Preliminary Analysis of Lunar Pit Crater Morphometry, Morphology, and Distribution

This study presents preliminary results of an investigation of pit craters on the lunar surface and their relationship to volatile concentrations. Pit craters are a special type of crater that contains a circular pit (negative relief feature) within the central region of the crater, which may be related to the presence and possible release of volatiles during crater formation. Most studies connecting volatiles to pit crater formation have been conducted on Mars and Ganymede (which are considered relatively volatile rich), but few have been conducted concerning pit craters on comparatively volatile-depleted bodies such as the Moon. The working hypothesis of this study is that volatiles play a role in pit crater formation on solid bodies throughout the solar system. A subset of the lunar complex crater population (20 - 60 km in diameter) was examined and pit craters from this population were identified and characterized using Lunar Orbital Laser Altimeter (LOLA) data as well as visual data sets from the Apollo and LRO/LROC. The smaller diameter was chosen because this is above the transition from simple to complex craters, while the upper limit was chosen to avoid the transition to peak-ring craters and multi-ring basins. The percentage of pit craters to the total 20-60 km complex crater population is being determined independently for highland and maria terrains to identify proposed increases in the percentages of pit craters in the highlands as opposed to the maria, as the former has a higher percentage of volatiles in the lunar regolith. The ratio of pit craters to the total crater population 20-60 km in diameter will be compared to the populations on both Mars and Ganymede, which are celestial bodies that are considered to have sizable pit crater populations. It is expected that the lunar pit crater population will be much less than that of Ganymede or Mars. Lastly, morphometric and morphologic analyses will be performed on each pit crater to better understand the physical characteristics of pit craters on a celestial body that has a very low volatile percentage. Ultimately, the multivariate techniques used here will aid in defining pit craters versus other structures across the solar system, with special emphasis focusing on the drier bodies.