LATITUDINAL VARIATION OF AEROSOL SIZES INFERRED FROM TITANS SHADOW

We measured the location, size, and shape of Titan's shadow in five im ages taken with the Hubble Space Telescope in 1995. We inferred the al titude of Titan's optical limb at wavelengths of 337-954 nm to an accu racy of 15 km. At each wavelength, altitudes are constant north of -5 degrees and also constant but lower south of -50 degrees latitude, wit h a linear transition region inbetween. The amplitude of the variation of altitude with latitude increases from close to zero at wavelength 337 nm to 130 km at 954 nm. We conclude that Titan's aerosols are larg er (0.3 mu m mean radius) at northern latitudes where we probe the det ached haze layer than at southern latitudes (0.1 mu m south of -50 deg rees) where we probe the main haze layer below. The geometric cross se ction of aerosols at probed altitudes (similar to 300 km) does not sho w a significant latitudinal variation. The wavelength dependence of th e size of Titan's shadow is not consistent with a spherical shape of a erosols, but gives evidence of their fractal nature. (C) 1997 Academic Press.