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Cometary ion dynamics observed in the close vicinity of comet 67P/Churyumov–Gerasimenko during the intermediate activity period

Bercic, L; Behar, E; Nilsson, H; Nicolaou, G; Stenberg Wieser, G; Wieser, M; Goetz, C; (2018) Cometary ion dynamics observed in the close vicinity of comet 67P/Churyumov–Gerasimenko during the intermediate activity period. Astronomy and Astrophysics (A&A) , 613 , Article A57. 10.1051/0004-6361/201732082. Green open access

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Abstract

Aims. Cometary ions are constantly produced in the coma, and once produced they are accelerated and eventually escape the coma. We describe and interpret the dynamics of the cometary ion flow, of an intermediate active comet, very close to the nucleus and in the terminator plane. Methods. We analysed in situ ion and magnetic field measurements, and characterise the velocity distribution functions (mostly using plasma moments). We propose a statistical approach over a period of one month. Results. On average, two populations were observed, separated in phase space. The motion of the first is governed by its interaction with the solar wind farther upstream, while the second one is accelerated in the inner coma and displays characteristics compatible with an ambipolar electric field. Both populations display a consistent anti-sunward velocity component. Conclusions. Cometary ions born in different regions of the coma are seen close to the nucleus of comet 67P/Churyumov–Gerasimenko with distinct motions governed in one case by the solar wind electric field and in the other case by the position relative to the nucleus. A consistent anti-sunward component is observed for all cometary ions. An asymmetry is found in the average cometary ion density in a solar wind electric field reference frame, with higher density in the negative (south) electric field hemisphere. There is no corresponding signature in the average magnetic field strength.

Type: Article
Title: Cometary ion dynamics observed in the close vicinity of comet 67P/Churyumov–Gerasimenko during the intermediate activity period
Open access status: An open access version is available from UCL Discovery
DOI: 10.1051/0004-6361/201732082
Publisher version: https://doi.org/10.1051/0004-6361/201732082
Language: English
Additional information: This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: comets: general, comets: individual: 67P/Churyumov–Gerasimenko, plasmas, methods: observational, space vehicles: instruments
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics
URI: https://discovery.ucl.ac.uk/id/eprint/10051655
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