Illumination and Thermal Environment at (4) Vesta and (1) Ceres

The Dawn mission has orbited and extensively explored asteroid (4) Vesta and dwarf planet (1) Ceres, acquiring high-resolution datasets of these important bodies for the context of the asteroid belt and the formation of the Solar System. In particular, through its long low-altitude mapping orbital phases, the Dawn Framing Camera (FC) obtained global coverage with optimal geometry for stereo reconstruction of their shape and orientation. The illumination conditions of airless bodies directly control their thermal environment, which bears on the presence and distribution of volatiles, with implications for such processes throughout the Solar System. We develop a radiosity-based modeling tool, and apply it to Vesta and Ceres using the Dawn-derived shapes. Recognizing that some parameters are still not known with great certainty (e.g., photometric and surface thermal properties), we will present average illumination and thermal maps of Vesta, naturally improved with respect to pre-Dawn Vesta studies. We will also produce such maps for Ceres, but with focus instead on continuing the study of polar craters, particularly those that host bright crater floor deposits, extending the previous permanent shadow vs. obliquity history study with thermal modeling.