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Alessandro Morbidelli - One of the best experts on this subject based on the ideXlab platform.
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comets as collisional fragments of a primordial planetesimal disk
Astronomy and Astrophysics, 2015Co-Authors: Alessandro Morbidelli, H RickmanAbstract:Context. The Rosetta mission and its exquisite measurements have revived the debate on whether comets are pristine planetesimals or collisionally evolved objects. Aims. We investigate the collisional Evolution experienced by the precursors of current comet nuclei during the early stages of the Solar System in the context of the so-called Nice model. Methods. We considered two environments for the collisional Evolution: (1) the transplanetary planetesimal disk, from the time of gas removal until the disk was dispersed by the migration of the ice giants; and (2) the dispersing disk during the time that the scattered disk was formed. We performed simulations using different methods in the two cases to determine the number of destructive collisions typically experienced by a comet nucleus of 2 km radius. Results. In the widely accepted scenario, where the dispersal of the planetesimal disk occurred at the time of the Late Heavy Bombardment about 4 Gy ago, comet-sized planetesimals have a very low probability of surviving destructive collisions in the disk. On the extreme assumption that the disk was dispersed directly upon gas removal, a significant fraction of the planetesimals might have remained intact. However, these survivors would still bear the marks of many nondestructive impacts. Conclusions. The Nice model of Solar System Evolution predicts that typical km-sized comet nuclei are predominantly fragments resulting from collisions experienced by larger parent bodies. An important goal for future research is to investigate whether the observed properties of comet nuclei are compatible with such a collisional origin.
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comets as collisional fragments of a primordial planetesimal disk
arXiv: Earth and Planetary Astrophysics, 2015Co-Authors: Alessandro Morbidelli, H RickmanAbstract:The Rosetta mission and its exquisite measurements have revived the debate on whether comets are pristine planetesimals or collisionally evolved objects. We investigate the collisional Evolution experienced by the precursors of current comet nuclei during the early stages of the Solar System, in the context of the so-called "Nice Model". We consider two environments for the collisional Evolution: (1) the trans-planetary planetesimal disk, from the time of gas removal until the disk was dispersed by the migration of the ice giants, and (2) the dispersing disk during the time that the scattered disk was formed. Simulations have been performed, using different methods in the two cases, to find the number of destructive collisions typically experienced by a comet nucleus of 2km radius. In the widely accepted scenario, where the dispersal of the planetesimal disk occurred at the time of the Late Heavy Bombardment about 4Gy ago, comet-sized planetesimals have a very small chance to survive against destructive collisions in the disk. On the extreme assumption that the disk was dispersed directly upon gas removal, there is a chance for a significant fraction of the planetesimals to remain intact. However, these survivors would still bear the marks of many non-destructive impacts. Thus, the Nice Model of Solar System Evolution predicts that typical km-sized comet nuclei are predominantly fragments resulting from collisions experienced by larger parent bodies. An important goal for further research is to investigate, whether the observed properties of comet nuclei are compatible with such a collisional origin.
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Depletion and Excitation of the Asteroid Belt by Migrating Planets
2012Co-Authors: Kevin J. Walsh, Alessandro Morbidelli, Sean N. Raymond, David P. O'brien, Avi MandellAbstract:A model of early inner Solar System Evolution whereby the gas-driven migration of Jupiter and Saturn truncates the disk of planetesimals and creates a depleted and dynamically excited asteroid belt populated from two parent populations.
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The onset of the lunar cataclysm as recorded in its ancient crater populations
Earth and Planetary Science Letters, 2012Co-Authors: Simone Marchi, William F. Bottke, David A. Kring, Alessandro MorbidelliAbstract:Abstract The earliest bombardment history of the Moon potentially provides powerful constraints for Solar System Evolution models. A major uncertainty, however, is how much of this history is actually recorded in lunar craters. For example, some argue that most ancient lunar craters and basins were produced by a declining bombardment of leftover planetesimals produced by terrestrial planet formation processes. Others believe that most lunar craters and large basins were formed in a narrow time interval between 3.8 and 4.0 Ga, the so-called lunar cataclysm. In the light of recent improvements in our understanding of early Solar System Evolution, it is possible that the contributions from both scenarios could be represented in the lunar crater record. If so, when did the declining bombardment end and the lunar cataclysm begin? Here we show, using new counts of 15–150 km diameter craters on the most ancient lunar terrains, that the craters found on or near Nectaris basin appear to have been created by projectiles hitting twice as fast as those that made the oldest craters on various Pre-Nectarian-era terrains. This dramatic velocity increase is consistent with the existence of a lunar cataclysm and potentially with a late reconfiguration of giant planet orbits, which may have strongly modified the source of lunar impactors. This work also suggests that the lunar cataclysm may have started near the formation time of Nectaris basin. This possibility implies that South Pole-Aitken basin (SPA), the largest lunar basin and one of the oldest by superposition, was not created during the cataclysm. This view is strengthened by our interpretation that a substantial fraction of ancient craters on SPA were made by low velocity impactors. Finally, we believe these results shed new light on the impact history of the primordial Earth.
