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Alessandro Morbidelli - One of the best experts on this subject based on the ideXlab platform.
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Terrestrial Planet Formation Constrained by the Structure of the Asteroid Belt
2015Co-Authors: Alessandro Morbidelli, Sean N. Raymond, André Izidoro, Othon, WinterAbstract:Reproducing the large mass ratio between the Earth and Mars requires that the Terrestrial Planets formed from a narrow annulus, with a steep mass density gradient beyond 1 AU (Hansen, 2009). The Grand Tack scenario (Walsh et al., 2011) invokes a specific migration history of the giant Planets of the Solar System to remove most of the mass initially beyond 1 AU and to leave the asteroid belt on an excited dynamical state. However, one could also invoke that the steep mass density gradient was achieved by the migration and pile-up of a large amount of small particles induced by gas-drag. This process has been proposed to explain the formation of close-in super Earths in extrasolar systems (e.g. Chatterjee and Tan, 2015). Here we show that the asteroid belt orbital excitation provides a crucial constraint against this scenario for the Solar System. We achieve this result by performing a series of numerical simulations of Terrestrial Planet formation and asteroid belt evolution, starting from disks of Planetesimals and Planetary embryos with various radial density gradients. Jupiter and Saturn are assumed on their current, non-migrating orbits. We find that disks with shallow density gradients allow the dynamical excitation of the asteroid belt by a self-stirring process, but lead inevitably to the formation of a Mars analog which is significantly more massive than the real Planet. Instead, a disk with a surface density gradient proportional to 1/r^5 beyond 1 AU allows us to reproduce the Earth/Mars mass ratio, but leaves the asteroid belt on a dynamical state way too cold compared to the real belt. Therefore, we conclude that no disk profile can explain at the same time the structure of the Terrestrial Planet system and of the asteroid belt. Thus, the asteroid belt has to have been depleted and dynamically excited by an external agent as, for instance, in the Grand Tack scenario.
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Terrestrial Planet formation constrained by Mars and the structure of the asteroid belt
Monthly Notices of the Royal Astronomical Society, 2015Co-Authors: André Izidoro, Alessandro Morbidelli, Sean N. Raymond, Othon C. WinterAbstract:Reproducing the large Earth/Mars mass ratio requires a strong mass depletion in solids within the protoPlanetary disc between 1 and 3 au. The Grand Tack model invokes a specific migration history of the giant Planets to remove most of the mass initially beyond 1 au and to dynamically excite the asteroid belt. However, one could also invoke a steep density gradient created by inward drift and pile-up of small particles induced by gas drag, as has been proposed to explain the formation of close-in super-Earths. Here we show that the asteroid belt's orbital excitation provides a crucial constraint against this scenario for the Solar system. We performed a series of simulations of Terrestrial Planet formation and asteroid belt evolution starting from discs of Planetesimals and Planetary embryos with various radial density gradients and including Jupiter and Saturn on nearly circular and coplanar orbits. Discs with shallow density gradients reproduce the dynamical excitation of the asteroid belt by gravitational self-stirring but form Mars analogues significantly more massive than the real Planet. In contrast, a disc with a surface density gradient proportional to r-5.5 reproduces the Earth/Mars mass ratio but leaves the asteroid belt in a dynamical state that is far colder than the real belt. We conclude that no disc profile can simultaneously explain the structure of the Terrestrial Planets and asteroid belt. The asteroid belt must have been depleted and dynamically excited by a different mechanism such as, for instance, in the Grand Tack scenario.
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Terrestrial Planet formation constrained by Mars and the structure of the asteroid belt
Monthly Notices of the Royal Astronomical Society, 2015Co-Authors: André Izidoro, Alessandro Morbidelli, Sean N. Raymond, Othon C. WinterAbstract:Reproducing the large Earth/Mars mass ratio requires a strong mass depletion in solids within the protoPlanetary disc between 1 and 3 au. The Grand Tack model invokes a specific migration history of the giant Planets to remove most of the mass initially beyond 1 au and to dynamically excite the asteroid belt. However, one could also invoke a steep density gradient created by inward drift and pile-up of small particles induced by gas drag, as has been proposed to explain the formation of close-in super-Earths. Here we show that the asteroid belt's orbital excitation provides a crucial constraint against this scenario for the Solar system. We performed a series of simulations of Terrestrial Planet formation and asteroid belt evolution starting from discs of Planetesimals and Planetary embryos with various radial density gradients and including Jupiter and Saturn on nearly circular and coplanar orbits. Discs with shallow density gradients reproduce the dynamical excitation of the asteroid belt by gravitational self-stirring but form Mars analogues significantly more massive than the real Planet. In contrast, a disc with a surface density gradient proportional to r-5.5 reproduces the Earth/Mars mass ratio but leaves the asteroid belt in a dynamical state that is far colder than the real belt. We conclude that no disc profile can simultaneously explain the structure of the Terrestrial Planets and asteroid belt. The asteroid belt must have been depleted and dynamically excited by a different mechanism such as, for instance, in the Grand Tack scenario.
