Phase-ratio images of the surface of Mercury: Evidence for differences in sub-resolution texture

Analysis of images that were obtained at different phase angles can give clues to the texture of a planetary surface. Here we describe MESSENGER phase-ratio images for features on the surface of Mercury, including hollows on the floor of Eminescu basin, a pyroclastic deposit found within the Caloris basin, and a dark impact-melt flow produced by the impact that formed Waters crater. The results indicate that hollows and the pyroclastic material are characterized by finer particle size or smoother sub-resolution roughness than the ordinary impact-generated regolith. The impact melt flow appears to have a surface that is rougher or consists of coarser particle sizes than the nearby background.