Flybys in protoplanetary discs: I. Gas and dust dynamics

ABSTRACT We explore dust flow in the hottest parts of protoplanetary discs using the forces of gravity, gas drag, and radiation pressure. Our main focus is on the optically thin regions of dusty disc, where the dust is exposed to the most extreme heating conditions and dynamical perturbations: the surface of optically thick disc and the inner dust sublimation zone. We utilize results from two numerically strenuous fields of research. The first is the quasi-stationary solutions on gas velocity and density distributions from mangetohydrodynamical (MHD) simulations of accretion discs. This is critical for implementing a more realistic gas drag impact on dust movements. The second is the optical depth structure from a high-resolution dust radiation transfer. This step is critical for a better understanding of dust distribution within the disc. We describe a numerical method that incorporates these solutions into the dust dynamics equations. We use this to integrate dust trajectories under different disc wind models and show how grains end up trapped in flows that range from simple accretion on to the star to outflows into outer disc regions. We demonstrate how the radiation pressure force plays one of the key roles in this process and cannot be ignored. It erodes the dusty disc surface, reduces its height, resists dust accretion on to the star, and helps the disc wind in pushing grains outwards. The changes in grain size and porosity significantly affect the results, with smaller and porous grains being influenced more strongly by the disc wind and radiation pressure.

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Influence of growth on dust settling and migration in protoplanetary discs

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311020540 ◽

2010 ◽

Vol 6 (S276) ◽

pp. 405-406

Author(s):

Elisabeth Crespe ◽

Jean-Francois Gonzalez ◽

Guillaume Laibe ◽

Sarah T. Maddison ◽

Laure Fouchet

Keyword(s):

Growth Rate ◽

Central Star ◽

Constant Growth Rate ◽

Grain Growth Model ◽

Dust Dynamics ◽

And Migration ◽

Dust Distribution ◽

Constant Growth ◽

Gas Drag ◽

Protoplanetary Discs

AbstractTo form meter-sized pre-planetesimals in protoplanetary discs, dust aggregates have to decouple from the gas at a distance far enough from the central star so they are not accreted. Dust grains are affected by gas drag, which results in a vertical settling towards the mid-plane, followed by radial migration. To have a better understanding of the influence of growth on the dust dynamics, we use a simple grain growth model to determine the dust distribution in observed discs. We implement a constant growth rate into a gas+dust hydrodynamics SPH code and vary the growh rate to study the resulting effect on dust distribution. The growth rate allows us to determine the relative importance between friction and growth.We show that depending on the growth rate, a range of dust distribution can result. For large enough growth rates, grains can decouple from the gas before being accreted onto the central star, thus contributing as planetary building rocks.

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On the origin of wide-orbit ALMA planets: giant protoplanets disrupted by their cores

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2497 ◽

2019 ◽

Vol 489 (4) ◽

pp. 5187-5201 ◽

Cited By ~ 2

Author(s):

J Humphries ◽

S Nayakshin

Keyword(s):

Gravitational Instability ◽

Energy Output ◽

Planetary Satellites ◽

Multiple Cores ◽

Dust Dynamics ◽

Jovian Planets ◽

Core Accretion ◽

Collapse Phase ◽

Partial Destruction ◽

Protoplanetary Discs

ABSTRACT Recent ALMA observations may indicate a surprising abundance of sub-Jovian planets on very wide orbits in protoplanetary discs that are only a few million years old. These planets are too young and distant to have been formed via the core accretion (CA) scenario, and are much less massive than the gas clumps born in the classical gravitational instability (GI) theory. It was recently suggested that such planets may form by the partial destruction of GI protoplanets: energy output due to the growth of a massive core may unbind all or most of the surrounding pre-collapse protoplanet. Here we present the first 3D global disc simulations that simultaneously resolve grain dynamics in the disc and within the protoplanet. We confirm that massive GI protoplanets may self-destruct at arbitrarily large separations from the host star provided that solid cores of mass ∼10–20 M⊕ are able to grow inside them during their pre-collapse phase. In addition, we find that the heating force recently analysed by Masset & Velasco Romero (2017) perturbs these cores away from the centre of their gaseous protoplanets. This leads to very complicated dust dynamics in the protoplanet centre, potentially resulting in the formation of multiple cores, planetary satellites, and other debris such as planetesimals within the same protoplanet. A unique prediction of this planet formation scenario is the presence of sub-Jovian planets at wide orbits in Class 0/I protoplanetary discs.

