基于全景相机数据的嫦娥四号着陆区次级坑统计分析

Statistical Analysis of Secondary Craters in the Chang’E-4 Landing Area Based on Panoramic Camera Data

玉兔二号月球车在嫦娥四号着陆区发现了许多坑缘呈破碎石块状的小型撞击坑,其直径大多在亚米级,过去对于这种小尺度撞击坑的研究大多源于Apollo、Surveyor、Ranger系列任务,然而当时获取的影像质量较低,且并未覆盖月球背面。小尺度撞击坑在月球表面分布十分广泛,与月球最表层的演化密切相关,因此对其展开研究具有重要的意义。本文利用嫦娥四号任务获取的高分辨率全景影像,统计了8、9、11~15月昼影像中新鲜撞击坑的直径、频数、深度等信息,并根据这些撞击坑和周围石块的形态特征,推测这些坑应该形成于不同方向的二次撞击事件,这为揭示玉兔二号月球车行进途中观测物质的来源提供了重要信息。小型二次撞击坑从深径比中难以与一次撞击坑区分,且一般处于饱和状态,因此应避免使用小尺寸的撞击坑进行定年。

Many fresh small sized(mostly in diameter of sub-meter) impact craters which have blocky-rim exposed in the regolith were encountered by the Yutu-2 rover in the Chang′E-4 landing area. Due to the limitation of low resolution of images, such kind of small sized impact craters were mostly found in images from the Ranger, Surveyor, Apollo missions in the past, nevertheless those images of low quality did not cover the area of lunar farside. Small sized impact craters are widely distributed in the lunar surface and they are closely related to the evolution of lunar regolith. Therefore, it is significant to study these craters in fine scales. In this paper, the very high resolution images acquired by the CE-4 Panoramic camera(Pancam) in 8 th, 9 th, 11 th-15 th lunar days are used to analyse information including the diameter, frequency, and depth of these fresh impact craters. Combining with the morphological characteristics of these impact craters and boulders, it is inferred that these craters could be mostly formed by secondary impact events in different directions. This provides important information for revealing the source of the material observed during the journey of the Yutu-2 rover. Small sized secondary impact craters are difficult to be distinguished from primary impact craters in the ratio of depth to diameter, and they are generally in a saturated state. Therefore, small sized craters should be avoided to be used for the size-frequency dating.