Geophysical data from Dawn’s mission revealed complex and divergent internal structure evolutionary paths for Vesta and Ceres. Dawn’s data indicated that Vesta has a differentiated internal structure with uncompensated topography and Ceres is partially differentiated with compensated topography. Vesta experienced a magma ocean state, leading to effective early shape relaxation. Vesta’s current non-hydrostatic shape is dominated by Rheasilvia and Veneneia impact basins, formed when Vesta was too rigid to relax. However, northern terrains still reflect its pre-impact, closer-to-hydrostatic shape. Ceres incorporated abundant volatile material upon its accretion and subsequently underwent ice–rock fractionation. Observed surface aqueous alteration indicates extensive past hydrothermal circulation that facilitated efficient heat transfer and preserved Ceres’ interior in a relatively cool state. Lower viscosities at depth allowed isostatic compensation of Ceres’ long-wavelength topography. The high inferred abundance of water ice, hydrated salts, and/or clathrate phases suggest previous globally significant regions of solute-rich fluids that froze from the surface inward, leading to the vertical density gradient inferred from Dawn’s Second Extended Mission (XM2) high-resolution gravity data. This, coupled with thermal modeling, indicated that Ceres could have brine reservoirs, at least regionally, which were likely mobilized by the Occator crater-forming impact, leading to long-lived brine extrusion and faculae formation.

Within the general framework of differentiation in the early solar system, the asteroid Vesta is a particularly interesting case study. First, its size is well constrained, simplifying modeling efforts that can concentrate on bodies of relevant size. Second, the rich diversity of HED meteorites provides constraints on bulk composition and a unique opportunity to confront predictions of numerical models with petrologic reality. Finally, the Dawn mission, in addition to confirming the link between Vesta and the HED’s, also provides critical constraints on the internal density structure and composition of the asteroid. In this chapter we begin by considering petrologic and geochemical constraints on the bulk composition and differentiation time-scales of Vesta, before presenting modeling efforts to understand its chemical and physical evolution. The modeling indicates accretion within the first million years of solar system history and complex thermal and chemical retroactions linked to the redistribution of 26Al during transport of melt toward the surface. Formation of a shallow magma ocean is predicted, leading to a vertically stratified mineralogical structure with olivine sequestered at depth and protracted cooling at depth. These features are consistent with the essential features of HED petrology and chronology and observations of the Dawn mission.

Geochemical measurements and constraints on the origin of the two best-studied bodies: the Moon and Mars

This chapter reviews what is known about the fate of carbon during early differentiation of inner solar system planets. It reviews the nature of carbon fractionation in a magma ocean as compared to the core, mantle, and atmosphere, and how this may have varied between planetary bodies in the solar system. It discusses whether magma ocean processes could have established the present-day budget of carbon in Earth’s bulk silicate, and also reviews possibilities for the early temporal evolution of the mantle carbon budget through core formation, later veneer addition, and magma ocean crystallization processes.