Effective ion speeds at ∼200–250 km from comet 67P/Churyumov–Gerasimenko near perihelion

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Title: Effective ion speeds at ∼200–250 km from comet 67P/Churyumov–Gerasimenko near perihelion
Authors: Vigren, E
André, M
Edberg, NJT
Engelhardt, IAD
Eriksson, AI
Galand, M
Goetz, C
Henri, P
Heritier, K
Johansson, FL
Nilsson, H
Odelstad, E
Rubin, M
Stenberg-Wieser, G
Tzou, C-Y
Vallières, X
Item Type: Journal Article
Abstract: In 2015 August, comet 67P/Churyumov–Gerasimenko, the target comet of the ESA Rosetta mission, reached its perihelion at ∼1.24 au. Here, we estimate for a three-day period near perihelion, effective ion speeds at distances ∼200–250 km from the nucleus. We utilize two different methods combining measurements from the Rosetta Plasma Consortium (RPC)/Mutual Impedance Probe with measurements either from the RPC/Langmuir Probe or from the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA)/Comet Pressure Sensor (COPS) (the latter method can only be applied to estimate the effective ion drift speed). The obtained ion speeds, typically in the range 2–8 km s−1, are markedly higher than the expected neutral outflow velocity of ∼1 km s−1. This indicates that the ions were de-coupled from the neutrals before reaching the spacecraft location and that they had undergone acceleration along electric fields, not necessarily limited to acceleration along ambipolar electric fields in the radial direction. For the limited time period studied, we see indications that at increasing distances from the nucleus, the fraction of the ions’ kinetic energy associated with radial drift motion is decreasing.
Issue Date: 13-Jun-2017
Date of Acceptance: 9-Jun-2017
URI: http://hdl.handle.net/10044/1/56686
DOI: https://dx.doi.org/10.1093/mnras/stx1472
ISSN: 0035-8711
Publisher: Oxford University Press
Start Page: S142
End Page: S148
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 Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Sponsor/Funder: Science and Technology Facilities Council (STFC)
European Space Agency / Estec
Funder's Grant Number: ST/N000692/1
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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