Observation of a New Type of Low Frequency Waves at Comet 67P/Churyumov-Gerasimenko
physics.space-ph
/ Authors
I. Richter, C. Koenders, H. -U. Auster, D. Fruehauff, C. Goetz, P. Heinisch, C. Perschke, U. Motschmann, B. Stoll, K. Altwegg
and 16 more authors
J. Burch, C. Carr, E. Cupido, A. Eriksson, P. Henri, R. Goldstein, J. -P. Lebreton, P. Mokashi, Z. Nemeth, H. Nilsson, M. Rubin, K. Szegoe, B. T. Tsurutani, C. Vallat, M. Volwerk, K. -H. Glassmeier
/ 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 ($δB/B \sim 1$), 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.