The Experts below are selected from a list of 234 Experts worldwide ranked by ideXlab platform
Wim Van Westrenen - One of the best experts on this subject based on the ideXlab platform.
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Carbon as the dominant light element in the Lunar Core
American Mineralogist, 2017Co-Authors: E S Steenstra, Yanhao Lin, N Rai, Max Jansen, Wim Van WestrenenAbstract:Geophysical and geochemical observations point to the presence of a light element in the Lunar Core, but the exact abundance and type of light element are poorly constrained. Accurate constraints on Lunar Core composition are vital for models of Lunar Core dynamo onset and demise, Core formation conditions (e.g., depth of the Lunar magma ocean or LMO) and therefore formation conditions, as well as the volatile inventory of the Moon. A wide range of previous studies considered S as the dominant light element in the Lunar Core. Here, we present new constraints on the composition of the Lunar Core, using mass-balance calculations, combined with previously published models that predict the metal-silicate partitioning behavior of C, S, Ni, and recently proposed new bulk silicate Moon (BSM) abundances of S and C. We also use the bulk Moon abundance of C and S to assess the extent of their devolatilization. We observe that the Ni content of the Lunar Core becomes unrealistically high if shallow ( 3 GPa) LMO scenarios are considered for S and C. The moderately siderophile metal-silicate partitioning behavior of S during Lunar Core formation, combined with the low BSM abundance of S, yields only
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carbon as the dominant light element in the Lunar Core
American Mineralogist, 2017Co-Authors: E S Steenstra, Yanhao Lin, N Rai, Max Jansen, Wim Van WestrenenAbstract:Geophysical and geochemical observations point to the presence of a light element in the Lunar Core, but the exact abundance and type of light element are poorly constrained. Accurate constraints on Lunar Core composition are vital for models of Lunar Core dynamo onset and demise, Core formation conditions (e.g., depth of the Lunar magma ocean or LMO) and therefore formation conditions, as well as the volatile inventory of the Moon. A wide range of previous studies considered S as the dominant light element in the Lunar Core. Here, we present new constraints on the composition of the Lunar Core, using mass-balance calculations, combined with previously published models that predict the metal-silicate partitioning behavior of C, S, Ni, and recently proposed new bulk silicate Moon (BSM) abundances of S and C. We also use the bulk Moon abundance of C and S to assess the extent of their devolatilization. We observe that the Ni content of the Lunar Core becomes unrealistically high if shallow ( 3 GPa) LMO scenarios are considered for S and C. The moderately siderophile metal-silicate partitioning behavior of S during Lunar Core formation, combined with the low BSM abundance of S, yields only <0.16 wt% S in the Core, virtually independent of the pressure (P) and temperature (T) conditions during Core formation. Instead, our analysis suggests that C is the dominant light element in the Lunar Core. The siderophile behavior of C during Lunar Core formation results in a Core C content of ~0.6-4.8 wt%, with the exact amount depending on the Core formation conditions. A C-rich Lunar Core could explain (1) the existence of a present-day molten outer Core, (2) the estimated density of the Lunar outer Core, and (3) the existence of an early Lunar Core dynamo driven by compositional buoyancy due to Core crystallization. Finally, our calculations suggest the C content of the bulk Moon is close to its estimated abundance in the bulk silicate Earth (BSE), suggesting more limited volatile loss during the Moon-forming event than previously thought.
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Lunar Core formation new constraints from metal silicate partitioning of siderophile elements
Earth and Planetary Science Letters, 2014Co-Authors: N Rai, Wim Van WestrenenAbstract:Abstract Analyses of Apollo era seismograms, Lunar laser ranging data and the Lunar moment of inertia suggest the presence of a small, at least partially molten Fe-rich metallic Core in the Moon, but the chemical composition and formation conditions of this Core are not well constrained. Here, we assess whether pressure–temperature conditions can be found at which the Lunar silicate mantle equilibrated with a Fe-rich metallic liquid during Core formation. To this end, we combine measurements of the metal–silicate partitioning behavior of siderophile elements with the estimated depletion due to Core formation in those elements in the silicate mantle of the Moon. We also explore how the presence of the light element sulfur (suggested by seismic models to be present in the Core at concentrations of up to 6 wt%) in the Lunar Core affects Core formation models. We use published metal–silicate partitioning data for Ni, Co, W, Mo, P, V and Cr in the Lunar pressure range (1 atm–5 GPa) and characterize the dependence of the metal/silicate partition coefficients ( D ) on temperature, pressure, oxygen fugacity and composition of the silicate melt and the metal. If the Core is assumed to consist of pure iron, Core–mantle equilibration conditions that best satisfy Lunar mantle depletions of five siderophile elements—Ni, Co, W, Mo and P—are a pressure of 4.5 ( ± 0.5 ) GPa and a temperature of 2200 K. The Lunar mantle depletions of Cr and V are also consistent with metal–silicate equilibration in this pressure and temperature range if 6 wt% S is incorporated into the Lunar Core. Our results therefore suggest that metal–silicate equilibrium during Lunar Core formation occurred at depths close to the present-day Lunar Core–mantle boundary. This provides independent support for both the existence of a deep magma ocean in the Moon in its early history and the presence of significant amounts of sulfur in the Lunar Core.
