Presentation #303.01 in the session History of the Early Solar System.
The inner solar system’s modern orbital architecture provides inferences into the time of terrestrial planet formation; a ~100 Myr epoch of planet growth via collisions with planetesimals and other proto-planets. While classic numerical simulations of this scenario adequately reproduced the correct number of terrestrial worlds, their semi-major axes and approximate formation timescales, these models were unable to replicate the Earth-Mars and Venus-Mercury mass ratios (~9 and 15, respectively). At present, a number of independent models are capable of consistently generating Mars-like planets and simultaneously satisfying various important observational and geochemical constraints. With the “small Mars problem” reduced to a debate over the efficacy of different models, the formation of the solar system’s smallest planet has increasingly been the focus of recent theoretical investigations. I will present new results from a collection of companion studies designed to identify viable formation models capable of consistently generating Mercury-like planets. In particular, I will introduce a model where proto-Earth and proto-Venus initially form in the vicinity of Mercury’s modern orbit before migrating outward due to interactions with the primordial nebular gas. In successful simulations, Earth and Venus accrete excessive material from the Mercury-region as they migrate, thus allowing a small Mercury to form in dynamical isolation from the other terrestrial worlds. In addition to explaining the precise masses and orbits of all four inner planets, our model is capable of replicating differences between the inferred isotopic compositions of Earth and Mars.