scholarly journals Thermal evolution of the Earth's core during its formation taking into account heat release from the short-lived radioisotopes 26Al and 60Fe

LITOSFERA ◽  
2021 ◽  
Vol 21 (2) ◽  
pp. 256-261
Author(s):  
A. N. Antipin ◽  
M. G. Mindubaev
Keyword(s):  
Heat Release ◽  
Thermal Evolution ◽  
Carbonaceous Chondrites ◽  
Research Subject ◽  
The Core ◽  
Temperature Distributions ◽  
Mhd Dynamo ◽  
Dynamo Mechanism ◽  
Account Heat ◽  
Fractional Content

Research subject. Based on the two-stage mechanism of the Earth's heterogeneous accumulation, previously proposed by V.N. Anfilogov and Yu.V. Khachay, the thermal evolution of the core during its formation was studied. Account is taken of both the heat release from 26Al, the content of which was established with a fairly reliable accuracy, and that from 60Fe.Materials and methods. The methods of mathematical modelling were used. Calculations were carried out for three estimates of the fractional content of the radioisotope 60Fe to stable 56Fe at the time of CAI formation (Ca-Al-In- clusions, calcium- and aluminium-rich inclusions found in carbonaceous chondrites) based on the results of various authors.Results. As a result of numerical experiments, variants of the temperature and melting temperature distributions at different stages of the core formation for different 60Fe/56Fe ratios were obtained.Conclusions. The results show that the central region of the forming core can remain melted even by the end of its accumulation. As a consequence, in this region for this time, the conditions for free thermal convection and, accordingly, for the implementation of the MHD dynamo mechanism remain.

scholarly journals Nuclear equation of state and neutron star cooling

2017 ◽  
Vol 26 (04) ◽  
pp. 1750015 ◽  
Author(s):  
Yeunhwan Lim ◽  
Chang Ho Hyun ◽  
Chang-Hwan Lee
Keyword(s):  
Neutron Star ◽  
Equation Of State ◽  
Neutron Stars ◽  
Nuclear Matter ◽  
Thermal Evolution ◽  
Observation Data ◽  
Nuclear Equation Of State ◽  
The Core ◽  
Dense Nuclear Matter ◽  
Nuclear Models

In this paper, we investigate the cooling of neutron stars with relativistic and nonrelativistic models of dense nuclear matter. We focus on the effects of uncertainties originated from the nuclear models, the composition of elements in the envelope region, and the formation of superfluidity in the core and the crust of neutron stars. Discovery of [Formula: see text] neutron stars PSR J1614−2230 and PSR J0343[Formula: see text]0432 has triggered the revival of stiff nuclear equation of state at high densities. In the meantime, observation of a neutron star in Cassiopeia A for more than 10 years has provided us with very accurate data for the thermal evolution of neutron stars. Both mass and temperature of neutron stars depend critically on the equation of state of nuclear matter, so we first search for nuclear models that satisfy the constraints from mass and temperature simultaneously within a reasonable range. With selected models, we explore the effects of element composition in the envelope region, and the existence of superfluidity in the core and the crust of neutron stars. Due to uncertainty in the composition of particles in the envelope region, we obtain a range of cooling curves that can cover substantial region of observation data.

Adiabatic Heat Flow in Mercury with a Fe-8.5wt%Si Core

2021 ◽  
Author(s):  
Meryem Berrada ◽  
Richard Secco ◽  
Wenjun Yong
Keyword(s):  
Thermal Conductivity ◽  
Heat Flow ◽  
Internal Structure ◽  
High Pressures ◽  
Inner Core ◽  
Thermal Evolution ◽  
The Core ◽  
Thermally Driven ◽  
Wire Method ◽  
Core Conditions