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Lunar Core formation: New constraints from metal–silicate partitioning of siderophile elements
Earth and Planetary Science Letters, 2014Co-Authors: N Rai, Wim Van WestrenenAbstract:Abstract Analyses of Apollo era seismograms, Lunar laser ranging data and the Lunar moment of inertia suggest the presence of a small, at least partially molten Fe-rich metallic Core in the Moon, but the chemical composition and formation conditions of this Core are not well constrained. Here, we assess whether pressure–temperature conditions can be found at which the Lunar silicate mantle equilibrated with a Fe-rich metallic liquid during Core formation. To this end, we combine measurements of the metal–silicate partitioning behavior of siderophile elements with the estimated depletion due to Core formation in those elements in the silicate mantle of the Moon. We also explore how the presence of the light element sulfur (suggested by seismic models to be present in the Core at concentrations of up to 6 wt%) in the Lunar Core affects Core formation models. We use published metal–silicate partitioning data for Ni, Co, W, Mo, P, V and Cr in the Lunar pressure range (1 atm–5 GPa) and characterize the dependence of the metal/silicate partition coefficients ( D ) on temperature, pressure, oxygen fugacity and composition of the silicate melt and the metal. If the Core is assumed to consist of pure iron, Core–mantle equilibration conditions that best satisfy Lunar mantle depletions of five siderophile elements—Ni, Co, W, Mo and P—are a pressure of 4.5 ( ± 0.5 ) GPa and a temperature of 2200 K. The Lunar mantle depletions of Cr and V are also consistent with metal–silicate equilibration in this pressure and temperature range if 6 wt% S is incorporated into the Lunar Core. Our results therefore suggest that metal–silicate equilibrium during Lunar Core formation occurred at depths close to the present-day Lunar Core–mantle boundary. This provides independent support for both the existence of a deep magma ocean in the Moon in its early history and the presence of significant amounts of sulfur in the Lunar Core.
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Formation and evolution of a Lunar Core from ilmenite-rich magma ocean cumulates
Earth and Planetary Science Letters, 2010Co-Authors: Jellie De Vries, Arie P. Van Den Berg, Wim Van WestrenenAbstract:Abstract In the absence of comprehensive seismic data coverage, the size, composition and physical state of the Lunar Core are still debated. It has been suggested that a dense ilmenite-rich layer, which originally crystallised near the top of the Lunar magma ocean, may have sunk to the centre of the Moon to form either an outer Core, surrounding a small metallic inner Core, or a complete Core if the Lunar metallic iron content is insignificant. Here we study the formation, gravitational stability and thermal evolution of both an ilmenite-rich outer Core and a full ilmenite-rich Core, using a two-dimensional cylindrical thermo-chemical convection model. Gravity acceleration in the Lunar mantle decreases quickly with depth. Since the gravity acceleration directly influences the buoyancy of materials, the low gravity acceleration near the centre was explicitly taken into account. Core formation and evolution were investigated by assessing the effects of varying two parameters, the Mg# (density) and the internal heat production of the ilmenite-rich layer. Varying these parameters changes the compositional and thermal buoyancy of the dense layer. Models show that a stable ilmenite-rich (outer) Core may indeed have formed in the Lunar interior and that its density depends on the internal heating in and the Mg# of the ilmenite-rich layer. Furthermore, the sharpness of the Core-mantle boundary is shown to depend on the internal heat production in the ilmenite-rich material. Surprisingly, a higher internal heat production results in a sharper Core-mantle boundary and a higher ilmenite content in the Core. This is caused by lower viscosities as a result of higher temperatures. Although maximum Core temperatures vary between different models by 700–1000 K around 2 Gyr after the start of the models, present-day estimates vary by only about 350–500 K. Further narrowing of the range of internal heating values is essential for a better determination of both the present day Lunar Core temperature and its physical state.
