Simulation of Impact-induced seismic shaking on asteroid (25143) Itokawa to address its resurfacing process

TL;DR

This work tests whether seismic shaking from the Kamoi crater-forming impact could drive Itokawa’s observed spatial variation in space weathering and constrain its interior. By coupling a 3D diffusion-based seismic-energy propagation model on a realistic Itokawa shape with a simplified landslide toy model, the authors estimate surface accelerations and boulder displacements. They find that even low-energy seismic input can destabilize surface materials and that resulting boulder motions reproduce the global and regional weathering patterns, implying a seismic diffusivity of $K \approx 10^3$–$2\times10^3~\mathrm{m^2 s^{-1}}$ and seismic efficiency $\eta \approx 5\times10^{-8}$–$5\times10^{-7}$, consistent with a strongly scattering rubble-pile interior containing tens-of-meter-scale blocks. These results support the hypothesis that Itokawa’s fresh terrains can arise from impact-induced seismic resurfacing, and they demonstrate that space weathering distributions can serve as dynamical diagnostics of asteroid interiors, with potential applications to other rubble-pile bodies in future missions.

Abstract

The surface of asteroid (25143) Itokawa shows both fresh and mature terrains, despite its short space weathering timescale of approximately 1000 years, as inferred from recent studies. Seismic shaking triggered by the impact that formed the 8-meter Kamoi crater has been proposed as a possible explanation for the diversity. This study aims to examine whether the seismic shaking induced by the impact could account for the observed spatial variations in space weathering and further constrain the internal structure of Itokawa. Assuming that the Kamoi crater was formed by a recent impact, we conducted three-dimensional seismic wave propagation simulations and applied a simplified landslide model to estimate surface accelerations and boulder displacements. Our results show that even a low-energy case (1 % of the nominal seismic energy) produces surface accelerations sufficient to destabilize the surface materials. The simulated boulder displacements are consistent with the observed distribution of space weathering degrees even on the opposite hemisphere. We estimate the seismic diffusivity to be 1000-2000 m2 s-1 and the seismic efficiency to be in the range of 5.0 x 10-8 to 5.0 x 10-7, implying that Itokawa's interior contains blocks tens of meters across and acts as a strongly scattering medium.

Figures (11)

• Figure 1: 3D views of (a) the original shape model of Itokawa with 49 152 facets from Gaskell2020, and (b) the simplified model with 1 024 facets used in this study. The blue star denotes the location of the Kamoi crater. Red (A) and green (B) facets correspond to facet numbers 152 and 93, respectively, and are used for comparison in Fig. \ref{['fig:acceleration']} and Fig. \ref{['fig:x_facet']}
• Figure 2: Surface acceleration on the Kamoi (western) side (a-d) and the opposite (eastern) side (e-h) caused by seismic wave propagation at (a, e) 0 s (initial condition), (b, f) 0.1 s, (c, g) 0.4 s, (d, h) 10 s after the impact.
• Figure 3: Time-varying acceleration experienced by each facet. (a) Acceleration at facet number 152 for different diffusivity values: $K = 1\,000~\mathrm{m^{2}\,s^{-1}}$ (Simulation 2, dotted), $K = 2\,000~\mathrm{m^{2}\,s^{-1}}$ (Simulation 1, solid), and $K = 3\,000~\mathrm{m^{2}\,s^{-1}}$ (Simulation 3, dashed). (b) Acceleration at facet number 152 for different seismic efficiency values: $\eta = 5.0 \times 10^{-8}$ (Simulation 5, dotted), $\eta = 1.0 \times 10^{-7}$ (Simulation 1, solid), and $\eta = 5.0 \times 10^{-7}$ (Simulation 8, dashed). (c, d) Same as (a, b), respectively, but for facet number 93. The horizontal dotted line represents the gravitational acceleration at each facet. The vertical dashed line marks $t = 10$ seconds, when the simulation ends and exponential decay extrapolation begins.
• Figure 4: Ratio of maximum surface acceleration to local gravitational acceleration on the Kamoi side (Western; panels a–d) and the opposite side (Eastern; panels e–h) for different $\eta$ values. All simulations assume a constant $K$ value of 2,000. Panels are arranged such that $\eta$ decreases from left to right. Each column corresponds to an $\eta$ value of $5\times10^{-7}$, $1\times10^{-7}$, $5\times10^{-8}$, and $1\times10^{-9}$, respectively.
• Figure 5: Ratio of maximum surface acceleration from simulations with extremely low ($K = 200~\mathrm{m^{2}\,s^{-1}}$, panels a, c) and high ($K = 200\,000~\mathrm{m^{2}\,s^{-1}}$, panels b, d) diffusivity values with respect to the nominal case. Panels (a) and (b) show the Kamoi side, while panels (c) and (d) show the opposite side.