Planet Formation by Coagulation: A Focus on Uranus and Neptune

Goldreich, Peter; Lithwick, Yoram; Sari, Re’em

doi:10.1146/annurev.astro.42.053102.134004

Cited by 286 publications

(388 citation statements)

References 100 publications

Supporting

Mentioning

375

Contrasting

Unclassified

Order By: Relevance

“…Goldreich et al (2004) already pointed out that the presence of a large amount of small planetesimals would help to accelerate planetary formation. If the planetesimal disk is dominated by big bodies, the time-scale to form solid embryos able to bind a significant envelope and start the gaseous runaway accretion would be too long to complete the formation in less than 10 Myr.…”

Section: Discussionmentioning

confidence: 99%

Simultaneous formation of solar system giant planets

Guilera

Fortier

Brunini

et al. 2011

A&A

View full text Add to dashboard Cite

Context. In the last few years, the so-called "Nice model" has become increasingly significant for studying the formation and evolution of the solar system. According to this model, the initial orbital configuration of the giant planets was much more compact than the one we observe today. Aims. We study the formation of the giant planets in connection with several parameters that describe the protoplanetary disk. We aim to establish which conditions enable their simultaneous formation in line with the initial configuration proposed by the Nice model. We focus on the conditions that lead to the simultaneous formation of two massive cores, corresponding to Jupiter and Saturn, which are able to reach the cross-over mass (where the mass of the envelope of the giant planet equals the mass of the core, and gaseous runway starts), while two other cores that correspond to Uranus and Neptune have to be able to grow to their current masses. Methods. We compute the in situ planetary formation, employing the numerical code introduced in our previous work for different density profiles of the protoplanetary disk. Planetesimal migration is taken into account and planetesimals are considered to follow a size distribution between r min p (free parameter) and r max p = 100 km. The core's growth is computed according to the oligarchic growth regime.Results. The simultaneous formation of the giant planets was successfully completed for several initial conditions of the disk. We find that for protoplanetary disks characterized by a power law (Σ ∝ r −p ), flat surface density profiles (p ≤ 1.5) favor the simultaneous formation. However, for steep slopes (p ∼ 2, as previously proposed by other authors) the simultaneous formation of the solar system giant planets is unlikely. Conclusions. The simultaneous formation of the giant planets -in the context of the Nice model -is favored by flat surface density profiles. The formation time-scale agrees with the estimates of disk lifetimes if a significant mass of the solids accreted by the planets is contained in planetesimals with radii <1 km.

show abstract

Section: Discussionmentioning

confidence: 99%

Simultaneous formation of solar system giant planets

Guilera

Fortier

Brunini

et al. 2011

A&A

View full text Add to dashboard Cite

show abstract

“…1 shows the evolution of the RMS eccentricity of stars in the stellar disk, using a similar setup as used by Alexander et al (2007) 2.2 Multi-mass components and mass segregation Stellar scattering had also been considered for multi-mass stellar populations in the dispersion dominated regime . In this regime, for two mass populations, Goldreich et al (2004) suggest that the treatment of the problem only depends on the amplitude of the velocity dispersion (σ2) of the lighter objects, with mass M2, compared with the Hill velocity of the more massive components , with mass M1. The Hill velocity for the more massive stars is defined as…”

Section: Relaxation and Single-star Scatteringmentioning

confidence: 99%

“…In the shear dominated regime, not discussed here, it is necessary to take into account the tidal gravity of the central black hole. When the velocity dispersion of the low-mass stars satisfies vesc,1 > σ2 > vH,1, with vesc,1 the escape velocity from massive stars, the exchange of momentum between the heavier and lighter bodies occurs through collisionless gravitational deflections, where gravitational focusing is important (Goldreich et al 2004).…”

Section: Relaxation and Single-star Scatteringmentioning

confidence: 99%

Short- and long-term evolution of a stellar disc around a massive black hole: the role of the cusp, stellar evolution and binaries

Mikhaloff¹,

Perets²

2016

Mon. Not. R. Astron. Soc.