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High-resolution simulations of planetesimal formation in turbulent protoplanetary discs

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311019995 ◽

2010 ◽

Vol 6 (S276) ◽

pp. 89-94

Author(s):

Anders Johansen ◽

Hubert Klahr ◽

Thomas Henning

Keyword(s):

High Resolution ◽

Computer Simulations ◽

Large Scale ◽

Dynamical Friction ◽

Magnetorotational Instability ◽

Dust Dynamics ◽

Protoplanetary Discs

AbstractWe present high resolution computer simulations of dust dynamics and planetesimal formation in turbulence triggered by the magnetorotational instability. Particles representing approximately meter-sized boulders clump in large scale overpressure regions in the simulation box. These overdensities readily contract due to the combined gravity of the particles to form gravitationally bound clusters with masses ranging from a few to several ten times the mass of the dwarf planet Ceres. Gravitationally bound clumps are observed to collide and merge at both moderate and high resolution. The collisional products form the top end of a distribution of planetesimal masses ranging from less than one Ceres mass to 35 Ceres masses. It remains uncertain whether collisions are driven by dynamical friction or underresolution of clumps.

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Dust dynamics and vertical settling in gravitoturbulent protoplanetary discs

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa567 ◽

2020 ◽

Vol 493 (4) ◽

pp. 4631-4642 ◽

Cited By ~ 1

Author(s):

A Riols ◽

B Roux ◽

H Latter ◽

G Lesur

Keyword(s):

Gravitational Instability ◽

Scale Height ◽

Small Scale ◽

Vertical Diffusion ◽

Inertial Wave ◽

Dust Dynamics ◽

Self Gravity ◽

Gas Accretion ◽

Protoplanetary Discs

Abstract Gravitational instability (GI) controls the dynamics of young massive protoplanetary discs. Apart from facilitating gas accretion on to the central protostar, it must also impact on the process of planet formation: directly through fragmentation, and indirectly through the turbulent concentration of small solids. To understand the latter process, it is essential to determine the dust dynamics in gravitoturbulent flow. For that purpose, we conduct a series of 3D shearing box simulations of coupled gas and dust, including the gas’s self-gravity and scanning a range of Stokes numbers, from 10 −3 to ∼0.2. First, we show that the vertical settling of dust in the mid-plane is significantly impeded by gravitoturbulence, with the dust scale height roughly 0.6 times the gas scale height for centimetre grains. This is a result of the strong vertical diffusion issuing from (i) small-scale inertial-wave turbulence feeding off the GI spiral waves and (ii) the larger scale vertical circulations that naturally accompany the spirals. Second, we show that at R = 50 au concentration events involving submetre particles and yielding order 1 dust-to-gas ratios are rare and last for less than an orbit. Moreover, dust concentration is less efficient in 3D than in 2D simulations. We thus conclude that GI is not especially prone to the turbulent accumulation of dust grains. Finally, the large dust scale height measured in simulations could be, in the future, compared with that of edge-on discs seen by ALMA, thus aiding detection and characterization of GI in real systems.

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Grand Challenges in Protoplanetary Disc Modelling

Publications of the Astronomical Society of Australia ◽

10.1017/pasa.2016.45 ◽

2016 ◽

Vol 33 ◽

Cited By ~ 32

Author(s):

Thomas J. Haworth ◽

John D. Ilee ◽

Duncan H. Forgan ◽

Stefano Facchini ◽

Daniel J. Price ◽

...

Keyword(s):

Radiative Transfer ◽

The Self ◽

Future Research ◽

Short Introduction ◽

Grand Challenges ◽

Consistent Calculation ◽

Self Consistent ◽

Dust Dynamics ◽

Protoplanetary Discs

AbstractThe Protoplanetary Discussions conference—held in Edinburgh, UK, from 2016 March 7th–11th—included several open sessions led by participants. This paper reports on the discussions collectively concerned with the multi-physics modelling of protoplanetary discs, including the self-consistent calculation of gas and dust dynamics, radiative transfer, and chemistry. After a short introduction to each of these disciplines in isolation, we identify a series of burning questions and grand challenges associated with their continuing development and integration. We then discuss potential pathways towards solving these challenges, grouped by strategical, technical, and collaborative developments. This paper is not intended to be a review, but rather to motivate and direct future research and collaboration across typically distinct fields based on community-driven input, to encourage further progress in our understanding of circumstellar and protoplanetary discs.

