Thermodynamic and transport properties of meteor melt constituents from ab initio simulations: MgSiO 3, SiO 2, and MgO

Abstract

Recent experiments have suggested that melt flow plays a critical role in the ablation of meteoroids during atmospheric entry. Thus, modeling ablation requires knowledge of the melt properties of meteoritic constituents. These properties, however, are poorly understood and difficult to obtain with experimental techniques at entry conditions. An alternative means of obtaining high-temperature melt properties is through ab initio molecular dynamics (AIMD) simulations. Such simulations are performed here to characterize the melt properties of enstatite (MgSiO 3), which is prevalent in certain types of chondrites, and its constitutive oxides (SiO 2 and MgO). The structure, thermodynamic properties (density, bulk modulus, heat capacity, and coefficient of thermal expansion), and transport properties (diffusion and viscosity) are computed across the entire liquid phase and agree well with the limited number of available experiments. The high fidelity AIMD results are compared against less accurate models for melt property determination, which include classical molecular dynamics simulations and empirical mixture rules. Properties obtained from these alternative models generally show large relative errors compared to experiment, with viscosity, in particular, having errors of up to 98%. The present results highlight the potential of AIMD simulations to provide "quantitatively accurate" properties for melts of complex silicates found in meteorites and terrestrial rocks.