The Experts below are selected from a list of 138 Experts worldwide ranked by ideXlab platform
Angelo Pio Rossi - One of the best experts on this subject based on the ideXlab platform.
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On the chronology of Lunar Origin and evolution
The Astronomy and Astrophysics Review, 2013Co-Authors: Johannes Geiss, Angelo Pio RossiAbstract:An Origin of the Moon by a Giant Impact is presently the most widely accepted theory of Lunar Origin. It is consistent with the major Lunar observations: its exceptionally large size relative to the host planet, the high angular momentum of the Earth–Moon system, the extreme depletion of volatile elements, and the delayed accretion, quickly followed by the formation of a global crust and mantle.
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On the chronology of Lunar Origin and evolution
The Astronomy and Astrophysics Review, 2013Co-Authors: Johannes Geiss, Angelo Pio RossiAbstract:An Origin of the Moon by a Giant Impact is presently the most widely accepted theory of Lunar Origin. It is consistent with the major Lunar observations: its exceptionally large size relative to the host planet, the high angular momentum of the Earth–Moon system, the extreme depletion of volatile elements, and the delayed accretion, quickly followed by the formation of a global crust and mantle. According to this theory, an impact on Earth of a Mars-sized body set the initial conditions for the formation and evolution of the Moon. The impact produced a protoLunar cloud. Fast accretion of the Moon from the dense cloud ensured an effective transformation of gravitational energy into heat and widespread melting. A “Magma Ocean” of global dimensions formed, and upon cooling, an anorthositic crust and a mafic mantle were created by gravitational separation. Several 100 million years after Lunar accretion, long-lived isotopes of K, U and Th had produced enough additional heat for inducing partial melting in the mantle; lava extruded into large basins and solidified as titanium-rich mare basalt. This delayed era of extrusive rock formation began about 3.9 Ga ago and may have lasted nearly 3 Ga. A relative crater count timescale was established and calibrated by radiometric dating (i.e., dating by use of radioactive decay) of rocks returned from six Apollo landing regions and three Luna landing spots. Fairly well calibrated are the periods ≈4 Ga to ≈3 Ga BP (before present) and ≈0.8 Ga BP to the present. Crater counting and orbital chemistry (derived from remote sensing in spectral domains ranging from γ - and x-rays to the infrared) have identified mare basalt surfaces in the Oceanus Procellarum that appear to be nearly as young as 1 Ga. Samples returned from this area are needed for narrowing the gap of 2 Ga in the calibrated timescale. The Lunar timescale is not only used for reconstructing Lunar evolution, but it serves also as a standard for chronologies of the terrestrial planets, including Mars and possibly early Earth. The Moon holds a historic record of Galactic cosmic-ray intensity, solar wind composition and fluxes and composition of solids of any size in the region of the terrestrial planets. Some of this record has been deciphered. Secular mixing of the Sun was constrained by determining ^3He/^4He of solar wind helium stored in Lunar fines and ancient breccias. For checking the presumed constancy of the impact rate over the past ≈3.1 Ga, samples of the youngest mare basalts would be needed for determining their radiometric ages. Radiometric dating and stratigraphy has revealed that many of the large basins on the near side of the Moon were created by impacts about 4.1 to 3.8 Ga ago. The apparent clustering of ages called “Late Heavy Bombardment (LHB)” is thought to result from migration of planets several 100 million years after their accretion. The bombardment, unexpectedly late in solar system history, must have had a devastating effect on the atmosphere, hydrosphere and habitability on Earth during and following this epoch, but direct traces of this bombardment have been eradicated on our planet by plate tectonics. Indirect evidence about the course of bombardment during this epoch on Earth must therefore come from the Lunar record, especially from additional data on the terminal phase of the LHB. For this purpose, documented samples are required for measuring precise radiometric ages of the Orientale Basin and the Nectaris and/or Fecunditatis Basins in order to compare these ages with the time of the earliest traces of life on Earth. A crater count chronology is presently being built up for planet Mars and its surface features. The chronology is based on the established Lunar chronology whereby differences between the impact rates for Moon and Mars are derived from local fluxes and impact energies of projectiles. Direct calibration of the Martian chronology will have to come from radiometric ages and cosmic-ray exposure ages measured in samples returned from the planet.
Johannes Geiss - One of the best experts on this subject based on the ideXlab platform.
