Growth of asteroids, planetary embryos, and Kuiper belt objects by chondrule accretion

Chondrules are millimeter-sized spherules that dominate primitive meteorites (chondrites) originating from the asteroid belt. The incorporation of chondrules into asteroidal bodies must be an important step in planet formation, but the mechanism is not understood. We show that the main growth of asteroids can result from gas drag–assisted accretion of chondrules. The largest planetesimals of a population with a characteristic radius of 100 km undergo runaway accretion of chondrules within ~3 My, forming planetary embryos up to Mars’s size along with smaller asteroids whose size distribution matches that of main belt asteroids. The aerodynamical accretion leads to size sorting of chondrules consistent with chondrites. Accretion of millimeter-sized chondrules and ice particles drives the growth of planetesimals beyond the ice line as well, but the growth time increases above the disc lifetime outside of 25 AU. The contribution of direct planetesimal accretion to the growth of both asteroids and Kuiper belt objects is minor. In contrast, planetesimal accretion and chondrule accretion play more equal roles in the formation of Moon-sized embryos in the terrestrial planet formation region. These embryos are isolated from each other and accrete planetesimals only at a low rate. However, the continued accretion of chondrules destabilizes the oligarchic configuration and leads to the formation of Mars-sized embryos and terrestrial planets by a combination of direct chondrule accretion and giant impacts.

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Forming terrestrial planets and delivering water

Proceedings of the International Astronomical Union ◽

10.1017/s174392131600572x ◽

2015 ◽

Vol 11 (A29B) ◽

pp. 427-430

Author(s):

Kevin J. Walsh

Keyword(s):

Planet Formation ◽

Semimajor Axis ◽

Giant Planet ◽

Terrestrial Planet ◽

Giant Planets ◽

Asteroid Belt ◽

Terrestrial Planets ◽

The Earth ◽

Building Models ◽

Rich Material

AbstractBuilding models capable of successfully matching the Terrestrial Planet's basic orbital and physical properties has proven difficult. Meanwhile, improved estimates of the nature of water-rich material accreted by the Earth, along with the timing of its delivery, have added even more constraints for models to match. While the outer Asteroid Belt seemingly provides a source for water-rich planetesimals, models that delivered enough of them to the still-forming Terrestrial Planets typically failed on other basic constraints - such as the mass of Mars.Recent models of Terrestrial Planet Formation have explored how the gas-driven migration of the Giant Planets can solve long-standing issues with the Earth/Mars size ratio. This model is forced to reproduce the orbital and taxonomic distribution of bodies in the Asteroid Belt from a much wider range of semimajor axis than previously considered. In doing so, it also provides a mechanism to feed planetesimals from between and beyond the Giant Planet formation region to the still-forming Terrestrial Planets.

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N-body Simulations of Planet Formation

Symposium - International Astronomical Union ◽

10.1017/s0074180900206980 ◽

2003 ◽

Vol 208 ◽

pp. 25-35 ◽

Cited By ~ 1

Author(s):

Shigeru Ida ◽

Eiichiro Kokubo ◽

Junko Kominami

Keyword(s):

Final Stage ◽

Planet Formation ◽

Planetary Systems ◽

Terrestrial Planet ◽

The Other ◽

Other Hand ◽

Giant Impacts ◽

Gas Accretion

Accretion from many small planetesimals to planets is reviewed. Solid protoplanets accrete through runaway and oligarchic growth until they become isolated. The isolation mass of protoplanets in terrestrial planet region is about 0.1-0.2 Earth mass, which suggests giant impacts among the protoplanets in the final stage of terrestrial planet formation. On the other hand, the isolation mass in Jupiter's and Saturn's orbits is about a few to 5 Earth masses, which may be massive enough to trigger gas accretion onto the cores. The isolation mass in Uranus and Neptune's orbits is as large as their present cores. Extending the above arguments to extrasolar planetary systems that are formed from disks with various initial masses, we also discuss diversity of extrasolar planetary systems.

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Linking the Origin of Asteroids to Planetesimal Formation in the Solar Nebula

Proceedings of the International Astronomical Union ◽

10.1017/s1743921315010406 ◽

2015 ◽

Vol 10 (S318) ◽

pp. 1-8 ◽

Cited By ~ 7

Author(s):

Hubert Klahr ◽

Andreas Schreiber

Keyword(s):

Numerical Simulations ◽

Turbulent Flows ◽

Kuiper Belt ◽

Asteroid Belt ◽

Kuiper Belt Objects ◽

Physical Size ◽

Zonal Flows ◽

Numerical Resolution ◽

Streaming Instability ◽

Current Paradigm

AbstractThe asteroids (more precisely: objects of the main asteroid belt) and Kuiper Belt objects (more precisely: objects of the cold classical Kuiper Belt) are leftovers of the building material for our earth and all other planets in our solar system from more than 4.5 billion years ago. At the time of their formation those were typically 100 km large objects. They were called planetesimals, built up from icy and dusty grains. In our current paradigm of planet formation it was turbulent flows and metastable flow patterns, like zonal flows and vortices, that concentrated mm to cm sized icy dust grains in sufficient numbers that a streaming instability followed by a gravitational collapse of these particle clump was triggered. The entire picture is sometimes referred to as gravoturbulent formation of planetesimals. What was missing until recently, was a physically motivated prediction on the typical sizes at which planetesimals should form via this process. Our numerical simulations in the past had only shown a correlation between numerical resolution and planetesimal size and thus no answer was possible (Johansen et al.2011). But with the lastest series of simulations on JUQUEEN (Stephan & Doctor 2015), covering all the length scales down to the physical size of actual planetesimals, we were able to obtain values for the turbulent particle diffusion as a function of the particle load in the gas. Thus, we have all necessary data at hand to feed a 'back of the envelope' calculation that predicts the size of planetesimals as result of a competition between gravitational concentration and turbulent diffusion. Using the diffusion values obtained in the numerical simulations it predicts planetesimal sizes on the order of 100 km, which suprisingly coincides with the measured data from both asteroids (Bottke et al.2005) as well from Kuiper Belt objects (Nesvorny et al.2011).

