Extremely Low-Frequency Waves Inside the Diamagnetic Cavity of Comet 67P/Churyumov-Gerasimenko

B. Madsen (1, 2) , C. Wedlund (2) , A. Eriksson (3) , C. Goetz (4) , T. Karlsson (5) , H. Gunell (6) , A. Spicher , Pierre Henri (7) , Xavier Vallieres (7) , W. Miloch (2)

1 DTU - Danmarks Tekniske Universitet = Technical University of Denmark
2 UiO - University of Oslo
3 IRF - Swedish Institute of Space Physics [Kiruna]
4 IGEP - Institut für Geophysik und Extraterrestrische Physik [Braunschweig]
5 Department of Space and Plasma Physics [Stockholm]
6 BIRA-IASB - Belgian Institute for Space Aeronomy / Institut d'Aéronomie Spatiale de Belgique
7 LPC2E - Laboratoire de Physique et Chimie de l'Environnement et de l'Espace

The European Space Agency/Rosetta mission to comet 67P/Churyumov-Gerasimenko has provided several hundred observations of the cometary diamagnetic cavity induced by the interaction between outgassed cometary particles, cometary ions, and the solar wind magnetic field. Here we present the first electric field measurements of four preperihelion and postperihelion cavity crossings on 28 May 2015 and 17 February 2016, using the dual-probe electric field mode of the Langmuir probe (LAP) instrument of the Rosetta Plasma Consortium. We find that on large scales, variations in the electric field fluctuations capture the cavity and boundary regions observed in the already well-studied magnetic field, suggesting the electric field mode of the LAP instrument as a reliable tool to image cavity crossings. In addition, the LAP electric field mode unravels for the first time extremely low-frequency waves within two cavities. These low-frequency electrostatic waves are likely triggered by lower-hybrid waves observed in the surrounding magnetized plasma.

Keywords: Plasma measurements; Comet 67P; Diamagnetic cavity; ESA/Rosetta; Langmuir probe; Low-frequency waves

Domains: Sciences of the Universe [physics]; Astrophysics [astro-ph]

B. Madsen, C. Wedlund, A. Eriksson, C. Goetz, T. Karlsson, et al.. Extremely Low-Frequency Waves Inside the Diamagnetic Cavity of Comet 67P/Churyumov-Gerasimenko. Geophysical Research Letters, 2018, 45 (9), pp.3854 - 3864. ⟨10.1029/2017GL076415⟩. ⟨insu-01897767⟩