The phase- and color-ratio techniques as applied to Dawn images of the dwarf planet Ceres and asteroid (4) Vesta

Identification of regolith structure anomalies on atmosphereless Solar System bodies is important as an indicator of the surface changes. With the phase ratio method, we are able to map phase curve slopes and distinguish the areas with different regolith optical roughness. These areas are caused by topographic slope processes, formation of new craters and the possible effects of endogenous processes. Global mapping of asteroid (4) Vesta and the dwarf planet Ceres from two orbits High Altitude Mapping Orbit (HAMO) and Low Altitude Mapping Orbit (LAMO) provide the necessary data for applying the phase-ratio technique to these bodies. Using multispectral images from the Dawn Framing Camera (FC) for the dwarf planet Ceres and the asteroid (4) Vesta, phase-ratio and color-ratio methods were applied for selected areas on surfaces of Vesta (Laelia, Laeta, Aricia, Vibidia) and Ceres (Ahuna Mons, craters Occator, Oxo, Xevioso). The phase-ratio method gives us a good tool for both bodies, Ceres and Vesta, to detect changes in regolith structure associated with mass movement due to slope processes on crater walls and hillsides, as well as with ejecta from the youngest craters.