scholarly journals Partial core vaporization during giant impacts inferred from the entropy and the critical point of iron

2021 ◽  
Author(s):  
Zhi Li ◽  
Razvan Caracas ◽  
François Soubiran
Keyword(s):  
Critical Point ◽  
Large Fraction ◽  
Iron Core ◽  
The Moon ◽  
Earth Planet ◽  
Density Region ◽  
Giant Impact ◽  
Giant Impacts ◽  
Core Conditions ◽  
Dynamics Simulations

<h3>The prevailing theory of the origin of the Moon is the giant impact hypothesis, in which a Mars-sized impactor collides with the proto-Earth in the late stage of accretion, and the Moon is subsequently formed from the proto-lunar disk made of the ejected materials. As the laboratory-scale experiments are not able to simulate planetary-scale impacts, our understanding of the giant impact mostly comes from hydrodynamic simulations. However, the results of these simulations heavily depend upon the available equation of state to describe the thermodynamic response of the constituent materials of the proto-Earth and impactor to shock waves.</h3><h3> </h3><h3>Iron as a building block material of the terrestrial planets naturally received significant attention. But the major effort has been put to determine its phase diagram up to the Earth’s core conditions (126-360 GPa and 3000-7000 K) and beyond. The studies of iron at low densities are still scarce and the position of the critical point (CP) is uncertain. As the liquid-vapor dome ends at CP, the position of the latter determines the time evolution of the proto-lunar disk during its condensation.</h3><h3> </h3><h3>In order to assess whether the core of the planets undergoes significant vaporization during a giant impact, we employ <em>ab initio</em> molecular-dynamics simulations to explore iron over a wide density region encompassing the critical point (CP) and the Hugoniot lines of the shocked iron cores. We determine the critical point of iron in the temperature range of 9000-9350 K, and the density range of 1.85-2.40 g/cm<sup>3</sup>, corresponding to a pressure range of 4-7 kbars [1]. This implies that the iron core of the proto-Earth may become supercritical after giant impacts. We show that the iron core of Theia partially vaporized during the Giant Impact. Part of this vapour may have remained in the disk, to eventually participate in the Moon’s small core. Similarly, during the late veneer stage a large fraction of the planetesimals have their cores undergoing partial vaporization. This would help to mix the highly siderophile elements into magma ponds or oceans.</h3><h3> </h3><h3>References:</h3><h3>[1] Z. Li, R. Caracas, F. Soubiran, Partial core vaporization during Giant Impacts inferred from the entropy and the critical point of iron, Earth Planet. Sci. Letters, 2020, https://doi.org/10.1016/j.epsl.2020.116463</h3><h3> </h3>

scholarly journals Isotopic evidence for the formation of the Moon in a canonical giant impact

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Sune G. Nielsen ◽  
David V. Bekaert ◽  
Maureen Auro
Keyword(s):  
Solar System ◽  
Isotope Fractionation ◽  
Main Stage ◽  
The Moon ◽  
Giant Impact ◽  
Bulk Silicate Earth ◽  
The Earth ◽  
The Standard Model ◽  
Isotopic Measurements ◽  
Origin Of The Moon

AbstractIsotopic measurements of lunar and terrestrial rocks have revealed that, unlike any other body in the solar system, the Moon is indistinguishable from the Earth for nearly every isotopic system. This observation, however, contradicts predictions by the standard model for the origin of the Moon, the canonical giant impact. Here we show that the vanadium isotopic composition of the Moon is offset from that of the bulk silicate Earth by 0.18 ± 0.04 parts per thousand towards the chondritic value. This offset most likely results from isotope fractionation on proto-Earth during the main stage of terrestrial core formation (pre-giant impact), followed by a canonical giant impact where ~80% of the Moon originates from the impactor of chondritic composition. Our data refute the possibility of post-giant impact equilibration between the Earth and Moon, and implies that the impactor and proto-Earth mainly accreted from a common isotopic reservoir in the inner solar system.

