OPTICAL REFLECTANCE POLARIMETRY OF SATURNS GLOBE AND RINGS .2. INTERPRETATIONS FOR THE B-RING

The light reflected by Saturn's rings acquires some polarization which varies with phase angle, wavelength, and position on the rings. The information produced about the nature of the bodies in Ring B are the following: (a) Visible light reflected by the surfaces of the blocks shows a variation of polarization with phase angle which is characteristic of solid pieces at least several millimeters across, with a polarimetric albedo in orange light of about 0.45. This albedo decreases toward shorter wavelengths and the polarization behaves accordingly. These results resemble laboratory measurements with dirty ice. (b) In the uv, the albedo decreases to 0.20. The polarization is no longer characteristic of blocks but of smaller grains, whose scattering properties dominate those of the larger blocks, which are too dark. (c) In addition to the directly reflected light, the polarization due to Ring B shows a component either normal or parallel to the radius vector, but varying with time. This component is produced partly by the permanent effect of light scattered onto the ring by the globe and partly by organized structures in the ring. Elongated or striated blocks facing toward the planet, or blocks partly aligned in chains, are possible causes of the polarization observed; more probably, gravitational aggregations of particles along the direction of orbital motion may be involved. However, disturbances may occur which disorganize these structures on all parts of the ring and compete with reorganization: perturbation by satellites, collisions with external bodies, or gravitational instabilities may cause those disturbances. © 1979.