The role of density perturbation on planet formation by pebble accretion

Andama, Geoffrey; Ndugu, Nelson; Anguma, S. K.; Jurua, Edward

doi:10.1093/mnras/stac772

Cited by 6 publications

(2 citation statements)

References 178 publications

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“…Nevertheless, for planetesimal formation to take place at the water-ice line in stellar environments with sub-solar metallicities, the surrounding discs must be turbulent enough in order to produce relatively small size pebbles and scale down the loss of pebbles via radial drift on short dynamical timescales. However, at low viscosities, the presence of pressure bumps could also slow down grain migration (Pinilla et al 2012;Andama et al 2022), which could allow more planetesimals to form at the ice line (e.g. Stammler et al 2019).…”

Section: Dependence On Metallicitymentioning

confidence: 99%

“…These planetesimals could coalesce into a planetary embryo that could accrete any subsequent pebbles that accumulate at the ice line. Moreover, the planetary embryo at the water-ice line could accrete the accumulated pebbles very efficiently before they are converted into planetesimals (Morbidelli 2020;Izidoro et al 2021;Andama et al 2022) or accrete other planetesimals within this region (Chambers 2023;.…”

Section: Dependence On Disc Massmentioning

confidence: 99%

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Which stars can form planets: Planetesimal formation at low metallicities

Andama,

Mah,

Bitsch

2024

A&A

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The diversity of exoplanets has been linked to the disc environment in which they form, where the host star metallicity and the formation pathways play a crucial role. In the context of the core accretion paradigm, the initial stages of planet formation require the growth of dust material from micrometre-sized to planetesimal-sized bodies before core accretion can kick in. Although numerous studies have been conducted on planetesimal formation, it is still poorly understood how this process takes place in low-metallicity stellar environments. In this work, we explore how planetesimals are formed in stellar environments with primarily low metallicities. We performed global 1D viscous disc evolution simulations, including the growth of dust particles and the evaporation and condensation of chemical species at ice lines. We followed the formation of planetesimals during disc evolution and tested different metallicities, disc sizes, and turbulent viscosity strengths. We find that at solar and sub-solar metallicities, there is a significant increase in the midplane dust-to-gas mass ratios at the ice lines, but this leads to planetesimal formation only at the water--ice line. In our simulations Fe/H $= -0.6$ is the lower limit of metallicity for planetesimal formation where a few Earth masses of planetesimals can form. Our results further show that for such extreme disc environments, large discs are more conducive than small discs for forming large amounts of planetesimals at a fixed metallicity because the pebble flux can be maintained for a longer time, resulting in a longer and more efficient planetesimal formation phase. At lower metallicities, planetesimal formation is less supported in quiescent discs compared to turbulent discs, which produce larger amounts of planetesimals, because the pebble flux can be maintained for a longer time. The amount of planetesimals formed at sub-solar metallicities in our simulations places a limit on core sizes that could potentially result only in the formation of super-Earths.

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Section: Dependence On Metallicitymentioning

confidence: 99%

Section: Dependence On Disc Massmentioning

confidence: 99%

Which stars can form planets: Planetesimal formation at low metallicities

Andama,

Mah,

Bitsch

2024

A&A

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The impact of dust evolution on the dead zone outer edge in magnetized protoplanetary disks

Delage,

Gárate,

Okuzumi

et al. 2023

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Context. The dead zone outer edge corresponds to the transition from the magnetically dead to the magnetorotational instability (MRI) active regions in the outer protoplanetary disk midplane. It has been previously hypothesized to be a prime location for dust particle trapping. A more consistent approach to access such an idea has yet to be developed, since the interplay between dust evolution and MRI-driven accretion over millions of years has been poorly understood. Aims. We provide an important step toward a better understanding of the MRI–dust coevolution in protoplanetary disks. In this pilot study, we present a proof of concept that dust evolution ultimately plays a crucial role in the MRI activity. Methods. First, we study how a fixed power-law dust size distribution with varying parameters impacts the MRI activity, especially the steady-state MRI-driven accretion, by employing and improving our previous 1+1D MRI-driven turbulence model. Second, we relax the steady-state accretion assumption in this disk accretion model, and partially couple it to a dust evolution model in order to investigate how the evolution of dust (dynamics and grain growth processes combined) and MRI-driven accretion are intertwined on million-year timescales, from a more sophisticated modeling of the gas ionization degree. Results. Dust coagulation and settling lead to a higher gas ionization degree in the protoplanetary disk, resulting in stronger MRI-driven turbulence as well as a more compact dead zone. On the other hand, fragmentation has an opposite effect because it replenishes the disk in small dust particles which are very efficient at sweeping up free electrons and ions from the gas phase. Since the dust content of the disk decreases over millions of years of evolution due to radial drift, the MRI-driven turbulence overall becomes stronger and the dead zone more compact until the disk dust-gas mixture eventually behaves as a grain-free plasma. Furthermore, our results show that dust evolution alone does not lead to a complete reactivation of the dead zone. For typical T-Tauri stars, we find that the dead zone outer edge is expected to be located roughly between 10 au and 50 au during the disk lifetime for our choice of the magnetic field strength and configuration. Finally, the MRI activity evolution is expected to be crucially sensitive to the choice made for the minimum grain size of the dust distribution. Conclusions. The MRI activity evolution (hence the temporal evolution of the MRI-induced α parameter) is controlled by dust evolution and occurs on a timescale of local dust growth, as long as there are enough dust particles in the disk to dominate the recombination process for the ionization chemistry. Once that is no longer the case, the MRI activity evolution is expected to be controlled by gas evolution and occurs on a viscous evolution timescale.

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Rapid formation of massive planetary cores in a pressure bump

Lau

Drążkowska

Stammler

et al. 2022

A&A

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Context. Models of planetary core growth by either planetesimal or pebble accretion are traditionally disconnected from the models of dust evolution and formation of the first gravitationally bound planetesimals. State-of-the-art models typically start with massive planetary cores already present. Aims. We aim to study the formation and growth of planetary cores in a pressure bump, motivated by the annular structures observed in protoplanetary disks, starting with submicron-sized dust grains. Methods. We connect the models of dust coagulation and drift, planetesimal formation in the streaming instability, gravitational interactions between planetesimals, pebble accretion, and planet migration into one uniform framework. Results. We find that planetesimals forming early at the massive end of the size distribution grow quickly, predominantly by pebble accretion. These few massive bodies grow on timescales of ∼100 000 years and stir the planetesimals that form later, preventing the emergence of further planetary cores. Additionally, a migration trap occurs, allowing for retention of the growing cores. Conclusions. Pressure bumps are favourable locations for the emergence and rapid growth of planetary cores by pebble accretion as the dust density and grain size are increased and the pebble accretion onset mass is reduced compared to a smooth-disc model.

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The role of density perturbation on planet formation by pebble accretion

Cited by 6 publications

References 178 publications

Which stars can form planets: Planetesimal formation at low metallicities

Which stars can form planets: Planetesimal formation at low metallicities

The impact of dust evolution on the dead zone outer edge in magnetized protoplanetary disks

Rapid formation of massive planetary cores in a pressure bump

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