Plasma parameters near the comet Halley bow shock

Authors:
  • AJA. D. Johnstone
    A. D. Johnstone
  • RKR. L. Kessel
    R. L. Kessel
  • DHD. E. Huddleston
    D. E. Huddleston
  • BWB. Wilken
    B. Wilken
  • KJK. Jockers
    K. Jockers
  • FNF. M. Neubauer
    F. M. Neubauer
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Abstract
We present the plasma data from the Johnstone Plasma Analyser (JPA) instrument on Giotto for the inbound and outbound crossings of the structures which up to now were assumed to be bow shocks at comet Halley. Proton bulk parameters from the Fast Ion Sensor (FIS) inbound have been analyzed taking into account the wider downstream distributions which require a different analysis method from the upstream solar wind. The water group densities from the Implanted Ion Sensor (IIS) are obtained using updated processing procedures. These densities are consistent with the density inferred from the slowdown of the solar wind. The cometary ion pressure dominates in the shock region. The outbound parameters are presented from IIS for the first time. The inbound and outbound data are used to infer the shock normal directions from Rankine‐Hugoniot analyses. We calculate the fast mode Mach numbers of the shock structures moving into the upstream solar wind following the method of Smith et al. (1986), giving values of 1.1–1.8 (inbound) and 1.6–1.7 (outbound). The positions of the shock features are consistent with the inferred critical point in the solar wind flow. In addition, both the solar wind protons and the water group ion populations are observed to thermalize across the shock region, and we therefore conclude that the comet Halley bow shock features were indeed shocks.

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