Model-Observation Comparisons of Electron Number Densities in the Coma of 67P/Churyumov–Gerasimenko During 2015 January

Abstract : During 2015 January 9–11, at a heliocentric distance of ~2.58–2.57 au, the ESA Rosetta spacecraft resided at a cometocentric distance of ~28 km from the nucleus of comet 67P/Churyumov–Gerasimenko, sweeping the terminator at northern latitudes of 43°N–58°N. Measurements by the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis/Comet Pressure Sensor (ROSINA/COPS) provided neutral number densities. We have computed modeled electron number densities using the neutral number densities as input into a Field Free Chemistry Free model, assuming H2O dominance and ion-electron pair formation by photoionization only. A good agreement (typically within 25%) is found between the modeled electron number densities and those observed from measurements by the Mutual Impedance Probe (RPC/MIP) and the Langmuir Probe (RPC/LAP), both being subsystems of the Rosetta Plasma Consortium. This indicates that ions along the nucleus-spacecraft line were strongly coupled to the neutrals, moving radially outward with about the same speed. Such a statement, we propose, can be further tested by observations of H3O+/H2O+ number density ratios and associated comparisons with model results.
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E. Vigren, K. Altwegg, N. J. T. Edberg, A. I. Eriksson, M. Galand, et al.. Model-Observation Comparisons of Electron Number Densities in the Coma of 67P/Churyumov–Gerasimenko During 2015 January . Astronomical Journal, American Astronomical Society, 2016, 152 (59), 8 p. ⟨10.3847/0004-6256/152/3/59⟩. ⟨insu-01373684⟩

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