A Brief History of Ceres

Abstract:

Available observations and thermal simulations suggest that Ceres is a warm icy body differentiated in a rocky core and icy shell. This model is supported by recent detection of a cloud of water vapor sourced from a couple of regions at the surface of the asteroid (Kueppers et al. (2014) Nature 505, 525). Combining geophysical tools developed for icy satellite modeling and hydrogeochemistry modeling, we derive interior and geological evolution scenarios for a variety of assumptions on the asteroid’s accretional environment.

Key events include (1) the early differentiation of a rocky core accompanied by a phase of intensive hydration in high pH environment. These conditions are favorable to the production of brucite and carbonates, as well as the redistribution of certain elements, e.g., potassium, from the rock to the aqueous phase; (2) an episode of partial dehydration of the core accompanied by a major heat pulse and further rock leaching; (3) efficient convection, including a phase in the mobile-lid regime that could have been responsible for the recent emplacement of Ceres’ surface.

It is important to keep in mind that Ceres is a small object whose main heat source is limited to long-lived radioisotope decay. Hence it is unlikely, from a basic thermal standpoint, that this object could maintain cryovolcanic activity at present. However, we will also report on a scenario in which potassium-40 has been extensively leached from the rock and is now concentrated in thick salt cumulates at the interface between the rocky core and shell, as was proposed for Europa (Prieto-Ballesteros and Kargel (2005) Icarus 173, 212). Low salt thermal conductivity combined with potassium-40 abundance may lead to partial melting. Whether or not this warm layer at the base of the icy shell can promote a late phase of cryovolcanism will be evaluated and presented at the meeting.

We will compare the implications of these models against other models for the emplacement of Ceres’ surface whose extensive geological and compositional mapping by the Dawn spacecraft will be our primary source of information on Ceres’ origin and evolution.

Acknowledgements: This work is being conducted at the Jet Propulsion Laboratory, California Institute of Technology, under contract to NASA. Government sponsorship acknowledged.