The history of the core dynamos of Mars and the Moon inferred from their crustal magnetization: a brief review

2019 ◽  
Vol 56 (9) ◽  
pp. 917-931
Author(s):  
Jafar Arkani-Hamed
Keyword(s):  
The Moon ◽  
Positive Mass ◽  
Polar Wander ◽  
The Core ◽  
True Polar Wander ◽  
History Of ◽  
Giant Impacts ◽  
Crustal Magnetization ◽  
Multiple Impact ◽  
Thermochemical Convection

The core dynamos of Mars and the Moon have distinctly different histories. Mars had no core dynamo at the end of accretion. It took ∼100 Myr for the core to create a strong dynamo that magnetized the martian crust. Giant impacts during 4.2–4.0 Ga crippled the core dynamo intermittently until a thick stagnant lithosphere developed on the surface and reduced the heat flux at the core–mantle boundary, killing the dynamo at ∼3.8 Ga. On the other hand, the Moon had a strong core dynamo at the end of accretion that lasted ∼100 Myr and magnetized its primordial crust. Either precession of the core or thermochemical convection in the mantle or chemical convection in the core created a strong core dynamo that magnetized the sources of the isolated magnetic anomalies in later times. Mars and the Moon indicate dynamo reversals and true polar wander. The polar wander of the Moon is easier to explain compared to that of Mars. It was initiated by the mass deficiency at South Pole Aitken basin, which moved the basin southward by ∼68° relative to the dipole axis of the core field. The formation of mascon maria at later times introduced positive mass anomalies at the surface, forcing the Moon to make an additional ∼52° degree polar wander. Interaction of multiple impact shock waves with the dynamo, the abrupt angular momentum transfer to the mantle by the impactors, and the global overturn of the core after each impact were probably the factors causing the dynamo reversal.

scholarly journals Finite-size transitions in complex membranes

2020 ◽  
Author(s):  
M. Girard ◽  
T. Bereau
Keyword(s):  
Experimental Evidence ◽  
Critical Point ◽  
Finite Size ◽  
Underlying Mechanism ◽  
Large Temperature ◽  
Strong Argument ◽  
Biological Regulation ◽  
Critical Manifold ◽  
Critical Composition ◽  
Dynamics Simulations

ABSTRACTThe lipid raft hypothesis postulates that cell membranes possess some degree of lateral organization. The last decade has seen a large amount of experimental evidence for rafts. Yet, the underlying mechanism remains elusive. One hypothesis that supports rafts relies on the membrane to lie near a critical point. While supported by experimental evidence, the role of regulation is unclear. Using both a lattice model and molecular dynamics simulations, we show that lipid regulation of a many-component membrane can lead to critical behavior over a large temperature range. Across this range, the membrane displays a critical composition due to finite-size effects. This mechanism provides a rationale as to how cells tune their composition without the need for specific sensing mechanisms. It is robust and reproduces important experimentally verified biological trends: membrane-demixing temperature closely follows cell growth temperature, and the composition evolves along a critical manifold. The simplicity of the mechanism provides a strong argument in favor of the critical membrane hypothesis.SIGNIFICANCEWe show that biological regulation of a large amount of phospholipids in membranes naturally leads to a critical composition for finite-size systems. This suggests that regulating a system near a critical point is trivial for cells. These effects vanish logarithmically and therefore can be present in micron-sized systems.

scholarly journals Boundary conditions for the formation of the Moon

2015 ◽  
Vol 95 (2) ◽  
pp. 131-139 ◽  
Author(s):  
M. Reuver ◽  
R.J. de Meijer ◽  
I.L. ten Kate ◽  
W. van Westrenen
Keyword(s):  
Angular Momentum ◽  
Boundary Conditions ◽  
Total Angular Momentum ◽  
Nuclear Explosion ◽  
Moment Of Inertia ◽  
The Moon ◽  
Moon System ◽  
Giant Impact ◽  
The Earth ◽  
The Impact

