Multiple Scattering of Light in a Spherical Cometary Atmosphere with an Axisymmetric Dust Jet

We have developed a numerical solution for the anisotropic multiple scattering of light in a cometary atmosphere. The atmo-sphere is assumed to be a spherical shell illuminated by parallel solar rays. The spatial variation of dust in the coma is symmetric about he Sun-comet axis. Multiple scattering of photons is deter-mined by lambda iteration. We study two model dust profiles: (1) a spherically symmetric profile and (2) an axisymmetric dust jet at the comet's ubsolar point. Calculation is made of the flux of visible energy impinging on the nucleus urface, the mean intensity of visible light through-out 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 urface does the radiant flux exceed the visible flux at the subsolar point of a bare nucleus. ~ t992 Academic Pres~, Inc. 1