Closed depressions on the surface of the Moon

Abstract

This paper provides a new view of the lunar surface by using maps of its closed depressions which are not limited to impact craters. On the lunar landscape, in addition to impact craters of all sizes, there is a rich variety of other types of closed depressions related to impact, volcanism, tectonics and gravitational processes. Kilometre-scale closed depressions have been identified, delineated and mapped on the surface of the Moon by using the digital elevation model provided by the Lunar Orbiter Laser Altimeter (LOLA) instrument onboard the Lunar Reconnaissance Orbiter (LRO) spacecraft together with a pit filling algorithm. The map of closed depressions is a raster map of the same size and spatial resolution as the digital elevation model used to generate it and each pixel provides the depth with respect to the rim of the depression. A number of test sites were chosen to illustrate the methodology including impact basins, maria, highlands, volcanic terrain, intermediate terrain and modified terrain. These maps of closed depressions can be analysed in terms of their location, abundance, size, orientation, depth, geometry, asymmetry and irregularity together with other morphometric parameters. On average, 71% of the surface of the Moon is covered by closed depressions and that number decreases to around 55% for volcanic terrains. The histogram of the depths of the highlands test site can be considered as the standard depth histogram in which impact craters of all sizes cover the entire terrain. The histograms of the other zones vary from that standard profile. The ultimate purpose of this paper is to provide a tool for mapping closed-depressions on the lunar surface which may assist planetary geologists to identify geological processes and recognize geological formations in the study of the geology and geomorphology of the Moon.