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K. Rages (SPRI/Ames), H. B. Hammel (MIT), G. W. Lockwood (Lowell Obs.)
Images of Uranus obtained in July 1997 with the Planetary Camera on the Hubble Space Telescope show latitudes as far north as 30\arcdeg . In the southern hemisphere, Uranus continues to display a relatively bright polar cap down to 40-45\arcdeg S, as it did at the time of the Voyager encounter in January 1986. The polar cap is easily visible at wavelengths longward of 600 nm, and is extremely prominent in the continuum filter at 953 nm, while being somewhat obscured in the methane band filter at 890 nm. At wavelengths between 300 and 600 nm, both the polar cap and lower southern latitudes (65\arcdeg S and 22\arcdeg S respectively) have darkened since the Voyager encounter, contributing to Uranus' secular variability. Uranus' limb darkening has also increased somewhat, with the greatest change taking place at 22\arcdeg S in the 619 nm methane band filter, where a slight limb darkening may have appeared after Voyager saw only limb brightening. We will use radiative transfer modeling to characterize the changes in Uranus' atmospheric structure underlying these changes in the appearance of the planet's southern hemisphere, and to determine the vertical structure of the atmosphere at low northern latitudes, with results to be presented at the meeting.
The author(s) of this abstract have provided an email address for comments about the abstract: rages@gal.arc.nasa.gov