8351(  2) - 12/18/98 16:41  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      8351
                                                       Version: 2
                                                       Check-in Date: 18-Dec-1998
                                                                      16:39:56

1.Proposal Title:
Changes in Uranus' Atmosphere Since the Voyager Encounter
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2. Proposal For  3. Cycle
AR               8
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4. Investigators
                                                                                     Contact?
    PI: Kathy Rages                       NASA Ames Research Center (Space Physics
                                          Research Institute)
   CoI: Dr. Heidi Hammel                  Massachusetts Institute of Technology         N
   CoI: Dr. G. W. Lockwood                Lowell Observatory                            N
   CoI: Dr. Christopher McKay             NASA Ames Research Center                     N

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5. Abstract

We propose to combine all the available WFPC2 and NICMOS images of Uranus to
investigate the causes of Uranus' long- term temporal variability, including several
discrete clouds which apparently have lifetimes of several months. The PI has
already developed atmospheric scattering models to fit the Voyager observations of
Uranus' southern hemisphere (Rages Etal 1991, Rages and Pollack 1994), and is now
modifying them to reproduce the Cycle 6 WFPC2 observations of Hammel et al. We
propose to enhance the vertical resolution of the Cycle 6 models by inclusion of the
Cycle 7 data of Tomasko et al., and to model observations from previous cycles to
investigate the timing of possible changes in (1) the methane cloud's altitude,
optical thickness, and single scattering albedo; (2) aerosol absorption below the
base of the methane cloud; and (3) height of the putative H_2S cloud at ~3 bars. We
will examine northern latitudes up to ~30degrees N to check for possible hemispheric
asymmetries in the atmospheric structure. We will also study how the structure of
the discrete clouds differs from that of the surrounding atmosphere. The work
proposed here complements our previous Cycle 6, approved Cycle 7 and requested Cycle
8 observations of Uranus by (1) extending the wavelength range for modeling of our
pre-1998 observations and (2) using data from 1994 and 1995 to partially fill the 10
-year gap since the Voyager encounter.
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  Data Distribution

  Paper Products:  NO
  Media:           ELECTRONIC
  Blocking Factor: 10
  Ship To:         PI_Address
  Ship Via:
  Email:
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                                                8351(  2) - 12/18/98 16:41  - [  2]

            Summary Form for Proposal  8351

  Item                         Used in this proposal
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  Proposal Category            AR
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