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Terrestrial Planet Formation in the Presence of Migrating Super-Earths
2014Co-Authors: André Izidoro, Alessandro Morbidelli, Sean N. RaymondAbstract:Super-Earths with orbital periods less than 100 days are extremely abundant around Sun-like stars. It is unlikely that these Planets formed at their current locations. Rather, they likely formed at large distances from the star and subsequently migrated inward. In this work we use N-body simulations to study the effect of super-Earths on the accretion of rocky Planets. In our simulations, one or more super-Earths migrates inward through a disk of Moon-size to Mars-size protoPlanetary embryos and much smaller Planetesimals embedded in a gaseous disk. In order to qualitatively cover possible scenarios of type-I migration for super-Earths, we have performed simulations considering many different migration speeds and configurations for these bodies. Fast-migrating super-Earths, where super-Earth’s migration is comparable to the traditional type-I isothermal regime (τmig∼0.01-0.1 Myr), only have a modest effect on the protoPlanetary embryos and Planetesimals. Sufficient material survives to form rocky, Earth-like Planets on orbits exterior to the super-Earths'. In contrast, slowly-migrating super-Earths shepherd rocky material interior to their orbits and strongly deplete the Terrestrial Planet-forming zone. In this situation any Earth-sized Planets in the habitable zone are extremely volatile-rich and are therefore probably not Earth-like.
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lunar and Terrestrial Planet formation in the grand tack scenario
Philosophical Transactions of the Royal Society A, 2014Co-Authors: Seth A. Jacobson, Alessandro MorbidelliAbstract: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.
Sean N. Raymond - One of the best experts on this subject based on the ideXlab platform.
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The early instability scenario: Terrestrial Planet formation during the giant Planet instability, and the effect of collisional fragmentation
Icarus, 2019Co-Authors: Matthew Clement, Sean N. Raymond, Nathan Kaib, John Chambers, Kevin WalshAbstract:The solar system's dynamical state can be explained by an orbital instability among the giant Planets. A recent model has proposed that the giant Planet instability happened during Terrestrial Planet formation. This scenario has been shown to match the inner solar system by stunting Mars' growth and preventing Planet formation in the asteroid belt. Here we present a large sample of new simulations of the "Early Instability" scenario. We use an N-body integration scheme that accounts for collisional fragmentation, and also perform a large set of control simulations that do not include an early giant Planet instability. Since the total particle number decreases slower when collisional fragmentation is accounted for, the growing Planets' orbits are damped more strongly via dynamical friction and encounters with small bodies that dissipate angular momentum (eg: hit-and-run impacts). Compared with simulations without collisional fragmentation, our fully evolved systems provide better matches to the solar system's Terrestrial Planets in terms of their compact mass distribution and dynamically cold orbits. Collisional processes also tend to lengthen the dynamical accretion timescales of Earth analogs, and shorten those of Mars analogs. This yields systems with relative growth timescales more consistent with those inferred from isotopic dating. Accounting for fragmentation is thus supremely important for any successful evolutionary model of the inner solar system.
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The Delivery of Water During Terrestrial Planet Formation
Space Science Reviews, 2018Co-Authors: David P. O'brien, Sean N. Raymond, André Izidoro, Seth A. Jacobson, David C. RubieAbstract:The Planetary building blocks that formed in the Terrestrial Planet region were likely very dry, yet water is comparatively abundant on Earth. Here we review the various mechanisms proposed for the origin of water on the Terrestrial Planets. Various in-situ mechanisms have been suggested, which allow for the incorporation of water into the local Planetesimals in the Terrestrial Planet region or into the Planets themselves from local sources, although all of those mechanisms have difficulties. Comets have also been proposed as a source, although there may be problems fitting isotopic constraints, and the delivery efficiency is very low, such that it may be difficult to deliver even a single Earth ocean of water this way. The most promising route for water delivery is the accretion of material from beyond the snow line, similar to carbonaceous chondrites, that is scattered into the Terrestrial Planet region as the Planets are growing. Two main scenarios are discussed in detail. First is the classical scenario in which the giant Planets begin roughly in their final locations and the disk of Planetesimals and embryos in the Terrestrial Planet region extends all the way into the outer asteroid belt region. Second is the Grand Tack scenario, where early inward and outward migration of the giant Planets implants material from beyond the snow line into the asteroid belt and Terrestrial Planet region, where it can be accreted by the growing Planets. Sufficient water is delivered to the Terrestrial Planets in both scenarios. While the Grand Tack scenario provides a better fit to most constraints, namely the small mass of Mars, Planets may form too fast in the nominal case discussed here. This discrepancy may be reduced as a wider range of initial conditions is explored. Finally, we discuss several more recent models that may have important implications for water delivery to the Terrestrial Planets.
