HR: 14:40h
AN: U23A-05    [Abstracts]
TI: Haze Measurements in Titan's Atmosphere
AU: * Tomasko, M
EM: mtomasko@lpl.arizona.edu
AF: Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721 United States
AU: Doose, L
EM: ldoose@lpl.arizona.edu
AF: Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721 United States
AU: Lemmon, M
EM: lemmon@physics.tamu.edu
AF: Department of Physics, Texas A&M University, College Station, TX 78412 United States
AU: Karkoschka, E
EM: erich@pirl.lpl.arizona.edu
AF: Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721 United States
AB: The optical properties and distribution of haze in Titan's atmosphere were measured along the Huygens descent trajectory. The Descent Imager/Spectral Radiometer instrument used 343 spectral channels in the wavelength range from 350 to 1600 nm to characterize the haze. Measurements of direct + diffuse and diffuse-only intensities at altitudes from 140 km to the surface reveal the vertical distribution of optical depth, single scattering albedo, and particle phase function. These properties may be related to physical properties of the scattering haze through T-matrix computations of binary cluster-cluster fractal aggregate scatterers. The optical depth varies from about 2 at 938 nm to 7.5 at 531 nm, decreasing with wavelength approximately as λ^-2.1 . The particles are distributed approximately uniformly with altitude from the surface to near 80 km. Their number densities fall off exponentially above 80 km with a scale height near 60 km. The scattering particles are brighter than would be expected using the tholin refractive indices of Khare and Sagan, and they are brighter at low altitudes compared to high altitudes. Clear altitude regions, such as would occur if particles grew rapidly and fell from the atmosphere, are not seen. Polarization measurements from DISR confirm the scattering haze must have a small dimension near 0.05 , and this is taken to be the radius of "monomers" forming the fractal aggregates. The shape of the radiation field is well-fit for particles containing 200 to 500 monomers. The growth of methane absorption bands as Huygens fell into the atmosphere yields measurements of transmission vs. path length, which can be used to derive methane absorption coefficients for Titan's temperature and pressures.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0343 Planetary atmospheres (5210, 5405, 5704)
DE: 6281 Titan
SC: Union [U]
MN: Fall Meeting 2005