Effective ion speeds at ∼200–250 km from comet 67P/Churyumov–Gerasimenko near perihelion
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Published version
Author(s)
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.
Date Issued
2017-06-13
Date Acceptance
2017-06-09
Citation
Monthly Notices of the Royal Astronomical Society, 2017, 469 (Suppl_2), pp.S142-S148
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
Science and Technology Facilities Council (STFC)
European Space Agency / Estec
Grant Number
ST/N000692/1
4000119035/16/ES/JD
Subjects
0201 Astronomical And Space Sciences
Astronomy & Astrophysics
Publication Status
Published
Date Publish Online
2017-06-13