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Abstract:
The Occator crater on the dwarf planet Ceres is outstanding because of its relatively low age (~22 Ma) and extremely young (≤4 Ma) and bright faculae on an otherwise mostly dark body (ratio of reflectances bright/dark >5). Knowledge of the faculae origin is key to understanding the cerean interior and evolution. New photometric comparisons, obtained using data from the Dawn Framing Camera (FC), of Occator's faculae and suitable reference sites elsewhere on Ceres, refine earlier results of unusual photometric behavior at these faculae. An apparent change of reflectance dominated by a dependence on the emission angle, for fixed phase angles, at the floor faculae in all filters of the Dawn FC is confirmed, while selected reference areas do not show this effect. There is no evidence for an instrumental or geometry-based origin of this local phenomenon, which has been measured for a period of four years by Dawn. While the found change of reflectance hints at a source not located on the surface, and possibly linked with the local morphology and composition, no unambiguous origin or source material can yet be identified. Thus, these results strengthen the haze hypothesis at the Occator crater on Ceres.
