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

The discovery of over 4500 extra-solar planets has created a need for modelling their interior structure and dynamics. 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. We used high-energy lasers at the National Ignition Facility and in-situ x-ray diffraction to determine the melting point of iron up to 1000 GPa, three times the pressure of Earth’s inner core. We used our observation to determine the length of dynamo action during core solidification to the hexagonal close-packed structure. We find that terrestrial exoplanets with four to six times Earth’s mass have the longest dynamos, which provide important shielding against cosmic radiation.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.