Even in an age when New Horizons snaps portraits of Pluto and Curiosity traverses the surface of Mars, the center of our own planet remains a mystery. Earth’s core is anisotropic: The way that a seismic wave behaves as it travels through the core depends on the direction of the wave. But scientists aren’t quite sure why.
The property is likely related to the structure of the iron alloy that makes up the core. In a new paper, Lincot et al. explore the properties associated with one such potential structure. The team aimed to find out if inner-core anisotropy arises from the plastic deformation—that is, bending without breaking—of a cubic phase of this material.
They started with a microscopic cubic structure of iron and then reconstructed the history of a virtual inner core composed of that structure. Then they sent 100,000 simulated seismic rays through their virtual present-day core. They calculated the travel time of each of the rays.
The authors found that plastic deformation of cubic phases of iron cannot produce global inner-core anisotropy above 0.5%. This is far below seismic observations of inner-core anisotropy. If the inner-core material is indeed cubic, the authors conclude, then the anisotropic quality must come from some other mechanism. Potential sources include solidification texturing, grain growth, and melt inclusions. Or the iron alloy could have a hexagonal structure instead of a cubic one. Ultimately, the authors’ work contributes to a better understanding of our home planet and the geophysical processes that shape it through its history. (Geophysical Research Letters, doi:10.1002/2014GL062862, 2015)
—Shannon Palus, Freelance Writer
Citation: Palus, S. (2015), The enigmatic core properties of the inner Earth, Eos, 96, doi:10.1029/2015EO038169. Published on 28 October 2015.