Candy Wrapper for the Earth's inner core

Up-to-fivefold reverberating waves through the Earth's center and distinctly anisotropic innermost inner core

Probing the Earth's center is critical for understanding planetary formation and evolution. However, geophysical inferences have been challenging due to the lack of seismological probes sensitive to the Earth's center. Here, by stacking waveforms recorded by a growing number of global seismic stations, we observe up-to-fivefold reverberating waves from selected earthquakes along the Earth's diameter. Differential travel times of these exotic arrival pairs, hitherto unreported in seismological literature, complement and improve currently available information. The inferred transversely isotropic inner-core model contains a ~650-km thick innermost ball with P-wave speeds ~4% slower at ~50° from the Earth's rotation axis. In contrast, the inner core's outer shell displays much weaker anisotropy with the slowest direction in the equatorial plane. Our findings strengthen the evidence for an anisotropically-distinctive innermost inner core and its transition to a weakly anisotropic outer shell, which could be a fossilized record of a significant global event from the past.

Cooperative diffusion in body-centered cubic iron in Earth and super-Earths' inner core conditions

The physical chemistry of iron at the inner-core conditions is key to understanding the evolution and habitability of Earth and super-Earth planets. Based on full first-principles simulations, we report cooperative diffusion along the longitudinally fast⟨111⟩directions of body-centered cubic (bcc) iron in temperature ranges of up to 2000-4000 K below melting and pressures of ∼300-4000 GPa. The diffusion is due to the low energy barrier in the corresponding direction and is accompanied by mechanical and dynamical stability, as well as strong elastic anisotropy of bcc iron. These findings provide a possible explanation for seismological signatures of the Earth's inner core, particularly the positive correlation between P wave velocity and attenuation. The diffusion can also change the detailed mechanism of core convection by increasing the diffusivity and electrical conductivity and lowering the viscosity. The results need to be considered in future geophysical and planetary models and should motivate future studies of materials under extreme conditions.

Ni Doping: A Viable Route to Make Body-Centered-Cubic Fe Stable at Earth’s Inner Core

With the goal of answering the highly debated question of whether the presence of Ni at the Earth’s inner core can make body-centered cubic (bcc) Fe stable, we performed a computational study based on first-principles calculations on bcc, hexagonal closed packed (hcp), and face-centered cubic (fcc) structures of the Fe1−xNix alloys (x = 0, 0.0312, 0.042, 0.0625, 0.084, 0.125, 0.14, 0.175) at 200–364 GPa and investigated their relative stability. Our thorough study reveals that the stability of Ni-doped bcc Fe is crucially dependent on the nature of the distribution of Ni in the Fe matrix. We confirm this observation by considering several possible configurations for a given concentration of Ni doping. Our theoretical evidence suggests that Ni-doped bcc Fe could be a stable phase at the Earth’s inner core condition as compared to its hcp and fcc counterparts.