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O.S. Barnouin-Jha, A.F. Cheng (The Johns Hopkins University Applied Physics Laboratory)
Collisions play an important role in influencing the evolution of asteroids. The history of these collisions is documented in crater distributions observed over the surface of asteroids, which integrate the impact flux it has experienced. This flux depends on the asteroid's orbital and spin-axis evolution, its surface properties, and its impactor population. This study predicts variations in impact flux and hence crater distribution over the surface of asteroids by calculating the directions and magnitudes of impact velocities on objects within the inner solar system. Combining these predictions to observed distributions and morphologies of craters should improve our understanding of the collisonal, orbital and spin axis evolution of asteroids as well as of the structure and populations of the asteroid belt.
Previous estimates of impact flux and cratering distributions have been based on the Opik method and extensions of it. These studies define a target volume, within which collisions are possible, based upon the size of a target asteroid and its Keplerian elements. In the current study, a new method is used to compute the distribution of impacts. Instead of defining a target volume, a number of elementary areas dA are defined on a triaxial ellipsoid representing a target asteroid. We then assume that the known asteroids with absolute magnitude H > 15 trace the total population of impactors in the inner solar system. By constructing a table of these known asteroids in semi-major axis, eccentricity and inclination, we compute the probability that dA of the target asteroid will be impacted at a specified speed and direction. This probability permits computing the impact flux and crater number distribution averaged over the target asteroid's orbit and spin.
As a test, we apply our model to observation of asteroid [243] Ida. We also predict the crater distribution on [433] Eros for various models of its orbital and spin pole evolution.