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

Eos ◽  
2021 ◽  
Vol 102 ◽  
Author(s):  
Megan Kalomiris
Keyword(s):  
Gravitational Field ◽  
Outer Core ◽  
Earth’S Core ◽  
Earth's Core

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

Fast (non-)diffusive Quasi-Geostrophic Magneto-Coriolis Modes in the Earth's core

2021 ◽  
Author(s):  
Felix Gerick ◽  
Dominique Jault ◽  
Jerome Noir
Keyword(s):  
Magnetic Field ◽  
Magnetic Energy ◽  
Three Dimensional ◽  
Outer Core ◽  
Equatorial Region ◽  
Earth’S Core ◽  
Earth's Core ◽  
Strong Focusing ◽  
Geomagnetic Observations ◽  
And Diffusion

<p> Fast changes of Earth's magnetic field could be explained by inviscid and diffusion-less quasi-geostrophic (QG) Magneto-Coriolis modes. We present a hybrid QG model with columnar flows and three-dimensional magnetic fields and find modes with periods of a few years at parameters relevant to Earth's core. These fast Magneto-Coriolis modes show strong focusing of their kinetic and magnetic energy in the equatorial region, while maintaining a relatively large spatial structure along the azimuthal direction. Their properties agree with some of the observations and inferred core flows. We find additionally, in contrast to what has been assumed previously, that these modes are not affected significantly by magnetic diffusion. The model opens a new way of inverting geomagnetic observations to the flow and magnetic field deep within the Earth's outer core.</p>

scholarly journals Self-diffusion coefficient and sound velocity of Fe-Ni-O fluid: implications for the stratification of Earth’s outer core

2021 ◽  
Author(s):  
Wei-Jie Li ◽  
Zi Li ◽  
Chong-Jie Mo ◽  
Xian-Tu He ◽  
Cong Wang ◽  
...  
Keyword(s):  
Diffusion Coefficient ◽  
Sound Velocity ◽  
Outer Core ◽  
The Self ◽  
Ab Initio Molecular Dynamics ◽  
Earth Model ◽  
Earth’S Core ◽  
Earth's Core ◽  
Self Diffusion ◽  
Self Diffusion Coefficient

Abstract It is experimentally reported that the stratified layer atop Earth’s outer core is hundreds of kilometers thick with a maximum sound velocity reduction of 0.3% relative to the preliminary reference Earth model. However, why the sound velocity atop the outer core is reduced remains theoretically unclear. In this paper, the Ni and vital light O in the outer core were both considered to have implications for the stratification of Earth’s core, including the stratification thickness and the sound velocity profile. Ab initio molecular dynamics simulations were performed on the Fe-Ni-O fluid under the conditions of Earth’s outer core, and the self-diffusion coefficients and ion-ion dynamic structure factors were calculated. The self-diffusion coefficient of O is (19.56±0.83)×10-9 m2s-1 at the core-mantle boundary. Combining the diffusion equation with the time evolution of the O self-diffusion coefficient, the calculated stratification thickness at present is 194.7 km. The calculated ion-ion dynamic structural factors indicate that the sound velocity in the outmost outer core near the stratified layer is 7.86 km/s. These results show that Fe-Ni-O is a possible composition of the stratified layer atop the outer core featuring an appropriate thickness and a reduced sound velocity, thereby shedding light on the dynamic behavior of Earth’s core.

Thermodynamics from first principles: temperature and composition of the Earth’s core

2003 ◽  
Vol 67 (1) ◽  
pp. 113-123 ◽  
Author(s):  
D. Alfé ◽  
M. J. Gillan ◽  
G. D. Price
Keyword(s):  
Melting Temperature ◽  
First Principles ◽  
Inner Core ◽  
Melting Curve ◽  
Outer Core ◽  
Earth’S Core ◽  
Earth's Core ◽  
The Core ◽  
Core Conditions ◽  
Main Ideas

AbstractWe summarize the main ideas used to determine the thermodynamic properties of pure systems and binary alloys from first principles calculations. These are based on the ab initio calculations of free energies. As an application we present the study of iron and iron alloys under Earth,s core conditions. In particular, we report the whole melting curve of iron under these conditions, and we put constraints on the composition of the core. We found that iron melts at 6350士600 K at the pressure corresponding to the boundary between the solid inner core and the liquid outer core (ICB). We show that the core could not have been formed from a binary mixture of Fe with S, Si or O and we propose a ternary or quaternary mixture with 8—10% of S/Si in both liquid and solid and an additional ~8% of oxygen in the liquid. Based on this proposed composition we calculate the shift of melting temperature with respect to the melting temperature of pure Fe of ~—700 K, so that our best estimate for the temperature of the Earth's core at ICB is 5650±600 K.

