Iron phase diagram: Our results (red open squares for solid hcp and red full square for liquid Fe) are compared with previous results and extrapolation obtained in the literature from diamond-anvil-cell compression [4, 6, 36], shock-waves experiments [8, 9, 10, 11, 12, 13], and ab initio simulations [1, 2, 3]. The ICB pressure of 330 GPa is shown with a dashed blue line.Taking advantage of the new opportunities provided by x-ray free electron laser (FEL) sources when coupled to a long laser pulse as available at the Linear Coherent Light Source (LCLS), we have performed x-ray absorption near-edge spectroscopy (XANES) of laser shock compressed iron up to 420 GPa (±50) and 10 800 K (±1390). Visible diagnostics coupled with hydrodynamic simulations were used to infer the thermodynamical conditions along the Hugoniot and the release adiabat. A modification of the pre-edge feature at 7.12 keV in the XANES spectra is observed above pressures of 260 GPa along the Hugoniot. Comparing with ab initio calculations and with previous laser-heated diamond cell data, we propose that such changes in the XANES pre-edge could be a signature of molten iron. This interpretation then suggests that iron is molten at pressures and temperatures higher than 260 GPa (±29) and 5680 K (±700) along the principal Fe Hugoniot.
