Cratering experiments on the self armoring of coarse-grained granular targets
Cratering experiments on the self armoring of coarse-grained granular targets
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DOI：
10.1016/j.icarus.2012.06.041
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发表时间：
2012-08-01
期刊：
影响因子：
3.2
通讯作者：
Nakamura, A. M.
中科院分区：
文献类型：
--
作者：
Guettler, C.;Hirata, N.;Nakamura, A. M.
最近发表的小行星25143 Itokawa和433 Eros的陨石坑统计数据显示，大约在2000年之前，陨石坑的数量显著减少。直径100米。人们提出的解释这种缺乏陨石坑的可能机制是地震陨石坑擦除和粗糙的自我装甲，巨石覆盖的小行星表面。虽然地震震动已经在这方面进行了研究，但装甲的概念缺乏更深入的检查和实验基础。因此，我们提出了玻璃珠弹丸撞击颗粒玻璃珠目标，其中弹丸和目标的晶粒尺寸在一个相似的范围内的弹坑实验。冲击速度在200-300 m/s（-1）的范围内。我们发现，弹坑变得暗淡和不规则的形状，只要目标颗粒大于弹丸的尺寸和颗粒的弹坑很少形成时，弹丸和目标颗粒之间的尺寸比约为1：10或更小。在这种情况下，我们观察到在第一次撞击的目标颗粒中形成强度确定的弹坑。我们提出了一个简单的模型的基础上转移的动量从弹丸到这个第一个目标颗粒，这是能够解释我们的结果，只有一个单一的自由参数，这是而且很好地确定了以前的实验。基于对Itokawa和Eros上典型的弹丸尺寸和巨石尺寸的估计，考虑到我们的结果对于km/s（-1）的撞击速度也具有代表性，铠装应该在它们的演变中发挥重要作用。(C)2012 Elsevier Inc. All rights reserved.
Recently published crater statistics on the small Asteroids 25143 Itokawa and 433 Eros show a significant depletion of craters below approx. 100 m in diameter. Possible mechanisms that were brought up to explain this lack of craters were seismic crater erasure and self armoring of a coarse, boulder covered asteroid surface. While seismic shaking has been studied in this context, the concept of armoring lacks a deeper inspection and an experimental ground truth. We therefore present cratering experiments of glass bead projectiles impacting into granular glass bead targets, where the grain sizes of projectile and target are in a similar range. The impact velocities are in the range of 200-300 m s(-1). We find that craters become fainter and irregular shaped as soon as the target grains are larger than the projectile sizes and that granular craters rarely form when the size ratio between projectile and target grain is around 1:10 or smaller. In that case, we observe a formation of a strength determined crater in the first struck target grain instead. We present a simple model based on the transfer of momentum from the projectile to this first target grain, which is capable to explain our results with only a single free parameter, which is moreover well determined by previous experiments. Based on estimates of typical projectile size and boulder size on Itokawa and Eros, given that our results are representative also for km s(-1) impact velocities, armoring should play an important role for their evolution. (C) 2012 Elsevier Inc. All rights reserved.