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T. W. Momary, K. H. Baines, R. A. West (JPL/Caltech)
Contemporaneous observations of the Great Red Spot, obtained within 10.5 hours of each other, by both the WFPC2 on board the Hubble Space Telescope and by Galileo/NIMS, provide a basis for exploring the spectral character of the region. We acquired spectral maps on June 26-27, 1996, extending from 0.21 microns to 2.73 microns, compiling the first spectral maps of the GRS encompassing the UV to the Near-IR. Preliminary results suggest that there are distinct spectral regions within the GRS. In particular, there exists a brighter feature in the northeastern regions of the GRS which appears to extend to a higher altitude than the core central region. This cloud is on average 12% brighter than the center of the GRS in methane absorption bands, while being an average 8% dimmer than the core region in continuum wavelengths, suggestive of altitude differences between the two regions. The distinct color differences between various regions within the Spot are evidenced by brightness variations of up to 25% between regions in some wavelengths. All areas of the GRS reach a minimum brightness at approximately 0.35 microns with the bright cloud region having an I/F of 0.27 and the center of the GRS having an I/F of 0.22 (i.e. the central region being 20% dimmer than the higher cloud; this compares to an I/F of 0.39 and 0.38 respectively at 0.21 microns). We are exploring models with phosphine and sulfur that have this similar spectral signature. Results will be presented.