Models of Ceres' Surface as a Function of Origin and Evolution Scenarios

After its spectacular encounter with Vesta, the Dawn spacecraft is now on its way to the largest object in the main belt, Ceres. The last few years have seen a growing interest in the origin and evolution of this object and increased observational constraints on its geophysical properties and surface chemistry. In 2005, McCord and Sotin (2005) introduced the idea that Ceres could have held a deep ocean for some period of time. Rivkin (2006) discovered carbonates at the surface of Ceres, evidence for chemistry in aqueous environments, an idea reinforced by and Milliken and Rivkin's (2009) suggestion that brucite is a major component of Ceres' surface. See also Rivkin et al. (this conference) for the state of the art on Ceres' surface composition inferred from astronomical observations. In parallel, recent developments in Solar system dynamical evolution (Walsh et al. 2011; Grazier et al. 2012) and cosmochemistry models (Dodson-Robinson et al. 2009) and measurements (d'Alexander et al. 2012) indicate that asteroid volatiles may have been supplied from different sources and included second-phase low-eutectic impurities such as ammonia hydrates. Hence, the upcoming rendezvous of Dawn at Ceres offers the prospect of obtaining constraints on the origin of volatiles in the main belt and the habitability potential of large wet asteroids such as Ceres. Ceres' surface chemistry is the product of multiple parameters and processes: (1) the composition of accreted materials, volatile composition, and the possibility for hydrothermal activity in planetesimals prior to accretion in Ceres (i.e., in objects of the size of chondrite parent bodies); (2) evolution of the rock and ocean chemistry as a consequence of one or several episodes of hydrothermal activity (Castillo-Rogez and McCord 2010), (3) the transportation mechanism that may encompass solid-state convection or cryovolcanism and act as a possible filter against certain species in the ocean; (4) exogenic processing (esp. UV photolysis) whose impact may depend to some extent on the possible presence of a remnant magnetic field. In order to approach this problem we have modeled the evolution of Ceres by combining physical and chemical modeling and covering a broad parametric space that encompass the various scenarios proposed for Ceres' volatile origin. From this modeling we have inferred constrained on Ceres surface physical and chemical properties and established some pathways to infer constraints on Ceres' origin, evolution, and current state from prospective observations with Dawn. Acknowledgements: Part of this work has been conducted at the Jet Propulsion Laboratory, California Institute of Technology, under contract to NASA. Alexander, C. M. O'D., et al. (2012) Sciencexpress report, doi: 10.1126/science.1223474; Castillo-Rogez, J. C., McCord, T. B. (2010) Icarus 205, 443-459, doi:10.1016/j.icarus.2009.04.008; Dodson-Robinson, S. E., et al. (2009) Icarus 200, 672; McCord, T. B., Sotin, C. (2005) J. Geophys. Res. 110, CiteID E05009; Milliken, R. E., Rivkin, A. S. (2009) Nature Geosci. 2, 258-261, doi:10.1038/ngeo478; Rivkin et al. (2006) Icarus, 185; Walsh, K. J. et al. (2011) Nature 745, doi:10.1038/nature10201.