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W.M. Grundy, J.R. Spencer, M.W. Buie (Lowell Obs.)
Near-infrared spectral observations of Europa emerging from Jupiter's shadow were obtained with IRTF\slash SpeX on 2001-01-21 and 2001-01-28 UT\null. We exploit temperature-dependent features in the near-infrared optical constants of water ice to determine the magnitude and rate of post-eclipse warming of water ice at Europa's surface. These measurements will be interpreted via radiative transfer and thermophysical models of icy regions of Europa's surface to constrain thermal inertias in these regions, with important implications for their near-surface mechanical properties.
The technique of remote thermometry via reflectance spectroscopy complements more conventional methods based on direct measurement of thermally emitted radiation, because reflectance spectroscopy preferentially probes areas having higher albedos and thus lower equilibrium temperatures, the opposite of the regions which dominate thermal emission.
During eclipse disappearances and re-emergences, Europa is briefly illuminated by sunlight which passes through Jupiter's atmosphere, and so shows absorption features due to Jovian CH4\null. This type of experiment could potentially provide a new way of probing the Jovian atmosphere.
This work was supported by NASA grants NAG5-9004 and NAG5-10159 to Lowell Observatory.