Shock Melting and Melt Deposit Patterns in Oblique Impacts: Insights From Numerical Simulations

Abstract

Hypervelocity impacts induce shock melting and distribute melted materials across planetary surfaces. The impact angle significantly affects melt production and ejecta formation, but systematic studies of these processes in oblique impacts are limited. Here, we employ the shock physics code iSALE-3D to systematically simulate shock melting, crater excavation, ejection, and melt deposition under lunar gravity conditions with varying impact angles (10°–90°) and impactor diameters (1–30 km), producing transient craters with diameters ranging from ∼10 to 200 km. Simulation results show that the total melt volume decreases by ∼25% when the impact angle drops from 90$°$ (i.e., vertical impact) to 45$°$, and by ∼85% when the angle reduces to 25$°$ (i.e., highly oblique impact). The ratio of ejected to generated melt generally remains constant for impact angles >25$°$, but increases significantly at lower impact angles. With more oblique impacts, melt deposits around craters gradually exhibit an uprange zone of avoidance, similar to the pattern of the entire ejecta blanket. Melt content within the ejecta generally increases with distance from the crater. For impact angles exceeding 45°, crossrange and downrange melt distributions closely resemble those generated by vertical impacts. Notably, our results demonstrate that impact angles <45$°$ produce considerably reduced melt quantity and melt fraction in ejecta relative to vertical impacts, underscoring the critical role of considering impact angle when examining melt production in impact cratering.