Core metamorphism controls the dynamic habitability of mid-sized ocean worlds-The case of Ceres.

Ceres's surface mineralogy and density structure indicate an aqueous past. Observations from the Dawn mission revealed that Ceres likely hosted a global subsurface ocean in its early history, which was the site of pervasive aqueous alteration of accreted material. Subsurface environmental constraints inferred from Ceres's surface mineralogy, combined with Ceres's high abundance of carbon, suggest that the dwarf planet may have been habitable for microbial life. We present a coupled chemical and thermal evolution model tracking Ceres's interior aqueous environment through time. If the rocky interior reached ≳550 K, then fluids released by rock metamorphism would have promoted conditions favorable for habitability by introducing redox disequilibrium into the ocean, a source of chemical energy for chemotrophs. We find that this period would have been between ~0.5 and 2 billion years after Ceres's formation. Since then, Ceres's ocean has likely become a cold, concentrated brine with fewer sources of energy, making it less likely to be habitable at present.