scholarly journals Dawes Review 7: The Tidal Downsizing Hypothesis of Planet Formation

2017 ◽  
Vol 34 ◽  
Author(s):  
Sergei Nayakshin
Keyword(s):  
Excited State ◽  
Dynamic Systems ◽  
Planet Formation ◽  
Brown Dwarfs ◽  
Population Synthesis ◽  
Open Questions ◽  
New Interpretation ◽  
Dust Grain ◽  
Grain Dynamics ◽  
Massive Cores

AbstractTidal Downsizing scenario of planet formation builds on ideas proposed by Gerard Kuiper in 1951. Detailed simulations of self-gravitating discs, gas fragments, dust grain dynamics, and planet evolutionary calculations are summarised here and used to build a predictive population synthesis. A new interpretation of exoplanetary and debris disc data, the Solar System's origins, and the links between planets and brown dwarfs is offered. Tidal Downsizing predicts that presence of debris discs, sub-Neptune mass planets, planets more massive than ~ 5 Jupiter masses and brown dwarfs should not correlate strongly with the metallicity of the host. For gas giants of ~ Saturn to a few Jupiter mass, a strong host star metallicity correlation is predicted only inwards of a few AU from the host. Composition of massive cores is predicted to be dominated by rock rather than ices. Debris discs made by Tidal Downsizing have an innermost edge larger than about 1 au, have smaller total masses and are usually in a dynamically excited state. Planet formation in surprisingly young or very dynamic systems such as HL Tau and Kepler-444 may be a signature of Tidal Downsizing. Open questions and potential weaknesses of the hypothesis are pointed out.

scholarly journals Diverse outcomes of planet formation and composition around low-mass stars and brown dwarfs

2019 ◽  
Author(s):  
Y Miguel ◽  
A Cridland ◽  
C W Ormel ◽  
J J Fortney ◽  
S Ida
Keyword(s):  
Planet Formation ◽  
Planetary Systems ◽  
Brown Dwarfs ◽  
Population Synthesis ◽  
Optimal Conditions ◽  
Low Mass Stars ◽  
Water Fraction ◽  
Low Mass ◽  
M Stars ◽  
Mass Form

Abstract The detection of Earth-size exoplanets around low-mass stars –in stars such as Proxima Centauri and TRAPPIST-1– provide an exceptional chance to improve our understanding of the formation of planets around M stars and brown dwarfs. We explore the formation of such planets with a population synthesis code based on a planetesimal-driven model previously used to study the formation of the Jovian satellites. Because the discs have low mass and the stars are cool, the formation is an inefficient process that happens at short periods, generating compact planetary systems. Planets can be trapped in resonances and we follow the evolution of the planets after the gas has dissipated and they undergo orbit crossings and possible mergers. We find that formation of planets above Mars mass and in the planetesimal accretion scenario, is only possible around stars with masses M⋆ ≥ 0.07Msun and discs of Mdisc ≥ 10−2 Msun. We find that planets above Earth-mass form around stars with masses larger than 0.15 Msun, while planets larger than 5 M⊕ do not form in our model, even not under the most optimal conditions (massive disc), showing that planets such as GJ 3512b form with another, more efficient mechanism. Our results show that the majority of planets form with a significant water fraction; that most of our synthetic planetary systems have 1, 2 or 3 planets, but planets with 4,5,6 and 7 planets are also common, confirming that compact planetary systems with many planets should be a relatively common outcome of planet formation around small stars.

scholarly journals Metallicity effect and planet mass function in pebble-based planet formation models

2018 ◽  
Vol 619 ◽  
pp. A174 ◽  
Author(s):  
N. Brügger ◽  
Y. Alibert ◽  
S. Ataiee ◽  
W. Benz
Keyword(s):  
Internal Structure ◽  
Planet Formation ◽  
Large Fraction ◽  
Mass Function ◽  
Planetary Atmosphere ◽  
Population Synthesis ◽  
Core Accretion ◽  
Mass Functions ◽  
Synthesis Approach ◽  
Gaseous Envelope

