scholarly journals On the vortex evolution in non-isothermal protoplanetary discs

2020 ◽  
Vol 493 (2) ◽  
pp. 3014-3025
Author(s):  
D Tarczay-Nehéz ◽  
Zs Regály ◽  
E Vorobyov
Keyword(s):  
Large Scale ◽  
Planet Formation ◽  
Dead Zone ◽  
Giant Planet ◽  
Building Blocks ◽  
Outer Edge ◽  
Wave Instability ◽  
Large Scale Vortex ◽  
Self Gravity ◽  
Protoplanetary Discs

ABSTRACT It is believed that large-scale horseshoe-like brightness asymmetries found in dozens of transitional protoplanetary discs are caused by anticyclonic vortices. These vortices can play a key role in planet formation, as mm-sized dust – the building blocks of planets – can be accumulated inside them. Anticyclonic vortices are formed by the Rossby wave instability, which can be excited at the gap edges opened by a giant planet or at sharp viscosity transitions of accretionally inactive regions. It is known that vortices are prone to stretching and subsequent dissolution due to disc self-gravity for canonical disc masses in the isothermal approximation. To improve the hydrodynamic model of protoplanetary discs, we include the disc thermodynamics in our model. In this paper, we present our results on the evolution of the vortices formed at the outer edge of an accretionally inactive region (dead zone) assuming an ideal equation of state and taking PdV work, disc cooling in the β-approximation, and disc self-gravity into account. Thermodynamics affects the offset and the mode number (referring to the number of small vortices at the early phase) of the RWI excitation, as well as the strength, shape, and lifetime of the large-scale vortex formed through merging of the initial small vortices. We found that the inclusion of gas thermodynamics results in stronger, however decreased lifetime vortices. Our results suggest that a hypothetical vortex-aided planet formation scenario favours effectively cooling discs.

Planet Formation in Transition Discs

2020 ◽  
Author(s):  
Daniel Cummins ◽  
James Owen
Keyword(s):  
Large Scale ◽  
Planet Formation ◽  
Formation Processes ◽  
Primary Interest ◽  
Rapid Formation ◽  
Planetary Embryo ◽  
Large Scale Vortex ◽  
Resolution Imaging ◽  
Formation And Evolution ◽  
The Impact

<p>High-resolution imaging of protoplanetary discs has revealed their wealth of substructure. Perhaps the most striking observation has been the presence of large-scale crescent-shaped features, which have been interpreted as large quantities of dust trapped in anticyclonic vortices. Such regions of high dust-to-gas ratios are expected to promote planet formation processes, so understanding their formation and evolution is of primary interest.<br />Gas-only hydrodynamics simulations have demonstrated that the thermal feedback from a planetary embryo undergoing rapid formation by pebble accretion can trigger the generation a large-scale vortex. However, the ability for such a vortex to trap dust and the impact this has on the forming planet are yet to be investigated. I will present results from hydrodynamics simulations of a disc containing both gas and dust, showing the efficiency with which dust grains accumulate in a vortex, and discuss the consequences this has for the growth of the planetary embryo.</p>

The chemical content of planet-forming disks: towards a comparison with comets to unveil the origin of the Solar System

2020 ◽  
Author(s):  
Linda Podio ◽  
Antonio Garufi ◽  
Claudio Codella ◽  
Davide Fedele ◽  
Kazi Rygl ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Solar System ◽  
Radial Distribution ◽  
Organic Molecules ◽  
Planet Formation ◽  
Giant Planet ◽  
Protoplanetary Disks ◽  
Building Blocks ◽  
Early Solar System ◽  
Outer Disk

