Catastrophic Impacts in the Gravity Regime

Details Catastrophic Impacts in the Gravity Regime Catastrophic Impacts in the Gravity Regime

Mar 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996lpi....27..777l&link_type=abstract

Lunar and Planetary Science, volume 27, page 777

Astronomy and Astrophysics

Astrophysics

4

Collisions, Collisions: Asteroid, Disruptions: Collisional, Impacts, Models: Hydrodynamic

Scientific paper

The collisional evolution of the asteroids is often modelled by analogy with small-scale, strength dominated laboratory impact experiments. Recent calculations Holsapple, however, suggest that gravity dominates over strength in determining impact behavior for silicate objects larger than ~6 km diameter. Thus, results from strength dominated impacts may not apply to most numbered asteroids or to most meteorite parent bodies. To investigate catastrophic impacts (i.e., those that erode ~50% of the target's mass) on gravity dominated objects, we wrote a three-dimensional Smoothed Particle Hydrodynamics (SPH) computer code that includes a rigorous treatment of gravity. We modelled the impacts of variously sized silicate projectiles onto silicate targets 10 to 1000 km in diameter at impact speeds of 3, 5, or 7 km/s and angles of 15, 45, or 75 degrees. The impact energy is increasingly partitioned into projectile and target kinetic energy at higher impact speeds and larger projectile:target size ratios. Particle velocity distributions are complex in shape and evolve continuously throughout each simulation. The amount of material permanently ejected from the target is roughly proportional to the projectile mass when the speed, angle, and target size are held constant. The catastrophic threshold (Q*) for 50% target mass removal occurs at projectile kinetic energy per unit target mass (specific energy) equal to 8 x 10^3, 3 x 10^4, 8 x 10^4, 3 x 10^5, and 1.5 x 10^6 J/kg for target diameters of 10, 31.6, 100, 316, and 1000 km, respectively. Projectile material was not retained on targets smaller than 1000 km diameter. The collisions modeled here may launch ejecta into closed satellite orbits. Material strongly heated in our simulations usually escapes; the retained heat produces volume averaged impact heating of <10 degrees C per event for asteroids

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