月球哥白尼纪次级坑的形态特征及其空间分布

Morphological features and spatial distribution of the lunar Copernican secondary craters

月球次级坑是月球上的一种地质特征,易与初级坑相混淆,对月表定年影响大,同时对主撞击坑的撞击方向有一定的指示意义,因此识别和筛选出次级坑是一项重要的工作。综合考虑撞击坑空间分布位置和直径关系,选取哥白尼纪5个典型撞击坑为研究对象,基于遥感影像和地形数据,通过总结相关学者对特定形态指标与次级坑定量关系的研究,构建4个形态指标(不规则度、椭圆度、深径比、坑缘高度与直径比)及其参数范围,进行次级坑的智能化识别、提取与空间分布研究。最终识别出次级坑总数量为17 811个,在此基础上构建了包含位置、大小、形状、距离和方向5大类的数据库;并研究了距主坑边缘不同距离范围内次级坑的规模和空间分布特征;提出了基于次级坑主轴方向判定撞击坑入射方向的新方法。研究结果表明:①在规模大小上,月海次级坑直径大小主要集中在初级坑直径的(2. 7±0. 11)%以下;月陆次级坑直径大小主要集中在初级坑直径的(3±0. 3)%以下;在空间分布上,月海与月陆次级坑分布规律相一致,次级坑数量占总次级坑数量的90%时,其分布距离是最大分布距离的(57±7)%;②Tycho撞击坑的入射方向为W-E方向,Copernicus撞击坑和Kepler撞击坑的入射方向为SE-NW方向,Aristarchus撞击坑和Jackson撞击坑的入射方向为NW-SE方向。这些认识将对更准确地开展撞击坑撞击方向的研究提供参考。

Lunar secondary crater,a kind of geological feature that is easily confused with the primary craters on the Moon,can introduce significant errors in lunar dating.However,it can be used to determine the impact direction of the primary crater,so it is important to identify secondary craters.In this paper,based on remote sensing data and topography data,comprehensive consideration of the spatial location and diameter of the lunar primary crater,the authors selected five typical Copernican primary craters to study the quantitative morphological indices so as to characterize their secondary craters,including depth-diameter ratio,rim height-diameter ratio,irregularity,and ellipticity.On such a basis,the intelligent identification,extraction and spatial distribution of secondary craters were studied.As a result,a total of 17 811 secondary craters were detected,from which a geodatabase was established that included five categories according to location,size,morphological indices,distance,and impact direction of secondary craters.The scale and distribution characteristics of secondary craters were studied based on the distance range from primary crater edge.A new method based on secondary crater major axis was developed.Some conclusions have been reached:①As for craters size,the lunar mare secondary crater diameter is(2.7±0.11)%of its primary crater diameter,the lunar highland secondary crater diameter is(3±0.3)%of its primary crater diameter.The spatial distribution law is consistent between lunar highland and lunar mare.The secondary distribution distance is(57±7)%of the maximum distribution distance.②The impact direction of the Tycho crater is W-E.The impact directions of the Copernicus crater and the Kepler crater are SE-NW.The impact directions of the Aristarchus crater and the Jackson crater are NW-SE.This study will be helpful for more accurate study of crater impact direction.