Rapid Variations of Earth’s Core Magnetic Field

Evidence of fast variations in the Earth’s core field are seen both in magnetic observatory and satellite records. We present here how they have been identified at the Earth’s surface from ground-based observatory records and how their spatio-temporal structure is now characterised by satellite data. It is shown how their properties at the core mantle boundary are extracted through localised and global modelling processes, paying particular attention to their time scales. Finally are listed possible types of waves in the liquid outer core, together with their main properties, that may give rise to these observed fast variations.

Thermal conductivity of Fe-Si alloys and thermal stratification in Earth’s core

Light elements in Earth’s core play a key role in driving convection and influencing geodynamics, both of which are crucial to the geodynamo. However, the thermal transport properties of iron alloys at high-pressure and -temperature conditions remain uncertain. Here we investigate the transport properties of solid hexagonal close-packed and liquid Fe-Si alloys with 4.3 and 9.0 wt % Si at high pressure and temperature using laser-heated diamond anvil cell experiments and first-principles molecular dynamics and dynamical mean field theory calculations. In contrast to the case of Fe, Si impurity scattering gradually dominates the total scattering in Fe-Si alloys with increasing Si concentration, leading to temperature independence of the resistivity and less electron–electron contribution to the conductivity in Fe-9Si. Our results show a thermal conductivity of ∼100 to 110 W⋅m−1⋅K−1 for liquid Fe-9Si near the topmost outer core. If Earth’s core consists of a large amount of silicon (e.g., > 4.3 wt %) with such a high thermal conductivity, a subadiabatic heat flow across the core–mantle boundary is likely, leaving a 400- to 500-km-deep thermally stratified layer below the core–mantle boundary, and challenges proposed thermal convection in Fe-Si liquid outer core.

Can NASA’s Gravity Satellites Detect Motions in Earth’s Core?

Measurements of our planet’s gravitational field could expose processes in the fluid outer core—if scientists can decipher the signals.

Fe5S2 identified as a host for sulfur in Earth’s core

Planetary habitability, as we experience on Earth, is linked to a functioning geodynamo which is in part driven by the crystallization of the liquid iron-nickel-alloy core as a planet cools over time. Cosmochemical considerations suggest that sulfur is a candidate light alloying element in rocky planetary cores of varying sizes and oxidation states; such that, iron sulfide phase relations at extreme conditions contribute to outer core thermochemical convection and inner core crystallization in a wide range of planetary bodies. Here we experimentally investigate the structural properties of the Fe-S system and report the discovery of the sulfide, Fe5S2, crystallizing in equilibrium with iron at Earth’s outer core pressures and high temperatures. Using single-crystal X-ray diffraction techniques, Fe5S2 was determined to adopt the complex Ni5As2-type structure (P63cm, Z = 6). These results conclude that Fe5S2 is likely to crystallize at the interface of Earth’s core and mantle and will begin to crystallize during the freezing out of Earth and Venus’ core overtime. The increased metal-metal bonding measured in Fe5S2 compared to the other high P-T iron sulfides may contribute to signatures of higher conductivity from regions of Fe5S2 is crystallization. Fe5S2 could serve as a host for Ni and Si as has been observed in the related meteoritic phase, perryite, (Fe, Ni)8(P, Si)3, adding intricacies to elemental partitioning during inner core crystallization. The stability of Fe5S2 presented here is key to understanding the role of sulfur in the multicomponent crystallization sequences that drive the geodynamics and dictate the structures of Earth and rocky planetary cores.