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The Dynamical Structure of the Kuiper Belt and its Primordial Origin
arXiv: Astrophysics, 2007Co-Authors: Alessandro Morbidelli, Harold F. Levison, Rodney GomesAbstract:This chapter discusses the dynamical properties of the Kuiper belt population. Then, it focuses on the characteristics of the Kuiper belt that cannot be explained by its Evolution in the framework of the current Solar System. We review models of primordial Solar System Evolution that have been proposed to reproduce the Kuiper belt features, outlining advantages and problems of each of them.
Peter Cattermole - One of the best experts on this subject based on the ideXlab platform.
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Taylor, S. R. 2001. Solar System Evolution. A New Perspective, 2nd ed.xxiv + 460 pp. Cambridge, New York, Melbourne: Cambridge University Press. Price £60.00, US $90.00 (hard covers). ISBN 0 521 64130 6. Geol. Mag. 139, 2002
Geological Magazine, 2002Co-Authors: Peter CattermoleAbstract:Stuart Ross Taylor’s first edition of this book was published a decade ago, and has become a standard reference for anyone interested in Solar System Evolution. It tackled the problems of planetary formation head on, unflinchingly, and in a mere 330 pages. Much has happened in the sphere of planetary science since it was written: there have been new spacecraft missions to Mars, Venus, the Moon and the outer planets that have made major contributions to our knowledge; research into extra-terrestrial meteorites and small bodies has forged ahead; new theories of planet formation have emerged. This new edition is therefore most welcome and, some might say, overdue. Its expanded format – it is half as …
Gregory J. Retallack - One of the best experts on this subject based on the ideXlab platform.
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Murad, E. & Williams, I. P. (eds) 2002. Meteors in the Earth’s Atmosphere. Meteoroids and Cosmic Dust and their Interactions with the Earth’s Upper Atmosphere.: x + 322 pp. Cambridge, New York, Melbourne: Cambridge University Press. Price £60.00, US
Geological Magazine, 2003Co-Authors: Gregory J. RetallackAbstract:Chicken Little was right, the sky is falling, and as this volume informs us at the rate of 40 × 106 kg per year globally. Most of this incoming material is interstellar dust (50–700 μm diameter), about 4% of which reaches the surface unaltered. Other dust particles and meteoroids melt or are ablated on atmospheric entry, scattering metal ions 85–120 km above the surface of the Earth. Both the ions and particles are rich in carbon and iron, adding to planetary inventories of these biologically significant elements. This edited volume presents technical summaries of what and how we know about these phenomena, which have far-reaching implications for space travel, Solar System Evolution, origin of life, oceanic sedimentation, soil science, and marine and terrestrial ecoSystem nutrition. I was interested to learn, for example, that …
K. Miljković - One of the best experts on this subject based on the ideXlab platform.
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Subsurface morphology and scaling of lunar impact basins
Journal of Geophysical Research: Planets, 2016Co-Authors: K. Miljković, B. C. Johnson, J. Soderblom, Gareth S. Collins, Mark A. Wieczorek, Gregory A. Neumann, Maria T. ZuberAbstract:Impact bombardment during the first billion years after the formation of the Moon produced at least several tens of basins. The Gravity Recovery and Interior Laboratory (GRAIL) mission mapped the gravity field of these impact structures at significantly higher spatial resolution than previous missions, allowing for detailed subsurface and morphological analyses to be made across the entire globe. GRAIL-derived crustal thickness maps were used to define the regions of crustal thinning observed in centers of lunar impact basins, which represents a less unambiguous measure of a basin size than those based on topographic features. The formation of lunar impact basins was modeled numerically by using the iSALE-2D hydrocode, with a large range of impact and target conditions typical for the first billion years of lunar Evolution. In the investigated range of impactor and target conditions, the target temperature had the dominant effect on the basin subsurface morphology. Model results were also used to update current impact scaling relationships applicable to the lunar setting (based on assumed target temperature). Our new temperature-dependent impact-scaling relationships provide estimates of impact conditions and transient crater diameters for the majority of impact basins mapped by GRAIL. As the formation of lunar impact basins is associated with the first approximately 700 Myr of the Solar System Evolution when the impact flux was considerably larger than the present day, our revised impact scaling relationships can aid further analyses and understanding of the extent of impact bombardment on the Moon and terrestrial planets in the early Solar System.
