Saturn's Upper Atmospheric Hazes Observed by the Hubble Space Telescope

Abstract

We observed Saturn with the Hubble Space Telescope at wavelengths 0.30-0.89 μm for the purpose of determining the distribution of hazes. In the stratosphere, haze optical depths in the ultraviolet are essentially zero for midnorthern latitudes, are small (∼0.2) at low latitudes and mid-southern latitudes, but large (almost unity) above 70° north. The optical depth falls off sharply in the visible due to the small radii of the stratospheric aerosols (∼0.15 μm). The latitudinal distribution of tropospheric haze was found mostly consistent with previous investigations. It is completely different from the distribution of stratospheric haze since optical depths in the troposphere strongly increase from the north pole to the equator. In the ultraviolet, the stratospheric aerosols are darker than tropospheric aerosols. Latitudinal albedo and color variations in the visible, defining Saturn's belt and zone structure, can be explained by variations in the size of tropospheric aerosols (radii 1-2 μm). The unusual blue-green color of mid-southern latitudes in 1991 may be due to smaller radii (∼0.5 μm) in the troposphere. At wavelength 0.30 μm we found an indication of a gaseous absorption of ∼0.02 optical depth in the upper part of the stratosphere.