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Annales Geophysicae An open-access journal of the European Geosciences Union
Ann. Geophys., 33, 1031-1036, 2015
https://doi.org/10.5194/angeo-33-1031-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
ANGEO Communicates
19 Aug 2015
Observation of a new type of low-frequency waves at comet 67P/Churyumov-Gerasimenko
I. Richter1, C. Koenders1, H.-U. Auster1, D. Frühauff1, C. Götz1, P. Heinisch1, C. Perschke1,2, U. Motschmann2,3, B. Stoll1, K. Altwegg4, J. Burch5, C. Carr6, E. Cupido6, A. Eriksson7, P. Henri8, R. Goldstein5, J.-P. Lebreton8, P. Mokashi5, Z. Nemeth9, H. Nilsson10, M. Rubin4, K. Szegö9, B. T. Tsurutani11, C. Vallat12, M. Volwerk13, and K.-H. Glassmeier1 1Institut für Geophysik und extraterrestrische Physik, TU Braunschweig, Mendelssohnstr. 3, 38106 Braunschweig, Germany
2Institut für Theoretische Physik, TU Braunschweig, Mendelssohnstr. 3, 38106 Braunschweig, Germany
3German Aerospace Center (DLR), Institute of Planetary Research, Rutherfordstraße 2, 12489 Berlin, Germany
4Physikalisches Institut, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland
5Southwest Research Institute, P.O. Drawer 28510, San Antonio, TX 78228-0510, USA
6Imperial College London, Exhibition Road, London SW7 2AZ, UK
7Swedish Institute of Space Physics, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, Sweden
8Laboratoire de Physique et Chimie de l'Environnement et de l'Espace, UMR 7328 CNRS – Université d'Orléans, Orléans, France
9Wigner Research Centre for Physics, 1121 Konkoly Thege Street 29–33, Budapest, Hungary
10Swedish Institute of Space Physics, P.O. Box 812, 981 28 Kiruna, Sweden
11Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
12Rosetta Science Ground Segment, European Space Astronomy Centre, 28691 Villanueva de la Cañada, Madrid, Spain
13Space Research Institute, Austrian Academy of Sciences, Schmiedlstraße 6, 8042 Graz, Austria
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 (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.

Citation: Richter, I., Koenders, C., Auster, H.-U., Frühauff, D., Götz, C., Heinisch, P., Perschke, C., Motschmann, U., Stoll, B., Altwegg, K., Burch, J., Carr, C., Cupido, E., Eriksson, A., Henri, P., Goldstein, R., Lebreton, J.-P., Mokashi, P., Nemeth, Z., Nilsson, H., Rubin, M., Szegö, K., Tsurutani, B. T., Vallat, C., Volwerk, M., and Glassmeier, K.-H.: Observation of a new type of low-frequency waves at comet 67P/Churyumov-Gerasimenko, Ann. Geophys., 33, 1031-1036, https://doi.org/10.5194/angeo-33-1031-2015, 2015.
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We present a first report on magnetic field measurements made in the coma of comet 67P/C-G in its low-activity state. The plasma environment is dominated by quasi-coherent, large-amplitude, compressional magnetic field oscillations around 40mHz, differing from the observations at strongly active comets where waves at the cometary ion gyro-frequencies are the main feature. We propose a cross-field current instability associated with the newborn cometary ions as a possible source mechanism.
We present a first report on magnetic field measurements made in the coma of comet 67P/C-G in...
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