Contents of: VI/111/./abstract/THENCRE_GALSAT.abs

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SCIENTIFIC ABSTRACT

ISO is expected to make unique contributions to composition studies of
galilean satellites and asteroids with its spectroscopic capabilities,
especially at wavelengths 2.5-5 microns. These observations, using 
PHT S1-S2, will provide new insights into the chemical composition of 
the galilean satellites and the mineralogy of asteroids. They will 
have implications about the formation processes of these objects and 
the early history of the Solar System.

Galilean satellites are known to be very different from one another.
Io's surface is dominated by sulfur compounds, but their exact nature is
still controversial. The three other satellites are basically covered with
ice. A complete spectral coverage of the 2.5-12 micron range will help
to characterize their chemical nature, and will provide an important
input at the time of the satellites'exploration by the Galileo spacecraft.
Most of our knowledge about asteroids has come from visible and near-IR
spectro-photometry (below 2.5 microns). ISO observations at longer wavelengths 
will be essential for analysing, in particular, their carbonaceous content 
(around 3.4 microns), the nature of their hydrated minerals (in the 
2.6-3.1 micron range), and the nature of their silicate feature at 8-12 micron.

As a moderate spectral resolution is sufficient to explore the spectroscopic 
features of the solid surface material, we will use PHT S1 ans S2 which will
ensure maximum sensitivity. The PHT-S1 part will explore the reflected 
component (2.5-5 micron) and the PHT-S2 part (6-12 micron) will simultaneously 
provide the thermal component.

OBSERVATION SUMMARY

We plan to observe the following list of objects with PHT S1-S2 (AOT PHT40),
and with PHT P (AOT PHT03) in 2 filters (3.4 micron and 10 micron) for absolute
calibration. 
Table 1 gives the list of the targets with their class, their diameter, 
their flux at 3.3 micron, the total observing time of the 2 observations 
(AOT PHT03 and PHT40), the expected  S/N in the PHT-S spectrum at 3.3 micron, 
and the priority of the observation.
In the case of an autumn launch, 324 Bamberga is not observable; in the case
of a spring launch, 2 Pallas and 31 Euphrosyne are not observable; in the 
second case, 87 Sylvia is added to the list of targets.

TABLE 1
------------------------------------------------------------------------------
Object     Class       Diameter        3.3mu Flux    Obs.time  Exp.S/N   Prio.
                         (km)            (mJy)         (s)
------------------------------------------------------------------------------

GALILEAN SATELLITES
Io                       3632             6200        409         80      1
Europa                   3138             5100        429         80      1
Ganymede                 5262            16000        361         80      1
Callisto                 4800            15000        369         80      1
         
ASTEROIDS
1    Ceres     G          913             1700        404         40      1
2    Pallas    B-C (*)    583              710        679         40      1
3    Juno      S          220              400        917         40      1
4    Vesta     V          380             1200        549         40      1
10   Hygiea    C          443              410        917         40      3
52   Europa    CF         291              180        977         30      3
324  Bamber    CP  (**)   256              140       1132         30      3
704  Interam   C          338              240       1017         30      3
65   Cybele    C          311              200       1075         30      3
31   Euphrosy  C   (*)    270              150       1132         30      3
87   Sylvia    P   (**)   271              150        679         20      3
---------------------------------------------------------------------------
(*)  For autumn launch only
(**) For spring launch only

TOTAL TIME (s)  Autumn launch    Spring launch          
Priority 1      4117             3438
Priority 3      5118             5797
Total           9235             9235



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