Stellar Occultation Observations of Saturn's North Polar Temperature Structure

A. R. Cooray (MIT and U. of Chicago), J. L. Elliot (MIT and Lowell Observatory), A. S. Bosh (Lowell Observatory), L. A. Young (Boston University), M. A. Shure (Georgia State University)

We have observed a stellar occultation of GSC5249-01240 by Saturn's north polar region on November 20, 1995 from the IRTF. This is the first recorded occultation by the polar region of a giant planet. The occulted region extends 80 km in vertical height and 660 km in horizontal length, over a region from 82.5 to 85 degrees in planetocentric latitude and from 20 to 30 degrees in planetocentric longitude. Based on isothermal model fits to the light curve, we find an equivalent isothermal temperature of 132 tex2html_wrap_inline11 10 K at a pressure level of 1.6 tex2html_wrap_inline11 0.1 tex2html_wrap_inline15 bar, which corresponds to a half-light latitude of 83.2 tex2html_wrap_inline11 0.2 degrees and longitude of 24.1 tex2html_wrap_inline11 0.5 degrees. Using numerical inversion procedures, we have retrieved the temperature profile of the occulted region which suggests an increase in temperature (with radius) of 14.5 K between 6 and 10 tex2html_wrap_inline15 bars. We also find temperature fluctuations of 1 to 5 K, and if the observed temperature gradients of these fluctuations apply to the vertical direction only, then this region is super-adiabatic. More likely these thermal gradients are due to horizontal temperature variations.