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We investigate the patterns observed in ejecta curtain induced byhypervelocity impact (2-6 km/s) with a variety of the size and shape of targetparticles. We characterize the patterns by an angle, defined as the ratio ofthe characteristic length of the pattern obtained by Fourier transformation tothe distance from the impact point. This angle is found to be almost the sameas that obtained by the reanalysis of the patterns in the previous study atlower impact velocities (Kadono et al., 2015, Icarus 250, 215-221), which areconsistent with lunar crater-ray systems. Assuming that the pattern is formedby mutual collision of particles with fluctuation velocity in excavation flow,we evaluate an angle at which the pattern growth stops and show that this angleis the same in the order of magnitude as the ratio of the fluctuation velocityand the radial velocity. This relation is confirmed in the results ofexperiments and numerical simulations. Finally, we discuss the dependence ofthe patterns on impact conditions. The experiments show no dependence of theangle on impact velocity. This indicates that the ratio between the fluctuationand radial velocity components in excavation flow does not depend on impactvelocity. Moreover, the independences on particle size and particle shapesuggest that the angle characterizing the structure of the patterns does notdepend on cohesive force. Since cohesive forces should be related with elasticproperties of particles, the structure does not depend on elastic properties,though inelastic collisions are important for the persistence and contrast ofthe patterns.

Crater-ray formation through mutual collisions of hypervelocity-impact induced ejecta particles