Plasma parameters near the Comet Halley bow shock

Abstract

Plasma data from the Johnstone Plasma Analyzer on Giotto are used in a Rankine-Hugoniot analysis of Comet Halley bow shocks. The shock normals are obtained and compared with models and other estimates. Proton bulk parameters from the Fast Ion Sensor inbound are analyzed, and water group densities from the Implanted Ion Sensor (IIS) are obtained which are consistent with the density inferred from the slowdown of the solar wind. The cometary ion pressure dominates in the shock region. Outbound parameters from the IIS are presented for the first time. The fast mode Mach numbers of the shock structures moving into the upstream solar wind are calculated to be 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. Both the solar wind protons and the water group ion populations are observed to thermalize across the shock region, showing that the Comet Halley bow shock features are indeed shocks.