First detection of a diamagnetic cavity at comet 67P/Churyumov-Gerasimenko

C Goetz (1) , C Koenders (1) , I Richter (1) , Kathrin Altwegg (2) , J Burch (3) , C Carr (4) , E Cupido (4) , A Eriksson (5) , C Güttler (6) , Pierre Henri (7) , P Mokashi (8) , Z Nemeth (9) , H Nilsson (5) , M Rubin (2) , H Sierks (6) , B Tsurutani (10) , Charlotte Vallat (11) , M Volwerk (12) , K.-H Glassmeier (1)

1 Technische Universität Braunschweig = Technical University of Braunschweig [Braunschweig]
2 Physikalisches Institut [Bern]
3 Space Science Division [San Antonio]
4 Blackett Laboratory
5 IRF - Swedish Institute of Space Physics [Uppsala / Kiruna]
6 MPS - Max-Planck-Institut für Sonnensystemforschung = Max Planck Institute for Solar System Research
7 LPC2E - Laboratoire de Physique et Chimie de l'Environnement et de l'Espace
8 SwRI - Southwest Research Institute [San Antonio]
9 Wigner Research Centre for Physics [Budapest]
10 JPL - Jet Propulsion Laboratory
11 Octogone - Octogone Unité de Recherche Interdisciplinaire
12 IWF - Space Research Institute of Austrian Academy of Sciences

Context: The Rosetta magnetometer RPC-MAG has been exploring the plasma environment of comet 67P/Churyumov-Gerasimenko since August 2014. The first months were dominated by low-frequency waves which evolved into more complex features. However, at the end of July 2015, close to perihelion, the magnetometer detected a region that did not contain any magnetic field at all. Aims: These signatures match the appearance of a diamagnetic cavity as was observed at comet 1P/Halley in 1986. The cavity here is more extended than previously predicted by models and features unusual magnetic field configurations, which need to be explained Methods: The onboard magnetometer data were analyzed in detail and used to estimate the outgassing rate. A minimum variance analysis was used to determine boundary normals. Results. Our analysis of the data acquired by the Rosetta Plasma Consortium instrumentation confirms the existence of a diamagnetic cavity. The size is larger than predicted by simulations, however. One possible explanation are instabilities that are propagating along the cavity boundary and possibly a low magnetic pressure in the solar wind. This conclusion is supported by a change in sign of the Sun-pointing component of the magnetic field. Evidence also indicates that the cavity boundary is moving with variable velocities ranging from 230−500 m/s.

Mots clés: comets: individual: 67P/Churyumov-Gerasimenko; plasmas; magnetic fields; data analysis

Domaines: Astrophysique [astro-ph]

C Goetz, C Koenders, I Richter, Kathrin Altwegg, J Burch, et al.. First detection of a diamagnetic cavity at comet 67P/Churyumov-Gerasimenko. Astronomy and Astrophysics - A&A, 2016, 588, pp.A24. ⟨10.1051/0004-6361/201527728⟩. ⟨insu-01318108⟩