Spectroscopic study of comet Halley by the Vega 2 three-channel spectrometer

Abstract

The three-channel spectrometer (TKS) aboard the Vega 2 spacecraft recorded infrared and visible spectra near the nucleus of comet Halley. Spectra in the range 0.95–1.9 µm at a distance of 300 km from the nucleus reveal the H2O 1.38-µm band and OH bands, the latter excited by dissociation of a parent molecule. Their production rates are 4 × 1029 and 1.7 × 1030 molecules s−1, respectively. The dust particle density is 0.35 g cm−3, typical of fluffy particles of interplanetary dust. Emissions of 10 species are observed in the range 275–715 nm at ∼4,000 km from the nucleus, and 6 of them are analysed in terms of production rates: QOH = 2×1030, QCH = 1029, = 6×1027, = 3×1027, QCN = 1027 and QNH = 2 × 1026, all in molecules s−1. The difference between the OH and H2O production rates is puzzling and needs further analysis. Ionic emissions, not discussed here, are prominent in the tailward part of the comet.