Structural evolution of liquid silicates under conditions in Super-Earth interiors

Molten silicates existing at depth play a pivotal role in planetary evolution. However, the determination of the local structure and physical properties of liquid silicates under extreme pressure and temperature conditions has been hindered by the inherent experimental complexity of such measurements. In this study, we present an in situ X-ray diffraction investigation of liquid silicates conducted at the Matter in Extreme Conditions (MEC) end-station of the Linear Coherent Linac Source (LCLS) at SLAC National Accelerator Laboratory. The combination of the ultrabright X-ray source and a high-power optical laser allowed us to successfully probe the local atomic arrangement of shock-compressed liquid (Mg,Fe)SiO3 with a range of Fe content, spanning pressures from 81(9) to 385(40) GPa. This experimental dataset is then compared to ab initio molecular dynamics performed under similar pressure-temperature conditions. Our results reveal a continuous densification of the O-O and Mg-Si networks beyond the pressure range found at the interior of the Earth, which can alter the properties of melts at these extreme conditions. This may have a considerable impact on the early stages of planetary evolution, resulting in substantial differences in the differentiation processes between smaller rocky planets, such as Earth and Venus in our solar system, and super-Earths, i.e., exoplanets with masses nearly three times larger than that of Earth.