Earth Sciences

Ab initio calculations on the free energy and high P – T elasticity of face-centred-cubic iron Lidunka Vocadlo, IanWood, Dario Alfè and   G.D. Price. Earth and Planetary Science Letters 268 (2008) 444–449

Just when we thought we had nearly settled on a particular phase (or two) of iron for the inner core, further calculations now show that a third phase is definitely in the running - the face-centred-cubic phase.

The free energies of the candidates (hexagonal, body-centred-cubic and face-centred-cubic) at core conditions are very similar (all within ~35 meV) - this means that they all might be stable, especially in the presence of light elements (known to exist in the core). However, the shear wave velocities of these phases of pure iron, and iron alloyed with light elements, are all significantly higher than those inferred from seismology.

The mineralogical and seismological models may be reconciled if there was partial melt in the inner core, combined with a high degree of crystalline alignment of the solid phase(s).