<p>How have planets formed in the Solar System? And what chemical composition they inherited from their natal environment? Is the chemical composition passed unaltered from the earliest stages of the formation of the Sun to its disk and then to the planets which assembled in the disk? Or does it reflects chemical processes occurring in the disk and/or during the planet formation process? And what was the role of comets in the delivery of volatiles and prebiotic compounds to early Earth?</p> <p>A viable way to answer these questions is to observe protoplanetary disks around young Sun-like stars and compare their chemical composition with that of the early Solar System, which is imprinted in comets. The impacting images recently obtained by millimetre arrays of antennas such as ALMA provided the first observational evidence of ongoing planet formation in 0.1-1 million years old disks, through rings and gaps in their dust and gas distribution. The chemical composition of the forming planets and small bodies clearly depends on the location and timescale for their formation and is intimately connected to the spatial distribution and abundance of the various molecular species in the disk. The chemical characterisation of disks is therefore crucial.</p> <p>This field, however, is still in its infancy, because of the small sizes of disks (~100 au) and to the low gas-phase abundance of molecules (abundances with respect to H<sub>2</sub> down to 10<sup>-12</sup>), which requires an unprecedented combination of angular resolution and sensitivity. I will show the first pioneering results obtained as part of the ALMA chemical survey of protoplanetary disks in the Taurus star forming region (ALMA-DOT program). Thanks to the ALMA images at ~20 au resolution, we recovered the radial distribution and abundance of diatomic molecules (CO and CN), S-bearing molecules (CS, SO, SO<sub>2</sub>, H<sub>2</sub>CS), as well as simple organics (H<sub>2</sub>CO and CH<sub>3</sub>OH) which are key for the formation of prebiotic compounds. Enhanced H<sub>2</sub>CO emission in the cold outer disk, outside the CO snowline, suggests that organic molecules may be efficiently formed in disks on the icy mantles of dust grain. This could be the dawn of ice chemistry in the disk, producing ices rich of complex organic molecules (COMs) which could be incorporated by the bodies forming in the outer disk region, such as comets.<span class="Apple-converted-space"> </span></p> <p>The next step is the comparison of the molecules radial distribution and abundance in disks with the chemical composition of comets, which are the leftover building blocks of giant planet cores and other planetary bodies. The first pioneering results in this direction have been obtained thanks to the ESA’s <em>Rosetta </em>mission, which allowed obtaining in situ measurements of the COMs abundance on the comet 67P/Churyumov-Gerasimenko. The comparison with three protostellar solar analogs observed on Solar System scales has shown comparable COMs abundance, implying that the volatile composition of comets and planetesimals may be partially inherited from the protostellar stage. The advent of new mission, devoted to sample return such as AMBITION will allow us to do a step ahead in this direction.</p> <p> </p>

scholarly journals TW Hya: an old protoplanetary disc revived by its planet

2020 ◽  
Author(s):  
Sergei Nayakshin ◽  
Takashi Tsukagoshi ◽  
Cassandra Hall ◽  
Allona Vazan ◽  
Ravit Helled ◽  
...  
Keyword(s):  
Planet Formation ◽  
Gravitational Instability ◽  
Giant Planet ◽  
Emission Feature ◽  
Time Dependent ◽  
Dust Particles ◽  
Dark Ring ◽  
Build Time ◽  
Core Accretion ◽  
Protoplanetary Discs

Abstract Dark rings with bright rims are the indirect signposts of planets embedded in protoplanetary discs. In a recent first, an azimuthally elongated AU-scale blob, possibly a planet, was resolved with ALMA in TW Hya. The blob is at the edge of a cliff-like rollover in the dust disc rather than inside a dark ring. Here we build time-dependent models of TW Hya disc. We find that the classical paradigm cannot account for the morphology of the disc and the blob. We propose that ALMA-discovered blob hides a Neptune mass planet losing gas and dust. We show that radial drift of mm-sized dust particles naturally explains why the blob is located on the edge of the dust disc. Dust particles leaving the planet perform a characteristic U-turn relative to it, producing an azimuthally elongated blob-like emission feature. This scenario also explains why a 10 Myr old disc is so bright in dust continuum. Two scenarios for the dust-losing planet are presented. In the first, a dusty pre-runaway gas envelope of a ∼40 M⊕ Core Accretion planet is disrupted, e.g., as a result of a catastrophic encounter. In the second, a massive dusty pre-collapse gas giant planet formed by Gravitational Instability is disrupted by the energy released in its massive core. Future modelling may discriminate between these scenarios and allow us to study planet formation in an entirely new way – by analysing the flows of dust and gas recently belonging to planets, informing us about the structure of pre-disruption planetary envelopes.

scholarly journals Harvesting the decay energy of 26Al to drive lightning discharge in protoplanetary discs

2017 ◽  
Vol 609 ◽  
pp. A31 ◽  
Author(s):  
Anders Johansen ◽  
Satoshi Okuzumi
Keyword(s):  
Large Scale ◽  
Mass Density ◽  
Lightning Discharge ◽  
Plane Layer ◽  
Building Blocks ◽  
Decay Energy ◽  
Positron Energy ◽  
Positron Emission ◽  
Nuclear Battery ◽  
Protoplanetary Discs