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On the chronology of Lunar Origin and evolution
The Astronomy and Astrophysics Review, 2013Co-Authors: Johannes Geiss, Angelo Pio RossiAbstract:An Origin of the Moon by a Giant Impact is presently the most widely accepted theory of Lunar Origin. It is consistent with the major Lunar observations: its exceptionally large size relative to the host planet, the high angular momentum of the Earth–Moon system, the extreme depletion of volatile elements, and the delayed accretion, quickly followed by the formation of a global crust and mantle.
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On the chronology of Lunar Origin and evolution
The Astronomy and Astrophysics Review, 2013Co-Authors: Johannes Geiss, Angelo Pio RossiAbstract:An Origin of the Moon by a Giant Impact is presently the most widely accepted theory of Lunar Origin. It is consistent with the major Lunar observations: its exceptionally large size relative to the host planet, the high angular momentum of the Earth–Moon system, the extreme depletion of volatile elements, and the delayed accretion, quickly followed by the formation of a global crust and mantle. According to this theory, an impact on Earth of a Mars-sized body set the initial conditions for the formation and evolution of the Moon. The impact produced a protoLunar cloud. Fast accretion of the Moon from the dense cloud ensured an effective transformation of gravitational energy into heat and widespread melting. A “Magma Ocean” of global dimensions formed, and upon cooling, an anorthositic crust and a mafic mantle were created by gravitational separation. Several 100 million years after Lunar accretion, long-lived isotopes of K, U and Th had produced enough additional heat for inducing partial melting in the mantle; lava extruded into large basins and solidified as titanium-rich mare basalt. This delayed era of extrusive rock formation began about 3.9 Ga ago and may have lasted nearly 3 Ga. A relative crater count timescale was established and calibrated by radiometric dating (i.e., dating by use of radioactive decay) of rocks returned from six Apollo landing regions and three Luna landing spots. Fairly well calibrated are the periods ≈4 Ga to ≈3 Ga BP (before present) and ≈0.8 Ga BP to the present. Crater counting and orbital chemistry (derived from remote sensing in spectral domains ranging from γ - and x-rays to the infrared) have identified mare basalt surfaces in the Oceanus Procellarum that appear to be nearly as young as 1 Ga. Samples returned from this area are needed for narrowing the gap of 2 Ga in the calibrated timescale. The Lunar timescale is not only used for reconstructing Lunar evolution, but it serves also as a standard for chronologies of the terrestrial planets, including Mars and possibly early Earth. The Moon holds a historic record of Galactic cosmic-ray intensity, solar wind composition and fluxes and composition of solids of any size in the region of the terrestrial planets. Some of this record has been deciphered. Secular mixing of the Sun was constrained by determining ^3He/^4He of solar wind helium stored in Lunar fines and ancient breccias. For checking the presumed constancy of the impact rate over the past ≈3.1 Ga, samples of the youngest mare basalts would be needed for determining their radiometric ages. Radiometric dating and stratigraphy has revealed that many of the large basins on the near side of the Moon were created by impacts about 4.1 to 3.8 Ga ago. The apparent clustering of ages called “Late Heavy Bombardment (LHB)” is thought to result from migration of planets several 100 million years after their accretion. The bombardment, unexpectedly late in solar system history, must have had a devastating effect on the atmosphere, hydrosphere and habitability on Earth during and following this epoch, but direct traces of this bombardment have been eradicated on our planet by plate tectonics. Indirect evidence about the course of bombardment during this epoch on Earth must therefore come from the Lunar record, especially from additional data on the terminal phase of the LHB. For this purpose, documented samples are required for measuring precise radiometric ages of the Orientale Basin and the Nectaris and/or Fecunditatis Basins in order to compare these ages with the time of the earliest traces of life on Earth. A crater count chronology is presently being built up for planet Mars and its surface features. The chronology is based on the established Lunar chronology whereby differences between the impact rates for Moon and Mars are derived from local fluxes and impact energies of projectiles. Direct calibration of the Martian chronology will have to come from radiometric ages and cosmic-ray exposure ages measured in samples returned from the planet.
Kaveh Pahlevan - One of the best experts on this subject based on the ideXlab platform.
