Comet Halley-solar wind interaction from electron measurements aboard Giotto

The Giotto probe's three-dimensional electron spectrometer has obtained data that illustrate the complex interactions between comet Halley and the solar wind. As Giotto approached the comet, it traversed several regions exhibiting different plasma characteristics: a large upstream region, a foreshock, a bow wave whose apex lies at about 400,000 km, a transition region, a region permanently and strongly contaminated by cometary ions, a collision pause, and various inner regions up to the inner coma, including a region of depleted hot plasma.