High‐speed impact ejecta at velocities comparable to the impact velocity are expected to contribute to material transport between planetary bodies and deposition of ejecta far from the impact crater. We investigated the behavior of high‐speed ejecta produced at angles of 45° and 90°, using both experimental and numerical methods. The experimental system developed at the Planetary Exploration Research Center of Chiba Institute of Technology (Japan) allowed us to observe the initial growth of the ejecta. We succeeded in imaging high‐speed ejecta at 0.2 μs intervals for impacts of polycarbonate projectiles of 4.8 mm diameter onto a polycarbonate plate at an impact velocity of ~4 km s⁻¹. Smoothed particle hydrodynamics (SPH) simulations of various numerical resolutions were conducted for the same impact conditions as pertaining to the experiments. We compared the morphology and velocities of the ejecta for the experiments and simulations, and we confirmed a close match for high‐resolution simulations (with ≥10⁶ SPH particles representing the projectile). According to the ejecta velocity distributions obtained from our high‐resolution simulations, the ejection velocities of the high‐speed ejecta for oblique impacts are much greater than those for vertical impacts. The translational motion of penetrating projectiles parallel to the target surface in oblique impacts could cause long‐term, sustained acceleration at the root of the ejecta.

中文翻译：

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使用超高速成像和SPH模拟观察到的撞击点附近的撞击弹射物，以及两种方法的比较

预计以与撞击速度相当的速度产生的高速撞击射流将有助于行星体之间的物质传输以及远离撞击坑的射流沉积。我们使用实验和数值方法研究了以45°和90°角产生的高速喷射的行为。由日本千叶工业大学行星探索研究中心开发的实验系统使我们能够观察到喷射器的初始生长。我们成功地以0.2μs的间隔对高速喷射成像，以4.8 mm s ^-1的撞击速度将4.8 mm直径的聚碳酸酯弹丸撞击到聚碳酸酯板上。在与实验有关的相同冲击条件下，进行了各种数值分辨率的平滑粒子流体动力学（SPH）模拟。我们比较了形态和喷出物用于实验和模拟的速度，我们证实了用于高分辨率模拟一个接近的匹配（具有≥ 10 ⁶ 表示弹丸SPH颗粒）。根据从我们的高分辨率模拟获得的喷射速度分布，斜冲击时高速喷射器的喷射速度远大于垂直冲击时的喷射速度。在倾斜撞击中，平行于目标表面的穿透弹丸的平移运动可能会在弹射体根部引起长期持续的加速。