from Part II - Key Results from Dawn’s Exploration of Vesta and Ceres
Published online by Cambridge University Press: 01 April 2022
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.
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