Ceres’ Occator crater and its faculae explored through geologic mapping

Occator crater is one of the most recognizable features on Ceres because of its interior bright regions, which are called the Cerealia Facula and Vinalia Faculae. Here we use high-resolution images from Dawn (∼35 m/pixel) to create a detailed geologic map that focuses on the interior of Occator crater and its ejecta. Occator's asymmetric ejecta indicates that the Occator-forming impactor originated from the northwest at an angle of ∼30–45° perhaps closer to ∼30° Some of Occator's geologic units are analogous to the units of other complex craters in the region: the ejecta, crater terrace material, hummocky crater floor material and talus material. The geologic units that make Occator unique are the bright Occator pit/fracture material (this is the unit that corresponds to the Cerealia Facula and Vinalia Faculae) and the extensive, well-preserved lobate materials. We propose that the lobate materials are a slurry of impact-melted and non-impact-melted target material, which flowed around the crater interior before solidifying to form deposits geomorphologically consistent with impact melts elsewhere in the Solar System. We sub-divide the lobate materials on the basis of their surface textures. It is likely that knobby or smooth lobate materials form if the lobate material entrains or does not entrain blocks, respectively. Post-impact inflation is suggested to form the hummocky lobate material. The Vinalia Faculae formed within the hummocky lobate material. We find that the knobby lobate material and the outer edge of the Cerealia Facula formed prior to the central pit. The central dome formed after the formation of the central pit, while the majority of the Cerealia Facula (besides the outer edge) could have formed, continued to form and/or have been modified after the formation of the central pit. The Cerealia Facula may have initially been emplaced in a similar process to the Vinalia Faculae, and the surface of the Cerealia Facula appear to have somewhat darkened over time. The insights into Occator crater and its faculae derived from our geologic mapping will be synthesized together with inputs from all of the studies in this special issue in Scully et al. (2018a).