Diamagnetic region(s): structure of the unmagnetized plasma around Comet 67P/CG

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Title: Diamagnetic region(s): structure of the unmagnetized plasma around Comet 67P/CG
Authors: Henri, P
Vallières, X
Hajra, R
Goetz, C
Richter, I
Glassmeier, K-H
Galand, M
Rubin, M
Eriksson, AI
Nemeth, Z
Vigren, E
Beth, A
Burch, JL
Carr, C
Nilsson, H
Tsurutani, B
Wattieaux, G
Item Type: Journal Article
Abstract: The ESA’s comet chaser Rosetta has monitored the evolution of the ionized atmosphere of comet 67P/Churyumov–Gerasimenko (67P/CG) and its interaction with the solar wind, during more than 2 yr. Around perihelion, while the cometary outgassing rate was highest, Rosetta crossed hundreds of unmagnetized regions, but did not seem to have crossed a large-scale diamagnetic cavity as anticipated. Using in situ Rosetta observations, we characterize the structure of the unmagnetized plasma found around comet 67P/CG. Plasma density measurements from RPC-MIP are analysed in the unmagnetized regions identified with RPC-MAG. The plasma observations are discussed in the context of the cometary escaping neutral atmosphere, observed by ROSINA/COPS. The plasma density in the different diamagnetic regions crossed by Rosetta ranges from ∼100 to ∼1500 cm−3. They exhibit a remarkably systematic behaviour that essentially depends on the comet activity and the cometary ionosphere expansion. An effective total ionization frequency is obtained from in situ observations during the high outgassing activity phase of comet 67P/CG. Although several diamagnetic regions have been crossed over a large range of distances to the comet nucleus (from 50 to 400 km) and to the Sun (1.25–2.4 au), in situ observations give strong evidence for a single diamagnetic region, located close to the electron exobase. Moreover, the observations are consistent with an unstable contact surface that can locally extend up to about 10 times the electron exobase.
Issue Date: 21-Jun-2017
Date of Acceptance: 16-Jun-2017
URI: http://hdl.handle.net/10044/1/56683
DOI: https://dx.doi.org/10.1093/mnras/stx1540
ISSN: 0035-8711
Publisher: Oxford University Press
Start Page: S372
End Page: S379
Journal / Book Title: Monthly Notices of the Royal Astronomical Society
Volume: 469
Issue: Suppl_2
Copyright Statement: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2017 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Sponsor/Funder: Imperial College Trust
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
Faculty of Natural Sciences

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