Multiple scattering of light in a spherical cometary atmosphere with an axisymmetric dust jet

Abstract

We have developed a numerical solution for the anisotropic multiple scattering of light in a cometary atmosphere. The atmosphere is assumed to be a spherical shell illuminated by parallel solar rays. The spatial variation of dust in the coma is symmetric about the Sun-comet axis. Multiple scattering of photons is determined by lambda iteration. We study two model dust profiles: (1) a spherically symmetric profile and (2) an axisymmetric dust jet at the comet's subsolar point. Calculation is made of the flux of visible energy impinging on the nucleus surface, the mean intensity of visible light throughout the coma, and an approximate solution for the flux of thermal radiation at the comet surface due to emission from dust particles in the coma. We determine conditions under which single and multiple scattering each become significant. Under all conditions examined, at no point on the nucleus surface does the radiant flux exceed the visible flux at the subsolar point of a bare nucleus.