NEW INSIGHTS ABOUT OCCATOR’S BRIGHT FACULAE DERIVED FROM GEOLOGIC MAPPING OF HIGHEST RESOLUTION OBSERVATIONS OF CERES

Since the Dawn spacecraft began orbiting Ceres in 2015, one of the most intriguing surface features have been the bright regions (faculae) in the 92 km diameter Occator crater. Cerealia Facula is the central bright region and Vinalia Faculae are bright regions in the eastern floor. Occator also contains extensive lobate materials and a central dome within a central pit. Dawn data obtained from orbits of ≧385 km altitude led to the conclusion that Occator and the faculae’s formation was either entirely driven by impact-induced processes, or that there may also have been an endogenic component to their formation (synthesized in Scully et al., 2018). Dawn has now observed Ceres from its lowest altitude orbits of ≧35 km. We find that the new ≧35 km altitude data corroborate many of the ≧385 km altitude-based results/hypotheses. However, in some cases, more analysis appears to be required. For example, based on the ≧385 km altitude data, the Vinalia Faculae were hypothesized to originate from prominent fractures, but initial analysis of the ≧35 km altitude data appear to indicate that the fractures are younger. To unravel relationships such as this, we create a detailed geologic map of Occator’s interior using the ≧35 km altitude Framing Camera data, from which we derive a relative stratigraphy for features in the crater. Using the map and stratigraphy, we test whether all features in Occator are likely the result of the evolution/solidification of an impact slurry, or whether endogenically-driven cryovolcanism also occurred. For example, we test whether freezing of an impact slurry could have squeezed brines/other volatile rich materials to the surface, forming the central dome, perched bright materials, channel-like features and isolated mounds. We also use the map and stratigraphy to investigate: (a) the origin of mounds in the lobate materials, (b) the origin of the dark material, (c) the distribution and size of small bright/dark depressions, to infer their formation mechanism and the subsurface distribution of bright/dark materials, (d) whether the prominent fractures associated with the Vinalia Faculae were reactivated, and (e) the strength of materials. Part of this work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract to NASA. Government sponsorship acknowledged.