On the Altitude Dependence of Aerosol Volume Scattering Coefficient in the Saturn’s Atmosphere. I. Integral Disk

Abstract

Current studies dealing with the vertical structure, composition, and microphysical characteristics of the aerosol component in the atmosphere of Saturn are reviewed. When considering the methods used in the model analysis of giant planets atmospheres, the disadvantages of forcibly assigning the number of aerosol layers and their parameters that are artificially included into the model of the vertical structure of the atmosphere are pointed out. At the same time, the advantages of the effective optical depth (EOD) method are considered. This method makes it possible to determine a qualitative pattern of the altitude distribution of cloud layers in the giant planets atmospheres and to calculate a set of microphysical parameters of their aerosol component, while no particular vertical structure is preliminary assigned to the model. The EOD method is used to determine the pressure dependence of aerosol volume scattering coefficient in the upper atmosphere of Saturn from the reflectance spectra of its integral disk measured in the methane absorption bands at 619, 727, 842, 864, and 887 nm. The model assumptions, the quantitative relationships between the main atmospheric gases, and the size distribution parameters of aerosol particles are described. It has been found that aerosols with varying scattering properties are continuously present at all of the examined altitude levels in Saturn’s atmosphere. The altitudes at which the aerosol layers become densest were determined. In the atmosphere of the planet, the most powerful cloud system exhibits two maxima in the volume-scattering coefficient at levels of approximately 270 and 430 mbar and an intermediate thickening at approximately 1.0 bar. In a pressure range of 2.2−8.0 bar, there is an extended aerosol layer, where the scattering is strongest in a pressure interval of 3.8−4.8 bar depending on the methane absorption band analyzed. The significant dispersion differences, which were revealed in the composite dependence of the aerosol volume scattering coefficient, may indicate changes in the radius and/or nature of aerosol particles in the lower layers of Saturn’s atmosphere.