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The Delivery of Water During Terrestrial Planet Formation
Space Science Reviews, 2018Co-Authors: David P. O'brien, Sean N. Raymond, André Izidoro, Seth A. Jacobson, David C. RubieAbstract:The Planetary building blocks that formed in the Terrestrial Planet region were likely very dry, yet water is comparatively abundant on Earth. We review the various mechanisms proposed for the origin of water on the Terrestrial Planets. Various in-situ mechanisms have been suggested, which allow for the incorporation of water into the local Planetesimals in the Terrestrial Planet region or into the Planets themselves from local sources, although all of those mechanisms have difficulties. Comets have also been proposed as a source, although there may be problems fitting isotopic constraints, and the delivery efficiency is very low, such that it may be difficult to deliver even a single Earth ocean of water this way. The most promising route for water delivery is the accretion of material from beyond the snow line, similar to carbonaceous chondrites, that is scattered into the Terrestrial Planet region as the Planets are growing. Two main scenarios are discussed in detail. First is the classical scenario in which the giant Planets begin roughly in their final locations and the disk of Planetesimals and embryos in the Terrestrial Planet region extends all the way into the outer asteroid belt region. Second is the Grand Tack scenario, where early inward and outward migration of the giant Planets implants material from beyond the snow line into the asteroid belt and Terrestrial Planet region, where it can be accreted by the growing Planets. Sufficient water is delivered to the Terrestrial Planets in both scenarios. While the Grand Tack scenario provides a better fit to most constraints, namely the small mass of Mars, Planets may form too fast in the nominal case discussed here. This discrepancy may be reduced as a wider range of initial conditions is explored. Finally, we discuss several more recent models that may have important implications for water delivery to the Terrestrial Planets.
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Terrestrial Planet Formation Constrained by the Structure of the Asteroid Belt
2015Co-Authors: Alessandro Morbidelli, Sean N. Raymond, André Izidoro, Othon, WinterAbstract:Reproducing the large mass ratio between the Earth and Mars requires that the Terrestrial Planets formed from a narrow annulus, with a steep mass density gradient beyond 1 AU (Hansen, 2009). The Grand Tack scenario (Walsh et al., 2011) invokes a specific migration history of the giant Planets of the Solar System to remove most of the mass initially beyond 1 AU and to leave the asteroid belt on an excited dynamical state. However, one could also invoke that the steep mass density gradient was achieved by the migration and pile-up of a large amount of small particles induced by gas-drag. This process has been proposed to explain the formation of close-in super Earths in extrasolar systems (e.g. Chatterjee and Tan, 2015). Here we show that the asteroid belt orbital excitation provides a crucial constraint against this scenario for the Solar System. We achieve this result by performing a series of numerical simulations of Terrestrial Planet formation and asteroid belt evolution, starting from disks of Planetesimals and Planetary embryos with various radial density gradients. Jupiter and Saturn are assumed on their current, non-migrating orbits. We find that disks with shallow density gradients allow the dynamical excitation of the asteroid belt by a self-stirring process, but lead inevitably to the formation of a Mars analog which is significantly more massive than the real Planet. Instead, a disk with a surface density gradient proportional to 1/r^5 beyond 1 AU allows us to reproduce the Earth/Mars mass ratio, but leaves the asteroid belt on a dynamical state way too cold compared to the real belt. Therefore, we conclude that no disk profile can explain at the same time the structure of the Terrestrial Planet system and of the asteroid belt. Thus, the asteroid belt has to have been depleted and dynamically excited by an external agent as, for instance, in the Grand Tack scenario.
