Nature of the Venus Clouds as Derived from Their Polarization

Abstract

The linear polarization of sunlight reflected by Venus is analyzed by comparing observations with extensive multiple scattering computations. The analysis establishes that Venus is veiled by a cloud or haze layer of particles which have a narrow size distribution with a mean radius ~ 1 μ. The refractive index of the particles is 1.44 ± 0.015 at γ = 0.55 μ with a small normal dispersion, the refractive index decreasing from the ultraviolet toward the infrared. The particles exist at a high level in the atmosphere, with the optical thickness unity occurring where the pressure is about 50 mb.The particle properties deduced from the polarization eliminate all but one of the cloud compositions which have been proposed for Venus. A concentrated solution of sulfuric acid (H2SO4–H2O) provides good agreement with the polarization data.