Measuring the Melting Curve of Iron at Super-Earth Core Conditions by Dynamic Solidification

The prominence of iron in planetary interiors requires accurate and precise physical properties at extreme pressure and temperature. A first-order property of iron is the melting point, which is still debated for the conditions of Earth’s interior. Using precisely tuned laser pulses at the National Ignition Facility we were able to shock melt samples of iron and then further shocklessly compress the iron to pressures of 5 and 10 Mbar. We used in-situ x-ray diffraction to directly observe dynamic solidification of iron into the hexagonal close packed structure on the nanosecond timescale. From these experiments we determine the criteria for solidification and ultimately the melting point of iron up to 1000 GPa, three times the pressure of Earth’s inner core [1].

[1] Kraus et al., Measuring the melting curve of iron at super-Earth core conditions, Science, 375, 6577, 2022.