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

TL;DR

This study employs advanced electromagnetic scattering models to analyze Saturn's ring polarization data, constraining particle size, shape, and optical thickness, and highlighting the importance of weak localization effects.

Contribution

It introduces a physics-based model incorporating weak localization and nonsphericity to interpret polarization measurements, refining understanding of ring particle properties.

Findings

Particles are nearly spherical with small surface roughness.

Effective radii are constrained between 4 and 10 cm.

Optical thickness is estimated to be 2-3 or larger.

Abstract

We use a state-of-the-art physics-based model of electromagnetic scattering to analyze 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 nonsphericity. 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, favor the model of ring bodies in the form of nearly spherical particles with small-scale surface roughness, and rule out nonspherical particles with aspect ratios significantly exceeding 1.2. They also favor 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 greater than 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.