<p>Recent theoretical studies have tried to constrain Mercury’s internal structure and composition using thermal evolution models. The presence of a thermally stratified layer of Fe-S at the top of an Fe-Si core has been suggested, which implies a sub-adiabatic heat flow on the core side of the CMB. In this work, the adiabatic heat flow at the top of the core was estimated using the electronic component of thermal conductivity (k<sub>el</sub>), a lower bound for thermal conductivity. Direct measurements of electrical resistivity (ρ) of Fe-8.5wt%Si at core conditions can be related to k<sub>el</sub> using the Wiedemann-Franz law. Measurements were carried out in a 3000 ton multi-anvil press using a 4-wire method. The integrity of the samples at high pressures and temperatures was confirmed with electron-microprobe analysis of quenched samples at various conditions. Unexpected behaviour at low temperatures between 6-8 GPa may indicate an undocumented phase transition. Measurements of ρ at melting seem to remain constant at 127 µΩ·cm from 10-24 GPa, on both the solid and liquid side of the melting boundary. The adiabatic heat flow at the core side of Mercury’s core-mantle boundary is estimated between 21.8-29.5 mWm<sup>-2</sup>, considerably higher than most models of an Fe-S or Fe-Si core yet similar to models of an Fe core. Comparing these results with thermal evolution models suggests that Mercury’s dynamo remained thermally driven up to 0.08-0.22 Gyr, at which point the core became sub-adiabatic and stimulated a change from dominant thermal convection to dominant chemical convection arising from the growth of an inner core. Simply considering the internal structure of Mercury, these results support the capture of Mercury into a 3:2 resonance orbit during the thermally driven era of the dynamo.</p>

scholarly journals Magneto–rotational and Thermal Evolution of Magnetars with Crustal Magnetic Fields

2000 ◽  
Vol 177 ◽  
pp. 681-684 ◽  
Author(s):  
U. Geppert ◽  
D. Page ◽  
M. Colpi ◽  
T. Zannias
Keyword(s):  
Magnetic Fields ◽  
Binary Systems ◽  
Thermal Evolution ◽  
Related Question ◽  
Strong Magnetic Fields ◽  
X Ray ◽  
Soft Gamma Repeaters ◽  
Core Field ◽  
The Core ◽  
Crustal Field

The interpretation of Soft–Gamma–Repeaters (SGRs) and Anomalous X–Ray Pulsars (AXPs) as Magnetars (Thompson & Duncan 1996) raises again the issue of the generation of the ultra–strong magnetic fields (MFs) in neutron stars (NSs) and the related question of where these fields are anchored: in the core, penetrating the whole star, or confined to the crust. Recently, Heyl & Kulkarni (1998) considered the magneto–thermal evolution of magnetars with a core field. Since the assumption of a crustal field is at least not in disagreement with the observations of isolated pulsars (Urpin & Konenkov 1997) and of NSs in binary systems (Urpin, Geppert & Konenkov 1998, Urpin, Konenkov & Geppert 1998), here we would like to address the question whether the observations of SGRs and AXPs can be interpreted as magnetars having a crustal MF. Given the strength of the MF in magnetars we take into account, in an approximate manner, the strongly non–linear Hall effect on its decay. We intend to provide a contribution to an unified picture of NS MF evolution based on the crustal field hypothesis.

scholarly journals Thermal evolution of Earth with magnesium precipitation in the core

2017 ◽  
Vol 458 ◽  
pp. 263-272 ◽  
Author(s):  
Joseph G. O'Rourke ◽  
Jun Korenaga ◽  
David J. Stevenson
Keyword(s):  
Thermal Evolution ◽  
The Core

Linking the core heat content to Earth's accretion history

2020 ◽  
Author(s):  
Renaud Deguen ◽  
Vincent Clési
Keyword(s):  
Thermal State ◽  
Thermal Evolution ◽  
Heat Content ◽  
Magma Ocean ◽  
The Core ◽  
Current State ◽  
Partitioning Coefficients ◽  
The Mean ◽  
Mantle Diapirism ◽  
Do So

