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Multi-instrument analysis of far-ultraviolet aurora in the southern hemisphere of Comet 67P/Churyumov-Gerasimenko

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Title: Multi-instrument analysis of far-ultraviolet aurora in the southern hemisphere of Comet 67P/Churyumov-Gerasimenko
Authors: Stephenson, P
Galand, M
Feldman, PD
Beth, A
Rubin, M
Bockelée-Morvan, D
Biver, N
-C Cheng, Y
Parker, J
Burch, J
Johansson, FL
Eriksson, A
Item Type: Journal Article
Abstract: Aims. We aim to determine whether dissociative excitation of cometary neutrals by electron impact is the major source of far ultraviolet (FUV) emissions at comet 67P/Churyumov-Gerasimenko in the southern hemisphere at large heliocentric distances, both during quiet conditions and impacts of corotating interaction regions observed in the summer of 2016. Methods. We combined multiple datasets from the Rosetta mission through a multi-instrument analysis to complete the first forward modelling of FUV emissions in the southern hemisphere of comet 67P and compared modelled brightnesses to observations with the Alice FUV imaging spectrograph. We modelled the brightness of OI1356, OI1304, Lyman-β, CI1657, and CII1335 emissions, which are associated with the dissociation products of the four major neutral species in the coma: CO2, H2O, CO, and O2. The suprathermal electron population was probed by the Ion and Electron Sensor of the Rosetta Plasma Consortium (RPC/IES) and the neutral col umn density was constrained by several instruments: the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA), the Microwave Instrument for the Rosetta Orbiter (MIRO) and the Visual InfraRed Thermal Imaging Spectrometer (VIRTIS). Results. The modelled and observed brightnesses of the FUV emission lines agree closely when viewing nadir and dissociative excitation by electron impact is shown to be the dominant source of emissions away from perihelion. The CII1335 emissions are shown to be consistent with the volume mixing ratio of CO derived from ROSINA. When viewing the limb during the impacts of corotating interaction regions, the model reproduces brightnesses of OI1356 and CI1657 well, but resonance scattering in the extended coma may contribute significantly to the observed Lyman-β and OI1304 emissions. The correlation between variations in the suprathermal electron flux and the observed FUV line brightnesses when viewing the comet’s limb suggests electrons are accelerated on large scales and that they originate in the solar wind. This means that the FUV emissions are auroral in nature.
Issue Date: 19-Mar-2021
Date of Acceptance: 2-Dec-2020
URI: http://hdl.handle.net/10044/1/86588
DOI: 10.1051/0004-6361/202039155
ISSN: 0004-6361
Publisher: EDP Sciences
Start Page: 1
End Page: 19
Journal / Book Title: Astronomy and Astrophysics: a European journal
Volume: 647
Copyright Statement: ©ESO 2021
Sponsor/Funder: Science and Technology Facilities Council (STFC)
Funder's Grant Number: ST/N000692/1
Keywords: Science & Technology
Physical Sciences
Astronomy & Astrophysics
comets: individual: 67P/CG
ultraviolet: planetary systems
planets and satellites: aurorae
astro-ph.EP
astro-ph.EP
physics.space-ph
Astronomy & Astrophysics
0201 Astronomical and Space Sciences
Publication Status: Published
Article Number: A119
Online Publication Date: 2021-03-19
Appears in Collections:Space and Atmospheric Physics
Physics
Faculty of Natural Sciences