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) , Kathrin Altwegg (3) , J. Burch (4) , C. Carr (5) , E. Cupido (5) , A. Eriksson (6) , Pierre Henri (7) , R. Goldstein (4) , Jean-Pierre 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 / Kiruna]
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 Rosetta Science Ground Segment
11 IWF - Space Research Institute of Austrian Academy of Sciences

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.

Domaines: Astrophysique [astro-ph]

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, 2015, 33 (8), pp.1031-1036. ⟨10.5194/angeo-33-1031-2015⟩. ⟨insu-01352452⟩