<p>The composition of Earth's mantle, when compared to experimentally determined partitioning coefficients, can be used to constrain the conditions of equilibration - pressure P, temperature T, and oxygen fugacity fO<sub>2</sub> - of the metal and silicates during core-mantle differentiation.<br>This places constraints on the thermal state of the planet during its accretion, and it is tempting to try to use these data to estimate the heat content of the core at the end of accretion. To do so, we develop an analytical model of the thermal evolution of the metal phase during its descent through the solid mantle toward the growing core, taking into account compression heating,   viscous dissipation heating, and heat exchange with the surrounding silicates. For each impact, the model takes as initial condition the pressure and temperature at the base of the magma ocean, and gives the temperature of the metal when it reaches the core. The growth of the planet results in additional pressure increase and compression heating of the core. The thermal model is coupled to a Monte-Carlo inversion of the metal/silicates equilibration conditions (P, T, fO<sub>2</sub>) in the course of accretion from the abundance of Ni, Co, V and Cr in the mantle, and provides an estimate of the core heat content at the end of accretion for each geochemically successful accretion. The core heat content depends on the mean degree of metal-silicates equilibration, on the mode of metal/silicates separation in the mantle (diapirism, percolation, or dyking), but also very significantly on the shape of the equilibration conditions curve (equilibration P and T vs. fraction of Earth accreted). We find that many accretion histories which are successful in reproducing the mantle composition yield a core that is colder than its current state. Imposing that the temperature of the core at the end of accretion is higher than its current values therefore provides strong constraints on the accretion history. In particular, we find that the core heat content depends significantly on the last stages of accretion. </p>

scholarly journals Upper Devonian brachiopods from the core of the Kurgan-Uspenskaya-1 key borehole (south-western outlying areas of Western Siberia)

LITOSFERA ◽  
2021 ◽  
Vol 21 (4) ◽  
pp. 560-573
Author(s):  
A. G. Mizens ◽  
L. I. Mizens
Keyword(s):  
East European Platform ◽  
Western Siberia ◽  
Upper Devonian ◽  
Tectonic Block ◽  
Research Subject ◽  
The South ◽  
The Urals ◽  
East European ◽  
The Core ◽  
Host Rocks

Research subject. Brachiopods from the core of the Kurgan-Uspenskaya-1 parametric borehole. The borehole was drilled in the south of Western Siberia 80 km southeast of the Kurgan town. Brachiopods were collected at a depth of 1,525.4 m in the IV tectonic block (core interval 1,450–1,794 m) in the greenish-gray marls of the Famennian stage of the Upper Devonian.Materials and methods. The paleontological material is presented in the form of complete undamaged shells and individual valves of small- and medium-sized brachiopods. The safety of brachiopods makes it possible to determine their species and genera, sometimes in open nomenclature. The article provides a brief description of the available material.Results. 11 species of brachiopods of the subtype Rhynchonelliformea belonging to six orders and nine genera were identified. The following ten species were described: Orbinaria fallax (Pand.), Semiproductus amplus Bubl., Schuchertella sp., Dalejina? sp., Camarotoechia panderi (Sem.et Moell.), C. volucera Nal., Athyris tobolica Nal., Cleiothyridina tenuilineata (Row.), Cl. ex gr. pectinata (Sem. et Moell.), Retzia? sp. The presented information allows conclusions about the age of the sediments enclosing the brachiopods under study and expands the existing knowledge of both the composition of the Upper Famennian brachiopods of the basement of the south of Western Siberia and their geographical and stratigraphic distribution.Conclusion. An analysis of the stratigraphic distribution of the described brachiopods taking into account data on foraminifera allowed us to determine the age of the host rocks as the very top of the Famennian stage. The composition of the brachiopods allows these rocks to be correlated with coeval deposits of the East European Platform, Timan, the Urals, Kuzbass, the Gorny Altai, Kazakhstan and North America.

scholarly journals Conceptualisation of Youth Sociality in Post­Subcultural Research: Neo­Tribes Theory

2015 ◽  
pp. 24-28
Author(s):  
Elena I. Bulatova
Keyword(s):  
Cultural Studies ◽  
Research Subject ◽  
Traditional Concept ◽  
The Core ◽  
Core Idea

Investigates the approaches to conceptualising youth cultural studies within the post­subcultural theory. The author argues that the core idea of post­subcultural paradigm is the doubt in the metanarrative of “subculture.” In this situation, the heuristic potential of the new categorical apparatus designed to replace the traditional concept of “subculture” becomes a research subject.

scholarly journals Sculpting the valley in the radius distribution of small exoplanets as a by-product of planet formation: the core-powered mass-loss mechanism

2019 ◽  
Vol 487 (1) ◽  
pp. 24-33 ◽  
Author(s):  
Akash Gupta ◽  
Hilke E Schlichting
Keyword(s):  
Mass Loss ◽  
Thermal Evolution ◽  
Relative Magnitude ◽  
Occurrence Rate ◽  
Loss Mechanism ◽  
Water Ice ◽  
The Core ◽  
Planetary Cores ◽  
Short Period ◽  
Atmospheric Mass

