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

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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