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Catastrophic impacts on gravity dominated asteroids

Love, Stanley G. and Ahrens, Thomas J. (1996) Catastrophic impacts on gravity dominated asteroids. Icarus, 124 (1). pp. 141-155. ISSN 0019-1035. doi:10.1006/icar.1996.0195.

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We use the smoothed particle hydrodynamics method to simulate catastrophic collisions on silicate bodies whose impact response is dominated by gravity rather than material strength. Encounter speeds of 3, 5, and 7 km sec^(−1), impact angles of 15°, 45°, and 75°, and target diameters of 10 to 1000 km are investigated. The projectile and target materials are modelled using the Tillotson equation of state for granite. Our model treats gravity rigorously, but neglects strength and fracture effects. We calculate the initial hydrodynamic phase of each event; after the impact shock wave crosses the target, particle motions are nearly ballistic and can be treated analytically. Material that does not escape may reaccrete ∼1 hr to ∼1 yr after the impact. The partitioning of impact energy into heat and motion of projectile and target material favors kinetic energy at higher speeds and larger projectile:target diameter ratios, but does not depend on the absolute size scale of the event. After the impact, most of the kinetic energy is carried by a small amount of fast ejecta. Particle velocity distributions are not sensitive to size scale and have complex, evolving shapes that are poorly represented by simple approximations. The catastrophic threshold (impact energy per unit target mass required to permanently eject 50% of the target against gravity) ranges from 8 × 10^3J kg^(−1) at 10 km diameter to 1.5 × 10^6J kg^(−1) at 1000 km, varying as target diameter to the 1.13 ± 0.01 power. Extrapolating these results suggests that gravity dominance extends to stony bodies as small 250 ± 150 m in diameter, smaller than previously believed. This result implies that asteroids as small as a few hundred meters across may be “rubble piles.” Nearly catastrophic impacts can exhume target core material and catapult surface rocks to the antipodes (“scrambling” the target), but selective removal of the outer layers is inefficient. Most material strongly heated in these impacts escapes, limiting globally averaged heating from a single collision to ≤50°C for asteroids ≤1000 km in diameter.

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Additional Information:© 1996 by Academic Press, Inc. Received February 2, 1996; revised June 21, 1996. We thank Klaus Keil, Ed Scott, Tim McCoy, and Henning Haack for helpful explanations and discussions, and Erik Asphaug and Paolo Paolicchi for thoughtful and helpful reviews of this paper. This research was supported in part by NASA. The Cray Supercomputer used in this investigation was provided by funding from the NASA offices of Mission to Planet Earth, Aeronautics, and Space Science. Stanley G. Love is an O. K. Earl Postdoctoral Research Fellow in Planetary Science. This paper is Contribution 5649 of the Division of Geological and Planetary Sciences at the California Institute of Technology.
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Caltech Division of Geological and Planetary Sciences5649
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Official Citation:Stanley G. Love, Thomas J. Ahrens, Catastrophic Impacts on Gravity Dominated Asteroids, Icarus, Volume 124, Issue 1, November 1996, Pages 141-155, ISSN 0019-1035, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:50700
Deposited By: Tony Diaz
Deposited On:23 Oct 2014 16:22
Last Modified:10 Nov 2021 18:59

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