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J.E. Richardson, H.J. Melosh, R. Greenberg (Lunar and Planetary Laboratory)
High-resolution images of the surface of asteroid 433 Eros revealed evidence of downslope movement of a loose regolith layer, as well as the degradation and erasure of small impact craters (< 100 m diameter). One hypothesis to explain these observations is seismic reverberation following impact events. We use a combination of seismic and geomorphic modeling to analyze the response of regolith-covered topography, particularly craters, to impact-induced seismic shaking. Applying these results to a stochastic cratering model for the surface of Eros produces good agreement with the observed size-frequency distribution of craters, including a paucity of small craters. The lack of small craters is the result of seismic erasure, causing lower equilibrium count values than would otherwise be expected. Additionally, this low equilibrium level is a sensitive function of the assumed thickness of the mobilized regolith layer, for which we find a best fit corresponding to a thin 0.1 m: significantly less than the estimates of an average loose regolith thickness of 20-40 m from the NEAR observations. We infer from this that much of the regolith layer possesses a depth-dependent porosity and cohesion gradient (perhaps due to compaction from seismic shaking) causing the layer to slide at shallow depths. Despite uncertainties with regard to the asteroid’s true seismic and regolith properties, this work places constraints on these properties and demonstrates the ability of impact-induced seismic shaking of the asteroid to destabilize slopes, cause regolith to migrate downslope, and degrade or erase small craters.
The author(s) of this abstract have provided an email address for comments about the abstract: jrich@lpl.arizona.edu
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.