Suprathermal electrons near the nucleus of comet 67P/Churyumov-Gerasimenko at 3 AU: Model comparisons with Rosetta data

Madanian, H.; Cravens, T. E.; Rahmati, A.; Goldstein, R.; Burch, J.; Eriksson, A. I.; Edberg, N. J. T.; Henri, P.; Mandt, K.; Clark, G.; Rubin, Martin; Broiles, T.; Reedy, N. L. (2016). Suprathermal electrons near the nucleus of comet 67P/Churyumov-Gerasimenko at 3 AU: Model comparisons with Rosetta data. Journal of Geophysical Research: Space Physics, 121(6), pp. 5815-5836. AGU Publications 10.1002/2016JA022610

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Observations of the coma near the nucleus of comet 67P/Churyumov-Gerasimenko (67P) made by the IES (Ion and Electron Sensor) instrument onboard the Rosetta Orbiter during late 2014 showed that electron fluxes greatly exceeded solar wind electron fluxes. The IES is part of the Rosetta Plasma Consortium. This paper reports on electron energy spectra measured by IES near the nucleus as well as approximate densities and average energies for the suprathermal electrons when the comet was at a heliocentric distance of about 3 AU. Comparisons are made with electron densities measured by other instruments. The high electron densities observed (e.g., ne ≈ 10–100 cm−3) must be associated with the cometary ion density enhancement created mainly by the photoionization of cometary gas by solar radiation; there are other processes that also contribute. Quasineutrality requires that the electron and ion densities be the same, and under certain conditions an ambipolar electric field is required to achieve quasi-neutrality. We present the results of a test particle model of cometary ion pickup by the solar wind and a two-stream electron transport code and use these results to interpret the IES data. We also estimate the effects on the electron spectrum of a compression of the electron fluid parcel. The electrons detected by IES can have energies as high as about 100–200 eV near the comet on some occasions, in which case the hot electrons can significantly enhance ionization rates of neutrals via impact ionization.

Item Type:

Journal Article (Original Article)

Division/Institute:

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

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:

Katharina Weyeneth-Moser

Date Deposited:

18 Jul 2017 09:54

Last Modified:

18 Jul 2017 09:54

Publisher DOI:

10.1002/2016JA022610

BORIS DOI:

10.7892/boris.97010

URI:

https://boris.unibe.ch/id/eprint/97010

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