Chondrules in primitive meteorites likely formed by recrystallisation of dust aggregates that were flash-heated to nearly complete melting. Chondrules may represent the building blocks of rocky planetesimals and protoplanets in the inner regions of protoplanetary discs, but the source of ubiquitous thermal processing of their dust aggregate precursors remains elusive. Here we demonstrate that escape of positrons released in the decay of the short-lived radionuclide 26Al leads to a large-scale charging of dense pebble structures, resulting in neutralisation by lightning discharge and flash-heating of dust and pebbles. This charging mechanism is similar to a nuclear battery where a radioactive source charges a capacitor. We show that the nuclear battery effect operates in circumplanetesimal pebble discs. The extremely high pebble densities in such discs are consistent with conditions during chondrule heating inferred from the high abundance of sodium within chondrules. The sedimented mid-plane layer of the protoplanetary disc may also be prone to charging by the emission of positrons, if the mass density of small dust there is at least an order of magnitude above the gas density. Our results imply that the decay energy of 26Al can be harvested to drive intense lightning activity in protoplanetary discs. The total energy stored in positron emission is comparable to the energy needed to melt all solids in the protoplanetary disc. The efficiency of transferring the positron energy to the electric field nevertheless depends on the relatively unknown distribution and scale-dependence of pebble density gradients in circumplanetesimal pebble discs and in the protoplanetary disc mid-plane layer.

scholarly journals Effect of pebble flux-regulated planetesimal formation on giant planet formation

2020 ◽  
Vol 642 ◽  
pp. A75 ◽  
Author(s):  
Oliver Voelkel ◽  
Hubert Klahr ◽  
Christoph Mordasini ◽  
Alexandre Emsenhuber ◽  
Christian Lenz
Keyword(s):  
Ad Hoc ◽  
Planet Formation ◽  
Giant Planet ◽  
Circumstellar Disks ◽  
Giant Planets ◽  
Radial Density ◽  
Density Distributions ◽  
Gas Giant ◽  
Self Gravity ◽  
Dust Evolution

Context. The formation of gas giant planets by the accretion of 100 km diameter planetesimals is often thought to be inefficient. A diameter of this size is typical for planetesimals and results from self-gravity. Many models therefore use small kilometer-sized planetesimals, or invoke the accretion of pebbles. Furthermore, models based on planetesimal accretion often use the ad hoc assumption of planetesimals that are distributed radially in a minimum-mass solar-nebula way. Aims. We use a dynamical model for planetesimal formation to investigate the effect of various initial radial density distributions on the resulting planet population. In doing so, we highlight the directive role of the early stages of dust evolution into pebbles and planetesimals in the circumstellar disk on the subsequent planet formation. Methods. We implemented a two-population model for solid evolution and a pebble flux-regulated model for planetesimal formation in our global model for planet population synthesis. This framework was used to study the global effect of planetesimal formation on planet formation. As reference, we compared our dynamically formed planetesimal surface densities with ad hoc set distributions of different radial density slopes of planetesimals. Results. Even though required, it is not the total planetesimal disk mass alone, but the planetesimal surface density slope and subsequently the formation mechanism of planetesimals that enables planetary growth through planetesimal accretion. Highly condensed regions of only 100 km sized planetesimals in the inner regions of circumstellar disks can lead to gas giant growth. Conclusions. Pebble flux-regulated planetesimal formation strongly boosts planet formation even when the planetesimals to be accreted are 100 km in size because it is a highly effective mechanism for creating a steep planetesimal density profile. We find that this leads to the formation of giant planets inside 1 au already by pure 100 km planetesimal accretion. Eventually, adding pebble accretion regulated by pebble flux and planetesimal-based embryo formation as well will further complement this picture.

scholarly journals Formation of planetary populations − II. Effects of initial disc size and radial dust drift

2020 ◽  
Vol 493 (1) ◽  
pp. 1013-1033 ◽  
Author(s):  
Matthew Alessi ◽  
Ralph E Pudritz ◽  
Alex J Cridland
Keyword(s):  
Planet Formation ◽  
Dead Zone ◽  
Outer Edge ◽  
Type I ◽  
Population Synthesis ◽  
The Dead ◽  
Dust Evolution ◽  
Disc Size ◽  
Heat Transition