AbstractRecent measurements of the chemical and isotopic composition of lunar samples indicate that the Moon's bulk composition shows great similarities with the composition of the silicate Earth. Moon formation models that attempt to explain these similarities make a wide variety of assumptions about the properties of the Earth prior to the formation of the Moon (the proto-Earth), and about the necessity and properties of an impactor colliding with the proto-Earth. This paper investigates the effects of the proto-Earth's mass, oblateness and internal core-mantle differentiation on its moment of inertia. The ratio of angular momentum and moment of inertia determines the stability of the proto-Earth and the binding energy, i.e. the energy needed to make the transition from an initial state in which the system is a rotating single body with a certain angular momentum to a final state with two bodies (Earth and Moon) with the same total angular momentum, redistributed between Earth and Moon. For the initial state two scenarios are being investigated: a homogeneous (undifferentiated) proto-Earth and a proto-Earth differentiated in a central metallic and an outer silicate shell; for both scenarios a range of oblateness values is investigated. Calculations indicate that a differentiated proto-Earth would become unstable at an angular momentum L that exceeds the total angular momentum of the present-day Earth–Moon system (L0) by factors of 2.5–2.9, with the precise maximum dependent on the proto-Earth's oblateness. Further limitations are imposed by the Roche limit and the logical condition that the separated Earth–Moon system should be formed outside the proto-Earth. This further limits the L values of the Earth–Moon system to a maximum of about L/L0 = 1.5, at a minimum oblateness (a/c ratio) of 1.2. These calculations provide boundary conditions for the main classes of Moon-forming models. Our results show that at the high values of L used in recent giant impact models (1.8 < L/L0 < 3.1), the proposed proto-Earths are unstable before (Cuk & Stewart, 2012) or immediately after (Canup, 2012) the impact, even at a high oblateness (the most favourable condition for stability). We conclude that the recent attempts to improve the classic giant impact hypothesis by studying systems with very high values of L are not supported by the boundary condition calculations in this work. In contrast, this work indicates that the nuclear explosion model for Moon formation (De Meijer et al., 2013) fulfills the boundary conditions and requires approximately one order of magnitude less energy than originally estimated. Hence in our view the nuclear explosion model is presently the model that best explains the formation of the Moon from predominantly terrestrial silicate material.

Geochemical implications of the formation of the Moon by a single giant impact

Nature ◽  
1989 ◽  
Vol 338 (6210) ◽  
pp. 29-34 ◽  
Author(s):  
Horton E. Newsom ◽  
Stuart Ross Taylor
Keyword(s):  
The Moon ◽  
Giant Impact

scholarly journals Lunar and terrestrial planet formation in the Grand Tack scenario

2014 ◽  
Vol 372 (2024) ◽  
pp. 20130174 ◽  
Author(s):  
S. A. Jacobson ◽  
A. Morbidelli
Keyword(s):  
Total Mass ◽  
Planet Formation ◽  
Terrestrial Planet ◽  
Terrestrial Planets ◽  
The Moon ◽  
Giant Impact ◽  
Modal Mass ◽  
The Individual ◽  
Impact Phase ◽  
Geochemical Constraints

We present conclusions from a large number of N -body simulations of the giant impact phase of terrestrial planet formation. We focus on new results obtained from the recently proposed Grand Tack model, which couples the gas-driven migration of giant planets to the accretion of the terrestrial planets. The giant impact phase follows the oligarchic growth phase, which builds a bi-modal mass distribution within the disc of embryos and planetesimals. By varying the ratio of the total mass in the embryo population to the total mass in the planetesimal population and the mass of the individual embryos, we explore how different disc conditions control the final planets. The total mass ratio of embryos to planetesimals controls the timing of the last giant (Moon-forming) impact and its violence. The initial embryo mass sets the size of the lunar impactor and the growth rate of Mars. After comparing our simulated outcomes with the actual orbits of the terrestrial planets (angular momentum deficit, mass concentration) and taking into account independent geochemical constraints on the mass accreted by the Earth after the Moon-forming event and on the time scale for the growth of Mars, we conclude that the protoplanetary disc at the beginning of the giant impact phase must have had most of its mass in Mars-sized embryos and only a small fraction of the total disc mass in the planetesimal population. From this, we infer that the Moon-forming event occurred between approximately 60 and approximately 130 Myr after the formation of the first solids and was caused most likely by an object with a mass similar to that of Mars.

DETERMINATION OF THE VAPOR-LIQUID CRITICAL POINT FROM THE SHORT-TIME DYNAMICS

2001 ◽  
Vol 15 (12n13) ◽  
pp. 369-374 ◽  
Author(s):  
SHENG-YOU HUANG ◽  
XIAN-WU ZOU ◽  
ZHI-JIE TAN ◽  
ZHUN-ZHI JIN
Keyword(s):  
Critical Point ◽  
Early Time ◽  
Dynamic Scaling ◽  
Time Behavior ◽  
Time Dynamic ◽  
Time Dynamics ◽  
Dynamics Simulations ◽  
Average Potential Energy ◽  
Short Time ◽  
Vapor Liquid

Considering the average potential energy per particle as the parameter, we investigate the early-time dynamics of vapor-liquid transition in the critical region for 2D Lennard-Jones fluids by using NVT molecular dynamics simulations. The results verify the existence of short-time dynamic scaling in the fluid systems and show that the critical point Tc can be determined by the universal short-time behavior. The obtained value of Tc = 0.540 from the short-time dynamics is very close to the value of 0.533 from the Monte Carlo simulations in the equilibrium state of the systems.

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