Shock temperatures and melting of iron at Earth core conditions

The temperature of shock compressed iron has been measured to 340 GPa, using well characterized iron films sputtered on transparent diamond substrates and a 1 ns time-resolved optical method. We find a knee on the (P,T) iron Hugoniot indicating melting at 6350 K and 235 GPa and at 6720 K and 300 GPa. An extrapolation yields an iron melting temperature of 6830 (\ifmmode\pm\else\textpm\fi{} 500) K at 330 GPa, the pressure of the Earth inner-outer core boundary. Implication of the melting data for the iron phase diagram is also discussed.