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Origin of the Moon.
arXiv: Earth and Planetary Astrophysics, 2021Co-Authors: Robin M. Canup, Kaveh Pahlevan, S J Lock, Raluca Rufu, Kevin Righter, Nicolas Dauphas, Matija Ćuk, Sarah T. Stewart, Julien Salmon, Miki NakajimaAbstract:The Earth-Moon system is unusual in several respects. The Moon is roughly 1/4 the radius of the Earth - a larger satellite-to-planet size ratio than all known satellites other than Pluto's Charon. The Moon has a tiny core, perhaps with only ~1% of its mass, in contrast to Earth whose core contains nearly 30% of its mass. The Earth-Moon system has a high total angular momentum, implying a rapidly spinning Earth when the Moon formed. In addition, the early Moon was hot and at least partially molten with a deep magma ocean. Identification of a model for Lunar Origin that can satisfactorily explain all of these features has been the focus of decades of research.
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Speciation and dissolution of hydrogen in the proto-Lunar disk
Earth and Planetary Science Letters, 2016Co-Authors: Kaveh Pahlevan, Shun-ichiro Karato, Bruce FegleyAbstract:Abstract Despite very high temperatures accompanying Lunar Origin, indigenous water in the form of OH has been unambiguously observed in Apollo samples in recent years. Such observations have prompted questions about the abundance and distribution of Lunar hydrogen. Here, we investigate the related question of the Origin of Lunar H: is the hydrogen observed a remnant of a much larger initial inventory that was inherited from a “wet” Earth but partly depleted during the process of Origin, or was primordial hydrogen quantitatively lost from the Lunar material, with water being delivered to Lunar reservoirs via subsequent impacts after the Origins sequence? Motivated by recent results pointing to a limited extent of hydrogen escape from the gravity field of the Earth during Lunar Origin, we apply a newly developed thermodynamic model of liquid–vapor silicates to the proto-Lunar disk to interrogate the behavior of H as a trace element in the energetic aftermath of the giant impact. We find that: (1) pre-existing H-bearing molecules are rapidly dissociated at the temperatures considered (3100–4200 K) and vaporized hydrogen predominantly exists as OH(v), H(v) and MgOH(v) for nearly the full range of thermal states encountered in the proto-Lunar disk, (2) despite such a diversity in the vapor speciation – which reduces the water fugacity and favors hydrogen exsolution from co-existing liquids – the equilibration of the vapor atmosphere with the disk liquid results in significant dissolution of H into proto-Lunar magmas, and (3) equilibrium H isotopic fractionation in this setting is limited to
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Isotopes as tracers of the sources of the Lunar material and processes of Lunar Origin
Philosophical transactions. Series A Mathematical physical and engineering sciences, 2014Co-Authors: Kaveh PahlevanAbstract:Ever since the Apollo programme, isotopic abundances have been used as tracers to study Lunar formation, in particular to study the sources of the Lunar material. In the past decade, increasingly precise isotopic data have been reported that give strong indications that the Moon and the Earth9s mantle have a common heritage. To reconcile these observations with the Origin of the Moon via the collision of two distinct planetary bodies, it has been proposed (i) that the Earth–Moon system underwent convective mixing into a single isotopic reservoir during the approximately 10 3 year molten disc epoch after the giant impact but before Lunar accretion, or (ii) that a high angular momentum impact injected a silicate disc into orbit sourced directly from the mantle of the proto-Earth and the impacting planet in the right proportions to match the isotopic observations. Recently, it has also become recognized that liquid–vapour fractionation in the energetic aftermath of the giant impact is capable of generating measurable mass-dependent isotopic offsets between the silicate Earth and Moon, rendering isotopic measurements sensitive not only to the sources of the Lunar material, but also to the processes accompanying Lunar Origin. Here, we review the isotopic evidence that the silicate–Earth–Moon system represents a single planetary reservoir. We then discuss the development of new isotopic tracers sensitive to processes in the melt–vapour Lunar disc and how theoretical calculations of their behaviour and sample observations can constrain scenarios of post-impact evolution in the earliest history of the Earth–Moon system.
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Chemical and isotopic consequences of Lunar formation via giant impact
2010Co-Authors: Kaveh PahlevanAbstract:There is near consensus in the planetary science community that the Origin of the Moon can be traced to a massive interplanetary collision between a roughly Mars-sized object and the growing Earth towards the end of planetary accretion. Many in the geochemical community, however, have rightly expressed skepticism towards this hypothesis. The compositional signatures of the giant impact have never been clearly articulated, and no one has yet used the ideas of Lunar Origin to say something about the Lunar composition that was not previously known, that is, to make a prediction. The work presented here seeks to develop the theory of Lunar Origin with two goals in mind: of reconciling the predictions of the dynamical scenario with the observed signatures in the Lunar composition, and of making new predictions for the Lunar chemical and isotopic composition that can test and further constrain the theory through comparison with observations.
