Large-scale Roughness Properties of the Lunar North and South Polar Regions as Measured by the Lunar Orbiter Laser Altimeter (LOLA)

Abstract The lunar polar regions are high-priority targets for scientific investigation and exploration. To aid these endeavors, we produced enhanced altimetry data from the Lunar Orbiter Laser Altimeter for the north polar region, from which we computed new maps of surface height and slope as well as topographic roughness on horizontal baselines of 100–1600 m. We also produced a new map of permanently shadowed regions (PSRs) that contains fewer artifacts and is higher resolution than previous maps. These new maps were then compared to an analogous set previously produced for the south polar region. Generally, in both polar regions, more steeply sloped terrain is rougher at baselines ≲200 m and has a bluer roughness spectrum, a behavior hypothesized to be due to downslope mass transport. Roughness in the polar regions is also correlated with regolith temperature, and we discuss several possible causes including surface ice in unresolved cold traps, subsurface ice outside cold traps, and changes in the regolith’s geotechnical properties. In the north, there are more PSRs with areas ∼0.1–1.0 km 2 and fewer with areas >100 km 2 , which may be due to the north having a higher number of craters with diameters of hundreds of meters to ∼3 km. The new maps presented here have many applications in the scientific study and exploration of the lunar north polar region, such as geologic mapping, modeling of cold traps, landing-site characterization, traverse planning, and the interpretation of in situ and remote-sensing data.