Morphological analysis and mapping of complex craters of Copernican age: Crookes, Ohm and Stevinus

Abstract

The aim of this study is to analyze and compare morphological characters of three complex lunar impact craters- Crookes (10.3° S, 164.5° W), Ohm (18.4° N, 113.5° W) and Stevinus (32.5° S, 54.2° E), where Crookes and Ohm are located on the far side of the Moon and Stevinus is located on the near side of the Moon. High resolution data of Narrow Angle Camera (NAC) and Wide Angle Camera (WAC), onboard Lunar Reconnaissance Orbiter (LRO) of NASA is used for the morphological observations of all three craters. In this study we identify and compare various geomorphic features of three craters including central peak, central mounds, isolated mounds, diverse floor units: Hummocky, Intermediate and Smooth, melt ponds and cooling cracks. Using ArcGIS software, morphological maps of all three craters are generated where special attention is given to the crater floors, with NAC and WAC data as base-maps. Lunar Orbiter Laser Altimeter (LOLA) Digital Elevation Model (118 ​m) is used to generate elevation graphs for all three craters along four different topographic sections using which, relative elevation measurements of central peak, central mounds and raised crater rims and thickness of wall terraces are obtained. Using the ENvironment for Visualising Images (ENVI) software, 3-dimensional surface view models were generated. These 3D models give enhanced view of ‘highs’ and ‘lows’ of impact craters along with ponded surfaces trapped in between wall-terraces. All three craters are oblique impact craters with varying degrees of impact angles. Crookes exhibits later stage modification characters with an impact direction NNE and an impact angle between 15° and 45°. Ohm exhibits elongated crater planform with zone of avoidance in NNE direction. The impact angle is between 30° and 45°. Stevinus represents an impact angle higher than 15° and lower than 40°. The study reveals that there are striking similarities in the morphological features of these three craters of the same age along with few distinct characters of their own.