Equation of state controls on pressure relaxation during hypervelocity impact cratering: insights from smoothed particle hydrodynamics simulations

초록

Hypervelocity impacts of asteroids and comets generate pressures of several hundred gigapascals, producing extreme pressure-temperature conditions responsible for shock metamorphism and high-pressure mineral formation. Numerical modeling of impact processes commonly employs different equations of state (EOS), with peak pressure and pressure-time evolution serving as primary metrics for interpreting shock conditions. However, systematic comparisons of pressure relaxation behavior and decompression pathways across different EOS under identical impact conditions remain limited. Moreover, the temporal development of pressure under varying impact angles requires further quantitative evaluation. In this study, we performed smoothed particle hydrodynamics simulations of a 1-km-diameter dunite projectile impacting a granite target at 18 km/s. Vertical (90 degrees) and oblique (45 degrees) impacts were modeled using the Tillotson, Mie-Gr & uuml;neisen, and Stiffened Gas EOS. Across both impact angles, peak pressures remained on the order of several hundred gigapascals in the target (similar to 330-480 GPa) and projectile (similar to 280-520 GPa). In contrast, pressure relaxation patterns during decompression differed substantially. The Tillotson EOS exhibited the most rapid pressure relaxation, whereas the Mie-Gr & uuml;neisen EOS sustained elevated pressures longest. The Stiffened Gas EOS showed intermediate relaxation behavior. In oblique impacts, downrange migration of the contact zone resulted in sustained compressive loading and delayed peak-pressure formation, independent of EOS selection. High-pressure conditions persisted longer than in vertical impacts, resulting in prolonged pressure residence times. These results demonstrate that EOS selection and impact angle jointly control pressure-time trajectories rather than peak pressure alone. Our approach provides a reference for considering EOS-dependent pressure-temperature-time histories in future studies of natural impact craters.

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