New calibrated dataset of the Galileo-NIMS observations of the Jovian satellite Ganymede and mapping of its water ice grain sizes and non-ice components

Details New calibrated dataset of the Galileo-NIMS observations of the Jovian satellite Ganymede and mapping of its water ice grain sizes and non-ice components New calibrated dataset of the Galileo-NIMS observations of the Jovian satellite Ganymede and mapping of its water ice grain sizes and non-ice components

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p51e1163h&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #P51E-1163

Other

[5422] Planetary Sciences: Solid Surface Planets / Ices, [5460] Planetary Sciences: Solid Surface Planets / Physical Properties Of Materials, [5464] Planetary Sciences: Solid Surface Planets / Remote Sensing, [6222] Planetary Sciences: Solar System Objects / Ganymede

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, sometimes modifying missing or incorrect navigation parameters, and removing radiation spikes. We have recalibrated 26 of the total of about 28 Ganymede NIMS observations to date, and are working on the last two that are affected by interference from parts of the spacecraft ("booms"). We make amorphous-crystalline maps as described previously and grain size measurements using the recalibrated spectra. The model includes linear mixing of ice and non-ice, which is appropriate for 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 for each place), and overall and short-long wave scaled spectra of Ganymede, Europa and Callisto-like non-ice minerals, we make high quality fits to each Ganymede spectra. 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 500 µm or more. This is probably the result of micrometeorite gardening combined with particle radiation effects at the poles and on the trailing side. The non-ice materials are consistent with the Ganymede hydrate over much of the equatorial regions becoming more hydrated (Europa-like) at latitudes >45 degrees. Callisto non-ice material occurs fractionally in the vicinity of dark ray craters. This research is funded through the NASA Outer Planets Research Program.

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