[48.07] Comparing the size-frequency distributions of asteroid families to those produced by SPH/{\it N}-body impact simulations

36th DPS Meeting, 8-12 November 2004
Session 48 Asteroid Dynamics
Oral, Friday, November 12, 2004, 3:30-5:00pm, Clark

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[48.07] Comparing the size-frequency distributions of asteroid families to those produced by SPH/N-body impact simulations

D. D. Durda, W. F. Bottke, D. Nesvorný (SWRI), E. Asphaug (UCSC), D. C. Richardson (Univ. Maryland)

We investigate the morphology of size-frequency distributions (SFDs) resulting from impacts into 100-km diameter parent asteroids, represented by a suite of 160 SPH/N-body simulations conducted to study asteroid satellite formation (Durda et al. 2004; Icarus 170, 243-257). The spherical basalt projectiles range in diameter from 10 to 46 km (in equally-spaced mass increments in logarithmic space, covering six discrete sizes), impact speeds range from 2.5 to 7 km/s (generally in 1 km/s increments), and impact angles range from 15^\circ to 75^\circ (nearly head-on to very oblique) in 15^\circ increments. For a given impact speed, the shape of the SFD tends to be more ``concave" for the smallest impactors (cratering events) and more ``convex" for the largest impactors (supercatastrophic disruption). At the transition point where ``concave" cratering SFDs begin to transform into more linear power law SFDs, the largest remnant has a diameter of ~ 20 km. That transition occurs at smaller impactor sizes for greater impactor speeds and at greater impactor sizes for larger impactor angles. Impacts that maximize the number of similar-size largest remnants (at ~ 20 km) occur at impact speeds of 6-7 km/s with 25-34 km diameter impactors; larger impactors at higher speeds are required to achieve the same results for oblique impacts as for smaller impactors at lower speeds impacting more nearly head-on. The SFDs with the very shallowest slopes overall derive from impacts at about 4-6 km/s with 25-34 km diameter impactors. These modeled SFD morphologies match very well the observed SFDs of actual asteroid families. We find that there are ~ 20 families produced by catastrophic breakups in the main belt from D > 100 km parent bodies. This suggests that the threshold specific energy, Q^*_D, is very close to that predicted by Benz and Asphaug (1999; Icarus 142, 5-20).

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