The Origin of Comets in the Solar Nebula: A Unified Model

Weidenschilling, S. J.

doi:10.1006/icar.1997.5712

Cited by 388 publications

(396 citation statements)

References 36 publications

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“…Here we aim to show the general evolution of how water vapor and ice could be distributed in protoplanetary disks by modeling all of the physics that control the evolution of the four species which have the most distinct dynamical behavior. Thus our model is an improvement over the single-size model at a given location of Stepinski and Valageas (1997), but is simpler to evolve than the full size distribution of Weidenschilling (1997) (or other similar studies) and accounts for the diversity of physical behaviors involved. In general, water vapor will be transported by the same processes that transport the rest of the nebular gas (diffusion and advection).…”

Section: Evolution Of the Water Distributionmentioning

confidence: 98%

“…The likelihood of significant particle growth leads us to doubt the reality of the T 2 dependence found by Pollack et al (1994) and assumed by Cassen (1994), which is a tiny-particle property, so we will assume a temperatureindependent opacity per gram of solid material. Results of Weidenschilling (1997Weidenschilling ( , 2000 using detailed particle growth models, tend to find the "dust" regime (microns to tens of centimeters radius) has a mass distribution m(a) with equal mass per bin of width a (equal to the particle radius); that is, then, n (a) a 4 = constant, or n (a) ∝ a −4 . From figure 10 of Miyake and Nakagawa (1993) we see that, very roughly, the opacity of such a distribution, ranging from microns to centimeters, can be approximated by something like Cassen's adopted 5 cm 2 g −1 (because the steep powerlaw emphasizes particles at the small end of the range), over the wavelength range 1-100µm characterizing nebula blackbody radiation.…”

Section: Evolution Of the Nebular Gasmentioning

confidence: 99%

“…This timescale is set by the competing effects of particle growth from collisions that arise due to brownian motion, turbulence, or differential drift and particle destruction or erosion from energetic collisions. The importance and efficiency of these processes is uncertain (Weidenschilling and Cuzzi, 1993;Weidenschilling, 1997;Dullemond and Dominik, 2005;Cuzzi and Weidenschilling, 2005). Here we assume that t coag ranges from 10 3 -10 5 years at 1 AU, consistent with timescales estimated by other authors (Cassen, 1996;Beckwith et al, 2000).…”

Section: Growth Of Migratorsmentioning

confidence: 99%

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The evolution of the water distribution in a viscous protoplanetary disk

Ciesla

Cuzzi

2006

Icarus

314

356

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Astronomical observations have shown that protoplanetary disks are dynamic objects through which mass is transported and accreted by the central star. This transport causes the disks to decrease in mass and cool over time, and such evolution is expected to have occurred in our own solar nebula. Age dating of meteorite constituents shows that their creation, evolution, and accumulation occupied several Myr, and over this time disk properties would evolve significantly. Moreover, on this timescale, solid particles decouple from the gas in the disk and their evolution follows a different path. It is in this context that we must understand how our own solar nebula evolved and what effects this evolution had on the primitive materials contained within it. Here we present a model which tracks how the distribution of water changes in an evolving disk as the water-bearing species experience condensation, accretion, transport, collisional destruction, and vaporization. Because solids are transported in a disk at different rates depending on their sizes, the motions will lead to water being concentrated in some regions of a disk and depleted in others. These enhancements and depletions are consistent with the conditions needed to explain some aspects of the chemistry of chondritic meteorites and formation of giant planets. The levels of concentration and depletion, as well as their locations, depend strongly on the combined effects of the gaseous disk evolution, the formation of rapidly migrating rubble, and the growth of immobile planetesimals. Understanding how these processes operate simultaneously is critical to developing our models for meteorite parent body formation in the solar system and giant planet formation throughout the galaxy. We present examples of evolution under a range of plausible assumptions and demonstrate how the chemical evolution of the inner region of a protoplanetary disk is intimately connected to the physical processes which occur in the outer regions.

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Section: Evolution Of the Water Distributionmentioning

confidence: 98%

Section: Evolution Of the Nebular Gasmentioning

confidence: 99%

Section: Growth Of Migratorsmentioning

confidence: 99%

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The evolution of the water distribution in a viscous protoplanetary disk

Ciesla

Cuzzi

2006

Icarus

314

356

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“…For compact spherical particles of size << λ, β = 2, while for Figure 2. A numerical simulation of particle size evolution within a protoplanetary disk (from [11]). The small grains in the disk stick and settle to the mid-plane, which creates a layer of centimeter size particles.…”