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Terrestrial Planet formation constrained by Mars and the structure of the asteroid belt
Monthly Notices of the Royal Astronomical Society, 2015Co-Authors: André Izidoro, Alessandro Morbidelli, Sean N. Raymond, Othon C. WinterAbstract:Reproducing the large Earth/Mars mass ratio requires a strong mass depletion in solids within the protoPlanetary disc between 1 and 3 au. The Grand Tack model invokes a specific migration history of the giant Planets to remove most of the mass initially beyond 1 au and to dynamically excite the asteroid belt. However, one could also invoke a steep density gradient created by inward drift and pile-up of small particles induced by gas drag, as has been proposed to explain the formation of close-in super-Earths. Here we show that the asteroid belt's orbital excitation provides a crucial constraint against this scenario for the Solar system. We performed a series of simulations of Terrestrial Planet formation and asteroid belt evolution starting from discs of Planetesimals and Planetary embryos with various radial density gradients and including Jupiter and Saturn on nearly circular and coplanar orbits. Discs with shallow density gradients reproduce the dynamical excitation of the asteroid belt by gravitational self-stirring but form Mars analogues significantly more massive than the real Planet. In contrast, a disc with a surface density gradient proportional to r-5.5 reproduces the Earth/Mars mass ratio but leaves the asteroid belt in a dynamical state that is far colder than the real belt. We conclude that no disc profile can simultaneously explain the structure of the Terrestrial Planets and asteroid belt. The asteroid belt must have been depleted and dynamically excited by a different mechanism such as, for instance, in the Grand Tack scenario.
André Izidoro - One of the best experts on this subject based on the ideXlab platform.
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The Delivery of Water During Terrestrial Planet Formation
Space Science Reviews, 2018Co-Authors: David P. O'brien, Sean N. Raymond, André Izidoro, Seth A. Jacobson, David C. RubieAbstract:The Planetary building blocks that formed in the Terrestrial Planet region were likely very dry, yet water is comparatively abundant on Earth. Here we review the various mechanisms proposed for the origin of water on the Terrestrial Planets. Various in-situ mechanisms have been suggested, which allow for the incorporation of water into the local Planetesimals in the Terrestrial Planet region or into the Planets themselves from local sources, although all of those mechanisms have difficulties. Comets have also been proposed as a source, although there may be problems fitting isotopic constraints, and the delivery efficiency is very low, such that it may be difficult to deliver even a single Earth ocean of water this way. The most promising route for water delivery is the accretion of material from beyond the snow line, similar to carbonaceous chondrites, that is scattered into the Terrestrial Planet region as the Planets are growing. Two main scenarios are discussed in detail. First is the classical scenario in which the giant Planets begin roughly in their final locations and the disk of Planetesimals and embryos in the Terrestrial Planet region extends all the way into the outer asteroid belt region. Second is the Grand Tack scenario, where early inward and outward migration of the giant Planets implants material from beyond the snow line into the asteroid belt and Terrestrial Planet region, where it can be accreted by the growing Planets. Sufficient water is delivered to the Terrestrial Planets in both scenarios. While the Grand Tack scenario provides a better fit to most constraints, namely the small mass of Mars, Planets may form too fast in the nominal case discussed here. This discrepancy may be reduced as a wider range of initial conditions is explored. Finally, we discuss several more recent models that may have important implications for water delivery to the Terrestrial Planets.
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The Delivery of Water During Terrestrial Planet Formation
Space Science Reviews, 2018Co-Authors: David P. O'brien, Sean N. Raymond, André Izidoro, Seth A. Jacobson, David C. RubieAbstract:The Planetary building blocks that formed in the Terrestrial Planet region were likely very dry, yet water is comparatively abundant on Earth. We review the various mechanisms proposed for the origin of water on the Terrestrial Planets. Various in-situ mechanisms have been suggested, which allow for the incorporation of water into the local Planetesimals in the Terrestrial Planet region or into the Planets themselves from local sources, although all of those mechanisms have difficulties. Comets have also been proposed as a source, although there may be problems fitting isotopic constraints, and the delivery efficiency is very low, such that it may be difficult to deliver even a single Earth ocean of water this way. The most promising route for water delivery is the accretion of material from beyond the snow line, similar to carbonaceous chondrites, that is scattered into the Terrestrial Planet region as the Planets are growing. Two main scenarios are discussed in detail. First is the classical scenario in which the giant Planets begin roughly in their final locations and the disk of Planetesimals and embryos in the Terrestrial Planet region extends all the way into the outer asteroid belt region. Second is the Grand Tack scenario, where early inward and outward migration of the giant Planets implants material from beyond the snow line into the asteroid belt and Terrestrial Planet region, where it can be accreted by the growing Planets. Sufficient water is delivered to the Terrestrial Planets in both scenarios. While the Grand Tack scenario provides a better fit to most constraints, namely the small mass of Mars, Planets may form too fast in the nominal case discussed here. This discrepancy may be reduced as a wider range of initial conditions is explored. Finally, we discuss several more recent models that may have important implications for water delivery to the Terrestrial Planets.
