Comet plasma tail formation - Giotto observations
Winningham, J. D.; Thomsen, M.; Borg, H.; Amata, E.; Formisano, V.; Wilken, B.; Coates, A.; Jockers, K.; Johnstone, A. D.; Heath, J.; Bryant, D. A.
Germany, United Kingdom
Abstract
The process of mass loading of the solar wind by cometary ions, which forms comet tails, has been observed throughout the coma of comet Halley. Three distinct regimes were found where the nature of the energy and momentum coupling between solar wind and cometary ions is different. Outside the bow shock, where there is little angular scattering of the freshly ionised particles, the coupling is described by the simple pickup trajectory and the energy is controlled by the angle between the flow and the magnetic field. Just inside the bow shock, there is considerable scattering accompanied by another acceleration process which raises some particle energies well above the straightforward pickup value. Finally, closer to the nucleus, the amount of scattering decreases and the coupling is once more controlled by the magnetic field direction.