Ejection velocities of ice fragments in oblique impacts of ice spheres

Reaccumulation conditions of icy planetesimals in collisional disruption were studied experimentally using a one-stage light gas gun set in a cold room (-18 degrees C). Oblique impacts between ice spheres were used to measure the velocity distributions of fragments. The impact velocities ranged from 170 to 640 m/s, and the projectile-to-target mass ratio was a constant and equal to 0.13. The collisional disruption was observed by ultra-high speed photography at a rate of 2x10(5) to 1x10(4) frames/s. As a result, we found that the minimum ejection velocity was related to the specific energy and the impact angle by: V-min = 0.092Q'(0.65), where Q' = Q(cos theta)(5).Q is the specific energy defined as a ratio of projectile kinetic energy to target mass. On the other hand, high velocity ejecta caused by jetting was observed around the impact point, and the normalized maximum velocity was found to range from 1.6 to 3.1, irrespective of impact angle and impact velocity. The reaccumulation conditions were estimated in oblique impacts of 480 m/s with a mass ratio of 0.13 by comparing the ejecta velocity with the escape velocity of the icy planet. As a result, it was clarified that icy planets with radii larger than 100 km can capture most of the fragments in collisions with impact angles from 0 to 50 degrees. (C) 1999 COSPAR. Published by Elsevier Science Ltd.