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Terrestrial Planet Formation Constrained by the Structure of the Asteroid Belt
2015Co-Authors: Alessandro Morbidelli, Sean N. Raymond, André Izidoro, Othon, WinterAbstract:Reproducing the large mass ratio between the Earth and Mars requires that the Terrestrial Planets formed from a narrow annulus, with a steep mass density gradient beyond 1 AU (Hansen, 2009). The Grand Tack scenario (Walsh et al., 2011) invokes a specific migration history of the giant Planets of the Solar System to remove most of the mass initially beyond 1 AU and to leave the asteroid belt on an excited dynamical state. However, one could also invoke that the steep mass density gradient was achieved by the migration and pile-up of a large amount of small particles induced by gas-drag. This process has been proposed to explain the formation of close-in super Earths in extrasolar systems (e.g. Chatterjee and Tan, 2015). Here we show that the asteroid belt orbital excitation provides a crucial constraint against this scenario for the Solar System. We achieve this result by performing a series of numerical simulations of Terrestrial Planet formation and asteroid belt evolution, starting from disks of Planetesimals and Planetary embryos with various radial density gradients. Jupiter and Saturn are assumed on their current, non-migrating orbits. We find that disks with shallow density gradients allow the dynamical excitation of the asteroid belt by a self-stirring process, but lead inevitably to the formation of a Mars analog which is significantly more massive than the real Planet. Instead, a disk with a surface density gradient proportional to 1/r^5 beyond 1 AU allows us to reproduce the Earth/Mars mass ratio, but leaves the asteroid belt on a dynamical state way too cold compared to the real belt. Therefore, we conclude that no disk profile can explain at the same time the structure of the Terrestrial Planet system and of the asteroid belt. Thus, the asteroid belt has to have been depleted and dynamically excited by an external agent as, for instance, in the Grand Tack scenario.
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Terrestrial Planet formation constrained by Mars and the structure of the asteroid belt
Monthly Notices of the Royal Astronomical Society, 2015Co-Authors: André Izidoro, Alessandro Morbidelli, Sean N. Raymond, Othon C. WinterAbstract:Reproducing the large Earth/Mars mass ratio requires a strong mass depletion in solids within the protoPlanetary disc between 1 and 3 au. The Grand Tack model invokes a specific migration history of the giant Planets to remove most of the mass initially beyond 1 au and to dynamically excite the asteroid belt. However, one could also invoke a steep density gradient created by inward drift and pile-up of small particles induced by gas drag, as has been proposed to explain the formation of close-in super-Earths. Here we show that the asteroid belt's orbital excitation provides a crucial constraint against this scenario for the Solar system. We performed a series of simulations of Terrestrial Planet formation and asteroid belt evolution starting from discs of Planetesimals and Planetary embryos with various radial density gradients and including Jupiter and Saturn on nearly circular and coplanar orbits. Discs with shallow density gradients reproduce the dynamical excitation of the asteroid belt by gravitational self-stirring but form Mars analogues significantly more massive than the real Planet. In contrast, a disc with a surface density gradient proportional to r-5.5 reproduces the Earth/Mars mass ratio but leaves the asteroid belt in a dynamical state that is far colder than the real belt. We conclude that no disc profile can simultaneously explain the structure of the Terrestrial Planets and asteroid belt. The asteroid belt must have been depleted and dynamically excited by a different mechanism such as, for instance, in the Grand Tack scenario.
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Terrestrial Planet formation constrained by Mars and the structure of the asteroid belt
Monthly Notices of the Royal Astronomical Society, 2015Co-Authors: André Izidoro, Alessandro Morbidelli, Sean N. Raymond, Othon C. WinterAbstract:Reproducing the large Earth/Mars mass ratio requires a strong mass depletion in solids within the protoPlanetary disc between 1 and 3 au. The Grand Tack model invokes a specific migration history of the giant Planets to remove most of the mass initially beyond 1 au and to dynamically excite the asteroid belt. However, one could also invoke a steep density gradient created by inward drift and pile-up of small particles induced by gas drag, as has been proposed to explain the formation of close-in super-Earths. Here we show that the asteroid belt's orbital excitation provides a crucial constraint against this scenario for the Solar system. We performed a series of simulations of Terrestrial Planet formation and asteroid belt evolution starting from discs of Planetesimals and Planetary embryos with various radial density gradients and including Jupiter and Saturn on nearly circular and coplanar orbits. Discs with shallow density gradients reproduce the dynamical excitation of the asteroid belt by gravitational self-stirring but form Mars analogues significantly more massive than the real Planet. In contrast, a disc with a surface density gradient proportional to r-5.5 reproduces the Earth/Mars mass ratio but leaves the asteroid belt in a dynamical state that is far colder than the real belt. We conclude that no disc profile can simultaneously explain the structure of the Terrestrial Planets and asteroid belt. The asteroid belt must have been depleted and dynamically excited by a different mechanism such as, for instance, in the Grand Tack scenario.