Context. One of the main scenarios of planet formation is the core accretion model where a massive core forms first and then accretes a gaseous envelope. This core forms by accreting solids, either planetesimals or pebbles. A key constraint in this model is that the accretion of gas must proceed before the dissipation of the gas disc. Classical planetesimal accretion scenarios predict that the time needed to form a giant planet’s core is much longer than the time needed to dissipate the disc. This difficulty led to the development of another accretion scenario, in which cores grow by accretion of pebbles, which are much smaller and thus more easily accreted, leading to more rapid formation. Aims. The aim of this paper is to compare our updated pebble-based planet formation model with observations, in particular the well-studied metallicity effect. Methods. We adopt the Bitsch et al. (2015a, A&A, 575, A28) disc model and the Bitsch et al. (2015b, A&A, 582, A112) pebble model and use a population synthesis approach to compare the formed planets with observations. Results. We find that keeping the same parameters as in Bitsch et al. (2015b, A&A, 582, A112) leads to no planet growth due to a computation mistake in the pebble flux (2018b). Indeed a large fraction of the heavy elements should be put into pebbles (Zpeb∕Ztot = 0.9) in order to form massive planets using this approach. The resulting mass functions show a huge amount of giants and a lack of Neptune-mass planets, which are abundant according to observations. To overcome this issue we include the computation of the internal structure for the planetary atmosphere in our model. This leads to the formation of Neptune-mass planets but no observable giants. Furthermore, reducing the opacity of the planetary envelope more closely matches observations. Conclusions. We conclude that modelling the internal structure for the planetary atmosphere is necessary to reproduce observations.

scholarly journals Magnetically induced termination of giant planet formation

2018 ◽  
Vol 619 ◽  
pp. A165 ◽  
Author(s):  
A. J. Cridland
Keyword(s):  
Magnetic Field ◽  
Cross Section ◽  
Planet Formation ◽  
Giant Planet ◽  
Effective Cross Section ◽  
Cold Start ◽  
Population Synthesis ◽  
Hot Start ◽  
Gas Accretion ◽  
Planetary Magnetic Field

Here a physical model for terminating giant planet formation is outlined and compared to other methods of late-stage giant planet formation. As has been pointed out before, gas accreting into a gap and onto the planet will encounter the planetary dynamo-generated magnetic field. The planetary magnetic field produces an effective cross section through which gas is accreted. Gas outside this cross section is recycled into the protoplanetary disk, hence only a fraction of mass that is accreted into the gap remains bound to the planet. This cross section inversely scales with the planetary mass, which naturally leads to stalled planetary growth late in the formation process. We show that this method naturally leads to Jupiter-mass planets and does not invoke any artificial truncation of gas accretion, as has been done in some previous population synthesis models. The mass accretion rate depends on the radius of the growing planet after the gap has opened, and we show that so-called hot-start planets tend to become more massive than cold-start planets. When this result is combined with population synthesis models, it might show observable signatures of cold-start versus hot-start planets in the exoplanet population.

Recent Progress on Planetary Dust Grain Dynamics

2007 ◽  
Author(s):  
J. E. Howard ◽  
Michail D. Todorov
Keyword(s):  
Recent Progress ◽  
Dust Grain ◽  
Grain Dynamics

scholarly journals Small dust grain dynamics on adaptive mesh refinement grids

2019 ◽  
Vol 626 ◽  
pp. A96 ◽  
Author(s):  
U. Lebreuilly ◽  
B. Commerçon ◽  
G. Laibe
Keyword(s):  
Finite Volume ◽  
Adaptive Mesh Refinement ◽  
Mesh Refinement ◽  
Adaptive Mesh ◽  
Uniform Grids ◽  
Dust Dynamics ◽  
Protostellar Collapse ◽  
Dust Grain ◽  
Grain Dynamics ◽  
Small Dust

