Analysis of the MESSENGER MASCS photometric targets part II: Photometric variability between geomorphological units

This study examines the level of structural uniformity within Mercury's regolith as a function of geomorphological unit. Using two categories of photometric models (Hapke versus Kaasalainen-Shkuratov), the variation between and within similar geomorphological units are examined with the Mercury Atmosphere and Surface Composition Spectrometer (MASCS) photometry sequence data sets. The results show evidence for variations in the spectral and photometric scattering properties both within similar geomorphological units and between different geomorphological units. The ejecta and cratering units show the largest differences between the modeling results, each indicating variations in different properties. The results for the intercrater materials, smooth materials, and dark materials show consistent results between both models. The variations include possible differences in grain structures, regolith compaction, and surface roughness on micron to millimeter scales.