9954(  1) - 04/04/03 10:35  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      9954
                                                       Version: 1
                                                       Check-in Date: 04-Apr-2003
                                                                      10:35:17

1.Proposal Title:
UVBRI Photometry of Janus and Epimetheus
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2. Proposal For  3. Cycle
AR               11
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4. Investigators
                                                                                     Contact?
    PI: Anne Verbiscer                    The University of Virginia

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5. Abstract

We will study the spectrophotometric properties of the small, coorbital saturnian
satellites Janus and Epimetheus using WFPC2 images obtained over the wavelength
range 336-1024 nm during the period September 1996 through January 2002. We will
produce broadband spectra and hence colors for each satellite which will address the
current discrepancy in the color of Janus. Poulet et al. (1999) found Janus to have
a pronounced redness over the wavelength range 0.3 to 0.7 microns, while a recent
study by French et al. (2002) found Janus to be more neutral. We will investigate
any leading/trailing hemisphere albedo dichotomies. Upon removal of any rotational
albedo effects, we will produce the first solar phase curves from data between 0.22
and 6.4 degrees in phase angle, possibly revealing for the first time the existence
of narrow opposition surges. In combination with available (Voyager) spacecraft data
at higher phase angles, we will produce the most complete phase curves to date for
these objects. We will apply the Hapke 2002 photometric equation to these phase
curves to relate the physical characteristics of the satellite surface to the
observed photometric properties. From these fits to the solar phase angle data we
will determine the geometric albedo in each filter, the single scattering albedo, in
addition to parameters which characterize the opposition effects due to shadow
hiding and coherent backscatter.
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                                                9954(  1) - 04/04/03 10:35  - [  2]

            Summary Form for Proposal  9954

  Item                         Used in this proposal
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  Proposal Category            AR
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