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Subsurface morphology and scaling of lunar impact basins
Journal of Geophysical Research. Planets, 2016Co-Authors: K. Miljković, G. Collins, M. Wieczorek, B. C. Johnson, J. Soderblom, G. Neumann, M. ZuberAbstract:Impact bombardment during the first billion years after the formation of the Moon produced at least several tens of basins. The Gravity Recovery and Interior Laboratory (GRAIL) mission mapped the gravity field of these impact structures at significantly higher spatial resolution than previous missions, allowing for detailed subsurface and morphological analyses to be made across the entire globe. GRAIL-derived crustal thickness maps were used to define the regions of crustal thinning observed in centers of lunar impact basins, which represents a less unambiguous measure of a basin size than those based on topographic features. The formation of lunar impact basins was modeled numerically by using the iSALE-2D hydrocode, with a large range of impact and target conditions typical for the first billion years of lunar Evolution. In the investigated range of impactor and target conditions, the target temperature had the dominant effect on the basin subsurface morphology. Model results were also used to update current impact scaling relationships applicable to the lunar setting (based on assumed target temperature). Our new temperature-dependent impact-scaling relationships provide estimates of impact conditions and transient crater diameters for the majority of impact basins mapped by GRAIL. As the formation of lunar impact basins is associated with the first~700 Myr of the Solar System Evolution when the impact flux was considerably larger than the present day, our revised impact scaling relationships can aid further analyses and understanding of the extent of impact bombardment on the Moon and terrestrial planets in the early Solar System.
Stephanie C. Werner - One of the best experts on this subject based on the ideXlab platform.
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Onset of giant planet migration before 4480 million years ago
The Astrophysical Journal, 2019Co-Authors: Stephen J. Mojzsis, Ramon Brasser, Nigel M. Kelly, Oleg Abramov, Stephanie C. WernerAbstract:Immediately after their formation, the terrestrial planets experienced intense impact bombardment by comets, leftover planetesimals from primary accretion, and asteroids. This temporal interval in Solar System Evolution, termed late accretion, thermally and chemically modified solid planetary surfaces and may have impeded the emergence of life on the Hadean Earth. The sources and tempo of late accretion are, however, vague. Here, we present a timeline that relates variably retentive radiometric ages from asteroidal meteorites, to new dynamical models of late accretion that invokes giant planet migration. Reconciliation of the geochronological data with dynamical models shows that giant planet migration immediately leads to an intense 30 Myr influx of comets to the entire Solar System. The absence of whole-sale crustal reset ages after 4450 Ma for the most resilient chronometers from Earth, Moon, Mars, Vesta and various meteorite parent bodies confines the onset of giant planet migration to no later than ca. 4480 Ma. Waning impacts from planetesimals, asteroids (and a minor cometary component) continue to strike the inner planets through a protracted monotonic decline in impactor flux; this is in agreement with predictions from crater chronology. Amended global 3-D thermal analytical bombardment models derived from our new impact mass-production functions show that persistent niches for prebiotic chemistry on the early Hadean Earth could endure late accretion for at least the last 4400 Myr.
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Moon, Mars, Mercury: Basin formation ages and implications for the maximum surface age and the migration of gaseous planets
Earth and Planetary Science Letters, 2014Co-Authors: Stephanie C. WernerAbstract:Abstract Basin formation ages for Moon, Mars and Mercury are determined by cratering statistics, compared and evaluated with respect to their maximum surface ages and available isotope ages, and two possible Solar System Evolution models. Both Mars and Mercury appear to have undergone significant resurfacing, so that at least the first 200–400 million years are not recorded on their surfaces. Basin frequency and crater frequencies below 150 km indicate that the Moon has the oldest surface, Mercury has an intermediate age, and Mars has the youngest preserved terrain. An offset between the basin size-frequency distribution, the smaller crater size-frequency distribution and the main belt asteroid size-frequency distribution is observed in all three cases, suggesting an age difference of about 150 Ma between basin and smaller crater distribution-based ages. I interpreted this in terms of lack of understanding of the basin formation process, and suggest that one possible explanation for the apparently under-representative basin frequency could be a different (lower) average impact velocity compatible with the ‘Nice’ flux model. The basin formation pattern derived with the standard monotonically decaying or the sawtooth-like Nice-model flux does not reveal a coherent picture according to the late heavy bombardment idea. This is here attributed to an incomplete understanding of the cratering rate ratios between the planetary bodies considered here. Because of the Moon's unique formation history, I also suggest that it is questionable whether the Moon is a suitable analogue for the formation, Evolution and cratering record of the other terrestrial bodies.