Secondary Electron Emission Induced by Gas and Dust Impacts on Giotto VEGA-1 and VEGA-2 in the Environment of Comet p/ Halley

Abstract

Giotto, Vega-1 and Vega-2 have been bombarded by a flow of gas and dust particles during their flyby of comet Halley. The emission of secondary electrons and sputtered ions caused by the large impact velocities (70-80 km s^-1) perturbed the plasma density in the spacecraft vicinity and was a possible source of interference for electric field and plasma measurements. Identical impact plasma detectors were mounted on the three space probes; the saturation currents of secondary electrons emitted from gold targets were measured once per second. The results obtained during the three flybys are presented and compared. Information about the gas density proffle and nucleus gas production rate can be derived from the measurements.