Observation of a new type of low-frequency waves at comet 67P/Churyumov-Gerasimenko

Richter, I.; Koenders, C.; Auster, H.-U.; Frühauff, D.; Götz, C.; Heinisch, P.; Perschke, C.; Motschmann, U.; Stoll, B.; Altwegg, Kathrin; Burch, J.; Carr, C.; Cupido, E.; Eriksson, A.; Henri, P.; Goldstein, R.; Lebreton, J.-P.; Mokashi, P.; Nemeth, Z.; Nilsson, H.; ... (2015). Observation of a new type of low-frequency waves at comet 67P/Churyumov-Gerasimenko. Annales geophysicae, 33(8), pp. 1031-1036. European Geosciences Union (EGU) 10.5194/angeo-33-1031-2015

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We report on magnetic field measurements made in the innermost coma of 67P/Churyumov-Gerasimenko in its low-activity state. Quasi-coherent, large-amplitude (δ B/B ~ 1), compressional magnetic field oscillations at ~ 40 mHz dominate the immediate plasma environment of the nucleus. This differs from previously studied cometary interaction regions where waves at the cometary ion gyro-frequencies are the main feature. Thus classical pickup-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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