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P. H. Schultz, C. M. Ernst, C. A. Eberhardy (Brown University), J. M. Sunshine (SAIC), M. F. A'Hearn (U. Maryland), Deep Impact Team
NASA’s Deep Impact mission was the first planned, hypervelocity probe designed to use its kinetic energy (19 gigajoules) to expose material from below a planetary body, specifically comet 9P/Tempel 1. The formation of the crater and the amount of ejecta also provide important data for the nature of the surface and subsurface through the observed response. Key observations include the amount of debris ejected, size of the crater, evolution of the ejecta (spatially and temporally), spectral emissions, and photometry. Laboratory impact experiments at the NASA Ames Vertical Gun Range provide one approach to calibrate this response. Based on such comparisons, the Deep Impact crater was formed by excavation of a loosely bonded, porous material with its final size largely controlled by the weak gravitational acceleration of the comet. The impact angle of 30° resulted in an asymmetric ejection of debris, including: a high-velocity (8-10km/sec) vapor plume traveling downrange, an uprange-directed plume, a high-angle ejecta plume of cooler debris, and an asymmetric curtain of ejecta from depth that became more symmetric with time. The evolution of the initial flash, convergence pattern for ejecta rays, and the downrange-moving center of symmetry are consistent with a highly porous upper surface (<0.3 g/cm3).
This work was funded by NASA through the Deep Impact project.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.