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Ring formation and dust dynamics in wind-driven protoplanetary discs: global simulations

Astronomy and Astrophysics ◽

10.1051/0004-6361/201937418 ◽

2020 ◽

Vol 639 ◽

pp. A95 ◽

Cited By ~ 3

Author(s):

A. Riols ◽

G. Lesur ◽

F. Menard

Keyword(s):

Large Scale ◽

Near Infrared ◽

Dust Emission ◽

Outer Part ◽

Ambipolar Diffusion ◽

Fluid Approximation ◽

Zonal Flows ◽

Large Scale Magnetic Field ◽

Dust Dynamics ◽

Protoplanetary Discs

Large-scale vertical magnetic fields are believed to play a key role in the evolution of protoplanetary discs. Associated with non-ideal effects, such as ambipolar diffusion, they are known to launch a wind that could drive accretion in the outer part of the disc (R > 1 AU). They also potentially lead to self-organisation of the disc into large-scale axisymmetric structures, similar to the rings recently imaged by sub-millimetre or near-infrared instruments (ALMA and SPHERE). The aim of this paper is to investigate the mechanism behind the formation of these gaseous rings, but also to understand the dust dynamics and its emission in discs threaded by a large-scale magnetic field. To this end, we performed global magneto-hydrodynamics (MHD) axisymmetric simulations with ambipolar diffusion using a modified version of the PLUTO code. We explored different magnetisations with the midplane β parameter ranging from 105 to 103 and included dust grains -treated in the fluid approximation- ranging from 100 μm to 1 cm in size. We first show that the gaseous rings (associated with zonal flows) are tightly linked to the existence of MHD winds. Secondly, we find that millimetre-size dust is highly sedimented, with a typical scale height of 1 AU at R = 100 AU for β = 104, compatible with recent ALMA observations. We also show that these grains concentrate into pressure maxima associated with zonal flows, leading to the formation of dusty rings. Using the radiative transfer code MCFOST, we computed the dust emission and make predictions on the ring-gap contrast and the spectral index that one might observe with interferometers like ALMA.

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Aeolian dust dynamics in the Fergana Valley, Central Asia, since ~30 ka inferred from loess deposits

Geoscience Frontiers ◽

10.1016/j.gsf.2021.101180 ◽

2021 ◽

Vol 12 (5) ◽

pp. 101180

Author(s):

Yue Li ◽

Yougui Song ◽

Dimitris G. Kaskaoutis ◽

Jinbo Zan ◽

Rustam Orozbaev ◽

...

Keyword(s):

Central Asia ◽

Aeolian Dust ◽

Dust Dynamics ◽

Loess Deposits

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MRI-active inner regions of protoplanetary discs. I. A detailed model of disc structure

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab920 ◽

2021 ◽

Vol 504 (1) ◽

pp. 280-299

Author(s):

Marija R Jankovic ◽

James E Owen ◽

Subhanjoy Mohanty ◽

Jonathan C Tan

Keyword(s):

Energy Transport ◽

Threshold Temperature ◽

Mass Star ◽

Dust Grains ◽

Solar Mass ◽

Detailed Model ◽

Short Period ◽

Pressure Maximum ◽

Ion Emission ◽

Protoplanetary Discs

ABSTRACT Short-period super-Earth-sized planets are common. Explaining how they form near their present orbits requires understanding the structure of the inner regions of protoplanetary discs. Previous studies have argued that the hot inner protoplanetary disc is unstable to the magnetorotational instability (MRI) due to thermal ionization of potassium, and that a local gas pressure maximum forms at the outer edge of this MRI-active zone. Here we present a steady-state model for inner discs accreting viscously, primarily due to the MRI. The structure and MRI-viscosity of the inner disc are fully coupled in our model; moreover, we account for many processes omitted in previous such models, including disc heating by both accretion and stellar irradiation, vertical energy transport, realistic dust opacities, dust effects on disc ionization, and non-thermal sources of ionization. For a disc around a solar-mass star with a standard gas accretion rate ($\dot{M}\, \sim \, 10^{-8}$ M⊙ yr−1) and small dust grains, we find that the inner disc is optically thick, and the accretion heat is primarily released near the mid-plane. As a result, both the disc mid-plane temperature and the location of the pressure maximum are only marginally affected by stellar irradiation, and the inner disc is also convectively unstable. As previously suggested, the inner disc is primarily ionized through thermionic and potassium ion emission from dust grains, which, at high temperatures, counteract adsorption of free charges on to grains. Our results show that the location of the pressure maximum is determined by the threshold temperature above which thermionic and ion emission become efficient.

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