File:Asteroid Impact Seismology.jpg

strength properties typical for crater scaling in lunar regolith (Y = 105 dyn/cm2). Note the monotonic trend increasing χ with asteroid diameter, for a given α—the proposed explanation for why larger asteroids have giant craters. Circles on each plot indicate the largest undegraded crater DL observed on each asteroid, from Table 1; if DL ∼ Dcrit this provides a direct estimate for velocity attenuation α in each asteroid. As noted in the text, for gravity scaling (Fig. 2a), asteroids of low density, or otherwise suspected of being highly porous (e.g., Mathilde, Phobos, Dactyl), appear to have the lowest attenuation coefficients. Deimos has anomalously low attenuation according to the model (α = 1.17), perhaps because it is anomalously young following a global resurfacing event and has not attained critical crater equilibrium. For strength scaling (Fig. 2b), Y = 105 dyn/cm2 is adopted as a typical strength of regolith-like materials. Interestingly, for most of the larger asteroids strength scaling gives about the same derived α as gravity scaling. Asteroids as small as Itokawa and Dactyl can only sustain their largest craters in the strength regime if they have high levels of attenuation even at seismic particle velocities.