论文标题
月球次级陨
Lunar Secondary Craters and Estimated Ejecta Block Sizes Reveal a Scale-dependent Fragmentation Trend
论文作者
论文摘要
行星撞击事件弹出大量的表面材料。火山口挖掘过程很难研究，尤其是单个喷射片段的细节尚不清楚。行星映射中相关的，持久的问题是，给定的火山口是由主要影响（小行星或彗星）引起的，还是是由射流片段产生的次级火山口。 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 速度。通过此分析，我们确认并扩展了射流尺寸速度分布中的可疑规模依赖趋势。随着弹出速度的增加，最大的弹射片段尺寸降低了得多（与较小的主要影响相比）。具体而言，我们表征了具有功率定律的给定弹出速度的最大喷射尺寸，并发现此处研究的主要陨石坑范围（直径为0.83-660 km），速度指数在大约-0.3和-3之间变化。 Jovian Moons Europa和Ganymede的数据证实了冰冷表面的类似趋势。在撞击过程中，没有通过分析理论形成Grady-kipp片段或铲子的分析理论，并建议对进一步的建模研究进行解释以解释这种规模依赖性效应。
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 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.
