Dynamical Origins of the Chemical Architecture of the Terrestrial Planets

The models most successful in reproducing the dynamical architecture of the inner Solar System invoke a single ring of rocky material that, over 100 Myr, accreted into the rocky planets. This paradigm explains the presence of two closely-spaced massive planets, Earth and Venus, and the low mass of Mercury and Mars (Hansen 2009). However, chemical and isotopic analyses have demonstrated that the Earth accreted from at least two different material reservoirs separated in space and time that differ in oxidation state (Rubie et al. 2011). Traces of this distinction are preserved today in the ordinary and enstatite chondrites, although Earth remains an isotopic end-member compared to known meteoritic material.

Our goal is to build a single self-consistent model of the Solar disk evolution, planetesimal formation, and terrestrial planet accretion compatible with all available constraints. We use GPU-accelerated dynamical simulations and modern disk paradigms to make testable predictions of the orbital architecture of the Solar System and the chemical and isotopic compositions of planets and small bodies (see Woo et al. 2023, 2024). I will discuss in particular the role of two gas-driven mechanisms in transporting material through the early Solar System. First, type I migration can carry large embryos to denser regions of the disk, leaving behind remnants that form Mercury and Mars. Secondly, sweeping secular resonances from the giant planets deliver oxidized proto-asteroid belt bodies that make up most of Mars and 25% of the Earth. After dissipation of the Solar nebula, the giant planet instability finishes terrestrial planet formation and implants asteroids in the main belt. While complex, this scenario simultaneously explains the heterogeneity of Earth's accretion, the chemical diversity seen in the asteroid belt, and the dynamical architecture of the terrestrial planets. Although fully matching the characteristics of the Solar System is a probabilistic endeavor given the stochastic nature of terrestrial planet accretion, our models regularly produce Solar System analogues without neglecting important physics.