Dust distribution in the inner coma of comet Halley: Comparison with models

Abstract

The images of the inner coma of comet Halley that were taken with the Giotto camera have been evaluated to obtain information on the near-nucleus dust distribution and its relationship to the nuclear source regions. Over two-thirds of the dust in the inner coma can be modeled remarkably well with only three source regions, each emitting dust into broad jets with opening half-angles of 30 to 50°. The dust in the jets is not sharply bounded but disperses with a Gaussian cross section, consistent with a model in which both gas and dust emissions are confined to finite source regions. Departures from the simple R −1 relationship for the radial distribution of dust near the nucleus are reproduced by a model that considers the source region as a composite of adjacent subareas, each emitting dust into cones with opening half-angles of about 10°. Comparison of the azimuthal and radial dust distributions with model predictions gives information on the coma dust, the dust-gas interaction, and the properties of the emitting regions.