8753(  1) - 12/30/99 13:03  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      8753
                                                       Version: 1
                                                       Check-in Date: 30-Dec-1999
                                                                      12:32:16

1.Proposal Title:
Probing the Surface Composition of Europa through Atmospheric Spectroscopy
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2. Proposal For  3. Cycle
AR               9
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4. Investigators
                                                                                     Contact?
    PI: Michael Brown                     Caltech

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5. Abstract

We propose to analyze previously obtained spectra of the vicinity of Europa to
search for magnesium in the satellite's atmosphere. Analysis of Galileo NIMS spectra
has led to the suggestion that magnesium is abundant on parts of the satellite as a
hydrated evaporite salt. This interpretation has been controversial, however, as
similar spectra could be produced by mostly pure water ice under special conditions.
In addition, the specific presence of magnesium is uncertain, as many hydrated salts
produce a similar spectrum. Any salts present on the surface of Europa will be
sputtered in the atmosphere where they are potentially detectable remotely. Our
previous groundbased observations have detected potassium and sodium in the
atmosphere of Europa, which are other possible components of salts on the surface.
Detection of magnesium would be a strong confirmation of the magnesium salt
interpretation of the NIMS data and would help to quantify the trace element
composition of the surface and possibly any subsurface liquid on the satellite.
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                                                8753(  1) - 12/30/99 13:03  - [  2]

            Summary Form for Proposal  8753

  Item                         Used in this proposal
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  Proposal Category            AR
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