David P. O'brien - One of the best experts on this subject based on the ideXlab platform.
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The Delivery of Water During Terrestrial Planet Formation
Space Science Reviews, 2018Co-Authors: David P. O'brien, Sean N. Raymond, André Izidoro, Seth A. Jacobson, David C. RubieAbstract:The Planetary building blocks that formed in the Terrestrial Planet region were likely very dry, yet water is comparatively abundant on Earth. Here we review the various mechanisms proposed for the origin of water on the Terrestrial Planets. Various in-situ mechanisms have been suggested, which allow for the incorporation of water into the local Planetesimals in the Terrestrial Planet region or into the Planets themselves from local sources, although all of those mechanisms have difficulties. Comets have also been proposed as a source, although there may be problems fitting isotopic constraints, and the delivery efficiency is very low, such that it may be difficult to deliver even a single Earth ocean of water this way. The most promising route for water delivery is the accretion of material from beyond the snow line, similar to carbonaceous chondrites, that is scattered into the Terrestrial Planet region as the Planets are growing. Two main scenarios are discussed in detail. First is the classical scenario in which the giant Planets begin roughly in their final locations and the disk of Planetesimals and embryos in the Terrestrial Planet region extends all the way into the outer asteroid belt region. Second is the Grand Tack scenario, where early inward and outward migration of the giant Planets implants material from beyond the snow line into the asteroid belt and Terrestrial Planet region, where it can be accreted by the growing Planets. Sufficient water is delivered to the Terrestrial Planets in both scenarios. While the Grand Tack scenario provides a better fit to most constraints, namely the small mass of Mars, Planets may form too fast in the nominal case discussed here. This discrepancy may be reduced as a wider range of initial conditions is explored. Finally, we discuss several more recent models that may have important implications for water delivery to the Terrestrial Planets.
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The Delivery of Water During Terrestrial Planet Formation
Space Science Reviews, 2018Co-Authors: David P. O'brien, Sean N. Raymond, André Izidoro, Seth A. Jacobson, David C. RubieAbstract:The Planetary building blocks that formed in the Terrestrial Planet region were likely very dry, yet water is comparatively abundant on Earth. We review the various mechanisms proposed for the origin of water on the Terrestrial Planets. Various in-situ mechanisms have been suggested, which allow for the incorporation of water into the local Planetesimals in the Terrestrial Planet region or into the Planets themselves from local sources, although all of those mechanisms have difficulties. Comets have also been proposed as a source, although there may be problems fitting isotopic constraints, and the delivery efficiency is very low, such that it may be difficult to deliver even a single Earth ocean of water this way. The most promising route for water delivery is the accretion of material from beyond the snow line, similar to carbonaceous chondrites, that is scattered into the Terrestrial Planet region as the Planets are growing. Two main scenarios are discussed in detail. First is the classical scenario in which the giant Planets begin roughly in their final locations and the disk of Planetesimals and embryos in the Terrestrial Planet region extends all the way into the outer asteroid belt region. Second is the Grand Tack scenario, where early inward and outward migration of the giant Planets implants material from beyond the snow line into the asteroid belt and Terrestrial Planet region, where it can be accreted by the growing Planets. Sufficient water is delivered to the Terrestrial Planets in both scenarios. While the Grand Tack scenario provides a better fit to most constraints, namely the small mass of Mars, Planets may form too fast in the nominal case discussed here. This discrepancy may be reduced as a wider range of initial conditions is explored. Finally, we discuss several more recent models that may have important implications for water delivery to the Terrestrial Planets.
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Migration & Extra-solar Terrestrial Planets: Watering the Planets
2012Co-Authors: Jade C. Carter-bond, David P. O'brien, Sean N. RaymondAbstract:A diverse range of Terrestrial Planet compositions is believed to exist within known extrasolar Planetary systems, ranging from those that are relatively Earth-like to those that are highly unusual, dominated by species such as refractory elements (Al and Ca) or C (as pure C, TiC and SiC)(Bond et al. 2010b). However, all prior simulations have ignored the impact that giant Planet migration during Planetary accretion may have on the final Terrestrial Planetary composition. Here, we combined chemical equilibrium models of the disk around five known Planetary host stars (Solar, HD4203, HD19994, HD213240 and Gl777) with dynamical models of Terrestrial Planet formation incorporating various degrees of giant Planet migration. Giant Planet migration is found to drastically impact Terrestrial Planet composition by 1) increasing the amount of Mg-silicate species present in the final body; and 2) dramatically increasing the efficiency and amount of water delivered to the Terrestrial bodies during their formation process.
