Spatial Distribution and Number Density of Scatterers in the Upper Uranian Atmosphere

C. M. Walter, M. S. Marley (NMSU), H. B. Hammel (MIT)

Since the visit by Voyager 2 in 1986 the amount of haze in the stratosphere and upper troposphere of Uranus has increased by an order of magnitude. The full disk albedo of the planet in narrowband near-infrared images of the planet taken at Apache Point Observatory from August 1995 to October 1996 is larger than can be accounter for by the Voyager haze. In an effort to confirm this and determine the spatial distribution of the haze we have examined high resolution images (FWHM = 0.3-0.5 tex2html_wrap_inline12 ) taken at the IRTF in Mauna Kea, HI in late August 1995.

The data was modeled by using center-to-limb fits of the photometric quantity I/F along specified latitudes. The model I/F values were computed using a multi-layer adding-doubling code. Our dataset consisted of several images in a broadband K filter spread over six nights. The K filter is particularly useful because it encompasses strong CH tex2html_wrap_inline18 and H tex2html_wrap_inline20 absorption bands, making this filter highly sensitive to the atmosphere above the CH tex2html_wrap_inline18 cloud. At these wavelengths the contribution to the reflected light by Rayleigh scattering is smaller than the component from scattering by the haze, which allows its effect to be effectively isolated and measured. Preliminary results confirm the order of magnitude increase, and show that the distribution of haze is uniform across the disk.

This work was supported by NASA grant NGT-51383.