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A. Sanchez-Lavega (Univ. Pais Vasco, Spain), J. R. Acarreta (KNMI, The Netherlands), P. Tanga (Obs. Turin, Italy)
To study the cloud morphology in Saturn's southern polar region (SPR, southward of 74 deg. South), we have analyzed high resolution images obtained in October 2000 with the 3.6 m TNG facility in La Palma Observatory (Spain) and a 1997 and 1999 series from Hubble Space Telescope archives. The wavelength coverage was from 218 to 1042 nm, including the 890-nm methane band. In all the wavelengths, the SPR is darker than surroundings although in the uv (218, 255 nm) the darker region extends to 63 deg. South. Two features detach from 336 to 1042 nm: The South Polar Belt (SPB, 76 deg. South) and a Polar Cap (85 deg. South). The SPB shows conspicuous morphology at red wavelengths, but it is no regular like the "Hexagon"-wave counterpart observed in the northern hemisphere. We were also unable to detect any spot at these latitudes (i.e. a counterpart to the North Polar Spot, NPS). This strongly supports the idea that the northern Hexagon is a wave forced by the NPS vortex. The second feature, the South Polar Cap, shows a reflectivity contrast reversal with surroundings from ultraviolet (were it is brighter) to red (where it shows darker). At red wavelengths it is very dark and small (radius of just 2 deg. centered on the pole). Preliminary photometry and radiative transfer modeling suggest that the SPR contains an optically thick aerosol layer extending vertically from about 20 mbar to 2.5 bar, but not ammonia cloud layer is retrieved at least up to this level. The cap is a region depleted of aerosol particles relative to surroundings.
Acknowledgements: This work has been supported from Spanish MCYT research project PNAYA2000-0932. We acknowledge the Space Telescope Science Institute and the ESO ST-ECF archive facilities for supplying us with the Hubble Space Telescope images.
The author(s) of this abstract have provided an email address for comments about the abstract: wupsalaa@bi.ehu.es