Brines on Ceres: Origins and Transport Processes

Abstract:

Ceres, the only dwarf planet in the inner solar system, appears to be volatile-rich. Observations returned by Dawn’s prime mission revealed a homogeneous surface composition consistent with global aqueous alteration, and a partially differentiated interior. Modeling of Ceres’ relaxed shape at long wavelength, constrained by density estimates from gravity modeling are consistent with a crust rich in silicates, ice, salts and clathrates, and a global muddy layer at the crust-mantle interface. Results obtained during the last phase of the Dawn mission show evidence of this deep brine in the relative youth and composition of the bright salt deposits, most notably within Occator crater, and the geologically-young Ahuna Mons, a 4-km high mountain that appears to be sourced from a deep muddy layer. Detailed study of brine effusion within Occator crater, coupled with geophysical analyses of the temperature structure and crust/mantle heterogeneities in the surrounding Hanami Planum region has resolved the debate on the origin of the faculae. These studies show that the two sources previously proposed (impact melt chamber and deep brine reservoirs) act jointly to explain long-lived brine effusion. The extent and nature of the deep liquid layer are still open questions, but the picture that has emerged from Dawn data supports the existence of a global muddy brine layer at the crust-mantle interface; brine-rich regions within the crust and upper mantle resulting from compositionally-driven variations in thermal conductivity; and near-surface hydrological systems driven by impact heating. The pervasive presence of subsurface brines and the ongoing geologic activity documented by Dawn’s observations establish Ceres as an important member of the many and varied ocean worlds within our solar system. Further exploration of Ceres, including a returned sample, as proposed in the “Exploration of Ceres’ Habitability” NASA Planetary Mission Concept Study, can address these important open questions and would greatly contribute to our understanding of evolutionary processes on ocean worlds.

Part of this work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004). Government sponsorship acknowledged.