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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

## Abstract

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.