How dust fragmentation may be beneficial to planetary growth by pebble accretion

Drążkowska, Joanna; Stammler, Sebastian Markus; Birnstiel, T.

doi:10.1051/0004-6361/202039925

Cited by 46 publications

(33 citation statements)

References 120 publications

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“…We would like to note as well that our finding of an approximately constant inward pebble mass flux of 10 −5 M ⊕ yr −1 from 1 to 8 Myr is in contradiction to what we would obtain using the pebble predictor by Drążkowska et al (2021). With the pebble predictor, the pebble flux at the dust trap should decrease by two orders of magnitude between 1-10 Myr.…”

Section: Planetesimal Belt Surface Density Profilecontrasting

confidence: 90%

The formation of wide exoKuiper belts from migrating dust traps

Miller,

Marino,

Stammler

et al. 2021

Preprint

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The question of what determines the width of Kuiper belt analogues (exoKuiper belts) is an open one. If solved, this understanding would provide valuable insights into the architecture, dynamics, and formation of exoplanetary systems. Recent observations by ALMA have revealed an apparent paradox in this field, the presence of radially narrow belts in protoplanetary discs that are likely the birthplaces of planetesimals, and exoKuiper belts nearly four times as wide in mature systems. If the parent planetesimals of this type of debris disc indeed form in these narrow protoplanetary rings via streaming instability where dust is trapped, we propose that this width dichotomy could naturally arise if these dust traps form planetesimals whilst migrating radially, e.g. as caused by a migrating planet. Using the dust evolution software D P , we find that if the initial protoplanetary disc and trap conditions favour planetesimal formation, dust can still effectively accumulate and form planetesimals as the trap moves. This leads to a positive correlation between the inward radial speed and final planetesimal belt width, forming belts up to ∼100 au over 10 Myr of evolution. We show that although planetesimal formation is most efficient in low viscosity (𝛼 = 10 −4 ) discs with steep dust traps to trigger the streaming instability, the large widths of most observed planetesimal belts constrain 𝛼 to values ≥ 4 × 10 −4 at tens of au, otherwise the traps cannot migrate far enough. Additionally, the large spread in the widths and radii of exoKuiper belts could be due to different trap migration speeds (or protoplanetary disc lifetimes) and different starting locations, respectively. Our work serves as a first step to link exoKuiper belts and rings in protoplanetary discs.

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Section: Planetesimal Belt Surface Density Profilecontrasting

confidence: 90%

The formation of wide exoKuiper belts from migrating dust traps

Miller,

Marino,

Stammler

et al. 2021

Preprint

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“…2.1) and depend on the initial solid to gas ratio ( 0 ). This approach is an improvement compared to previous planet formation simulations via pebble accretion, where mostly a simplified pebble growth and drift model is used (e.g., Bitsch et al 2015;Ndugu et al 2018), but approaches using a model with accretion rates depending on a full pebble size distribution have also been implemented in other works (Guilera et al 2020;Dr ążkowska et al 2021).…”

Section: Pebble Accretionmentioning

confidence: 99%

How drifting and evaporating pebbles shape giant planets

Bitsch

2021

A&A

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Recent observations of extrasolar gas giants suggest super-stellar C/O ratios in planetary atmospheres, while interior models of observed extrasolar giant planets additionally suggest high heavy element contents. Furthermore, recent observations of protoplanetary disks revealed super-solar C/H ratios, which are explained by inward drifting and evaporating pebbles enhancing the volatile content of the disk. We investigate in this work how the inward drift and evaporation of volatile-rich pebbles influences the atmospheric C/O ratio and heavy element content of giant planets growing by pebble and gas accretion. To achieve this goal, we perform semi-analytical 1D models of protoplanetary disks, including the treatment of viscous evolution and heating, pebble drift, and simple chemistry to simulate the growth of planets from planetary embryos to Jupiter-mass objects by the accretion of pebbles and gas while they migrate through the disk. Our simulations show that the composition of the planetary gas atmosphere is dominated by the accretion of vapor that originates from inward drifting evaporating pebbles at evaporation fronts. This process allows the giant planets to harbor large heavy element contents, in contrast to models that do not take pebble evaporation into account. In addition, our model reveals that giant planets originating farther away from the central star have a higher C/O ratio on average due to the evaporation of methane-rich pebbles in the outer disk. These planets can then also harbor super-solar C/O ratios, in line with exoplanet observations. However, planets formed in the outer disk harbor a smaller heavy element content due to a smaller vapor enrichment of the outer disk compared to the inner disk, where the very abundant water ice also evaporates. Our model predicts that giant planets with low or large atmospheric C/O should harbor a large or low total heavy element content. We further conclude that the inclusion of pebble evaporation at evaporation lines is a key ingredient for determining the heavy element content and composition of giant planets.

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“…In principle, dust growth should be significantly slower in low-metallicity environments. However, growth and therefore pebble accretion timescales are also sensitive to turbulence, fragmentation thresholds, and disk sizes (Drążkowska et al 2021).…”

Section: Formationmentioning

confidence: 99%

A large sub-Neptune transiting the thick-disk M4 V TOI-2406

Wells

Rackham

Schanche

et al. 2021

A&A

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Context. Large sub-Neptunes are uncommon around the coolest stars in the Galaxy and are rarer still around those that are metal-poor. However, owing to the large planet-to-star radius ratio, these planets are highly suitable for atmospheric study via transmission spectroscopy in the infrared, such as with JWST. Aims. Here we report the discovery and validation of a sub-Neptune orbiting the thick-disk, mid-M dwarf star TOI-2406. The star’s low metallicity and the relatively large size and short period of the planet make TOI-2406 b an unusual outcome of planet formation, and its characterisation provides an important observational constraint for formation models. Methods. We first infer properties of the host star by analysing the star’s near-infrared spectrum, spectral energy distribution, and Gaia parallax. We use multi-band photometry to confirm that the transit event is on-target and achromatic, and we statistically validate the TESS signal as a transiting exoplanet. We then determine physical properties of the planet through global transit modelling of the TESS and ground-based time-series data. Results. We determine the host to be a metal-poor M4 V star, located at a distance of 56 pc, with properties Teff = 3100 ± 75 K, M* = 0.162 ± 0.008M⊙, R* = 0.202 ± 0.011R⊙, and [Fe∕H] = −0.38 ± 0.07, and a member of the thick disk. The planet is a relatively large sub-Neptune for the M-dwarf planet population, with Rp = 2.94 ± 0.17R⊕ and P= 3.077 d, producing transits of 2% depth. We note the orbit has a non-zero eccentricity to 3σ, prompting questions about the dynamical history of the system. Conclusions. This system is an interesting outcome of planet formation and presents a benchmark for large-planet formation around metal-poor, low-mass stars. The system warrants further study, in particular radial velocity follow-up to determine the planet mass and constrain possible bound companions. Furthermore, TOI-2406 b is a good target for future atmospheric study through transmission spectroscopy. Although the planet’s mass remains to be constrained, we estimate the S/N using amass-radius relationship, ranking the system fifth in the population of large sub-Neptunes, with TOI-2406 b having a much lower equilibrium temperature than other spectroscopically accessible members of this population.

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How dust fragmentation may be beneficial to planetary growth by pebble accretion

Cited by 46 publications

References 120 publications

The formation of wide exoKuiper belts from migrating dust traps

The formation of wide exoKuiper belts from migrating dust traps

How drifting and evaporating pebbles shape giant planets

A large sub-Neptune transiting the thick-disk M4 V TOI-2406

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