Ion Velocity and Electron Temperature Inside and Around the Diamagnetic Cavity of Comet 67P

Odelstad, E.; Eriksson, A. I.; Johansson, F. L.; Vigren, E.; Henri, P.; Gilet, N.; Heritier, K. L.; Vallières, X.; Rubin, M.; André, M. (2018). Ion Velocity and Electron Temperature Inside and Around the Diamagnetic Cavity of Comet 67P. Journal of Geophysical Research: Space Physics, 123(7), pp. 5870-5893. AGU Publications 10.1029/2018ja025542

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A major point of interest in cometary plasma physics has been the diamagnetic cavity, an unmagnetized region in the innermost part of the coma. Here we combine Langmuir and Mutual Impedance Probe measurements to investigate ion velocities and electron temperatures in the diamagnetic cavity of comet 67P, probed by the Rosetta spacecraft. We find ion velocities generally in the range 2–4 km/s, significantly above the expected neutral velocity 1 km/s, showing that the ions are (partially) decoupled from the neutrals, indicating that ion-neutral drag was not responsible for balancing the outside magnetic pressure. Observations of clear wake effects on one of the Langmuir probes showed that the ion flow was close to radial and supersonic, at least with respect to the perpendicular temperature, inside the cavit y and possibly in the surrounding region as well. We observed spacecraft potentials  −5 V throughout the cavity, showing that a population of warm (∼5 eV) electrons was present throughout the parts of the cavity reached by Rosetta. Also, a population of cold (0.1 eV) electrons was consistently observed throughout the cavity, but less consistently in the surrounding region, suggesting that while Rosetta never entered a region of collisionally coupled electrons, such a region was possibly not far away during the cavity crossings.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Physics Institute > Space Research and Planetary Sciences
08 Faculty of Science > Physics Institute

UniBE Contributor:

Rubin, Martin

Subjects:

500 Science > 520 Astronomy
600 Technology > 620 Engineering
500 Science > 530 Physics

ISSN:

2169-9380

Publisher:

AGU Publications

Language:

English

Submitter:

Dora Ursula Zimmerer

Date Deposited:

30 Aug 2018 14:39

Last Modified:

01 Jan 2019 02:31

Publisher DOI:

10.1029/2018ja025542

BORIS DOI:

10.7892/boris.119610

URI:

https://boris.unibe.ch/id/eprint/119610

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