Potential for Ultra-High Pressure Liquid-Liquid Transition in MgSiO3

Here we report on laser-driven shock compression experiments to study the high-pressure equation of state of MgSiO₃, a major component of the terrestrial mantle and probable constituent of extrasolar rocky planets. Data were collected on both the Janus (LLNL) and Omega (LLE, Rochester) laser platforms. We extend equation of state measurements on MgSiO₃ single-crystal and glass samples to 5 Mbar and 18,000 K and report on the possibility of a first-order liquid/liquid transition around 4Mbar with an apparent increase in optical reflectivity (>20%) and density (>5%). These observations imply that the distinction between silicate and metallic constituents is blurred in deep planetary interiors and reveals the potential for unexpectedly complex chemistry in silicate liquids at high pressure and temperature. These conditions are particularly relevant for understanding early planetary evolution at the high temperatures and pressures present after the late-stage giant impact that formed the Moon.