Expectations for Crater Size and Photometric Evolution from the Deep Impact Collision |
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Authors: | Peter H Schultz Carolyn M Ernst Jennifer L B Anderson |
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Institution: | (1) Department of Geological Sciences, Brown University, Providence, RI, 02912-1846, U.S.A. |
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Abstract: | The NASA Discovery Deep Impact mission involves a unique experiment designed to excavate pristine materials from below the
surface of comet. In July 2005, the Deep Impact (DI) spacecraft, will release a 360 kg probe that will collide with comet
9P/Tempel 1. This collision will excavate pristine materials from depth and produce a crater whose size and appearance will
provide fundamental insights into the nature and physical properties of the upper 20 to 40 m. Laboratory impact experiments
performed at the NASA Ames Vertical Gun Range at NASA Ames Research Center were designed to assess the range of possible outcomes
for a wide range of target types and impact angles. Although all experiments were performed under terrestrial gravity, key
scaling relations and processes allow first-order extrapolations to Tempel 1. If gravity-scaling relations apply (weakly bonded
particulate near-surface), the DI impact could create a crater 70 m to 140 m in diameter, depending on the scaling relation
applied. Smaller than expected craters can be attributed either to the effect of strength limiting crater growth or to collapse
of an unstable (deep) transient crater as a result of very high porosity and compressibility. Larger then expected craters
could indicate unusually low density (< 0.3 g cm−3) or backpressures from expanding vapor. Consequently, final crater size or depth may not uniquely establish the physical
nature of the upper 20 m of the comet. But the observed ejecta curtain angles and crater morphology will help resolve this
ambiguity. Moreover, the intensity and decay of the impact “flash” as observed from Earth, space probes, or the accompanying
DI flyby instruments should provide critical data that will further resolve ambiguities. |
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Keywords: | Deep Impact porous targets comets oblique impact NASA Ames Vertical Gun Range laboratory experiments Comet 9P/Tempel 1 |
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