High-temperature miscibility of iron and rock during terrestrial planet formation

Abstract

The accretion of a terrestrial body and differentiation of its silicate/oxide mantle from iron core provide abundant energy for heating its interior to temperatures much higher than the present day Earth. The consequences of differentiation on the structure and composition of planets are typically addressed considering only the interaction of molten iron with an immiscible `rocky' phase. We demonstrate that mixing in a representative system of liquid or solid MgO and liquid iron to a single homogeneous liquid occurs at sufficiently low temperature to be present in the aftermath of a giant impact. Applying the thermodynamic integration technique to density functional theory molecular dynamics simulations, we determine the solvus closure temperature for the Fe-MgO system for pressures up to 400 GPa. Solvus closure occurs at $\sim$4000 K at low pressure, and has a weak positive pressure dependence, such that its gradient with respect to depth is less steep than an adiabatic temperature profile. This predicts a new mode of core-mantle differentiation following the most energetic giant impacts, with exsolution of iron from the mixture beginning in the outer layers of the planet. We demonstrate that high-temperature equilibration results in delivery of nominally insoluble Mg-rich material to the early core. Since MgO is the least soluble major mantle component in iron at low temperatures, these results may represent an upper bound on temperature for mixing in terrestrial planets.

arXiv comment10 pages, 9 figures, supplementary material

References in corpus (7)

• An Earth-sized planet with an Earth-like density
• Heat transport in giant (exo)planets: a new perspective
• The melting curve of MgO from first principles simulations
• All-Electron Path Integral Monte Carlo Simulations of Warm Dense Matter: Application to Water and Carbon Plasmas
• Rocky core solubility in Jupiter and giant exoplanets
• Sequestration of noble gases in giant planet interiors
• Solubility of Iron in Metallic Hydrogen and Stability of Dense Cores in Giant Planets

Cited by in corpus (10)

• A new ab initio equation of state of hcp-Fe and its implication on the interior structure and mass-radius relations of rocky super-Earths
• Near-equilibrium isotope fractionation during planetesimal evaporation
• The structure of terrestrial bodies: Impact heating, corotation limits and synestias
• Path integral Monte Carlo simulations of dense carbon-hydrogen plasmas
• The distribution of volatile elements during rocky planet formation
• The properties of heavy elements in giant planet envelopes
• Ab Initio Entropy Calculations of Water Predict the Interiors of Uranus and Neptune to be 15-30% Colder than Previous Models
• Coupled Thermal-Chemical Evolution Models of Sub-Neptunes Reveal Atmospheric Signatures of Their Formation Location
• Ab initio Simulations of Superionic H2O, H2O2, and H9O4 Compounds
• Structure and Melting of Fe, MgO, SiO2, and MgSiO3 in Planets: Database, Inversion, and Phase Diagram