Structure and evolution of the diamagnetic cavity at comet 67P/Churyumov–Gerasimenko

C. Goetz (1) , C. Koenders (1) , Hansen K.C. (2) , J Burch (3) , C. Carr (4) , A. Eriksson (5) , D. Frühauff , C. Güttler (6) , Pierre Henri (7) , H. Nilsson , I. Richter , M. Rubin , H. Sierks (6) , B. Tsurutani (8) , M. Volwerk , K.H. Glassmeier

1 IGEP - Institut für Geophysik und Extraterrestrische Physik [Braunschweig]
2 AOSS - Department of Atmospheric, Oceanic, and Space Sciences [Ann Arbor]
3 SwRI - Southwest Research Institute [San Antonio]
4 Space and Atmospheric Physics Group [London]
5 IRF - Swedish Institute of Space Physics [Uppsala]
6 MPS - Max-Planck-Institut für Sonnensystemforschung
7 LPC2E - Laboratoire de Physique et Chimie de l'Environnement et de l'Espace
8 JPL - Jet Propulsion Laboratory

The long duration of the Rosetta mission allows us to study the evolution of the diamagnetic cavity at comet 67P/Churyumov–Gerasimenko in detail. From 2015 April to 2016 February 665 intervals could be identified where Rosetta was located in a zero-magnetic-field region. We study the temporal and spatial distribution of this cavity and its boundary and conclude that the cavity properties depend on the long-term trend of the outgassing rate, but do not respond to transient events at the spacecraft location, such as outbursts or high neutral densities. Using an empirical model of the outgassing rate, we find a functional relationship between the outgassing rate and the distance of the cavity to the nucleus. There is also no indication that this unexpectedly large distance is related to unusual solar wind conditions. Because the deduced shape of the cavity boundary is roughly elliptical on small scales and the distances of the boundary from the nucleus are much larger than expected we conclude that the events observed by Rosetta are due to a moving instability of the cavity boundary itself.

Keywords: magnetic fields; plasmas; methods: data analysis; comets: individual: 67P

Domains: Sciences of the Universe [physics]; Astrophysics [astro-ph]; Physics [physics]; Physics [physics]; Space Physics [physics.space-ph]

C. Goetz, C. Koenders, Hansen K.C., J Burch, C. Carr, et al.. Structure and evolution of the diamagnetic cavity at comet 67P/Churyumov–Gerasimenko. Monthly Notices of the Royal Astronomical Society, 2017, 462 (Suppl 1), pp.S459-S467. ⟨10.1093/mnras/stw3148⟩. ⟨insu-02985726⟩