AbstractComposite images of the intensity of solar radiation scattered by dust in Halley’s coma are constructed by using the three-channel spectra obtained during the approach phase of the Vega 2 spacecraft. They cover a sector centered on the nucleus that has a radius of 40000 km and an angular extent of 50°. A radial plot of dust-scattered intensity shows that it varies as the inverse of impact parameter p where p is smaller than 3200 km or higher than 7000 km. In the intermediate 3200-7000 km distance range, the intensity varies as p−1.52. At longer distances, two jets are present with a contrast comparable to the gas jets which appear in the OH and CN images.The color of dust shows a slight excess of near-UV radiation in a diffuse region between 10000 and 30000 km which appears to be connected with the two jets. In the region called “valley”, between the jets at distances p > 25000 km, the dust-scattered intensity shows an excess of red. The color, expressed as the ratio of intensities at 377,482 and 607 nm is interpreted in terms of Mie theory. It is suggested that the dust particles progressively differentiate. A proportionally more important population of small submicronic grains appears at p > 8000 km. This population seems to correlate with the jets.
Spatial Distribution and Color of Dust in Halley’s Inner Coma