First in-situ detection of the cometary ammonium ion NH₄⁺ (protonated ammonia NH₃ ) in the coma of 67P/C-G near perihelion

Arnaud Beth (1) , Kathrin Altwegg (2) , Hans Balsiger (2) , Jean-Jacques Berthelier (3, 4) , Ursina Calmonte (2) , Michael R. Combi (5) , Johan de Keyser (6) , Frederik Dhooghe (6) , Björn Fiethe (7) , Stephen Fuselier (8, 9) , Marina Galand (1) , Sébastien Gasc (2) , Tamas I. Gombosi (5) , Kenneth C. Hansen (5) , Myrtha Hässig (9, 2) , Kevin L. Héritier (1) , Ernest Kopp (2) , Léna Le Roy (2) , E. Mandt (9, 8) , Solène Peroy (1) , Martin Rubin (2) , Thierry Sémon (2) , Chia-Yu Tzou (2) , Erik Vigren (10)

1 Department of Physics [Imperial College London]
2 Physikalisches Institut [Bern]
3 PLANETO - LATMOS
4 HELIOS - LATMOS
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 IDA - Institute of Computer and Network Engineering [Braunschweig]
8 SwRI - Southwest Research Institute [San Antonio]
9 UTSA Department of Physics and Astronomy [San Antonio]
10 IRF - Swedish Institute of Space Physics [Uppsala]

In this paper, we report the first in-situ detection of the ammonium ion NH₄⁺ at 67P/Churyumov-Gerasimenko (67P/C-G) in a cometary coma, using the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) / Double Focusing Mass Spectrometer (DFMS). Unlike neutral and ion spectrometers onboard previous cometary missions, the ROSINA/DFMS spectrometer, when operated in ion mode, offers the capability to distinguish NH₄⁺ from H₂O⁺ in a cometary coma. We present here the ion data analysis of mass-to-charge ratios 18 and 19 at high spectral resolution and compare the results with an ionospheric model to put the these results into context. The model confirms that the ammonium ion NH₄⁺ is one of the most abundant ion species, as predicted, in the coma near perihelion.

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

Domains: Ocean, Atmosphere

Arnaud Beth, Kathrin Altwegg, Hans Balsiger, Jean-Jacques Berthelier, Ursina Calmonte, et al.. First in-situ detection of the cometary ammonium ion NH₄⁺ (protonated ammonia NH₃ ) in the coma of 67P/C-G near perihelion. Monthly Notices of the Royal Astronomical Society, 2016, 462 (Suppl_1), pp.S562-S572. ⟨10.1093/mnras/stw3370⟩. ⟨insu-01427998⟩