ABSTRACT Recent observations revealed a bimodal radius distribution of small, short-period exoplanets with a paucity in their occurrence, a radius ‘valley’, around 1.5–2.0 R⊕. In this work, we investigate the effect of a planet’s own cooling luminosity on its thermal evolution and atmospheric mass loss (core-powered mass-loss) and determine its observational consequences for the radius distribution of small, close-in exoplanets. Using simple analytical descriptions and numerical simulations, we demonstrate that planetary evolution based on the core-powered mass-loss mechanism alone (i.e. without any photoevaporation) can produce the observed valley in the radius distribution. Our results match the valley’s location, shape and slope in planet radius–orbital period parameter space, and the relative magnitudes of the planet occurrence rate above and below the valley. We find that the slope of the valley is, to first order, dictated by the atmospheric mass-loss time-scale at the Bondi radius and given by d logRp/d logP ≃ 1/(3(1 − β)) that evaluates to −0.11 for β ≃ 4, where Mc/M⊕ = (Rc/R⊕)β(ρc∗/ρ⊕)β/3 is the mass–radius relation of the core. This choice for β yields good agreement with observations and attests to the significance of internal compression for massive planetary cores. We further find that the location of the valley scales as $\rho _{\rm c*}^{-4/9}$ and that the observed planet population must have predominantly rocky cores with typical water–ice fractions of less than ${\sim } 20{{\, \rm per\, cent}}$. Furthermore, we show that the relative magnitude of the planet occurrence rate above and below the valley is sensitive to the details of the planet-mass distribution but that the location of the valley is not.

Transport of planktic foraminifera by ocean currents in the Uruguayan margin

2020 ◽  
Author(s):  
Anne Kruijt ◽  
Andrew Mair ◽  
Peter Nooteboom ◽  
Anna S. von der Heydt ◽  
Martin Ziegler ◽  
...  
Keyword(s):  
Biological Activity ◽  
General Circulation ◽  
Ocean Currents ◽  
Western Boundary ◽  
Planktic Foraminifera ◽  
The Core ◽  
Temperature Distributions ◽  
Species Analysis ◽  
Core Site ◽  
Ocean Conditions

<p><span>Fossils of planktic foraminifera are found in marine sediments and are widely used as a proxy for past ocean conditions. The habitat of these unicellular marine zooplankton ranges from tropical to polar regions and is mostly located in the upper mixed layer of the ocean. The foraminifera form a calcium carbonate ’shell’ around their cell during their lifespan. When they die, foraminifera lose their ability to control their buoyancy and their shells sink to the ocean floor. It is often assumed that the proxies which are derived from the shells in sediment cores represent ocean conditions above the location of deposition. However, foraminifera are transported by ocean currents, both during and after their lifespan. Hence, the paleoclimatic conditions recorded from their shells may originate far from the core site, generating large footprints in foraminifera-based paleoclimatic proxies.</span><span> </span></p><p><span>In this project, we quantify the influence of the transport by ocean currents on the proxy signal of foraminifera found at core sites in the Uruguayan margin of the Punta del Este basin. This is a region where two western boundary currents meet: The southward flowing Brazil current and the northward flowing Malvinas current. We use a high resolution (0.1° horizontally) ocean general circulation model to track virtual sinking particles and the local oceanic conditions along their pathways. These model results are compared to proxy- and species analysis from the core sites. We found that offsets in modelled proxy signals due to transport in the Uruguayan margin are strongly linked to the relative position of the core site to the Brazil-Malvinas confluence. These offsets are most pronounced in the tails of the temperature distributions where they can reach up to +/- 7°C at sites located in the confluence zone. Species analysis from core tops taken slightly north of this region show more cold water species than reflected by the modelled temperature distributions, suggesting biological activity and nutrient availability not taken into account in the model play an important additional role in the relative abundances of species. <br></span><span>Our model simulations have provided both a first order insight into the potential proxy-signal offsets in highly dynamic ocean regions and show that understanding of the interplay between transportation effects and the biological activity of foraminifera is crucial for the interpretation of these proxies.</span></p><p> </p>

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