INTERPRETATION OF HMC IMAGES BY A COMBINED THERMAL AND GASDYNAMIC MODEL

Images of comet Halley's nucleus taken by the HMC camera during the GI OTTO encounter in 1986 show that a major part of the total dust produc tion is localized in a few active areas which are the sources of gas-d ust jets. The global dust distribution in the inner coma is dominated by two main jets roughly directed to the sun. A combination of a 1D th ermal nucleus model with an axisymmetric continuum model of the jet ou tflow was used to investigate the properties of the inner coma. Detail ed investigations show that the characteristics of the observed jets c an be reproduced by outgassing from free sublimating active areas of a few km in diameter, a dust to gas ratio of 1-2.5 and a size distribut ion dominated by the larger grains. It is further shown that most of t he observational constraints provided by the HMC data can be met simul taneously by a model of three jets superimposed on a weak background.