DPS 34th Meeting, October 2002
Session 18. Outer Planet Atmospheres
Poster, Chair(s): , Tuesday, October 8, 2002, 3:30-6:00pm, Exhibit Hall

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[18.02] HST Constraints on the Vertical Structure and Spectral Properties of Particulates in the Great Red Spot and Associated Ammonia Ice Clouds

K. H. Baines, R. W. Carlson, T. W. Momary, G. S. Orton (Caltech/JPL)

High-spatial-resolution images of the Great Red Spot (GRS) and nearby ammonia ice clouds were obtained contemporaneously by the Galileo orbiter and the Hubble Space Telescope (HST) on June 26-27, 1996. We have begun a multi-wavelength study of the vertical structure and particle properties of these features using 23-color imagery spanning 0.74 to 5.2 microns obtained by the Near-Infrared Mapping Spectrometer (NIMS) on board Galileo, and complementary six-color imagery obtained by HST/WFPC spanning 0.22 to 0.95 microns. Here we present preliminary results from our analysis of HST images.

Joint analysis of the 0.89-micron methane band and nearby 0.95-micron continuum, utilizing the double Henyey-Greenstein phase functions of Tomasko et al. (Icarus 33, 558-592, 1978), places tight constraints on the cloudtop pressure and near-ir single-scattering albedos. Specifically, we find that the center of the GRS exhibits a cloudtop pressure 0.19-0.20 bars, placing it at a significantly higher altitude than the 0.33-bar cloudtop of the nearby prominent ammonia ice cloud located in the turbulent wake to the northwest of the GRS. Particles in the Great Red Spot exhibit significant UV absorption compared to those in the ammonia ice cloud. Specifically, we find single-scattering albedos of 0.70, 0.71, and 0.67 at, respectively, 0.218, 0.255, and 0.336 microns in the darkest UV region of the GRS, compared to 0.80 at 0.218 microns for the ammonia cloud. However, in the near-ir near 0.95 microns, both features exhibit significantly brighter single-scattering albedos near 0.98.

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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.