Effects of ejecta accumulation on the crater population of asteroid 433 Eros

Abstract

The crater population of asteroid 433 Eros exhibits a deficit in small crater diameters that has been suggested to result from impact-induced seismic shaking initiating downslope movements of regolith material, covering these small craters. As in lunar maria, saturation equilibrium was expected to characterize the crater population of Eros, but was surprisingly not shown by the data set. The surface of Eros displays evidence of burial by regolith especially for boulders, suggesting that ejecta coverage erases the craters in addition to seismic shaking erasure. In this work we investigate the production and erasure of craters by impact ejecta and compare derived crater size distributions with those measured for Eros. We simulate a bombardment of Eros by an impactor population derived from the Main Asteroid Belt and estimate the crater and ejecta characteristics with a scaling law, allowing ejecta to progressively create a regolith blanket. Assuming the contribution of the ejecta blanketing process only, we find a good agreement between the simulated and the observed population of 250 m to 4 km diameter craters for exposure times of 600 Ma and 400 Ma. This suggests a major impact or breakup that occurred about 500 Ma ago, inducing a surface reset. A mismatch for craters with a diameter smaller than ∼100 m remains, indicating that seismic shaking (or another erasure process) is still necessary to explain their low number. Our simulations emphasize the importance of an accurate modeling of both processes to fully understand and interpret the small body size-frequency crater curves. Copyright 2009 by the American Geophysical Union.