Modeling of Radio Emission from Saturn's Rings Including Wakes

Lawrence A. Molnar (Calvin College), David E. Dunn (U.C. Berkeley), J. Clark Cully (Calvin College), and David J. Young (Calvin College)
to be presented at the 32nd Annual Meeting of the Division for Planetary Sciences, October 23-27, 2000


We have extended the "simrings" radiative transfer software package (Dunn, Molnar and Fix 1999) to include idealized ring wakes. The package consists four principle, modular components: "simprob", which computes Mie scattering functions for individual particles specified by size and composition; "simrings", which uses a Monte Carlo simulation to compute the complete scattering function and thermal emission of a ring slab specified by particle size distribution and density (including the possibility of wake density enhancements); "simplot", which uses these functions along with geometric information and a full description of the planet brightness to compute the ring brightness as a function of azimuth as viewed from Earth; and "simcoord", which combines this information for a series of rings to make a final model of the radio emission as viewed on the sky.

We compare sample results from this package with those of a simple, analytic model that ignores multiple scattering. This allows us to show qualitatively under what conditions one might observe east-west asymmetry in the rings caused by multiple scattering off wakes (as we earlier suggested may be the case: Dunn, Molnar, and Fix 1996), and to quantitatively compare models with data maps.

The principle advantage of our idealized wakes is the relative ease with which we can consider a wide range of parameter space. The utility of this depends on these wakes having net scattering properties resembling those of more realistic wakes. We compare our idealized wakes with the gravitational simulations of Daisaka and Ida (1999) and find that this is the case for directly transmitted flux as a function of azimuth and inclination. As complete scattering properties of realistic simulations become available, we can use them as alternative inputs to "simplot", producing model radio maps for them.

Finally, we compare preliminary runs of the "simrings" package with radio data spanning a range of observing wavelengths and ring inclinations to demonstrate the sensitivity to various physical parameters of the rings.

This work was funded by a grant from Research Corporation.

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