Intensity profiles of dust near extended sources on comet Halley

Abstract

Images obtained by the cameras on board the spacecraft encounter-ing comet Halley in March 1986 showed that the dust activity was very non-uniform. Very fine structures (filaments) were observed as well as strong jet-like features originating from active areas¹. The dust particle density at large distances (R > 100 km) from the nucleus decreases proportional to 1/R², that is, the intensity decreases proportional to 1/R as expected for free outflow. Flattening of the profile is evident within several tens of kilometres of the nucleus. As we show here, this can be explained by a model that considers the extended size and non-uniformity of the active region on the surface. A critical scale length, defined by the opening angle of a jet-like feature and the size of the source, can be introduced to describe the flattening. The model is consistent with the observations and provides the basis for studying other mechan-isms such as particle fragmentation.