DPS 35th Meeting, 1-6 September 2003
Session 40. Outer Planets/Gas Giants IV
Poster, Highlighted on, Friday, September 5, 2003, 3:30-6:00pm, Sierra Ballroom I-II

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[40.15] Showing Their True Colors: The UV-Near-IR Spectral Properties of Tropospheric Cloud Particles in Jupiter's Great Red Spot and Environs from HST and Galileo/NIMS Center-to-Limb Spectral Maps

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

We use center-to-limb high-spatial-resolution spectral maps of Jupiter's Great Red Spot (GRS) and surroundings, spanning the uv to near-ir, to determine spectral character of major cloud features in the region. Multi-filter 29-color maps, spanning 0.22 to 5.2 microns, were obtained contemporaneously on 26-27 June 1996 by the Hubble Space Telescope and Galileo/NIMS. We determined vertical cloud structure and uv-near-ir single- scattering albedo spectra of tropospheric clouds in three locations: (1) the GRS central core near 20 degrees planetocentric latitude, (2) the South Tropical Zone (STrZ), 8 degrees latitude south of the GRS core, and (3) the fresh spectrally-identifiable ammonia ice cloud (SIAC) embedded in the GRS wake, some 10 degrees to the northwest.

Beyond 0.90 microns, particles are bright, except in the SIAC, which shows pronounced absorption near 1.95 and 3 microns. A distinct spectral feature also exists below 0.42 microns, having a sharp cut-on of absorption in the violet/blue between 0.34 and 0.41 microns and absorption persisting to shortward of 0.26 microns in all three regions. Our modeling thus far indicates that this 0.22-0.4-micron feature is too pronounced to be solely attributed to a stratospheric haze absorption. All three tropospheric cloud regions instead have a similar spectral character, with GRS particulates possessing an enhanced absorption feature, possibly due to greater concentration of a common material responsible for the uv/blue absorption. The SIAC appears to be the least uv-absorbing (single-scattering albedo ~0.95 at 0.26 microns), perhaps linked to its relatively young age, while the STrZ has a 0.26-micron single-scattering albedo of 0.8, significantly greater than the GRS (0.65-0.7). Our preliminary modeling thus indicates that the GRS is red due to (1) the high altitude of the anti-cyclonic feature, which limits the amount of Rayleigh-scattered light observable in the uv/blue, and (2) a larger concentration of the uv-blue absorber. The uv-visible spectral character of this common material appears consistent with the spectral character of polymeric sulfur, as depicted by Nelson and Hapke (Icarus 36, 304-329, 1978).

The author(s) of this abstract have provided an email address for comments about the abstract: momary@scn.jpl.nasa.gov

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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.