Permeability-limited compaction and (de)serpentinization of Ceres' rocky core preserve subsurface fluids

Abstract

Observations from NASA's Dawn mission suggest that Ceres' low-density rocky core remains porous and that brines have recently been extruded onto the surface. Despite abundant evidence of global aqueous alteration, little is known about the dynamics of fluid transport in Ceres' interior or whether subsurface fluids persist to the present day. We address three questions: (1) What controls the timescale of compaction and differentiation in volatile-rich planetesimals? (2) Can Ceres retain pore fluids over 4.5 Gyr? (3) How does the coupling between mineral dehydration-driven fluid production and compaction-driven fluid extraction affect Ceres' evolution? We present a coupled thermal, chemical and mechanical model that explicitly accounts for pore fluid generation, consumption and transport during Ceres' evolution. We show that compaction of Ceres' rocky core is likely limited by the pore fluid mobility (i.e., permeability/fluid viscosity ratio) rather than solid-state creep. Differentiation remains incomplete and porosity persists if the average permeability is approximately 10^ -15 ϕ^3 m2$, where ϕ is porosity. This delayed compaction produces a small but ongoing extrusion of pore fluids at rates of 10^4 to 10^5 m$^3/yr, consistent with recent brine activity on Ceres' surface. Fluids released during deserpentinization are partially extracted by an outward migrating porosity wave and partially consumed by reserpentinization upon cooling, resulting in olivine retention. The persistence of subsurface fluids and the de-/reserpentinization cycle (which may produce ) enhance Ceres' habitability. Moreover, ongoing fluid extrusion implies that signatures of Ceres' deep interior are still being transported to the surface, making surface sampling viable for detecting biosignatures if a subsurface biosphere exists. H2