STELLAR OCCULTATION OBSERVATIONS OF SATURNS NORTH-POLAR TEMPERATURE STRUCTURE

We have observed a stellar occultation of GSC5249-01240 by Saturn's no rth polar region on November 20, 1995 from NASA's Infrared Telescope F acility (IRTF). This is the first recorded occultation by the polar re gion of a giant planet. The occulted region extends 88 km in vertical height and 660 km in horizontal length, over a region from 82.5 degree s to 85 degrees in planetocentric latitude and from 20 degrees to 30 d egrees in planetocentric longitude. Based on isothermal model fits to the light curve, we find an equivalent isothermal temperature of 130 /- 10 K at a pressure level of 1.6 +/- 0.1 mu bar, which corresponds t o a half-light latitude of 83.2 +/- 0.2 degrees and longitude of 24.1 +/- 0.5 degrees. Using numerical inversion procedures, we have retriev ed the temperature profile of the occulted region, which suggests an i ncrease in temperature (with radius) of 14.5 K between 6 and 10 mu bar . We also find temperature fluctuations of 1 to 5 K along the path pro bed by the occultation; if the observed temperature gradients of these fluctuations apply to the vertical direction only, then this region i s super-adiabatic. More likely, these thermal gradients are due to a c ombination of diffractive scintillations and horizontal temperature va riations. Given that isothermal model fits and numerical inversions ca nnot separate individual contributions to observed temperature gradien ts, such as from vertical variations, horizontal variations, and scint illations, this occultation requires further study. (C) 1998 Academic Press.