Abstract

The Deep Impact flyby spacecraft includes a 1.08 to 4.5 μm infrared (IR) spectrometer. Although ice was not observed on surface in the impact region, strong absorptions near 3 μm due to water ice are detected in measurements of the ejecta from the impact event. Absorptions from water ice occur throughout the IR dataset beginning three seconds after impact through the end of observations, ~45 minutes after impact. Spatially and temporally resolved IR spectra of the ejecta are analyzed in conjunction with laboratory impact experiments. The results imply an internal stratigraphy for Tempel 1 consisting of devolatilized materials transitioning to unaltered components at a depth of approximately one meter. At greater depths, which are thermally isolated from the surface, water ice is present. Up to depths of 10 to 20 m, the maximum depths excavated by the impact, these pristine materials consist of very fine grained (1±1 μm) water ice particles, which are well-separated from refractory components.