Plasma waves confined to the diamagnetic cavity of comet 67P/Churyumov–Gerasimenko

H. Gunell (1, 2) , C. Goetz (3) , A. Eriksson (4) , H. Nilsson (4) , C Simon Wedlund (5) , Pierre Henri (6) , R. Maggiolo (7) , M. Hamrin (2) , Johan de Keyser (1) , M. Rubin (8) , G. Stenberg Wieser (4) , G. Cessateur (1) , F. Dhooghe (1) , A. Gibbons (1)

1 BIRA-IASB - Belgian Institute for Space Aeronomy / Institut d'Aéronomie Spatiale de Belgique
2 Umeå University
3 IGEP - Institut für Geophysik und Extraterrestrische Physik [Braunschweig]
4 IRF - Swedish Institute of Space Physics [Uppsala]
5 Department of Physics [Oslo]
6 LPC2E - Laboratoire de Physique et Chimie de l'Environnement et de l'Espace
7 CESR - Centre d'étude spatiale des rayonnements
8 Physikalisches Institut [Bern]

Ion acoustic waves were observed in the diamagnetic cavity of comet 67P/Churyumov– Gerasimenko by the Rosetta spacecraft on 2015 August 3, when the comet was 1.25 au from the Sun. Wave spectra recorded by the Langmuir probe (RPC-LAP), peak near 200 Hz, decrease for higher frequencies and reach the noise floor at approximately 1.5 kHz. These waves were observed only when the spacecraft was in the diamagnetic cavity or at its boundary, which is identified as a sharp drop in magnetic field magnitude, measured by RPC-MAG. The plasma, on both sides of the boundary, is dominated by a cold (a few hundred K) water group ion population, one cold (k B T e ∼ 0.1 eV) and one warm (k B T e ∼ 10 eV) electron population. The observations are interpreted in terms of current-driven ion acoustic waves, generated by currents that flow through bulges on the boundary of the diamagnetic cavity.

Keywords: methods: analytic; comets: individual: 67P/Churyumov-Gerasimenko; waves; plasmas; methods: data analysis

Domains: Astrophysics [astro-ph]

H. Gunell, C. Goetz, A. Eriksson, H. Nilsson, C Simon Wedlund, et al.. Plasma waves confined to the diamagnetic cavity of comet 67P/Churyumov–Gerasimenko. Monthly Notices of the Royal Astronomical Society, 2017, 469 (Suppl_2), pp.S84-S92. ⟨10.1093/mnras/stx1134⟩. ⟨insu-01670555⟩