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J. W. Hovenier, C. J. Braak, J. F. De Haan (Free University), L. D. Travis (GISS)
Photopolarimetry observations of Jupiter, made in 1997 by the Galileo Photopolarimeter/Radiometer, are presented. For various areas on the Jovian disk, the brightness and linear polarization of the reflected sunlight at wavelengths of 678 and 945 nm, and phase angles between 40 and 110 degrees, were measured. These measurements represent the first polarization measurements at phase angles unattainable from Earth since the Pioneer 11 flyby in 1974.
A first inspection of the data revealed two striking aspects: 1) Very high linear polarization (up to 70 per cent) in the South Polar Region at phase angles near 69 and 102 degrees and at both wavelengths. 2) Several instances of phase angles at which the degree of linear polarization vanishes in some of the observed regions.
The observed brightness and high linear polarization in the South Polar Region are discussed in terms of simple atmospheric models, involving scattering by molecules and particles above a cloud deck, for which we used a Lambertian surface. The multiple light scattering is computed using the adding/doubling method, taking polarization and all orders of scattering into account. Our analyses indicate a need for a more sophisticated model of the cloud reflectivity. For this purpose, we use parameterized scattering matrices. Some preliminary results will be presented.
The author(s) of this abstract have provided an email address for comments about the abstract: hovenier@nat.vu.nl