Plasma source and loss at comet 67P during the Rosetta mission

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Title: Plasma source and loss at comet 67P during the Rosetta mission
Authors: Heritier, K
Galand, M
Henri, P
Johansson, FL
Beth, A
Eriksson, AI
Vallières, X
Altwegg, K
Burch, JL
Carr, C
Ducrot, E
Hajra, R
Rubin, M
Item Type: Journal Article
Abstract: Context. The Rosetta spacecraft provided us with a unique opportunity to study comet 67P / Churyumov-Gerasimenko from a close perspective and over a two-year time period. Comet 67P is a weakly active comet. It was therefore unexpected to find an active and dynamic ionosphere where the cometary ions were largely dominant over the solar wind ions, even at large heliocentric distances. Aims. Our goal is to understand the di ff erent drivers of the cometary ionosphere and assess their variability over time and over the di ff erent conditions encountered by the comet during the Rosetta mission. Methods. We used a multi-instrument data-based ionospheric model to compute the total ion number density at the position of Rosetta. In-situ measurements from the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) and the Rosetta Plasma Consortium (RPC)–Ion and Electron Sensor (IES), together with the RPC–LAngmuir Probe instrument (LAP) were used to compute the local ion total number density. The results are compared to the electron densities measured by RPC–Mutual Impedance Probe (MIP) and RPC–LAP. Results. We were able to disentangle the physical processes responsible for the formation of the cometary ions throughout the two-year escort phase and we evaluated their respective magnitudes. The main processes are photo-ionization and electron-impact ionization. The latter is a significant source of ionization at large heliocentric distance ( > 2 au) and was predominant during the last four months of the mission. The ionosphere was occasionally subject to singular solar events, temporarily increasing the ambient energetic electron population. Solar photons were the main ionizer near perihelion at 1.3 au from the Sun, during summer 2015.
Issue Date: 18-Jun-2018
Date of Acceptance: 3-Jun-2018
ISSN: 0004-6361
Publisher: EDP Sciences
Journal / Book Title: Astronomy and Astrophysics
Copyright Statement: © ESO 2018
Sponsor/Funder: Science and Technology Facilities Council (STFC)
Science and Technology Facilities Council (STFC)
Science and Technology Facilities Council (STFC)
European Space Agency / Estec
European Space Agency / Estec
Funder's Grant Number: ST/K001698/1
Keywords: 0201 Astronomical And Space Sciences
Astronomy & Astrophysics
Publication Status: Published online
Online Publication Date: 2018-06-18
Appears in Collections:Space and Atmospheric Physics
Faculty of Natural Sciences

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