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Characterizing Cometary Electrons with Kappa DistributionsThe Rosetta spacecraft has escorted comet 67P/Churyumov-Gerasimenko since 6 August 2014 and has offered an unprecedented opportunity to study plasma physics in the coma. We have used this opportunity to make the first characterization of cometary electrons with kappa distributions. Two three-dimensional kappa functions were fit to the observations, which we interpret as two populations of dense and warm (density 10 cubic centimeters, temperature 2 times 10 (sup 5) degrees Kelvin, invariant kappa index 10 to 1000), and rarefied and hot (density equals 0.005 cubic centimeters, temperature 5 times 10 (sup 5) degrees Kelvin, invariant kappa index equals 1 to 10) electrons. We fit the observations on 30 October 2014 when Rosetta was 20 kilometers from 67P, and 3 Astronomical Units from the Sun. We repeated the analysis on 15 August 2015 when Rosetta was 300 kilometers from the comet and 1.3 Astronomical Units from the Sun. Comparing the measurements on both days gives the first comparison of the cometary electron environment between a nearly inactive comet far from the Sun and an active comet near perihelion. We find that the warm population density increased by a factor of 3, while the temperature cooled by a factor of 2, and the invariant kappa index was unaffected. We find that the hot population density increased by a factor of 10, while the temperature and invariant kappa index were unchanged. We conclude that the hot population is likely the solar wind halo electrons in the coma. The warm population is likely of cometary origin, but its mechanism for production is not known.
Document ID
20170003508
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Broiles, T. W.
(Southwest Research Inst. San Antonio, TX, United States)
Livadiotis, G.
(Southwest Research Inst. San Antonio, TX, United States)
Burch, J. L.
(Southwest Research Inst. San Antonio, TX, United States)
Chae, K.
(Southwest Research Inst. San Antonio, TX, United States)
Clark, G.
(Johns Hopkins Univ. Laurel, MD, United States)
Cravens, T. E.
(Kansas Univ. Lawrence, KS, United States)
Davidson, R.
(Maryland Univ. College Park, MD, United States)
Eriksson, A.
(Swedish Inst. of Space Physics Kiruna, Sweden)
Frahm, R. A.
(Southwest Research Inst. San Antonio, TX, United States)
Fuselier, S. A.
(Southwest Research Inst. San Antonio, TX, United States)
Goldstein, J.
(Southwest Research Inst. San Antonio, TX, United States)
Goldstein, R.
(Southwest Research Inst. San Antonio, TX, United States)
Henri, P.
(Centre National de la Recherche Scientifique Orleans, France)
Madanian, H.
(Kansas Univ. Lawrence, KS, United States)
Mandt, K.
(Southwest Research Inst. San Antonio, TX, United States)
Mokashi, P.
(Southwest Research Inst. San Antonio, TX, United States)
Pollock, C.
(Denali Scientific, LLC Healy, AK, United States)
Rahmati, A.
(California Univ. Berkeley, CA, United States)
Samara, M.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Schwartz, S. J.
(Imperial Coll. of London London, United Kingdom)
Date Acquired
April 17, 2017
Publication Date
August 23, 2016
Publication Information
Publication: Journal of Geophysical Research: Space Physics
Publisher: American Geophysical Union
Volume: 121
Issue: 8
ISSN: 2169-9380
e-ISSN: 2169-940
Subject Category
General
Report/Patent Number
GSFC-E-DAA-TN41022
Funding Number(s)
CONTRACT_GRANT: NASA-1345493(JPL)
Distribution Limits
Public
Copyright
Other

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