Photopolarimetry of planetary atmospheres: what observational data are essential for a unique retrieval of aerosol microphysics?

Abstract

We analyse the results of computations of the intensity and degree of linear polarization of diffusely reflected sunlight for the centre of a planetary disc in the phase-angle range 0° < α < 90°. The computations are performed using numerically exact T-matrix and vector radiative-transfer codes for several alternative models of the Jovian cloud layer derived previously from ground-based spectropolarimetric observations at phase angles α < 11°. Our results show that although these models reproduce the existing observational data equally well, they start to show significant polarization differences at phase angles α≥ 12°. Thus, using Jupiter as a ‘proving ground’, we conclude that only polarimetric data obtained over a wide range of phase angles (i.e. from spacecraft) may provide definitive constraints on aerosol shape and, as a consequence, ameliorate the ill-posed nature of the inverse remote-sensing problem.