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

Richter, I. and Koenders, C. and Auster, H.U. and Fruhauff, D. and Gotz, C. and Németh, Zoltán and Szegő, Károly (2015) Observation of a new type of low-frequency waves at comet 67P/Churyumov-Gerasimenko. ANNALES GEOPHYSICAE, 33 (8). pp. 1031-1036. ISSN 0992-7689

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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 (δB/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 new- born cometary ion currents as a possible source mechanism.

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