scholarly journals Experimental evidence for hydrogen incorporation into Earth’s core

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Shoh Tagawa ◽  
Naoya Sakamoto ◽  
Kei Hirose ◽  
Shunpei Yokoo ◽  
John Hernlund ◽  
...  
Keyword(s):  
Terrestrial Planet ◽  
Outer Core ◽  
Core Formation ◽  
Earth’S Core ◽  
Hydrogen Incorporation ◽  
Earth's Core ◽  
The Core ◽  
The Earth ◽  
Metal Silicate ◽  
Important Constituent

AbstractHydrogen is one of the possible alloying elements in the Earth’s core, but its siderophile (iron-loving) nature is debated. Here we experimentally examined the partitioning of hydrogen between molten iron and silicate melt at 30–60 gigapascals and 3100–4600 kelvin. We find that hydrogen has a metal/silicate partition coefficient DH ≥ 29 and is therefore strongly siderophile at conditions of core formation. Unless water was delivered only in the final stage of accretion, core formation scenarios suggest that 0.3–0.6 wt% H was incorporated into the core, leaving a relatively small residual H2O concentration in silicates. This amount of H explains 30–60% of the density deficit and sound velocity excess of the outer core relative to pure iron. Our results also suggest that hydrogen may be an important constituent in the metallic cores of any terrestrial planet or moon having a mass in excess of ~10% of the Earth.

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

2021 ◽  
Vol 119 (1) ◽  
pp. e2119001119
Author(s):  
Youjun Zhang ◽  
Kai Luo ◽  
Mingqiang Hou ◽  
Peter Driscoll ◽  
Nilesh P. Salke ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
High Pressure ◽  
Transport Properties ◽  
Outer Core ◽  
Earth’S Core ◽  
High Pressure And Temperature ◽  
Earth's Core ◽  
Mantle Boundary ◽  
Core Mantle Boundary ◽  
The 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.

scholarly journals Possible Changes in the Core-Mantle and Inner-Outer Core Boundaries

1972 ◽  
Vol 48 ◽  
pp. 179-181
Author(s):  
J. A. Jacobs
Keyword(s):  
Outer Core ◽  
Temporal Changes ◽  
Time Intervals ◽  
Earth’S Core ◽  
Earth's Core ◽  
Size And Shape ◽  
The Core ◽  
Earth’S Mantle ◽  
Short Time

This paper investigates the possibility that the boundaries between the Earth's mantle and core and between the inner and outer core might show temporal changes. The evolution of the Earth's core is not discussed, but the question is raised as to whether these boundaries might not undergo small changes both in size and shape over comparatively short time intervals.

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

2021 ◽  
Author(s):  
Claire Zurkowski ◽  
Barbara Lavina ◽  
Abigail Case ◽  
Kellie Swadba ◽  
Stella Chariton ◽  
...  
Keyword(s):  
Iron Sulfide ◽  
Inner Core ◽  
Outer Core ◽  
Iron Sulfides ◽  
Earth’S Core ◽  
Earth's Core ◽  
Planetary Cores ◽  
Wide Range ◽  
Metal Metal ◽  
The Stability

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.

The fine structure of the Earth's core

1964 ◽  
Vol 54 (5A) ◽  
pp. 1299-1313 ◽  
Author(s):  
R. D. Adams ◽  
M. J. Randall
Keyword(s):  
Fine Structure ◽  
Travel Time ◽  
Velocity Gradient ◽  
Inner Core ◽  
Outer Core ◽  
Earth’S Core ◽  
Time Curve ◽  
Earth's Core ◽  
The Core

Abstract Detailed study of arrivals from accurately fixed earthquakes has revealed additional complexity in the travel-time curve for PKP. A notation is introduced in which observations are denoted by P′ with a two-letter suffix indicating the branch to which they belong, namely P′AB, P′IJ, P′GH and P′DF. A new velocity solution for the Earth's core has been derived from these observations. This velocity solution differs from those previously suggested in having three discontinuous increases in velocity between the outer and inner core, at levels corresponding to 0.570, 0.455 and 0.362 times the radius of the core. This implies two shells, each between 300 and 400 km thick, surrounding the inner core; in each shell there is a small negative velocity gradient. The outer discontinuity is sufficiently shallow to prevent rays in the outer core from forming a caustic.

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