ABSTRACT Recent ALMA observations indicate that while a range of disc sizes exist, typical disc radii are small, and that radial dust drift affects the distribution of solids in discs. Here, we explore the consequences of these features in planet population synthesis models. A key feature of our model is planet traps – barriers to otherwise rapid type-I migration of forming planets – for which we include the ice line, heat transition, and outer edge of the dead zone. We find that the ice line plays a fundamental role in the formation of warm Jupiters. In particular, the ratio of super Earths to warm Jupiters formed at the ice line depends sensitively on the initial disc radius. Initial gas disc radii of ∼50 au results in the largest super Earth populations, while both larger and smaller disc sizes result in the ice line producing more gas giants near 1 au. This transition between typical planet class formed at the ice line at various disc radii confirms that planet formation is fundamentally linked to disc properties (in this case, disc size), and is a result that is only seen when dust evolution effects are included in our models. Additionally, we find that including radial dust drift results in the formation of more super Earths between 0.1 and 1 au, having shorter orbital radii than those produced in models where dust evolution effects are not included.

scholarly journals Fingerprints of giant planets in the composition of solar twins

2020 ◽  
Vol 493 (4) ◽  
pp. 5079-5088 ◽  
Author(s):  
Richard A Booth ◽  
James E Owen
Keyword(s):  
Refractory Material ◽  
Planet Formation ◽  
Initial Conditions ◽  
Giant Planet ◽  
Planetary Systems ◽  
Giant Planets ◽  
The Sun ◽  
Evolutionary Models ◽  
Refractory Elements ◽  
Protoplanetary Discs

ABSTRACT The Sun shows a ∼10 per cent depletion in refractory elements relative to nearby solar twins. It has been suggested that this depletion is a signpost of planet formation. The exoplanet statistics are now good enough to show that the origin of this depletion does not arise from the sequestration of refractory material inside the planets themselves. This conclusion arises because most sun-like stars host close-in planetary systems that are on average more massive than the Sun’s. Using evolutionary models for the protoplanetary discs that surrounded the young Sun and solar twins, we demonstrate that the origin of the depletion likely arises due to the trapping of dust exterior to the orbit of a forming giant planet. In this scenario, a forming giant planet opens a gap in the gas disc, creating a pressure trap. If the planet forms early enough, while the disc is still massive, the planet can trap ≳100 M⊕ of dust exterior to its orbit, preventing the dust from accreting on to the star in contrast to the gas. Forming giant planets can create refractory depletions of $\sim 5{-}15{{\ \rm per\ cent}}$, with the larger values occurring for initial conditions that favour giant planet formation (e.g. more massive discs that live longer). The incidence of solar twins that show refractory depletion matches both the occurrence of giant planets discovered in exoplanet surveys and ‘transition’ discs that show similar depletion patterns in the material that is accreting on to the star.

scholarly journals A new viscous instability in weakly ionised protoplanetary discs

2010 ◽  
Vol 6 (S274) ◽  
pp. 50-55
Author(s):  
Anders Johansen ◽  
Mariko Kato ◽  
Takayoshi Sano
Keyword(s):  
Transition Region ◽  
Turbulent Viscosity ◽  
Dead Zone ◽  
High Amplitude ◽  
Linear Instability ◽  
Outer Edge ◽  
Free Electrons ◽  
Viscous Instability ◽  
Pile Up ◽  
Protoplanetary Discs

AbstractLarge regions of protoplanetary discs are believed to be too weakly ionised to support magnetorotational instabilities, because abundant tiny dust grains soak up free electrons and reduce the conductivity of the gas. At the outer edge of this “dead zone”, the ionisation fraction increases gradually and the resistivity drops until the magnetorotational instability can develop turbulence. We identify a new viscous instability which operates in the semi-turbulent transition region between “dead” and “alive” zones. The strength of the saturated turbulence depends strongly on the local resistivity in this transition region. A slight increase (decrease) in dust density leads to a slight increase (decrease) in resistivity and a slight decrease (increase) in turbulent viscosity. Such spatial variation in the turbulence strength causes a mass pile-up where the turbulence is weak, leading to a run-away process where turbulence is weakened and mass continues to pile up. The final result is the appearance of high-amplitude pressure bumps and deep pressure valleys. Here we present a local linear stability analysis of weakly ionised accretion discs and identify the linear instability responsible for the pressure bumps. A paper in preparation concerns numerical results which confirm and expand the existence of the linear instability.

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