Comparison of the main magnetic and plasma features in the environments of comets Grigg-Skjellerup and Halley

Abstract

The successful flyby of Giotto at the weakly active comet P/Grigg-Skjellerup on July 10, 1992 has added a new set of observations to those obtained at the active comet P/Halley in March 1986 for the study of the solar wind - comet interaction. Despite the very different scales of the interaction regions for the two comets (10^6 km for Halley and 10^4 km only for GS, due to the two orders of magnitude difference in the neutral gas production rate) many similarities are revealed in their structure and in the characteristics of the main boundaries detected. the relevant electron plasma parameters and the magnetic field data are analysed and compared for the first time around the bow wave / bow shock and the magnetic pileup boundary. Their properties are discussed and compared with the Halley observations. We particularly show the intrinsic cometary nature of the MPB at comets.