Coherent backscattering and opposition effects observed in some atmosphereless bodies of the Solar System

The results of photometric and polarimetric observations carried out for some bright atmosphere less bodies of the Solar system near the zero phase angle reveal the simultaneous existence of two spectacular optical phenomena, the socalled brightness and polarization opposition effects. In a number of studies, these phenomena were explained by the influence of coherent backscattering. However, in general, the interference concept of coherent backscattering can be used only in the case where the particles are in the farfield zones of each other, i.e., when the scattering medium is rather rarefied. Because of this, it is important to prove rig orously and to demonstrate that the coherent backscattering effect may also exist in densely packed scattering media like regolith surface layers of celestial bodies. From the results of the computer modeling performed with the use of numerically exact solutions of the macroscopic Maxwell equations for discrete random media with different packing densities of particles, we studied the origin and evolution of all the opposition phenom ena predicted by the coherent backscattering theory for lowpackingdensity media. It has been shown that the predictions of this theory remain valid for rather high packing densities of particles that are typical, in par ticular, of regolith surfaces of the Solar system bodies. The results allow us to conclude that both opposition effects observed simultaneously in some highalbedo atmosphereless bodies of the Solar system are caused precisely by coherent backscattering of solar light in the regolith layers composed of microscopic particles.