Mathematics – Logic
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufm.p12b0495h&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #P12B-0495
Mathematics
Logic
5410 Composition, 5464 Remote Sensing, 6218 Jovian Satellites
Scientific paper
Spectra of the non-ice material on Callisto have been derived from telescopic spectra [Calvin and King, 1997] and from a few early NIMS observations of the leading hemisphere [McCord et al., 1998]. We use all available NIMS data sets to improve upon these works. Currently, by using 6 global-scale observations, we have derived average spectra in the 0.7 to 5 micron range for ice-poor regions over large longitude ranges. The non-ice components of the spectra were then derived by subtracting water-ice albedo models from those averages. The ice and non-ice materials on the surface of Callisto are assumed to be discretely mixed due to thermal segregation [Spencer, 1987] and Galileo SSI images provide compelling evidence of this [Klemaszewski, 1998; Moore et al., 1999; Greeley et al., 2000a,b]. Unmixing of the average spectrum of the ice-poor regions in each global observation shows that only a few percent of 50-micron or larger water-ice is present, as has previously shown to be the case for at least a few early NIMS observations [Hansen et al., 1998]. All resulting non-ice spectra are very similar and possess no discernable dependence on longitude. The reflectance spectrum increases from the visible to about 2.5 microns, possesses a strong 3-micron OH-stretch vibration absorption, and increases again to 5 microns, which is consistent with the previous telescopic and NIMS analyses. The spectra of the non-ice material also contains the absorption features due to CO2, SO2, CN, and SH that were identified by [McCord et al., 1998]. There is a very slight reddening in the .7 to 2.5-micron region with increasing phase angle (from about 5o to about 96o). By using all available high-spatial resolution observations of Callisto by NIMS from widely different regions we will report on the spectral nature of the non-ice material for ~ 10 to 50 km2 areas. By investigating the spectral nature of the non-ice material in localized areas we have investigated 1) spectral dependencies of the non-ice material that are associated with geologic features, 2) local variations in relative concentrations of the trace materials such as CO2 and SO2, and 3) a possible phase angle dependency at a smaller spatial scale then previously analyzed. Finally, we have made qualitative bulk compositional suggestions by comparing the non-ice spectra with spectra of analogue materials such as carbonaceous chondritic material (e.g. Johnson and Fanale, [1973]; Calvin and Clark, [1991]) and oxyhydroxides.
Hansen Gary B.
Hibbitts Ch. A.
McCord Th. B.
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