The Influence of Planetary Accretion on Mantle Oxidation State: Does Size Really Matter?

TRAPPIST-1, an ultra-cool dwarf star, hosts seven Earth-sized, temperate exoplanets. This situates this system, a compact analogue of the inner Solar System, as the optimal setting to study the evolution and formation of terrestrial planets that formed in the same protoplanetary disk and under similar conditions. Like the inner planets of the solar system, the TRAPPIST-1 system contains rocky planets that formed through accretion. Understanding how this system’s bodies grew and settled with equilibrium temperatures that can sustain liquid surface water is one of the driving questions of understanding planetary formation histories that yield habitable planets. Clarity surrounding the formation and accretion processes of rocky worlds still eludes us, and consequently, the physical and geochemical evolution of these planets needs further exploration. Utilizing N-Body simulations and geochemical modeling, this study explores how the core-mass fraction and mantle oxidation state of terrestrial bodies with varying initial parameters changes as they accrete over time. Specifically, we incorporate volatile reactions and metal-silicate partitioning to find the characteristics of bodies undergoing the metal-silicate fractionation processes inherent to planetary formation. This work strives to yield a greater understanding of the processes that contribute to planetary habitability, including volatile partitioning, its role in establishing a mantle redox state, and how these processes vary across a single planetary system.