First observations of energetic particles near comet Halley

The TUNDE-M energetic particle instrument aboard the Vega 1 spacecraft detected intense fluxes of energetic (≥40 keV) ions in the vicinity of comet Halley, starting at a distance of 107 km from closest approach. Three regions of differing ion characteristics have been identified. An outer region, several million kilometers in extent, contains pick-up ions in the solar wind. A second region, inside the bow shock (several hundred thousand kilometres in extent), contains the most intense fluxes, whereas the innermost region (several tens of thousands of kilometres) is characterized by lower intensities and sharp spikes near closest approach (∼8,900 km from the nucleus).