Vertical structure of the near-surface expanding ionosphere of comet 67P probed by Rosetta

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Title: Vertical structure of the near-surface expanding ionosphere of comet 67P probed by Rosetta
Authors: Heritier, KL
Henri, P
Vallières, X
Galand, M
Odelstad, E
Eriksson, AI
Johansson, FL
Altwegg, K
Behar, E
Beth, A
Broiles, TW
Burch, JL
Carr, CM
Cupido, E
Nilsson, H
Rubin, M
Vigren, E
Item Type: Journal Article
Abstract: The plasma environment has been measured for the first time near the surface of a comet. This unique data set has been acquired at 67P/Churyumov–Gerasimenko during ESA/Rosetta spacecraft's final descent on 2016 September 30. The heliocentric distance was 3.8 au and the comet was weakly outgassing. Electron density was continuously measured with Rosetta Plasma Consortium (RPC)–Mutual Impedance Probe (MIP) and RPC–LAngmuir Probe (LAP) during the descent from a cometocentric distance of 20 km down to the surface. Data set from both instruments have been cross-calibrated for redundancy and accuracy. To analyse this data set, we have developed a model driven by Rosetta Orbiter Spectrometer for Ion and Neutral Analysis–COmetary Pressure Sensor total neutral density. The two ionization sources considered are solar extreme ultraviolet radiation and energetic electrons. The latter are estimated from the RPC–Ion and Electron Sensor (IES) and corrected for the spacecraft potential probed by RPC–LAP. We have compared the results of the model to the electron densities measured by RPC–MIP and RPC–LAP at the location of the spacecraft. We find good agreement between observed and modelled electron densities. The energetic electrons have access to the surface of the nucleus and contribute as the main ionization source. As predicted, the measurements exhibit a peak in the ionospheric density close to the surface. The location and magnitude of the peak are estimated analytically. The measured ionospheric densities cannot be explained with a constant outflow velocity model. The use of a neutral model with an expanding outflow is critical to explain the plasma observations.
Issue Date: 12-Jun-2017
Date of Acceptance: 8-Jun-2017
ISSN: 0035-8711
Publisher: Oxford University Press
Start Page: S118
End Page: S129
Journal / Book Title: Monthly Notices of the Royal Astronomical Society
Volume: 469
Issue: Suppl_2
Copyright Statement: © 2017 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
Sponsor/Funder: Imperial College Trust
Science and Technology Facilities Council (STFC)
Science and Technology Facilities Council [2006-2012]
Science and Technology Facilities Council (STFC)
European Space Agency / Estec
Funder's Grant Number: N/A
Keywords: 0201 Astronomical And Space Sciences
Astronomy & Astrophysics
Publication Status: Published
Appears in Collections:Space and Atmospheric Physics

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