Analysis of the contact compression stage and ejecta motion in oblique impact cratering of meteorites

Craters on planetary surfaces typically result from oblique impacts of meteorites. The impact angle influences both the pressure-temperature distribution within the crater and the ejection motion. Consequently, these characteristics are crucial for understanding cratering due to meteorite oblique impacts. Previous studies indicate that the finite element-smoothed particle hydrodynamics (FE-SPH) adaptive coupling method enhances the simulation of ejecta details. Accordingly, this study utilizes the FE-SPH adaptive method to simulate the contact compression stage of meteorite oblique impacts at angles of 15°, 30°, 45°, and 60°. The simulated results demonstrate that the impact angle affects both the location and shape of the initial impact crater, as well as the ejecta distribution during the contact compression stage. Additionally, a cosine relationship between the ejecta distribution around the crater and the azimuthal angle was established using the Fourier series model. Furthermore, analysis of the temperature and pressure evolution revealed a relationship between the impact angle and the pressure-temperature peaks, validating the simulation results. We also observed temperature stratification in the ejecta which results in varying metamorphic characteristics of the ejecta at different impact angles. Based on the analysis of the jet motion, we proposed an oblique impact jet sequence model. This model illustrates the relationship between the jet sequence and impact angle, clarifies the mechanisms of jet temperature stratification, and connects these phenomena to the maximum jet velocity, which initially increases and then decreases with the impact angle. By integrating the shock wave propagation process, we introduced the concept of projectile grazing ejection and the critical grazing formula. This explains the extensive ejection of the projectile during low-angle impact.