DPS Pasadena Meeting 2000, 23-27 October 2000
Session 8. Asteroid Posters I - Physical Studies
Displayed, 1:00pm, Monday - 1:00pm, Friday, Highlighted Tuesday and Thursday, 3:30-6:30pm, C101-C105, C211

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[8.03] Asteroid depletion by collisions

O.S. Barnouin-Jha, Andrew Cheng (The Johns Hopkins University Applied Physics Laboratory)

A new numerical method is used to compute the distribution of impacts on the surface of asteroids. This method traces potential impactor orbits to asteroids and comets from triangular elementary areas defined on a triaxial ellipsoid representing a target asteroid. It then determines the probability that the potential impactor collides with the target surface area. Preliminary tests of this method show on a spherical target asteroid: (1) expected changes in impact flux as a function of the orbital semi-major axis, (2) expected differences in trailing versus leading edge impact flux as a function of position relative to the asteroid belt, and (3) an expected sin(2*theta) impact angle distribution over the entire asteroid.

The new numerical method also shows that impactors with low orbital eccentricity and low inclination are far more likely to collide with a target asteroid anywhere in the asteroid belt. We performed a statistical analysis and determined that relative to an assumed uniform random distribution of asteroids, observed asteroid are in fact depleted at low eccentricity and inclination.

We further examine the implications of this discovery using our new computational method. We investigate the distribution of impact velocities and crater production rates on Ida, Mathilde and Eros. Preliminary results show equilibrium crater densities are reached on Ida for D < 500 m within the lifetime of the asteroid belt, mainly by very low impact velocities ranging from 0 to 1 km/s. Higher average impact velocities on Ida are achievable if we eliminate low eccentricity and inclination orbits from the model. However, contrary to observation, Ida would not achieve equilibrium crater densities for D < 500 m. We can reconcile this discrepancy if low eccentricity and inclination asteroids were present earlier in the history of the solar system. If this scenario is correct, hypervelocity impacts (> 5 km/s) on asteroids may be infrequent compared to low velocity impacts of the distant past with implications for the style of cratering, block formation and fragmentation of asteroids.

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