Velocity distribution of high velocity small fragments produced in collisional disruption of simulated small bodies

在由星子形成行星的过程中，在许多小天体之间发生大规模灾难性破坏的许多结果中，碎片的速度分布是一个特别基本的量。在本研究中，我们在实验室进行了小尺度的高速碰撞实验，并试图系统地获得产生的碎片的速度分布。在实验中，小型尼龙球（直径7mm）被两级光气枪以2 - 4km/s的速度加速到球形玄武岩和石膏目标上。撞击中产生的碎片的运动被一台高速帧速摄像机记录了下来。还有一个频闪系统。在图像分析仪的辅助下，测定了尺寸大于1毫米的碎片的速度。在此粒径范围内，碎块速度小于100m/s左右，与玄武岩和灰岩碎块粒径的-1/3 ~ -1/16次方成正比。为了将其他实验结果外推到更大规模的碰撞中，我们做了一些考虑和实验。首先，小行星族之间轨道元素的分散表明，小行星族是以大约几百米/秒的速度从母小行星喷射出来的。这一事实（碎片较大，速度较快）与我们的实验结果（碎片较小，速度较慢）之间的明显矛盾应归因于激波上升和下降时间的差异；与实验室规模相比，它们在大规模碰撞中变得更长。由于破片速度与冲击波的传播和破坏过程密切相关，；并对曲面上的凹坑形成机理进行了研究。今后，有必要进行不同弹丸尺寸的冲击实验，建立适用于更大规模冲击破坏的速度分布规律。

Velocity distribution of the fragments is an especially fundamental quantity among many outcomes of the large scale catastrophic disruptions airong many small bodies during the formation the planets from planetesimals. In this study we made sirall scale high-velocity collsion experiments in the laboratory, and tried to obtain the velocty distribution of the produced fragments systematically. In the experiments, small nylon spheres (7mm in diameter)were accelerated by a two-stage light-gas gun at velocity 2 - 4km/s against spherical basalt and plaster targets. t4ovement of the fragments produced in the impact was recorded by a high-speed framiriq camera. and a strobe system. The velocities of the fragments of size larger than lmm were determined with the aid of an image-analyzer. The velocity of tl) ne fragments in this size range is less than about 100m/s, and proportional to -1/3 - -1/16 th power of the fragment size both for basalt and plaster tcirgets. To extrapolate other experimental results to the larger scale collisions, we made some considerations and experiments. First, dispersion of the orbital elements among asteroid families shows tliat family asteroids have been ejected from their parent asteroid at velocities of about a few hundred m/s. The apparent contradiction between this fact (larger fragments with higher velocity) and our experimental results (smaller fragments with lower velocity) should be attributed to the difference of rising' and falling time of the shock wave ; they become longer for large scale collision compared witti the laboratory scale. As the fragment velocity is closely related with the propagation of the shock wave and destruction' process, ; 4f-also studied on the mechanism of the cratering on curved surfaces. I'n the future, it is necessary to do impact experiments with varying projectile size to establish a scalitiq law for the velocity distribution which can be applicable for the larger scale impact disruption.