[Previous] | [Session 31] | [Next]
P. H. Schultz (Brown University)
In 2005, the Deep Impact Mission will witness the collision of a 350kg impactor into Comet P-Temple 1. Laboratory impact experiments provide scaling laws that relate impactor mass to crater diameter and depth for various target and impactor properties. A series of experiments have been performed at the NASA Ames Vertical Gun Range in order to assess the effects of the density and impedance ratio between target and impactor, target compressibility, target porosity, and impact angle. Although the maximum velocity achievable in the laboratory is below that for Deep Impact (7km/sec versus 10.3 km/sec), varying impactor diameter and velocity allows extrapolating beyond this range, for certain assumptions. This approach has been used for various particulate targets including pumice (1.1 to 1.5 g/cc, sand (1.7g/cc), vermiculite (0.09 g/cc), and micro-spheres (0.05g/cc), which provide the maximum possible diameter produced on Temple 1. Smaller sizes are expected if strength, rather than gravity, controls limits of crater growth or if internal energy losses (e.g., pore-space collapse) reduce the coupling efficiency. Crater size also can be augmented through back pressures created by vapor expansion within the crater cavity. The maximum predicted crater diameters (without back pressure) for the DI impact into a 0.3 g/cc porous target are: 89 m (pumice), 124 m (fine sand), 98m (fine sand with compaction losses). Formation times approach 200 seconds. Crater size, plume evolution (size and photometry), formation time, ejection (curtain) angle, and the ejecta deposit will all contribute to meaningful interpretations of the near-surface properties.