Section: Grain Growth Studiesmentioning

confidence: 99%

Imaging protoplanetary disks with a square kilometer array

Wilner

2004

New Astronomy Reviews

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The recent detections of extrasolar giant planets has revealed a surprising diversity of planetary system architectures, with many very unlike our Solar System. Understanding the origin of this diversity requires multiwavelength studies of the structure and evolution of the protoplanetary disks that surround young stars. Radio astronomy and the Square Kilometer Array will play a unique role in these studies by imaging thermal dust emission in a representative sample of protoplanetary disks at unprecedented sub-AU scales in the innermost regions, including the "habitable zone" that lies within a few AU of the central stars. Radio observations will probe the evolution of dust grains up to centimeter-sized "pebbles", the critical first step in assembling giant planet cores and terrestrial planets, through the wavelength dependence of dust emissivity, which provides a diagnostic of particle size. High resolution images of dust emission will show directly mass concentrations and features in disk surface density related to planet building, in particular the radial gaps opened by tidal interactions between planets and disks, and spiral waves driven by embedded protoplanets. Moreover, because orbital timescales are short in the inner disk, synoptic studies over months and years will show proper motions and allow for the tracking of secular changes in disk structure. SKA imaging of protoplanetary disks will reach into the realm of rocky planets for the first time, and they will help clarify the effects of the formation of giant planets on their terrestrial counterparts.

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“…In case of widespread collisional fragmentation, e.g. in the warmer terrestrial planet formation region, up to 80% of the solid material may be bound in small fragments 27,28 , in which case we must implicitly assume an augmentation in solids-to-gas ratio of up to 5.In our self-gravitating model we set ∆v = −0.02c s , but show in the Supplementary Information that gravitationally bound clusters also form for ∆v = −0.05c s , with a factor of two increase in column density threshold. The Supplementary Information also documents that typical boulder collisions happen at speeds below the expected destruction threshold 3 .…”

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confidence: 99%

Rapid planetesimal formation in turbulent circumstellar disks

Johansen

Oishi

Low

et al. 2007

Nature

1,112

977

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The initial stages of planet formation in circumstellar gas discs proceed via dust grains that collide and build up larger and larger bodies 1 . How this process continues from metre-sized boulders to kilometre-scale planetesimals is a major unsolved problem 2 : boulders stick together poorly 3 , and spiral into the protostar in a few hundred orbits due to a head wind from the slower rotating gas 4 . Gravitational collapse of the solid component has been suggested to overcome this barrier 1,5,6 . Even low levels of turbulence, however, inhibit sedimentation of solids to a sufficiently dense midplane layer 2, 7 , but turbulence must be present to explain observed gas accretion in protostellar discs 8 . Here we report the discovery of efficient gravitational collapse of boulders in locally overdense regions in the midplane. The boulders concentrate initially in transient high pressures in the turbulent gas 9 , and these concentra-1 arXiv:0708.3890v1 [astro-ph] 29 Aug 2007 tions are augmented a further order of magnitude by a streaming instability [10][11][12] driven by the relative flow of gas and solids. We find that gravitationally bound clusters form with masses comparable to dwarf planets and containing a distribution of boulder sizes. Gravitational collapse happens much faster than radial drift, offering a possible path to planetesimal formation in accreting circumstellar discs.Planet formation models typically treat turbulence as a diffusive process that opposes the gravitational sedimentation of solids to a high density midplane layer in circumstellar discs 7,13 . Recent models of solids moving in turbulent gas reveal that the turbulent motions not only mix them, but also concentrate metre-sized boulders in the transient gas overdensities 9 formed in magnetorotational turbulence 14 , in giant gaseous vortices 15,16 , and in spiral arms of self-gravitating discs 17 .Short-lived eddies at the dissipation scale of forced turbulence concentrate smaller millimetre-sized solids 18 . Some simulations mentioned above 9,11,12 were performed with the Pencil Code, which solves the magnetohydrodynamic (MHD) equations on a three-dimensional grid for a gas that interacts through drag forces with boulders. Boulders are represented as superparticles with independent positions and velocities, each having the mass of a huge number of boulders but the aerodynamic behaviour of a single boulder. We have now further developed the Pencil Code to include a fully parallel solver for the gravitational potential of the particles (see Supplementary Information). The particle density is mapped on the grid using the Triangular Shaped Cloud assignment scheme 19 and the gravitational potential of the solids is found using a Fast Fourier Transform method 20 . 2This allows us, for the first time, to simulate the dynamics of self-gravitating solid particles in magnetised, three-dimensional turbulence.We model a corotating, local box with linearised Keplerian shear that straddles the protoplanetary disc midplane and orbits the young star ...

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The Origin of Comets in the Solar Nebula: A Unified Model

Cited by 388 publications

References 36 publications

The evolution of the water distribution in a viscous protoplanetary disk

The evolution of the water distribution in a viscous protoplanetary disk

Imaging protoplanetary disks with a square kilometer array

Rapid planetesimal formation in turbulent circumstellar disks

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