Nathanaël Schaeffer - One of the best experts on this subject based on the ideXlab platform.
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Precessing spherical shells: flows, dissipation, dynamo and the Lunar Core
Geophysical Journal International, 2019Co-Authors: David Cébron, Raphaël Laguerre, Jerome Noir, Nathanaël SchaefferAbstract:Precession of planets or moons affects internal liquid layers by driving flows, instabilities and possibly dynamos. The energy dissipated by these phenomena can influence orbital parameters such as the planet's spin rate. However, there is no systematic study of these flows in the spherical shell geometry relevant for planets, and the lack of scaling law prevents convincing extrapolation to celestial bodies. We have run more than 900 simulations of fluid spherical shells affected by precession, to systematically study basic flows, instabilities, turbulence, and magnetic field generation. We observe no significant effects of the inner Core on the onset of the instabilities. We obtain an analytical estimate of the viscous dissipation, mostly due to boundary layer friction in our simulations. We propose theoretical onsets for hydrodynamic instabilities, and document the intensity of turbulent fluctuations. We extend previous precession dynamo studies towards lower viscosities, at the limits of today's computers. In the low viscosity regime, precession dynamos rely on the presence of large-scale vortices, and the surface magnetic fields are dominated by small scales. Interestingly, intermittent and self-killing dynamos are observed. Our results suggest that large-scale planetary magnetic fields are unlikely to be produced by a precession-driven dynamo in a spherical Core. But this question remains open as planetary Cores are not exactly spherical, and thus the coupling between the fluid and the boundary does not vanish in the relevant limit of small viscosity. Moreover, the fully turbulent dissipation regime has not yet been reached in simulations. Our results suggest that the melted Lunar Core has been in a turbulent state throughout its history. Furthermore, in the view of recent experimental results, we propose updated formulas predicting the fluid mean rotation vector and the associated dissipation in both the laminar and the turbulent regimes.
N Rai - One of the best experts on this subject based on the ideXlab platform.
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Carbon as the dominant light element in the Lunar Core
American Mineralogist, 2017Co-Authors: E S Steenstra, Yanhao Lin, N Rai, Max Jansen, Wim Van WestrenenAbstract:Geophysical and geochemical observations point to the presence of a light element in the Lunar Core, but the exact abundance and type of light element are poorly constrained. Accurate constraints on Lunar Core composition are vital for models of Lunar Core dynamo onset and demise, Core formation conditions (e.g., depth of the Lunar magma ocean or LMO) and therefore formation conditions, as well as the volatile inventory of the Moon. A wide range of previous studies considered S as the dominant light element in the Lunar Core. Here, we present new constraints on the composition of the Lunar Core, using mass-balance calculations, combined with previously published models that predict the metal-silicate partitioning behavior of C, S, Ni, and recently proposed new bulk silicate Moon (BSM) abundances of S and C. We also use the bulk Moon abundance of C and S to assess the extent of their devolatilization. We observe that the Ni content of the Lunar Core becomes unrealistically high if shallow ( 3 GPa) LMO scenarios are considered for S and C. The moderately siderophile metal-silicate partitioning behavior of S during Lunar Core formation, combined with the low BSM abundance of S, yields only
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carbon as the dominant light element in the Lunar Core
American Mineralogist, 2017Co-Authors: E S Steenstra, Yanhao Lin, N Rai, Max Jansen, Wim Van WestrenenAbstract:Geophysical and geochemical observations point to the presence of a light element in the Lunar Core, but the exact abundance and type of light element are poorly constrained. Accurate constraints on Lunar Core composition are vital for models of Lunar Core dynamo onset and demise, Core formation conditions (e.g., depth of the Lunar magma ocean or LMO) and therefore formation conditions, as well as the volatile inventory of the Moon. A wide range of previous studies considered S as the dominant light element in the Lunar Core. Here, we present new constraints on the composition of the Lunar Core, using mass-balance calculations, combined with previously published models that predict the metal-silicate partitioning behavior of C, S, Ni, and recently proposed new bulk silicate Moon (BSM) abundances of S and C. We also use the bulk Moon abundance of C and S to assess the extent of their devolatilization. We observe that the Ni content of the Lunar Core becomes unrealistically high if shallow ( 3 GPa) LMO scenarios are considered for S and C. The moderately siderophile metal-silicate partitioning behavior of S during Lunar Core formation, combined with the low BSM abundance of S, yields only <0.16 wt% S in the Core, virtually independent of the pressure (P) and temperature (T) conditions during Core formation. Instead, our analysis suggests that C is the dominant light element in the Lunar Core. The siderophile behavior of C during Lunar Core formation results in a Core C content of ~0.6-4.8 wt%, with the exact amount depending on the Core formation conditions. A C-rich Lunar Core could explain (1) the existence of a present-day molten outer Core, (2) the estimated density of the Lunar outer Core, and (3) the existence of an early Lunar Core dynamo driven by compositional buoyancy due to Core crystallization. Finally, our calculations suggest the C content of the bulk Moon is close to its estimated abundance in the bulk silicate Earth (BSE), suggesting more limited volatile loss during the Moon-forming event than previously thought.
