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D.E. Dunn (U.C. Berkeley), L.A. Molnar (Calvin College), J.D. Fix (U.A. Huntsville)
We present results of a radiative transfer code which models the scattering properties of the ring particles of Saturn. We use a Monte Carlo code which treats the ring particles as a uniform layer of spheres whose scattering properties are determined by a linear combination of Mie and isotropic phase functions. Other free parameters describe the particle size distribution and dirt fraction. The code is written in a general manner, allowing for later extension to full polarization, different geometries (e.g., wakes, monolayers), and different wavelength regimes (which have different phase functions and illumination geometries).
We use the code to model previously presented data acquired from the Very Large Array in November 1995 (inclination 2.68 deg.) and February 1997 (inclination -5 deg.). A total of eight maps with wavelengths ranging from 0.7 cm to 6.1 cm were modeled simultaneously. Good fits to the data were obtained by using values of the particle size distribution parameters taken from the literature and adjusting the relative importance of Mie scattering with wavelength and ring radius. Specifically, more isotropic phase functions were required at shorter wavelengths and at larger distances from Saturn. We interpret the wavelength dependence as a consequence of small scale surface irregularities on individual ring particles. We interpret the radial dependence as a consequence of increasing conglomeration of ring particles with radial distance associated with decreasing tidal stress. Published simulations of this process indicates these conglomerations are likely to be more irregularly shaped particles.