Abstract
Measurements made by the Galileo Near Infrared Mapping Spectrometer
(NIMS) have been used to calculate reflectance spectra for regions
of Europa. Many of these spectra show features indicative of water
ice. Others show asymmetric H2O absorption features suggesting hydrated
non-ice constituents such as hydrated sulfates and carbonates. Often,
both types of features are present. However, some previously published
NIMS spectra with strongly developed ice features did not show the
expected 1.04-mu m ice absorption band. This discrepancy has led
to questions regarding earlier interpretations of Europa's spectral
features. Recent work reveals that unexpected changes have occurred
in the spectral range covered by each NIMS detector and that an additional
calibration is required. Preliminary calibration values are given.
When this new calibration is applied, the 1.04-mu m feature emerges
clearly in those spectra where it was expected but absent previously,
thereby resolving the 1.04-mu m band discrepancy.
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