Characteristics of aerosol phenomena in Martian atmosphere from KRFM experiment data

Abstract

Photometric limb-to-limb profiles of Mars were obtained in eight narrow bands between 315 and 550 nm from the Phohos 2 spacecraft. Tentative results of the analysis are presented in terms of optical properties of the atmosphere and surface. The imaginary part of the refraction index k from 0.01 to 0.03 for 315 nm and from 0.005 to 0.01 for 550 nm was estimated for the “constant” dust haze, using Mie theory for spherical particles. These values of k are a few times higher than obtained by laboratory tests of terrestrial analogues including basalt, andesit and montmorillonite. Two explanations are possible: influence of irregular shape of particles and/or the presence of some more absorbing substances (such as goethite). Particle sizes of a few tenths of micrometres having a refraction index of 1.55 are compatible with the discussed model of the “constant” haze. The full shape of the near equatorial photometric profile on 550 nm can be explained by the slightly absorbed atmosphere (with optical depth 0.4 and imaginary part of the refraction index 0.0075) above the moonlike (roughness factor q ≅ 0) surface. Icy particles with the same average sizes as in the haze ( r m = 0.4 μm) but with more narrow size distribution can explain the bright spot above Arsia Mons. Optical depth τ ≅ 0.1 and column mass density 7·10 −5 g cm −2 of the icy clouds were evaluated.