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Terrestrial Planet formation
Proceedings of the National Academy of Sciences of the United States of America, 2011Co-Authors: Kevin Righter, David P. O'brienAbstract:Advances in our understanding of Terrestrial Planet formation have come from a multidisciplinary approach. Studies of the ages and compositions of primitive meteorites with compositions similar to the Sun have helped to constrain the nature of the building blocks of Planets. This information helps to guide numerical models for the three stages of Planet formation from dust to Planetesimals (∼106 y), followed by Planetesimals to embryos (lunar to Mars-sized objects; few × 106 y), and finally embryos to Planets (107–108 y). Defining the role of turbulence in the early nebula is a key to understanding the growth of solids larger than meter size. The initiation of runaway growth of embryos from Planetesimals ultimately leads to the growth of large Terrestrial Planets via large impacts. Dynamical models can produce inner Solar System configurations that closely resemble our Solar System, especially when the orbital effects of large Planets (Jupiter and Saturn) and damping mechanisms, such as gas drag, are included. Experimental studies of Terrestrial Planet interiors provide additional constraints on the conditions of differentiation and, therefore, origin. A more complete understanding of Terrestrial Planet formation might be possible via a combination of chemical and physical modeling, as well as obtaining samples and new geophysical data from other Planets (Venus, Mars, or Mercury) and asteroids.
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Dynamical Models of Terrestrial Planet Formation
Advanced Science Letters, 2011Co-Authors: Jonathan I. Lunine, David P. O'brien, Alessandro Morbidelli, Sean N. Raymond, Thomas R. Quinn, A. L. GrapsAbstract:We review the problem of the formation of Terrestrial Planets, with particular emphasis on the interaction of dynamical and geochemical models. The lifetime of gas around stars in the process of formation is limited to a few million years based on astronomical observations, while isotopic dating of meteorites and the Earth-Moon system suggest that perhaps 50-100 million years were required for the assembly of the Earth. Therefore, much of the growth of the Terrestrial Planets in our own system is presumed to have taken place under largely gas-free conditions, and the physics of Terrestrial Planet formation is dominated by gravitational interactions and collisions. The earliest phase of Terrestrial-Planet formation involve the growth of km-sized or larger Planetesimals from dust grains, followed by the accumulations of these Planetesimals into ∼100 lunar- to Mars-mass bodies that are initially gravitationally isolated from one-another in a swarm of smaller Planetesimals, but eventually grow to the point of significantly perturbing one-another. The mutual perturbations between the embryos, combined with gravitational stirring by Jupiter, lead to orbital crossings and collisions that drive the growth to Earth-sized Planets on a timescale of 107-108 years. Numerical treatment of this process has focussed on the use of symplectic integrators which can rapidy integrate the thousands of gravitationally-interacting bodies necessary to accurately model Planetary growth. While the general nature of the Terrestrial Planets-their sizes and orbital parameters-seem to be broadly reproduced by the models, there are still some outstanding dynamical issues. One of these is the presence of an embryo-sized body, Mars, in our system in place of the more massive objects that simulations tend to yield. Another is the effect such impacts have on the geochemistry of the growing Planets; re-equilibration of isotopic ratios of major elements during giant impacts (for example) must be considered in comparing the predicted compositions of the Terrestrial Planets with the geochemical data. As the dynamical models become successful in reproducing the essential aspects of our own Terrestrial Planet system, their utility in predicting the distribution of Terrestrial Planet systems around other stars, and interpreting observations of such systems, will increase.
Seth A. Jacobson - One of the best experts on this subject based on the ideXlab platform.
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constraints on Terrestrial Planet formation timescales and equilibration processes in the grand tack scenario from hf w isotopic evolution
Earth and Planetary Science Letters, 2019Co-Authors: Nicholas G Zube, F Nimmo, Rebecca A Fischer, Seth A. JacobsonAbstract:Abstract We examine 141 N-body simulations of Terrestrial Planet late-stage accretion that use the Grand Tack scenario, coupling the collisional results with a hafnium-tungsten (Hf-W) isotopic evolution model. Accretion in the Grand Tack scenario results in faster Planet formation than classical accretion models because of higher Planetesimal surface density induced by a migrating Jupiter. Planetary embryos that grow rapidly experience radiogenic ingrowth of mantle 182W that is inconsistent with the measured Terrestrial composition, unless much of the tungsten is removed by an impactor core that mixes thoroughly with the target mantle. For physically Earth-like surviving Planets, we find that the fraction of equilibrating impactor core k core ≥ 0.6 is required to produce results agreeing with observed Terrestrial tungsten anomalies (assuming equilibration with relatively large volumes of target mantle material; smaller equilibrating mantle volumes would require even larger k core ). This requirement of substantial core re-equilibration may be difficult to reconcile with fluid dynamical predictions and hydrocode simulations of mixing during large impacts, and hence this result does not favor the rapid Planet building that results from Grand Tack accretion.