Robin M. Canup - One of the best experts on this subject based on the ideXlab platform.
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Origin of the Moon.
arXiv: Earth and Planetary Astrophysics, 2021Co-Authors: Robin M. Canup, Kaveh Pahlevan, S J Lock, Raluca Rufu, Kevin Righter, Nicolas Dauphas, Matija Ćuk, Sarah T. Stewart, Julien Salmon, Miki NakajimaAbstract:The Earth-Moon system is unusual in several respects. The Moon is roughly 1/4 the radius of the Earth - a larger satellite-to-planet size ratio than all known satellites other than Pluto's Charon. The Moon has a tiny core, perhaps with only ~1% of its mass, in contrast to Earth whose core contains nearly 30% of its mass. The Earth-Moon system has a high total angular momentum, implying a rapidly spinning Earth when the Moon formed. In addition, the early Moon was hot and at least partially molten with a deep magma ocean. Identification of a model for Lunar Origin that can satisfactorily explain all of these features has been the focus of decades of research.
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The Impact Phase of Terrestrial Planet Accretion: Implications for Lunar Origin
1999Co-Authors: C. B. Agnor, Robin M. Canup, Harold F. LevisonAbstract:Two decades of analytical modeling and numerical simulation have revealed three general stages in the terrestrial accretion process: an early stage which commences with dust grains in a gas-rich nebula and ends with the formation of km-sized “planetesimals”; an intermediate stage in which planetesimals experience runaway growth and form Lunarsized “planetary embryos” in approximately 10 – 10 years; and a final stage dominated by mutual gravitational perturbations between planetary embryos, resulting in large, stochastic impact events and the formation of the final terrestrial planets after about 10 years. The prediction of a final impact-dominated phase coincides nicely with observed features in our solar system that are believed to be the result of giant impact events, including most significantly the Earth/Moon system.
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Evolution of a Terrestrial Multiple-Moon System
The Astronomical Journal, 1999Co-Authors: Robin M. Canup, Harold F. Levison, Glen R. StewartAbstract:The currently favored theory of Lunar Origin is the giant-impact hypothesis. Recent work that has modeled accretional growth in impact-generated disks has found that systems with one or two large moons and external debris are common outcomes. In this paper we investigate the evolution of terrestrial multiple-moon systems as they evolve due to mutual interactions (including mean motion resonances) and tidal interaction with Earth, using both analytical techniques and numerical integrations. We find that multiple-moon configurations that form from impact-generated disks are typically unstable: these systems will likely evolve into a single-moon state as the moons mutually collide or as the inner moonlet crashes into Earth.
Matija Cuk - One of the best experts on this subject based on the ideXlab platform.
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the Origin of the moon within a terrestrial synestia
Journal of Geophysical Research, 2018Co-Authors: S J Lock, S T Stewart, Michail I Petaev, Zoe M Leinhardt, M Mace, Stein B Jacobsen, Matija CukAbstract:The giant impact hypothesis remains the leading theory for Lunar Origin. However, current models struggle to explain the Moon's composition and isotopic similarity with Earth. Here we present a new Lunar Origin model. High-energy, high-angular momentum giant impacts can create a post-impact structure that exceeds the corotation limit (CoRoL), which defines the hottest thermal state and angular momentum possible for a corotating body. In a typical super-CoRoL body, traditional definitions of mantle, atmosphere and disk are not appropriate, and the body forms a new type of planetary structure, named a synestia. Using simulations of cooling synestias combined with dynamic, thermodynamic and geochemical calculations, we show that satellite formation from a synestia can produce the main features of our Moon. We find that cooling drives mixing of the structure, and condensation generates moonlets that orbit within the synestia, surrounded by tens of bars of bulk silicate Earth (BSE) vapor. The moonlets and growing moon are heated by the vapor until the first major element (Si) begins to vaporize and buffer the temperature. Moonlets equilibrate with BSE vapor at the temperature of silicate vaporization and the pressure of the structure, establishing the Lunar isotopic composition and pattern of moderately volatile elements. Eventually, the cooling synestia recedes within the Lunar orbit, terminating the main stage of Lunar accretion. Our model shifts the paradigm for Lunar Origin from specifying a certain impact scenario to achieving a Moon-forming synestia. Giant impacts that produce potential Moon-forming synestias were common at the end of terrestrial planet formation.
