Near‐ultraviolet scattering properties of Jupiter

The Voyager 2 photopolarimeter experiment obtained photometric observations of Jupiter at four phase angles between 20° and 80° and at various illumination angles from limb to terminator. These data were analyzed to determine the altitude distribution and scattering properties of the material responsible for Jupiter's low geometric albedo at 2400 A. In polar regions the absorber must be higher than 40 mbar. In mid-latitudes, center-to-limb measurements indicate that most of the absorbing material lies deeper than 100 mbar. Absolute reflectivity requires a considerable amount above 400 mbar. The maximum amount of solar UV flux below 2550 A available for heating the stratosphere at 20° latitude is only 10−4 of the solar constant at Jupiter. The latitudinal distribution of stratospheric absorbers suggests that energy deposition from the magnetosphere is important in their formation. We examine the scattering properties of model atmospheres containing three distinct aerosol size distributions. Rayleigh's phase function fits our data at several phase angles better than any particle phase function. We derive an upper limit to the column abundance of particles larger than 0.05-µm radius in the north tropical zone and north equatorial belt. These regions contain less than one extinction optical depth at 2400 A of such particles above the 100-mbar altitude. Rayleigh scattering from the top 100 mbar obscures effects due to scattering from the deeper absorbing particles over our range of phase angles. We are unable to determine whether the absorbers are particulate or molecular.