Context. Small dust grains are essential ingredients of star, disk and planet formation. Aims. We present an Eulerian numerical approach to study small dust grain dynamics in the context of star and protoplanetary disk formation. It is designed for finite volume codes. We use it to investigate dust dynamics during the protostellar collapse. Methods. We present a method to solve the monofluid equations of gas and dust mixtures with several dust species in the diffusion approximation implemented in the adaptive-mesh-refinement code RAMSES. It uses a finite volume second-order Godunov method with a predictor-corrector MUSCL scheme to estimate the fluxes between the grid cells. Results. We benchmark our method against six distinct tests, DUSTYADVECT, DUSTYDIFFUSE, DUSTYSHOCK, DUSTYWAVE, SETTLING, and DUSTYCOLLAPSE. We show that the scheme is second-order accurate in space on uniform grids and intermediate between second- and first-order on non-uniform grids. We apply our method on various DUSTYCOLLAPSE simulations of 1 M⊙ cores composed of gas and dust. Conclusions. We developed an efficient approach to treat gas and dust dynamics in the diffusion regime on grid-based codes. The canonical tests were successfully passed. In the context of protostellar collapse, we show that dust is less coupled to the gas in the outer regions of the collapse where grains larger than ≃100 μm fall significantly faster than the gas.

scholarly journals Low-mass Star Formation: Observations

2010 ◽  
Vol 6 (S270) ◽  
pp. 25-32 ◽  
Author(s):  
Neal J. Evans
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Planet Formation ◽  
Mass Star ◽  
Low Mass Stars ◽  
Chemical Changes ◽  
Open Questions ◽  
Low Mass ◽  
Over Time ◽  
The Imf

AbstractI briefly review recent observations of regions forming low mass stars. The discussion is cast in the form of seven questions that have been partially answered, or at least illuminated, by new data. These are the following: where do stars form in molecular clouds; what determines the IMF; how long do the steps of the process take; how efficient is star formation; do any theories explain the data; how are the star and disk built over time; and what chemical changes accompany star and planet formation. I close with a summary and list of open questions.

scholarly journals Special Session 7 Young Stars, Brown Dwarfs, and Protoplanetary Disks

2009 ◽  
Vol 5 (H15) ◽  
pp. 727-728
Author(s):  
Jane Gregorio-Hetem ◽  
Silvia Alencar
Keyword(s):  
Adaptive Optics ◽  
Planet Formation ◽  
Protoplanetary Disks ◽  
Brown Dwarfs ◽  
Young Stars ◽  
Special Session ◽  
Brown Dwarf ◽  
X Ray ◽  
Substellar Objects

In recent years our knowledge of star, brown dwarf and planet formation has progressed immensely due to new data in the IR domain (Spitzer telescope), new X-ray campaigns such as the Chandra Orion Ultradeep Project (COUP) and the X-ray Emission Survey of Taurus (XEST), with XMM-Newton, as well as adaptive optics results and synoptic studies of young stellar and substellar objects.

scholarly journals Disk Masses and Dust Evolution of Protoplanetary Disks around Brown Dwarfs

2021 ◽  
Vol 921 (2) ◽  
pp. 182
Author(s):  
Anneliese M. Rilinger ◽  
Catherine C. Espaillat
Keyword(s):  
Planet Formation ◽  
Spectral Energy ◽  
Star Forming ◽  
Star Forming Regions ◽  
Disk Mass ◽  
T Tauri ◽  
Multiple Regions ◽  
Disk Evolution ◽  
Dust Grain ◽  
Dust Evolution

Abstract We present the largest sample of brown dwarf (BD) protoplanetary disk spectral energy distributions modeled to date. We compile 49 objects with ALMA observations from four star-forming regions: ρ Ophiuchus, Taurus, Lupus, and Upper Scorpius. Studying multiple regions with various ages enables us to probe disk evolution over time. Specifically, from our models, we obtain values for dust grain sizes, dust settling, and disk mass; we compare how each of these parameters vary between the regions. We find that disk mass decreases with age. We also find evidence of disk evolution (i.e., grain growth and significant dust settling) in all four regions, indicating that planet formation and disk evolution may begin to occur at earlier stages. We generally find that these disks contain too little mass to form planetary companions, though we cannot rule out that planet formation may have already occurred. Finally, we examine the disk mass–host mass relationship and find that BD disks are largely consistent with previously determined relationships for disks around T Tauri stars.

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