Other
Scientific paper
Sep 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008dps....40.5906h&link_type=abstract
American Astronomical Society, DPS meeting #40, #59.06; Bulletin of the American Astronomical Society, Vol. 40, p.506
Other
1
Scientific paper
We have been calibrating and rectifying the Galileo-NIMS spectral images from Ganymede, the largest Jovian satellite. The spectral range of NIMS is from 0.8 to 5.3 μm, covering many overtone and some fundamental absorption bands of materials in reflected sunlight. The calibration involves determining detailed dark levels and patterns, applying an appropriate radiometric calibration, and sometimes modifying missing or incorrect navigation parameters. We have recalibrated 20 of the total of about 27 Ganymede NIMS observations to date, and are working on the last handful. After recalibration, we make amorphous-crystalline maps and grain size measurements as described for eight small points in Hansen and McCord (2004). The model includes linear mixing of ice and non-ice, which is appropriate for most of Ganymede due to thermal segregation of bright (ice) and dark (non-ice) materials. Using bi-directional scattering models for the water ice (with two distinct grain sizes possible), and overall and short-long wave scaled spectra of Ganymede, Europa and Callisto-like hydrated minerals, we can make high quality fits to each Ganymede spectra. Ultimately these maps of surface properties and other analysis (e.g., CO2 band-depth, tectonic lineaments and impact structures) will be combined in a global map of Ganymede in a GIS database being developed under another grant. The grain-size maps show larger grain sizes in the equatorial regions and on the trailing side, with leading side polar grain radii of 10 μm and trailing side equatorial grain radii of 80 μm or more. This is probably the result of micrometeorite gardening combined with particle radiation effects at the poles and on the trailing side. This research is funded through the NASA Outer Planets Research Program.
Hansen, G. B., and T. B. McCord (2004). J. Geophys. Res. 109, E01012, doi:10.1029/2003JE002149.
Hansen Gary B.
McCord Th. B.
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