INVESTIGATION OF LAYERED LUNAR LAVA FLOWS THROUGH LROC IMAGERY AND TERRESTRIAL ANALOGS

High resolution images of the lunar surface reveal layered deposits visible within the walls of impact craters, interpreted to be sequences of stacked lava flows. The aim of this research was to establish quantitative constraints on the thicknesses of individual flow units. The motivation for this project was to identify locations hosting intercalated units in paleoregoliths between layers, which may preserve snapshots of the ancient solar wind and other extra-lunar particles, ideal sampling localities for future lunar missions. Our approach involved mapping layered outcrops in Dawes Crater using high-resolution imagery acquired by the Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC), with constraints on flow unit dimensions provided by Lunar Orbiter Laser Altimeter (LOLA) data. We measured flow thicknesses of ~ 2 to > 20 m. However, there is considerable uncertainty in the definition of contacts between adjacent units, primarily because lighting angle and talus commonly obscures contacts and/or prevents lateral tracing of the flow units. To address these issues, we undertook a terrestrial analog study using World View 2 satellite imagery of layered lava sequences on Oahu, Hawai’i, which have a resolution comparable to LROC NAC images of 0.5 m. The layered lava sequences were analyzed in ArcGIS to obtain an estimate of the number and thicknesses of flow units before going into the field to ground truth the image analysis. The field and remote sensing measurements allowed us to determine the uncertainty on unit thicknesses. This in turn provided insight into the accuracy of measurements obtained from the lunar images. The terrestrial analog study of satellite images showed average flow thicknesses of 2.0 to 7.7 m. Measurements collected in the field yielded thicknesses ranging from 1.6 to 2.0 m. The lunar results compiled from Dawes Crater show an average mare flow thicknesses of 5.7 ± 4.7 m to 18.1 ± 8.9 m. Based on the terrestrial analog study, the image-derived flow thicknesses were overestimated by factors ranging from 1.0 to 4.5. Results indicate that although flow thicknesses can be better constrained with high resolution LRO imagery, estimates are likely larger than true flow thicknesses.