View full text Add to dashboard Cite

We study the dynamical evolution of a stellar disk orbiting a massive black hole. We explore the role of two-body relaxation, mass segregation, stellar evolution and binary heating in affecting the disk evolution, and consider the impact of the nuclear cluster structure and the stellar-disk mass-function. We use analytic arguments and numerical calculations, and apply them to study the evolution of a stellar disk (similar to that observed in the Galactic center; GC), both on the short (few Myr) and longer (100 Myr) evolutionary timescales. We find the dominant processes affecting the disk evolution are two-body relaxation and mass segregation where as binary heating have only a little contribution. Massive stars play a dominant role in kinematically heating low mass stars, and driving them to high eccentricities/inclinations. Multi-mass models with realistic mass-functions for the disk stars show the disk structure to be mass stratified, with the most massive stars residing in thinner structures. Stellar evolution plays an important role in decreasing the number of massive stars with time, thereby leading to slower relaxation, where the remnant compact objects of these stars are excited to higher eccentricities/inclinations. At these later evolutionary stages dynamical heating by the nuclear cluster plays a progressively more important role. We conclude that the high eccentricities and high inclination observed for the majority on the young O-stars in the Galactic Center suggest that the disk stars had been formed with initially high eccentricities, or that collective or secular processes (not explored here) dominate the disk evolution. The latter processes are less likely to produce mass stratification in the disk; detailed study of the mass-dependent kinematic properties of the disk stars could therefore provide a handle on the processes that dominate its evolution. Finally, we find that the disk structure is expected to keep its coherency, and be observed as a relatively thin disk even after 100 Myrs; two-body relaxation is too inefficient for the disk to assimilate into the nuclear cluster on such timescales. It therefore suggests earlier disks now containing only older, lower mass stars might still be observed in the Galactic center, unless destroyed/smeared by other non-two-body relaxation processes.

show abstract

“…These fragments can be kept dynamically cold, e.g., by mutual collisions or by gas drag. The accretion then takes place at low v a -the shear-dominated regime -which is very favorable for growth (Goldreich et al 2004). The generation of large amounts of fragments therefore can significantly boost accretion.…”

Section: Introductionmentioning

confidence: 99%

The effect of gas drag on the growth of protoplanets

Ormel¹,

Klahr

2010

A&A

579

641

View full text Add to dashboard Cite

Planetary bodies form by accretion of smaller bodies. It has been suggested that a very efficient way to grow protoplanets is by accreting particles of size km (e.g., chondrules, boulders, or fragments of larger bodies) as they can be kept dynamically cold. We investigate the effects of gas drag on the impact radii and the accretion rates of these particles. As simplifying assumptions we restrict our analysis to 2D settings, a gas drag law linear in velocity, and a laminar disk characterized by a smooth (global) pressure gradient that causes particles to drift in radially. These approximations, however, enable us to cover an arbitrary large parameter space. The framework of the circularly restricted three body problem is used to numerically integrate particle trajectories and to derive their impact parameters. Three accretion modes can be distinguished: hyperbolic encounters, where the 2-body gravitational focusing enhances the impact parameter; three-body encounters, where gas drag enhances the capture probability; and settling encounters, where particles settle towards the protoplanet. An analysis of the observed behavior is presented; and we provide a recipe to analytically calculate the impact radius, which confirms the numerical findings. We apply our results to the sweepup of fragments by a protoplanet at a distance of 5 AU. Accretion of debris on small protoplanets ( < ∼ 50 km) is found to be slow, because the fragments are distributed over a rather thick layer. However, the newly found settling mechanism, which is characterized by much larger impact radii, becomes relevant for protoplanets of ∼10 3 km in size and provides a much faster channel for growth.

show abstract

Planet Formation by Coagulation: A Focus on Uranus and Neptune

Cited by 286 publications

References 100 publications

Simultaneous formation of solar system giant planets

Simultaneous formation of solar system giant planets

Short- and long-term evolution of a stellar disc around a massive black hole: the role of the cusp, stellar evolution and binaries

The effect of gas drag on the growth of protoplanets

Contact Info

Product

Resources

About