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C. Dumas, R. J. Terrile (JPL), A. Burgasser (Caltech), R. Brown, M. Rieke, G. Schneider, R. Thompson (Univ. Arizona), D. Koerner (Univ. Pennsylvania)
Since Pluto formed from primitive solar nebula material that condensed at very low temperature (\le 50K), it's surface contains important information about the nature of the planetesimals that populate the outer regions of our solar system and the Kuiper belt. Because Pluto and its satellite Charon are separated by not more than 0.9 arcsecond, reflectance spectroscopy of this double system was previously obtained from the combined light of the two bodies. Some information about the composition of the individual objects could nevertheless be obtained while Pluto was eclipsing Charon. The surface of Pluto is believed to be covered by several ices (mainly N2 but also CH4 and CO) (Owen {\it et al.} 1993, {\it Science} {\bf 261}, 745-748) forming patches of bright N2 rich-regions and dark nitrogen-depleted areas distributed non-uniformely (Jewitt 1994, {\it AJ} {\bf 107}, 372-378). While its satellite Charon is believed to be mostly covered with H2O ice (Buie {\it et al.} 1987, {\it Nature} {\bf 329}, 522-523 --- Marcialis {\it et al.} 1987, {\it Science} {\bf 237}, 1349-1351) with few patches of a mixture of CO2 and CH4 ices (Roush {\it et al.} 1996, {\it Icarus} {\bf 119}, 214-218). HST/FOC observations of the surface of Pluto confirmed the presence of large albedo variations (Stern {\it et al.} 1997, {\it AJ} {\bf 113}, 827-843). \\ \indent We used HST/NICMOS to obtain reflectance spectroscopic measurements of the individual members of the Pluto/Charon system. These observations were executed during the two 1998 ``camera-3 campaigns'' and at the following orbital longitudes of Charon (0, 90o, 180o, 270o). The spectra of the two bodies were fully separated for orbital longitude 90o and 270o. We will present the preliminary analysis of the 0.8\mum-2.5\mum spectra of Pluto and Charon with a resolution of ~200/pixel. The data set is currently under reduction but we expect at this resolution to be able to identify the spectral signatures of the diverse icy compounds present on the surface of Pluto and Charon. The results of these observations will also strongly constrain the compositional models of Pluto's atmosphere.
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The author(s) of this abstract have provided an email address for comments about the abstract: Christophe.Dumas@jpl.nasa.gov