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Lunar Core formation new constraints from metal silicate partitioning of siderophile elements
Earth and Planetary Science Letters, 2014Co-Authors: N Rai, Wim Van WestrenenAbstract:Abstract Analyses of Apollo era seismograms, Lunar laser ranging data and the Lunar moment of inertia suggest the presence of a small, at least partially molten Fe-rich metallic Core in the Moon, but the chemical composition and formation conditions of this Core are not well constrained. Here, we assess whether pressure–temperature conditions can be found at which the Lunar silicate mantle equilibrated with a Fe-rich metallic liquid during Core formation. To this end, we combine measurements of the metal–silicate partitioning behavior of siderophile elements with the estimated depletion due to Core formation in those elements in the silicate mantle of the Moon. We also explore how the presence of the light element sulfur (suggested by seismic models to be present in the Core at concentrations of up to 6 wt%) in the Lunar Core affects Core formation models. We use published metal–silicate partitioning data for Ni, Co, W, Mo, P, V and Cr in the Lunar pressure range (1 atm–5 GPa) and characterize the dependence of the metal/silicate partition coefficients ( D ) on temperature, pressure, oxygen fugacity and composition of the silicate melt and the metal. If the Core is assumed to consist of pure iron, Core–mantle equilibration conditions that best satisfy Lunar mantle depletions of five siderophile elements—Ni, Co, W, Mo and P—are a pressure of 4.5 ( ± 0.5 ) GPa and a temperature of 2200 K. The Lunar mantle depletions of Cr and V are also consistent with metal–silicate equilibration in this pressure and temperature range if 6 wt% S is incorporated into the Lunar Core. Our results therefore suggest that metal–silicate equilibrium during Lunar Core formation occurred at depths close to the present-day Lunar Core–mantle boundary. This provides independent support for both the existence of a deep magma ocean in the Moon in its early history and the presence of significant amounts of sulfur in the Lunar Core.
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Lunar Core formation: New constraints from metal–silicate partitioning of siderophile elements
Earth and Planetary Science Letters, 2014Co-Authors: N Rai, Wim Van WestrenenAbstract:Abstract Analyses of Apollo era seismograms, Lunar laser ranging data and the Lunar moment of inertia suggest the presence of a small, at least partially molten Fe-rich metallic Core in the Moon, but the chemical composition and formation conditions of this Core are not well constrained. Here, we assess whether pressure–temperature conditions can be found at which the Lunar silicate mantle equilibrated with a Fe-rich metallic liquid during Core formation. To this end, we combine measurements of the metal–silicate partitioning behavior of siderophile elements with the estimated depletion due to Core formation in those elements in the silicate mantle of the Moon. We also explore how the presence of the light element sulfur (suggested by seismic models to be present in the Core at concentrations of up to 6 wt%) in the Lunar Core affects Core formation models. We use published metal–silicate partitioning data for Ni, Co, W, Mo, P, V and Cr in the Lunar pressure range (1 atm–5 GPa) and characterize the dependence of the metal/silicate partition coefficients ( D ) on temperature, pressure, oxygen fugacity and composition of the silicate melt and the metal. If the Core is assumed to consist of pure iron, Core–mantle equilibration conditions that best satisfy Lunar mantle depletions of five siderophile elements—Ni, Co, W, Mo and P—are a pressure of 4.5 ( ± 0.5 ) GPa and a temperature of 2200 K. The Lunar mantle depletions of Cr and V are also consistent with metal–silicate equilibration in this pressure and temperature range if 6 wt% S is incorporated into the Lunar Core. Our results therefore suggest that metal–silicate equilibrium during Lunar Core formation occurred at depths close to the present-day Lunar Core–mantle boundary. This provides independent support for both the existence of a deep magma ocean in the Moon in its early history and the presence of significant amounts of sulfur in the Lunar Core.
