Articles | Volume 34, issue 7
Ann. Geophys., 34, 609–622, 2016
Ann. Geophys., 34, 609–622, 2016

Regular paper 14 Jul 2016

Regular paper | 14 Jul 2016

Two-point observations of low-frequency waves at 67P/Churyumov-Gerasimenko during the descent of PHILAE: comparison of RPCMAG and ROMAP

Ingo Richter1, Hans-Ulrich Auster1, Gerhard Berghofer2, Chris Carr3, Emanuele Cupido3, Karl-Heinz Fornaçon1, Charlotte Goetz1, Philip Heinisch1, Christoph Koenders1, Bernd Stoll1, Bruce T. Tsurutani4, Claire Vallat5, Martin Volwerk2, and Karl-Heinz Glassmeier1 Ingo Richter et al.
  • 1Institut für Geophysik und extraterrestrische Physik, TU Braunschweig, Mendelssohnstr. 3, 38106 Braunschweig, Germany
  • 2Institut für Weltraumforschung, Schmiedlstraße 6, 8042 Graz, Austria
  • 3Imperial College London, Exhibition Road, London SW7 2AZ, UK
  • 4Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive Pasadena, CA 91109, USA
  • 5Rosetta Science Ground Segment, European Space Astronomy Centre, 28691 Villanueva de la Cañada, Madrid, Spain

Abstract. The European Space Agency's spacecraft ROSETTA has reached its final destination, comet 67P/Churyumov-Gerasimenko. Whilst orbiting in the close vicinity of the nucleus the ROSETTA magnetometers detected a new type of low-frequency wave possibly generated by a cross-field current instability due to freshly ionized cometary water group particles. During separation, descent and landing of the lander PHILAE on comet 67P/Churyumov-Gerasimenko, we used the unique opportunity to perform combined measurements with the magnetometers onboard ROSETTA (RPCMAG) and its lander PHILAE (ROMAP). New details about the spatial distribution of wave properties along the connection line of the ROSETTA orbiter and the lander PHILAE are revealed. An estimation of the observed amplitude, phase and wavelength distribution will be presented as well as the measured dispersion relation, characterizing the new type of low-frequency waves. The propagation direction and polarization features will be discussed using the results of a minimum variance analysis. Thoughts about the size of the wave source will complete our study.

Short summary
We have analysed the magnetic field measurements performed on the ROSETTA orbiter and the lander PHILAE during PHILAE's descent to comet 67P/Churyumov-Gerasimenko on 12 November 2014. We observed a new type of low-frequency wave with amplitudes of ~ 3 nT, frequencies of 20–50 mHz, wavelengths of ~ 300 km, and propagation velocities of ~ 6 km s−1. The waves are generated in a ~ 100 km region around the comet a show a highly correlated behaviour, which could only be determined by two-point observations.