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Plasma source and loss at comet 67P during the Rosetta mission
Imperial Coll London, Dept Phys, Prince Consort Rd, London SW7 2AZ, England.
Imperial Coll London, Dept Phys, Prince Consort Rd, London SW7 2AZ, England.
Univ Orleans, CNRS, LPC2E, F-45100 Orleans, France.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.ORCID iD: 0000-0002-5386-8255
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2018 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 618, article id A77Article in journal (Refereed) Published
Abstract [en]

Context. The Rosetta spacecraft provided us with a unique opportunity to study comet 67P/Churyumov-Gerasimenko (67P) from a close perspective and over a 2-yr 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 2-yr 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 4 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.

Place, publisher, year, edition, pages
EDP SCIENCES S A , 2018. Vol. 618, article id A77
Keywords [en]
comets: general, plasmas, space vehicles: instruments
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:uu:diva-368442DOI: 10.1051/0004-6361/201832881ISI: 000447121500001OAI: oai:DiVA.org:uu-368442DiVA, id: diva2:1269087
Available from: 2018-12-07 Created: 2018-12-07 Last updated: 2018-12-07Bibliographically approved

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Johansson, FredrikEriksson, Anders

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