Planetary impact events eject large volumes of surface material. Crater excavation processes are difficult to study, and in particular the details of individual ejecta fragments are not well understood. A related, enduring issue in planetary mapping is whether a given crater resulted from a primary impact (asteroid or comet) or instead is a secondary crater created by an ejecta fragment. With mapping and statistical analyses of six lunar secondary crater fields (including Orientale, Copernicus, and Kepler) we provide three new constraints on these issues: (1) estimation of the maximum secondary crater size as a function of distance from a primary crater on the Moon, (2) estimation of the size and velocity of ejecta fragments that formed these secondaries, and (3) estimation of the fragment size ejected at escape velocity. Through this analysis, we confirmed and extended a suspected scale‐dependent trend in ejecta size‐velocity distributions. Maximum ejecta fragment sizes fall off much more steeply with increasing ejection velocity for larger primary impacts (compared to smaller primary impacts). Specifically, we characterize the maximum ejecta sizes for a given ejection velocity with a power law and find that the velocity exponent varies between approximately −0.3 and −3 for the range of primary craters investigated here (0.83–660 km in diameter). Data for the Jovian moons Europa and Ganymede confirm similar trends for icy surfaces. This result is not predicted by analytical theories of formation of Grady‐Kipp fragments or spalls during impacts and suggests that further modeling investigations are warranted to explain this scale‐dependent effect.

中文翻译：

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月球次级陨石坑和估计的弹射块大小揭示了尺度依赖的破碎趋势

行星撞击事件会弹出大量表面物质。火山口的挖掘过程很难研究，尤其是单个弹射器碎片的细节还没有被很好地理解。行星测绘中一个相关的，持久的问题是给定的陨石坑是由主要撞击（小行星或彗星）产生的，还是由喷出碎片形成的次要陨石坑。通过对六个月球次生陨石坑场（包括Orientale，哥白尼和开普勒）的制图和统计分析，我们在这些问题上提供了三个新的约束条件：（1）估算最大次要陨石坑大小与到主坑的距离的函数。 Moon，（2）估算形成这些二次流的喷射碎片的大小和速度，（3）估算以逸散速度喷射的碎片大小。通过分析，我们证实并扩展了射血大小-速度分布中与规模有关的可疑趋势。对于较大的主要撞击（与较小的主要撞击相比），最大喷射碎片的大小随射速的增加而急剧下降。具体来说，我们利用幂律定性描述了给定喷射速度下的最大喷射量大小，发现对于这里研究的主要弹坑范围（直径为0.83至660 km），速度指数在大约-0.3和-3之间变化。欧洲木卫二和木卫三的卫星数据证实了冰面的相似趋势。撞击期间Grady-Kipp碎片或剥落形成的分析理论无法预测该结果，并建议进一步进行模型研究以解释这种与尺度有关的效应。