Circular polarization as an instrument for investigation of surfaces of atmosphereless celestial bodies. I. Laboratory measurements of highly absorptive substances.
Phase dependences of the circular polarization for light scattered from surfaces formed by layers of tiny powder particles were obtained with a high-precision Stokes polarimeter. Powders of nickel, iron and graphite which have large absorptive indices were used, the particles having similar sizes, but differing in shape. The measurements showed that highly absorptive substances demonstrate large values of circular polarization (more than 1%), especially for large phase angles. The trend of the circular polarization as a function of the phase angle turned out to depend strongly on structure characteristics of a surface. For a porous layer of particles, the absolute value of circular polarization increases slowly up to angles of α ≍ 150° and then decreases down to zero, retaining their sign at all phase angles. Measurements for a pressed layer of particles (graphite) showed that the phase curve demonstrates negative values of circular polarization at first, and then becomes positive reaching its maximum at α ≍ 130°. Hence, the circular polarization of light scattered by the surfaces of atmosphereless celestial bodies, by asteroids in particular, can give information about the presence of metals in the matter of their surface layers and about the presence of regolith on the surface of metalliferous objects.
Kinematika i Fizika Nebesnykh Tel
- Pub Date:
- April 1992
- Circular Polarization;
- Light Scattering;
- Planetary Surfaces;
- Surface Properties;
- Celestial Bodies;
- Metal Compounds;
- Lunar and Planetary Exploration