Modeling the aerosols in the atmosphere of Titan

A combination of laboratory experiments, theoretical modeling, and spacecraft in situ observations is employed to characterize the aerosols in the atmosphere of Titan. The scattering properties of model aerosols were measured using the Microwave Analog Light Scattering Facility at the University of Florida and complemented with theoretical modeling of single scattering characteristics and radiative transfer in Titan's atmosphere. This study compares these modeling results with photopolarimetric observations made over a range of phase angles by the Pioneer 11 and Voyagers 1 and 2 spacecraft approximately 20 years ago.;Important results of this work include a survey of the scattering properties of different particle shapes necessary to accurately interpret these observations without introducing non-physical assumptions about the particles or requiring additional free parameters to the radiative transfer models. Previous studies use calculation methods which, due to computing memory and processing time requirements, a priori exclude much of the phase space that the microwave analog laboratory is ideal for exploring. The goal of the present work, to directly constrain aerosol physical characteristics, is addressed by studying in a consistent manner how a variety of particle morphologies affect polarization and intensity measurements of Titan's atmosphere.;Single liquid drops are modeled using spheres for which scattering patterns can be easily calculated with Mie theory. Cubes are used as a representation of solids with sharp edges due to fragmentation. More complex particle morphologies are modeled as aggregates that are likely formed by collisions between semi-liquid spheres that stick together instead of merging. Radiative transfer calculations for model atmospheres containing these particles are constrained by direct comparison to in situ spacecraft observations. Based on these comparisons, many model morphologies are excluded from further consideration and the most plausible physical particle models suggest a combination of Rayleigh-like monomer particles and aggregates that are larger than those previously investigated provide the best fit to the existing data. Additional laboratory experiments and more refined modeling awaits the results of a new rich observational dataset following the Cassini/Huygens encounter with Titan in 2004.