Critical vaporization of MgSiO₃

Inhomogeneous ab initio molecular dynamics simulations show that vaporization of MgSiO₃ is incongruent and that the vapor phase is dominated by SiO and O₂ molecules. The vapor is strongly depleted in Mg at low temperature and approaches the composition of the liquid near the critical point. We find that the liquid–vapor critical temperature (6,600 ±150 K) is much lower than assumed in hydrodynamic simulations, pointing to much more extensive supercritical fluid after the Moon-forming impact than previously thought. The structure of the near-critical liquid is very different from what has been studied previously and includes a significant fraction (10%) of molecular species SiO and O₂.