David Cébron - One of the best experts on this subject based on the ideXlab platform.
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Precessing spherical shells: flows, dissipation, dynamo and the Lunar Core
Geophysical Journal International, 2019Co-Authors: David Cébron, Raphaël Laguerre, Jerome Noir, Nathanaël SchaefferAbstract:Precession of planets or moons affects internal liquid layers by driving flows, instabilities and possibly dynamos. The energy dissipated by these phenomena can influence orbital parameters such as the planet's spin rate. However, there is no systematic study of these flows in the spherical shell geometry relevant for planets, and the lack of scaling law prevents convincing extrapolation to celestial bodies. We have run more than 900 simulations of fluid spherical shells affected by precession, to systematically study basic flows, instabilities, turbulence, and magnetic field generation. We observe no significant effects of the inner Core on the onset of the instabilities. We obtain an analytical estimate of the viscous dissipation, mostly due to boundary layer friction in our simulations. We propose theoretical onsets for hydrodynamic instabilities, and document the intensity of turbulent fluctuations. We extend previous precession dynamo studies towards lower viscosities, at the limits of today's computers. In the low viscosity regime, precession dynamos rely on the presence of large-scale vortices, and the surface magnetic fields are dominated by small scales. Interestingly, intermittent and self-killing dynamos are observed. Our results suggest that large-scale planetary magnetic fields are unlikely to be produced by a precession-driven dynamo in a spherical Core. But this question remains open as planetary Cores are not exactly spherical, and thus the coupling between the fluid and the boundary does not vanish in the relevant limit of small viscosity. Moreover, the fully turbulent dissipation regime has not yet been reached in simulations. Our results suggest that the melted Lunar Core has been in a turbulent state throughout its history. Furthermore, in the view of recent experimental results, we propose updated formulas predicting the fluid mean rotation vector and the associated dissipation in both the laminar and the turbulent regimes.
Jerome Noir - One of the best experts on this subject based on the ideXlab platform.
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Precessing spherical shells: flows, dissipation, dynamo and the Lunar Core
Geophysical Journal International, 2019Co-Authors: David Cébron, Raphaël Laguerre, Jerome Noir, Nathanaël SchaefferAbstract:Precession of planets or moons affects internal liquid layers by driving flows, instabilities and possibly dynamos. The energy dissipated by these phenomena can influence orbital parameters such as the planet's spin rate. However, there is no systematic study of these flows in the spherical shell geometry relevant for planets, and the lack of scaling law prevents convincing extrapolation to celestial bodies. We have run more than 900 simulations of fluid spherical shells affected by precession, to systematically study basic flows, instabilities, turbulence, and magnetic field generation. We observe no significant effects of the inner Core on the onset of the instabilities. We obtain an analytical estimate of the viscous dissipation, mostly due to boundary layer friction in our simulations. We propose theoretical onsets for hydrodynamic instabilities, and document the intensity of turbulent fluctuations. We extend previous precession dynamo studies towards lower viscosities, at the limits of today's computers. In the low viscosity regime, precession dynamos rely on the presence of large-scale vortices, and the surface magnetic fields are dominated by small scales. Interestingly, intermittent and self-killing dynamos are observed. Our results suggest that large-scale planetary magnetic fields are unlikely to be produced by a precession-driven dynamo in a spherical Core. But this question remains open as planetary Cores are not exactly spherical, and thus the coupling between the fluid and the boundary does not vanish in the relevant limit of small viscosity. Moreover, the fully turbulent dissipation regime has not yet been reached in simulations. Our results suggest that the melted Lunar Core has been in a turbulent state throughout its history. Furthermore, in the view of recent experimental results, we propose updated formulas predicting the fluid mean rotation vector and the associated dissipation in both the laminar and the turbulent regimes.
