Weak localization of electromagnetic waves and radar polarimetry of Saturn's rings

Abstract

We use a state-of-the-art physics-based model of electromagnetic scattering to analyse average circular polarization ratios measured for the A and B rings of Saturn at a wavelength of 12.6 cm. This model is directly based on the Maxwell equations and accounts for the effects of polarization, multiple scattering, weak localization of electromagnetic waves and ring particle non-sphericity. Our analysis is based on the assumption that the observed polarization ratios are accurate, mutually consistent and show a quasi-linear dependence on the opening angle. Also, we assume that the ring system is not strongly stratified in the vertical direction. Our numerical simulations rule out the model of spherical ring particles, favour the model of ring bodies in the form of nearly spherical particles with small-scale surface roughness and rule out non-spherical particles with aspect ratios significantly exceeding 1.2. They also favour particles with effective radii in the range 4-10 cm and definitely rule out effective radii significantly smaller than 4 cm. Furthermore, they seem to rule out effective radii significantly >10 cm. The retrieved ring optical thickness values are in the range 2-3 or even larger. If the rings do have a wake-like horizontal structure, as has been recently suggested, then these optical thickness values should be attributed to an average wake rather than to the optical thickness averaged over the entire horizontal extent of the rings. © 2008 RAS.