached its highest outgassing rate and ion-neutral reactions started to take place at low cometocentric distances. Minor neutrals can efficiently capture protons from the ion population, making the protonated version of these neutrals a major ion species. So far, only NH>sup>+₄ has been reported at comet 67P. However, there are additional neutral species with proton affinities higher than that of water (besides NH3) that have been detected in the coma of comet 67P: CH₃OH, HCN, H₂CO and H₂S. Their protonated versions have all been detected. Statistics showing the number of detections with respect to the number of scans are presented. The effect of the negative spacecraft potential probed by the Rosetta Plasma Consortium (RPC)/LAngmuir Probe (LAP) on ion detection is assessed. An ionospheric model has been developed to assess the different ion density profiles and compare them to the ROSINA/DFMS measurements. It is also used to interpret the ROSINA/DFMS observations when different ion species have similar masses, and their respective densities are not high enough to disentangle them using the ROSINA/DFMS high resolution mode. The different ion species that have been reported in the coma of 67P are summarised and compared with the ions detected at comet 1P/Halley during the Giotto mission.

Keywords: Data analysis; UV radiation; Comets; Plasmas; Sun

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

Kevin L. Heritier, Kathrin Altwegg, Hans Balsiger, Jean-Jacques Berthelier, Arnaud Beth, et al.. Ion composition at comet 67P near perihelion: Rosetta observations and model-based interpretation. Monthly Notices of the Royal Astronomical Society, 2017, 469 (Suppl_2), pp.S427-S442. ⟨10.1093/mnras/stx1912⟩. ⟨insu-01575071⟩