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The Delivery of Water During Terrestrial Planet Formation
Space Science Reviews, 2018Co-Authors: David P. O'brien, Sean N. Raymond, André Izidoro, Seth A. Jacobson, David C. RubieAbstract:The Planetary building blocks that formed in the Terrestrial Planet region were likely very dry, yet water is comparatively abundant on Earth. Here we review the various mechanisms proposed for the origin of water on the Terrestrial Planets. Various in-situ mechanisms have been suggested, which allow for the incorporation of water into the local Planetesimals in the Terrestrial Planet region or into the Planets themselves from local sources, although all of those mechanisms have difficulties. Comets have also been proposed as a source, although there may be problems fitting isotopic constraints, and the delivery efficiency is very low, such that it may be difficult to deliver even a single Earth ocean of water this way. The most promising route for water delivery is the accretion of material from beyond the snow line, similar to carbonaceous chondrites, that is scattered into the Terrestrial Planet region as the Planets are growing. Two main scenarios are discussed in detail. First is the classical scenario in which the giant Planets begin roughly in their final locations and the disk of Planetesimals and embryos in the Terrestrial Planet region extends all the way into the outer asteroid belt region. Second is the Grand Tack scenario, where early inward and outward migration of the giant Planets implants material from beyond the snow line into the asteroid belt and Terrestrial Planet region, where it can be accreted by the growing Planets. Sufficient water is delivered to the Terrestrial Planets in both scenarios. While the Grand Tack scenario provides a better fit to most constraints, namely the small mass of Mars, Planets may form too fast in the nominal case discussed here. This discrepancy may be reduced as a wider range of initial conditions is explored. Finally, we discuss several more recent models that may have important implications for water delivery to the Terrestrial Planets.
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The Delivery of Water During Terrestrial Planet Formation
Space Science Reviews, 2018Co-Authors: David P. O'brien, Sean N. Raymond, André Izidoro, Seth A. Jacobson, David C. RubieAbstract:The Planetary building blocks that formed in the Terrestrial Planet region were likely very dry, yet water is comparatively abundant on Earth. We review the various mechanisms proposed for the origin of water on the Terrestrial Planets. Various in-situ mechanisms have been suggested, which allow for the incorporation of water into the local Planetesimals in the Terrestrial Planet region or into the Planets themselves from local sources, although all of those mechanisms have difficulties. Comets have also been proposed as a source, although there may be problems fitting isotopic constraints, and the delivery efficiency is very low, such that it may be difficult to deliver even a single Earth ocean of water this way. The most promising route for water delivery is the accretion of material from beyond the snow line, similar to carbonaceous chondrites, that is scattered into the Terrestrial Planet region as the Planets are growing. Two main scenarios are discussed in detail. First is the classical scenario in which the giant Planets begin roughly in their final locations and the disk of Planetesimals and embryos in the Terrestrial Planet region extends all the way into the outer asteroid belt region. Second is the Grand Tack scenario, where early inward and outward migration of the giant Planets implants material from beyond the snow line into the asteroid belt and Terrestrial Planet region, where it can be accreted by the growing Planets. Sufficient water is delivered to the Terrestrial Planets in both scenarios. While the Grand Tack scenario provides a better fit to most constraints, namely the small mass of Mars, Planets may form too fast in the nominal case discussed here. This discrepancy may be reduced as a wider range of initial conditions is explored. Finally, we discuss several more recent models that may have important implications for water delivery to the Terrestrial Planets.
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lunar and Terrestrial Planet formation in the grand tack scenario
Philosophical Transactions of the Royal Society A, 2014Co-Authors: Seth A. Jacobson, Alessandro MorbidelliAbstract: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.
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lunar and Terrestrial Planet formation in the grand tack scenario
arXiv: Earth and Planetary Astrophysics, 2014Co-Authors: Seth A. Jacobson, Alessandro MorbidelliAbstract: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 timescale 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 $\sim$60 and $\sim$130 My after the formation of the first solids, and was caused most likely by an object with a mass similar to that of Mars.
