Refractive Index of Aqueous HCl Solutions and the Composition of the Venus Clouds

Abstract

PROGRESS in the observation and theoretical interpretation of polarized reflected sunlight has led to a precise knowledge of the refractive index, particle size and shape, and altitude of the top of the Venus clouds1–3. Hansen concluded that the cloud particles are spherical liquid droplets of extremely uniform size, with mean radii very near 1 µm, with a refractive index of 1.45±0.02 near λ = 0.55 µm. These particles are found near the 50 mbar pressure level, compared with the usual estimates of 150 mbar for the “line-forming region” in which multiply scattered infrared photons undergo the most absorption and where the clouds become opaque enough to limit deeper penetration of sunlight. The temperature at the 150 mbar level is near 240 K. Theoretical calculations on the atmospheric structure above this level suggest a temperature possibly as low as 180–210 K at the 50 mbar level4.