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Catastrophic Collisions
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The response of cm-scale laboratory impact experiment targets to catastrophic collisions (those removing ~50% of the target's mass) is governed by material strength, while the impact behavior of ~10 km-scale planetary bodies depends on gravity. The boundary between strength and gravity dominance in catastrophic impacts lies at some intermediate size; estimates of that size for silicate bodies range from ~6 km to~100 km diameter. We extrapolate our new Smoothed Particle Hydrodynamics (SPH) catastrophic impact simulation results (Love and Ahrens 1996, "Catastrophic impacts on gravity dominated asteroids," Icarus 124, 141-155) for 10 to 1000 km diameter bodies to smaller sizes, yielding a new estimate of the boundary diameter: 250±150 m. The uncertainty reflects incomplete understanding of how strength decreases with increasing target size. The catastrophic impact specific energies (Q*) at these sizes are ~40 to ~200 J/kg. Our results imply that most numbered asteroids are gravity dominated, that bodies <1 km across may be gravity bound rubble piles rather than solid monoliths, and that km-sized Earth-approaching asteroids may have disruption energies higher than previously estimated (Fig 16). | ||||||
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