A formation mechanism for concentric ridges in ejecta surrounding impact craters in a layer of fine glass beads
A formation mechanism for concentric ridges in ejecta surrounding impact craters in a layer of fine glass beads
复制标题
一层细玻璃珠中撞击坑周围喷射物中同心脊的形成机制
DOI：
10.1016/j.icarus.2013.03.027
复制
发表时间：
2013
期刊：
影响因子：
3.2
通讯作者：
M.
中科院分区：
文献类型：
--
作者：
Suzuki;A. I.;Nakamura;A. M.;Kadono;T.;Wada;K.;Yamamoto;S.;& Arakawa;M.
喷出物的模式实验研究周围的陨石坑形成的玻璃珠层在低速垂直冲击。三种不同靶的组成玻璃珠的直径范围为53-63μm、90-106μm和355-500μm。撞击速度和环境压力的范围分别从几到240 ms − 1和从500 Pa到大气压。在陨石坑周围观察到各种喷出物模式，并根据它们是否有同心脊分为两大类。我们提出了一个可能的形成模型的脊，其中的尾流所产生的弹丸，因为它通过大气层造成的火山口边缘崩溃：该模型可以解释的观察结果，所产生的火山口边缘的崩溃程度取决于影响速度和环境压力。利用尾流引起的气流的流体阻力与轮缘退化部分的重力之比，计算了尾流侵蚀轮缘所需的冲击速度和环境压力的临界条件。这些条件与两个形态学类别之间的边界大致一致。因此，有可能是抛射体尾流触发了陨石坑边缘的坍塌，导致了一个拥抱地面的流动，沉降形成了本研究中观察到的远端脊。这一机制可能在有大气层的行星体上产生喷出物形态方面发挥作用。
Ejecta patterns are experimentally examined around craters formed in a layer of glass beads by vertical impacts at low velocities. The diameters of the constituent glass beads of three different targets range 53–63μm, 90–106μm, and 355–500μm. The impact velocities and ambient pressures range from a few to 240ms−1and from 500Pa to the atmospheric pressure, respectively. Various ejecta patterns are observed around craters and are classified into two major classes based on whether they have concentric ridges or not. We propose a possible formation model for the ridges in which the wake created by a projectile as it passes through the atmosphere causes the crater rim to collapse: The model can explain the observation that the degree of collapse of the resultant crater rim depends on the impact velocity and ambient pressure. Using the ratio between the hydrodynamic drag of the airflow induced by the wake and the gravitational force of the degraded part of the rim, we calculate the critical conditions of the impact velocity and ambient pressure necessary for the wake to erode the rim. The conditions turn out to be roughly consistent with the boundary between the two morphological classes. As a result, it is possible that the projectile wake triggers the collapse of the crater rim, leading to a ground-hugging flow that settles to form the distal ridge observed in this study. This mechanism may play a role in producing ejecta morphologies on planetary bodies with atmosphere.