Formation Age of Ernutet Crater, Ceres, and Implications for Origin of the Organics

Abstract Ceres is the largest body in the Main Asteroid Belt and has a unique composition characterized by products of aqueous alteration such as carbonates, ammoniated phyllosilicates, and organic materials in concentrated regions. A large organic region is associated with the 53 km diameter, relatively fresh crater, Ernutet, located in the northern hemisphere of Ceres. The isolated nature of the materials suggested delivery from impact (external source); yet high impact energy makes survivability of these materials unlikely. An internal source has also been suggested, but the localization is difficult to explain; thus, the origin of these organic materials on Ceres is still inconclusive. In this paper, we measure and classify superposed craters on Ernutet and its organic-rich ejecta to derive Ernutet’s absolute model formation age and provide new constraints on the origin of the organics. Cumulative crater size–frequency distributions are used along with the asteroid-derived model production function chronology to estimate an age of ∼400–900 Ma. Therefore, Ernutet is likely much older than the surface survivability of delivered organics, on the order of 10 7 yr, even with regolith mixing. In addition, we find the volume of observed organics is plausibly much larger than could be delivered by the Ernutet impactor. We conclude that the organics are more likely to have originated endogenically rather than exogenically on Ceres.