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The induced magnetosphere of comet Halley 4. Comparison of in situ observations and numerical simulations
Neubauer, F. M.; Gombosi, T. I.; Israelevich, P. L. +3 more
A comprehensive comparison between the results of a multiscale three-dimensional adaptive MHD model of the comet Halley magnetosphere and in situ observations by the Giotto mission is presented. It is shown how a steady state model can describe the effects of the varying IMF direction on the cometary magnetosphere. The simulation results reproduce…
The turbulent state of cometary ion pickup generated fluctuations near comet P/Halley
Krauklis, I.; Johnstone, A. D.
One of the principal effects of an outgassing comet is to introduce additional mass into the solar wind flow. This mass-loading process results in the generation of Alfvén waves via ion-cyclotron resonance. In the case of the Halley encounter this source of ``new'' fluctuations was introduced into a low speed solar wind 0.89 AU from the sun. Previ…
Bow shock analysis at comets Halley and Grigg-Skjellerup
Coates, A. J.; Neubauer, F. M.; Mazelle, C.
The interaction of an active comet with the solar wind is effected by the pickup of heavy cometary ions over extended regions of space. It was predicted before any spacecraft encounters with comets that a bow shock would form at a critical point in the mass-loaded flow. Here we present an analysis of the results from Giotto's encounters of comets …
Three-dimensional multiscale MHD model of cometary plasma environments
Gombosi, Tamas I.; De Zeeuw, Darren L.; Häberli, Roman M. +1 more
First results of a three-dimensional multiscale MHD model of the interaction of an expanding cometary atmosphere with the magnetized solar wind are presented. The model starts with a supersonic and super-Alfvènic solar wind far upstream of the comet (25 Gm upstream of the nucleus) with arbitrary interplanetary magnetic field orientation. The solar…
Heating of the thermal electrons in the coma of comet P/Halley
Geiss, Johannes; Altwegg, Kathrin; Balsiger, Hans +1 more
In the inner coma of a comet the total ion (or electron) density results from an equilibrium between ion production and ion destruction. The ions are mainly produced by photoionization of cometary gas, whereas the main destruction process is dissociative recombination of molecular ions with electrons. The reaction rate for the recombination depend…
Cometary ion pressure anisotropies at comets Halley and Grigg-Skjellerup
Coates, A. J.; Neubauer, F. M.; Johnstone, A. D.
Cometary water group ions are the dominant population controlling the interaction of comets with the solar wind. The distribution function of this population has important effects on the overall structure and boundaries in the comet-solar wind interaction and on the plasma wave activity produced. In this paper we present new results on the behavio…
Upstream and downstream propagating waves generated by pickup ions near comet Halley
Glassmeier, K. -H.; Neubauer, F. M.; Krauklis, I. +3 more
It is well known that most of the Alfvén waves generated in the solar wind by cometary ion pickup are propagating upstream in the solar wind reference frame. However, the magnitude of the small proportion propagating downstream is extremely important because it controls the amount of ion acceleration driven by the second order Fermi process. The v…
Magnetic field structure in the comet Grigg-Skjellerup pileup region
Coates, A. J.; Neubauer, F. M.; Israelevich, P. L. +1 more
The position of the Giotto spacecraft relative to comet Grigg-Skjellerup is found from the draping geometry based on the vector magnetic field data. It is shown that Giotto passed the cometary nucleus on the nightside. The behavior of the magnetic field vectors exhibits two different types in the pileup region. In the outer pileup region, the magn…
D/H and O-18/O-16 ratio in the hydronium ion and in neutral water from in situ ion measurements in comet Halley
Altwegg, K.; Balsiger, H.; Geiss, J.
The D/H ratio and the O-18/O-16 ratio in hydronium ions in the gas coma of comet Halley have been determined from ion data obtained by the high intensity sensor (HIS) of the ion spectometer (IMS) on board the spacecraft Giotto in 1986. The HIS instrument measured the reliable data for the water group ions over a large distance range from the nucle…
Structure of mass-loading shocks. 2. Comparison of theory and observation at comet Halley
Coates, A. J.; Neubauer, F. M.; Reme, H. +2 more
The multifluid diffusive model of G. P. Zank et al. (1994), which describes the interaction of the solar wind with a cometary plasma in the outer coma, has been used to model the structure of the Halley bow shock. The theoretical results are compared to in situ observations made by Giotto. We compare the solar wind and cometary ion number densitie…