Titan's vertical aerosol structure at the Huygens landing site: Constraints on particle size, density, charge, and refractive index

We present a one dimension simulation of Titan's aerosol distribution and compare our results with the haze optical properties retrieved by the DISR observations (Tomasko, M.G., Doose, L, Engel, S., Dafoe, LE., West, R., Lemmon, M., Karkoschka, E., See, C. [2008]. Planet. Space Sci. 56, 669-707). We set the mass production of aerosols in the thermosphere to 3 x 10(-14) g cm(-2) s(-1) and follow the evolution of the particles due to coagulation, sedimentation and atmospheric mixing. We use the observed aerosol phase functions at 100 km to constrain the particle's charge density to 15 e/mu m. With this charge density, the microphysical model predictions for the number of monomers, and the particle size and density, are in good agreement with the DISR measurements. In addition, we derive a new refractive index for the aerosols based on the single scattering albedo inferred from DISR measurements. The imaginary index is larger than previous estimates based on laboratory analogs, with an increasing absorption toward the near-IR. Our simulation provides a good description of the particle properties above 80 km, but we find that condensation effects must be included in order to interpret aerosol characteristics at lower altitudes. (C) 2010 Elsevier Inc. All rights reserved.