Ceres: Evoltion and Present State #2

The evolution of Ceres has been modeled (McCord and Sotin, 2005) and shown to predict that Ceres contained considerable water when formed, differentiated to form a hydrated silicate core, water mantle and frozen crust. The presence of water was shown to be critical to moderate the heating. The difference between the current day Vesta and Ceres was explained to depend on the exact time after CAIs that each object formed: early formation meant stronger short-lived radioactive nuclide (SLRN) heating and early loss of water, resulting in a much hotter object, like Vesta. One of the most likely models predicted a moment of inertia (MOI) that was later measured for Ceres (Thomas et al., 2005), confirming that Ceres is differentiated. We have improved on this early modeling attempt in a number of ways. Our results confirm the basic evolution scenario found earlier but show additional interesting aspects, and investigate some major processes, such as convection, mineralization, water loss, and processes taking place in the core: dehydration, magmatic activity, and possible separation of the metallic phase. We derive a series of models, requiring that they match both the shape data and are realistic from a thermal evolution perspective. These models bear a core stratified in hydrated, dehydrated silicate layers, and in some cases a metallic inner core. They all require a time of formation with respect to calcium-aluminum inclusions shorter than 5 My. McCord T. B. and C. Sotin (2005) J. Geophys. Res. Vol. 110. Thomas, P. C. et al. (2005) Nature 437, doi:10- 1038, 1-3. Part of this work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract to NASA.