Shear softening of Earth's inner core indicated by its high Poisson's ratio and elastic anisotropy

Earth's inner core exhibits an unusually high Poisson' ratio and noticeable elastic anisotropy. The mechanisms responsible for these features are crucial to understanding the Earth's core. Although different mechanisms have been proposed, few mechanisms can explain both enigmas simultaneously. This study indicates that the crystal with noticeable shear softening will have strong anisotropy and especially high Poisson's ratio simultaneously. Body-centred-cubic (bcc) iron shows shear instability at the inner-core pressures and can be dynamically stabilized by temperature and light elements. It is very likely that some combinations of light elements stabilize the bcc-lattice iron alloy at the inner-core conditions. Such a bcc-lattice phase could have strong anisotropy and the Poisson's ratio of Earth's inner core before shear instability.