Interpretation of Vega Observations at Comet Halley Applying Three-Dimensional MHD Simulations

摘要

In this work the velocity and density of the plasma flow were determined from Vega-1 and Vega-2 ion energy spectra at distances > 0.5 million km from the nucleus of comet Halley. Since the Solar Direction Analyser and the Cometary Ram Analyser of the PLASMAG instrument could observe the distribution of ions only in two limited sections of velocity space (and only the SDA worked aboard Vega-1), the predictions of a three-dimensional MHD simulation developed by Gombosi et al. (1996) were taken into account in order to find the best combination of the adjustable plasma parameters downstream of the bow shock. It was found that the density of the plasma flow was much higher when Vega-1 passed through the cometosheath compared to the Vega-2 flyby. The comparison of simulated and measured magnetic field profiles showed that there was a major disturbance in the interplanetary field after Vega-2 crossed the bow shock.