Multiple Scattering of Light in a Spherical Cometary Atmosphere with an Axisymmetric Dust Jet: II. Image Simulation

Abstract

A numerical solution for the multiple scattering of light in spherical axisymmetric geometry is used to simulate observations of a model comet atmosphere as it would be seen by a near-flying satellite or by general wide-angle imaging techniques that might resolve the nucleus. We consider a spherically symmetric dust distribution, an axisymmetric dust jet, and a hollow cone of dust about the subsolar point. We calculate the specific intensity of both single- and multiply scattered light. Nucleus visibility and overall coma appearance is examined for varying phase angle. The appearance of the hollow cone is found to be especially sensitive to viewing geometry; at a phase angle of 90[deg] it bears a strong resemblance to the "northern area of activity" observed by Giotto at Comet Halley. We also calculate the azimuth-integrated intensity, used by Thomas and Keller (1990, Ann. Geophys. 8, 147-166), as a measure of particle fragmentation Halley's coma, and examine the extent to which line-of-sight attenuation depletes the azimuth-integrated intensity near the nucleus, and multiple scattering enhances it.