Observation of a New Type of Low Frequency Waves at Comet 67P/Churyumov-Gerasimenko

I. Richter 1 C. Koenders 1 H. -U. Auster 1 D. Fruehauff 1 C. Goetz 1 P. Heinisch 1 C. Perschke 2, 1 U. Motschmann 2 B. Stoll 1 K. Altwegg 3 J. Burch 4 C. Carr 5 E. Cupido 5 A. Eriksson 6 Pierre Henri 7 R. Goldstein 4 J. -P. Lebreton 7 P. Mokashi 4 Z. Nemeth 8 H. Nilsson 6 M. Rubin 3 K. Szegoe 8 B. T. Tsurutani 9 C. Vallat 10 M. Volwerk 11 K. -H. Glassmeier 1
1 IGEP - Institut für Geophysik und Extraterrestrische Physik [Braunschweig]
2 Institut für Theoretische Physik [Braunschweig]
3 Physikalisches Institut [Bern]
4 SwRI - Southwest Research Institute [San Antonio]
5 Blackett Laboratory
6 IRF - Swedish Institute of Space Physics [Uppsala]
7 LPC2E - Laboratoire de Physique et Chimie de l'Environnement et de l'Espace
8 Wigner Research Centre for Physics [Budapest]
9 JPL - Jet Propulsion Laboratory
10 European Space Astronomy Centre - Rosetta Science Ground Segment
11 IWF - Space Research Institute of Austrian Academy of Sciences
Abstract : We report on magnetic field measurements made in the innermost coma of 67P/Churyumov-Gerasimenko in its low activity state. Quasi-coherent, large-amplitude ($\delta B/B \sim 1$), compressional magnetic field oscillations at $\sim$ 40 mHz dominate the immediate plasma environment of the nucleus. This differs from previously studied comet-interaction regions where waves at the cometary ion gyro-frequencies are the main feature. Thus classical pick-up ion driven instabilities are unable to explain the observations. We propose a cross-field current instability associated with newborn cometary ion currents as a possible source mechanism.
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I. Richter, C. Koenders, H. -U. Auster, D. Fruehauff, C. Goetz, et al.. Observation of a New Type of Low Frequency Waves at Comet 67P/Churyumov-Gerasimenko. Annales Geophysicae, European Geosciences Union, 2015, 33 (8), pp.1031-1036. ⟨10.5194/angeo-33-1031-2015⟩. ⟨insu-01352452⟩

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