An asteroid’s interior contributes to the response of its surface and shape to forces from space, including meteoroid impacts [e.g., Chapman 1996, Bottke et al. 2020], tidal effects [e.g., Hurford et al. 2016, Binzel et al. 2010], and solar radiation [Walsh et al. 2008]. Changes to asteroid surfaces from these external forces provide a record of the collisional and dynamical evolution of the inner Solar System [Bottke et al. 2020]. However, asteroid interiors remain poorly understood [Asphaug 2020].
(433) Eros is a 34 km x 11 km x 11 km diameter elongated near-Earth asteroid (NEA) with surface expressions that suggest a heavily fractured yet coherent interior, as evidenced by craters formed with structural control [Prockter et al. 2002] and by surface lineaments [Buczkowski et al. 2008], which are common features on 10-km-scale asteroids observed by spacecraft [Veverka et al. 1994, Barucci et al. 2015] that may be surface expressions of widespread interior fractures.
Here we report on measurements of the degradation of the D > 500 m crater population in the vicinity of the 7.5-km-diameter Shoemaker crater, indicating that seismic surface waves and crater ejecta, rather than seismic body waves [Richardson 2005, Thomas & Robinson 2005], erased craters with D < 500 m only up to 10 km away from the crater center. We use crater degradation measurements to estimate a surface wave seismic diffusivity of 0.02 km2/s for Eros regolith.
We determine from these observations that 10-100-km scale fractured asteroids strongly attenuate impact-induced seismic surface waves and seismic resurfacing is limited to local regions, less that 3 crater radii from the impact point.
Our results indicate that Shoemaker crater formed 6.5–31.8 Ma, while Eros was in a main-belt resonance zone. The age of Shoemaker crater coincides with the cosmic ray exposure age of some ordinary chondrites and the returned samples from the 0.3-km-diameter, S-type NEA Itokawa [Nagao et al. 2011]. The concurrence of ages suggests that large cratering impacts on to 10-km scale asteroids are an important source of NEAs and meteorites.