Projectile preservation during oblique hypervelocity impacts

Daly, R. T. and Schultz, P. H.

Meteorit Planet Sci. . doi:10.1111/maps.13081


“Impact angle plays a significant role in determining the fate of the projectile. In this study, we use a suite of hypervelocity impact experiments to reveal how impact angle affects the preservation, distribution, and physical state of projectile residues in impact craters. Diverse types of projectiles, including amorphous silicates, crystalline silicates, and aluminum, in two sizes (6.35 and 12.7 mm), were launched into blocks of copper or 6061 aluminum at speeds between 1.9 and 5.7 km s−1. Crater interiors preserve projectile residues in all cases, including conditions relevant to the asteroid belt. These residues consist of projectile fragments or projectile‐rich glasses, depending on impact conditions. During oblique impacts at 30° and 45°, the uprange crater wall preserves crystalline fragments of the projectile. The fragments of water‐rich projectiles such as antigorite remain hydrated. Several factors contribute to enhanced preservation on the uprange wall, including a weaker shock uprange, uprange acceleration as the shock reflects off the back of the projectile, and rapid quenching of melts along the projectile–target interface. These findings have two broader implications. First, the results suggest a new collection strategy for flyby sample return missions. Second, these results predict that the M‐type asteroid Psyche should bear exogenic, impactor‐derived debris. “