The upstream region, foreshock and bow shock wave at comet P/Halley from plasma electron measurements

Summary

We survey the plasma electron parameters from a distance 2.710⁶ km from the comet nucleus to the bow shock wave at about 1.1 10⁶ km and somewhat beyond. We describe the features of the electron foreshock lying outside the shock to a distance of about 230,000 km. It is a region of intense solar wind-comet plasma interaction in which energetic electrons are prominent. Several spikes of electrons whose energies extend to about 2.5 keV appear in front of the shock. These energetic electrons may have been accelerated in the same way electrons are accelerated at the Earth’s bow shock to energies of 1 to 10 keV. The direction of the electron bulk flow direction changes abruptly between 1920 and 1922 UT, and the flow speed begins a sharp decline at the same time. We believe the spacecraft has entered the bow shock wave sometime between 1920 and 1922 UT. We find that the electron density variations at P/Halley are very much smaller than those reported at Giacobini-Zinner.