The spatial distribution of dust jets seen at Vega-2 fly-by

One important physical characteristic of comet Halley is dust jet activity, seen from Earth as changing coma patterns. At spacecraft resolution it becomes possible to precisely locate the sources of active jets on an irregularly shaped nucleus. The data set employed in this analysis consists of 11 full-format (512×512 px) Vega-2 images taken over a 15 minute intervall starting approximately 370 sec before closest approach. The distance to the nucleus was always less than 45,000 km and become as close as 8030 km. Measurements of the position of the same feature seen on different images, together with knowledge of the changing spatial relationship between s/c and comet yield the absolute spatial orientation of the feature. Most of the active zones formed at least one quasi-linear structure on the surface. The authors found evidence of the activity of the dark hemisphere, at least one of the faint but active jet sources is there. Results are compared to ground observations.