Ultra High-Pressure Equation of State and Melting of MgSiO$_{3}$

New laser-driven shock experiments, using both single-crystal and glass starting materials, extend equation of state measurements on MgSiO$_{3}$ to 4.5 Mbar and 15,000 K. Simultaneous collection of temporally and spatially resolved velocimetry, pyrometry and reflectivity data document shock-induced melting at pressures above 275GPa, with an apparent increase in optical reflectivity ($>$20{\%}) and density (several percent). These observations indicate transformation to a metallic state upon melting, implying that the distinction between silicate and metallic constituents are blurred at Earth's core-mantle boundary. This was particularly the case at the high temperatures and pressures present after the late-stage giant impact that formed the Moon.