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

Heritier, K.L.; Galand, M.; Henri, P.; Johansson, F.L.; Beth, A.; Eriksson, A.I.; Vallières, X.; Altwegg, K.; Burch, J.L.; Carr, C.; Ducrot, E.; Hajra, R.; Rubin, M. (2018). Plasma source and loss at comet 67P during the Rosetta mission. Astronomy and astrophysics, 618, A77. EDP Sciences 10.1051/0004-6361/201832881

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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 different drivers of the cometary ionosphere and assess their variability over time and over the different 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.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Physics Institute > Space Research and Planetary Sciences

UniBE Contributor:

Altwegg, Kathrin and Rubin, Martin

Subjects:

500 Science > 520 Astronomy
600 Technology > 620 Engineering

ISSN:

0004-6361

Publisher:

EDP Sciences

Language:

English

Submitter:

Dora Ursula Zimmerer

Date Deposited:

30 Aug 2018 14:24

Last Modified:

13 Oct 2018 01:32

Publisher DOI:

10.1051/0004-6361/201832881

BORIS DOI:

10.7892/boris.119609

URI:

https://boris.unibe.ch/id/eprint/119609

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