Latitudinal Variation of Aerosol Sizes Inferred from Titan’s Shadow

wavelength dependence was investigated. Using a high We measured the location, size, and shape of Titan’s shadow in five images taken with the Hubble Space Telescope in 1995. phase-angle image in the clear filter (480 nm) from Voyager We inferred the altitude of Titan’s optical limb at wavelengths 2, Rages and Pollack (1983) found the altitude of the optiof 337–954 nm to an accuracy of 15 km. At each wavelength, cal limb higher at the equator than at the poles. altitudes are constant north of 258 and also constant but lower Imaging of Titan by the Hubble Space Telescope has south of 2508 latitude, with a linear transition region inbetween. the advantage of a wide wavelength range. However, limb The amplitude of the variation of altitude with latitude inprofiles of these images are greatly affected by the point creases from close to zero at wavelength 337 nm to 130 km at spread function of the telescope and by the limb darkening 954 nm. We conclude that Titan’s aerosols are larger (0.3 mm profile, both of which make measurements of the altitude mean radius) at northern latitudes where we probe the detached of the optical limb difficult. haze layer than at southern latitudes (0.1 mm south of 2508) Hubbard et al. (1993) constrained Titan’s haze properties where we probe the main haze layer below. The geometric cross by a stellar occultation in 1989. They determined an aerosol section of aerosols at probed altitudes (p300 km) does not show a significant latitudinal variation. The wavelength dependence size of 0.2 em, or a smaller mean size if the variance of of the size of Titan’s shadow is not consistent with a spherical the size distribution is large. They found a north–south shape of aerosols, but gives evidence of their fractal asymmetry of the altitude of the optical limb with the nature.  1997 Academic Press transition at 2208 latitude. Since occultation data are very