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Terrestrial Planet Formation: The Solar System and Other Systems

Symposium - International Astronomical Union ◽

10.1017/s0074180900217749 ◽

2004 ◽

Vol 202 ◽

pp. 159-166

Author(s):

Shigeru Ida ◽

Eiichiro Kokubo

Keyword(s):

Solar System ◽

Final Stage ◽

Extrasolar Planets ◽

Planet Formation ◽

Terrestrial Planet ◽

The Other ◽

Terrestrial Planets ◽

Giant Impacts ◽

Earth Like Planets ◽

Jovian Planet

Accretion of terrestrial planets and solid cores of jovian planets is discussed, based on the results of our N-body simulations. Protoplanets accrete from planetesimals through runaway and oligarchic growth until they become isolated. The isolation mass of protoplanets in terrestrial planet region is about 0.2 Earth mass, which suggests that in the final stage of terrestrial planet formation giant impacts between the protoplanets occur. On the other hand, the isolation mass in jovian planet region is about a few to 10 Earth masses, which may be massive enough to form a gas giant. Extending the above arguments to disks with various initial masses, we discuss diversity of planetary systems. We predict that the extrasolar planets so far discovered may correspond to the systems formed from disks with large initial masses and that the other disks with smaller masses, which are the majority of the disks, may form Earth-like planets.

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Formation of terrestrial planets

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319002308 ◽

2018 ◽

Vol 14 (S345) ◽

pp. 141-147

Author(s):

Eiichiro Kokubo

Keyword(s):

Final Stage ◽

Planet Formation ◽

Terrestrial Planet ◽

Dust Grains ◽

Dust Layer ◽

Elementary Processes ◽

Standard Scenario ◽

Giant Impacts ◽

Three Stages ◽

Stage 1

AbstractIn the standard formation scenario of planetary systems, planets form from a protoplanetary disk that consists of gas and dust. The scenario can be divided into three stages: (1) formation of planetesimals from dust, (2) formation of protoplanets from planetesimals, and (3) formation of planets from protoplanets. In stage (1), planetesimals form from dust through coagulation of dust grains and/or some instability of a dust layer. Planetesimals grow by mutual collisions to protoplanets or planetary embryos through runaway and oligarchic growth in stage (2). The final stage (3) of terrestrial planet formation is giant impacts among protoplanets while sweeping residual planetesimals. In the present paper, we review the elementary processes of terrestrial planet formation and discuss the extension of the standard scenario.

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Realistic collisional water transport during terrestrial planet formation

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936366 ◽

2020 ◽

Vol 634 ◽

pp. A76 ◽

Cited By ~ 2

Author(s):

C. Burger ◽

Á. Bazsó ◽

C. M. Schäfer

Keyword(s):

Water Content ◽

Water Transport ◽

Planet Formation ◽

Hybrid Approach ◽

Dynamical Evolution ◽

Terrestrial Planet ◽

Giant Planets ◽

Asteroid Belt ◽

Water Delivery ◽

Hit And Run

Context. According to the latest theoretical and isotopic evidence, Earth’s water content originates mainly from today’s asteroid belt region, or at least from the same precursor material. This suggests that water was transported inwards to Earth, and to similar planets in their habitable zone, via (giant) collisions of planetary embryos and planetesimals during the chaotic final phase of planet formation. Aims. In current dynamical simulations water delivery to terrestrial planets is still studied almost exclusively by assuming oversimplified perfect merging, even though water and other volatiles are particularly prone to collisional transfer and loss. To close this gap we have developed a computational framework to model collisional water transport by direct combination of long-term N-body computations with dedicated 3D smooth particle hydrodynamics (SPH) collision simulations of differentiated, self-gravitating bodies for each event. Methods. Post-collision water inventories are traced self-consistently in the further dynamical evolution, in accretionary or erosive as well as hit-and-run encounters with two large surviving bodies, where besides collisional losses, water transfer between the encountering bodies has to be considered. This hybrid approach enables us for the first time to trace the full dynamical and collisional evolution of a system of approximately 200 bodies throughout the whole late-stage accretion phase (several hundred Myr). As a first application we choose a Solar System-like architecture with already formed giant planets on either circular or eccentric orbits and a debris disk spanning the whole terrestrial planet region (0.5–4 au). Results. Including realistic collision treatment leads to considerably different results than simple perfect merging, with lower mass planets and water inventories reduced regularly by a factor of two or more. Due to a combination of collisional losses and a considerably lengthened accretion phase, final water content, especially with giant planets on circular orbits, is strongly reduced to more Earth-like values, and closer to results with eccentric giant planets. Water delivery to potentially habitable planets is dominated by very few decisive collisions, mostly with embryo-sized or larger objects and only rarely with smaller bodies, at least if embryos have formed throughout the whole disk initially. The high frequency of hit-and-run collisions and the differences to predominantly accretionary encounters, such as generally low water (and mass) transfer efficiencies, are a crucial part of water delivery, and of system-wide evolution in general.

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