A NEW INTERPRETATION OF SCATTERED-LIGHT MEASUREMENTS AT TITANS LIMB

Images of Titan, taken by Voyager 2 at phase angles Phi=140 degrees an d Phi=155 degrees have provided radial intensity profiles at the brigh t and dark limbs, which provide information on the vertical and latitu dinal distribution of organic hazes. In previous work, the deduced ext inction coefficient, using ad hoc particle sizes, was obtained without help of microphysics, and it appeared difficult to compare it with co efficients computed from theoretical models. We use here our fractal a pproach of microphysical modeling and optics of aggregates to compute intensity profiles of the main haze at the bright limb, and compare to the Voyager observations. Fractal aerosol distributions are obtained using different production altitudes and rates. Scattering and absorpt ion of light are described by an improved model, based on the use of f ractal aggregates made of spherical (Mie) particles. We show that the fractal dimension of aggregates has to be D-f approximate to 2, as pre dicted by microphysical arguments. Only a production altitude z(0) app roximate to 385 +/- 60 km, corresponding to a monomer radius r(m) appr oximate to 0.066 mu m, is fully consistent with both phase angle data. We also point out that the production rate of the aerosols decreases by a factor approximate to 2 between 30 degrees S and the midnorthern latitude and further, increases up to 80 degrees N. The average value of the production rate is Q approximate to 1.4 x 10(-13) kg/m(2)/s; we give arguments in favor of dynamical processes rather than of a purel y microphysical mechanisms to explain such latitudinal variations.