Description of the main boundaries seen by the Giotto electron experiment inside the Comet Halley-solar wind interaction regions

The GIOTTO electron plasma experiment identified several boundaries inside the comet Halley-solar wind region. Two of them are particularly interesting; they separate very different plasma regimes on quite sharp length scales and furthermore their existence was not foreseen in theoretical models. They are: - the limit between the transition region and the sheath detected at 550,000 km from the nucleus, and - the cometopause detected at 135,000 km from the nucleus. Characteristic features of the electron distribution functions and of the macroscopic parameters of the electron plasma through these main boundaries are described.