An approximation for the capture radius of gaseous protoplanets

Valletta, Claudio; Helled, Ravit

doi:10.1093/mnrasl/slab089

Cited by 7 publications

(13 citation statements)

References 19 publications

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“…Collisions between planets and planetesimals are detected using a direct search method, which requires the capture radius of the planet being known. We used the approximation from Valletta & Helled (2021) for planets that have attained a gaseous envelope (planets with masses above the pebble isolation mass), and assumed that the capture radius is equal to the core radius for lower planetary masses. Finally we describe the numerical setup and initialization of our N-body simulations.…”

Section: Modelmentioning

confidence: 99%

“…1. The capture radius during gas accretion was calculated using the approximation from Valletta & Helled (2021), which has two regimes depending on whether the planet is in the attached phase (M env < M core ) or the detached phase (M env > M core ). For the detached phase, we used the fit obtained at 10 7 yr. During the attached phase the envelope is enhanced, resulting in a large capture radius.…”

Section: Numerical Setup and Initializationmentioning

confidence: 99%

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A low accretion efficiency of planetesimals formed at planetary gap edges

Eriksson

Ronnet

Johansen

et al. 2022

A&A

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Observations and models of giant planets indicate that such objects are enriched in heavy elements compared to solar abundances. The prevailing view is that giant planets accreted multiple Earth masses of heavy elements after the end of core formation. Such late solid enrichment is commonly explained by the accretion of planetesimals. Planetesimals are expected to form at the edges of planetary gaps, and here we address the question of whether these planetesimals can be accreted in large enough amounts to explain the inferred high heavy element contents of giant planets. We performed a series of N-body simulations of the dynamics of planetesimals and planets during the planetary growth phase, taking gas drag into account as well as the enhanced collision cross section caused by the extended envelopes. We considered the growth of Jupiter and Saturn via gas accretion after reaching the pebble isolation mass and we included their migration in an evolving disk. We find that the accretion efficiency of planetesimals formed at planetary gap edges is very low: less than 10% of the formed planetesimals are accreted even in the most favorable cases, which in our model corresponds to a few Earth masses. When planetesimals are assumed to form beyond the feeding zone of the planets, extending to a few Hill radii from a planet, accretion becomes negligible. Furthermore, we find that the accretion efficiency increases when the planetary migration distance is increased and that the efficiency does not increase when the planetesimal radii are decreased. Based on these results, we conclude that it is difficult to explain the large heavy element content of giant planets with planetesimal accretion during the gas accretion phase. Alternative processes most likely are required, such as accretion of vapor deposited by drifting pebbles.

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Section: Modelmentioning

confidence: 99%

Section: Numerical Setup and Initializationmentioning

confidence: 99%

A low accretion efficiency of planetesimals formed at planetary gap edges

Eriksson

Ronnet

Johansen

et al. 2022

A&A

View full text Add to dashboard Cite

show abstract

“…Collisions between planets and planetesimals are detected using a direct search method, which requires that the capture radius of the planet is known. We use the approximation from Valletta & Helled (2021) for planets that have attained a gaseous envelope (planets with masses above the pebble isolation mass), and assume that the capture radius is equal to the core radius for lower planetary masses. Finally we describe the numerical setup and initialization of our N-body simulations.…”

Section: Modelmentioning

confidence: 99%

“…1. The capture radius during gas accretion is calculated using the approximation from Valletta & Helled (2021), which has two regimes depending on if the planet is in the attached phase (M env < M core ) or the detached phase (M env > M core ). For the detached phase we use the fit obtained at 10 7 yr. During the attached phase the envelope is enhanced, resulting in a large capture radius.…”

Section: Planet Growth-tracksmentioning

confidence: 99%

“…As mentioned above, decreasing the planetesimal size results in more gas-drag. Furthermore, it also results in an increased capture radius of the planets during the enhanced envelope phase (Valletta & Helled 2021), as smaller planetesimals can be captured further up in the atmosphere. The combined effect on the accretion efficiency of planetesimals, however, turns out to be small.…”

Section: Planetesimal Accretionmentioning

confidence: 99%

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A low accretion efficiency of planetesimals formed at planetary gap edges

Eriksson,

Ronnet,

Johansen

et al. 2022

Preprint

Self Cite

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Observations and models of giant planets indicate that such objects are enriched in heavy elements compared to solar abundances. The prevailing view is that giant planets accreted multiple Earth masses of heavy elements after the end of core formation. Such late solid enrichment is commonly explained by the accretion of planetesimals. Planetesimals are expected to form at the edges of planetary gaps, and here we address the question of whether these planetesimals can be accreted in large enough amounts to explain the inferred high heavy element contents of giant planets. We perform a series of N-body simulations of the dynamics of planetesimals and planets during the planetary growth phase, taking into account gas drag as well as the enhanced collision cross-section caused by the extended envelopes. We consider the growth of Jupiter and Saturn via gas accretion after reaching the pebble isolation mass and we include their migration in an evolving disk. We find that the accretion efficiency of planetesimals formed at planetary gap edges is very low: less than 10% of the formed planetesimals are accreted even in the most favorable cases, which in our model corresponds to a few Earth-masses. When planetesimals are assumed to form beyond the feeding zone of the planets, extending to a few Hill radii from a planet, accretion becomes negligible. Furthermore, we find that the accretion efficiency increases when the planetary migration distance is increased and that the efficiency does not increase when the planetesimal radii are decreased. Based on these results we conclude that it is difficult to explain the large heavy element content of giant planets with planetesimal accretion during the gas accretion phase. Alternative processes most likely are required, e.g. accretion of vapor deposited by drifting pebbles.

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Composition of giant planets: The roles of pebbles and planetesimals

Danti,

Bitsch,

Mah

2023

A&A

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One of the current challenges of planet formation theory is to explain the enrichment of observed exoplanetary atmospheres. While past studies have focused on scenarios where either pebbles or planetesimals are the main drivers of heavy element enrichment, here we combine the two approaches to understand whether the composition of a planet can constrain its formation pathway. We study three different formation scenarios: pebble accretion, pebble accretion with planetesimal formation inside the disc, and combined pebble and planetesimal accretion. We used the CHEMCOMP code to perform semi-analytical 1D simulations of protoplanetary discs, including viscous evolution, pebble drift, and simple chemistry to simulate the growth of planets from planetary embryos to gas giants as they migrate through the disc, while simultaneously tracking their composition. Our simulations confirm that the composition of the planetary atmosphere is dominated by the accretion of gas vapour enriched by inward-drifting and evaporating pebbles. Including planetesimal formation hinders this enrichment because many pebbles are locked into planetesimals and cannot evaporate and enrich the disc. This results in a dramatic drop in accreted heavy elements in the cases of planetesimal formation and accretion, demonstrating that planetesimal formation needs to be inefficient in order to explain planets with high heavy element content. On the other hand, accretion of planetesimals enhances the refractory component of the atmosphere, leading to low volatile-to-refractory ratios in the atmosphere, in contrast to the majority of pure pebble simulations. However, low volatile-to-refractory ratios can also be achieved in the pure pebble accretion scenario if the planet migrates all the way into the inner disc and accretes gas that is enriched in evaporated refractories. Distinguishing these two scenarios requires knowledge about the planet’s atmospheric C/H and O/H ratios, which are much higher in the pure pebble scenario compared to the planetesimal formation and accretion scenario. This implies that a detailed knowledge of the composition of planetary atmospheres could help to distinguish between the different formation scenarios.

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An approximation for the capture radius of gaseous protoplanets

Cited by 7 publications

References 19 publications

A low accretion efficiency of planetesimals formed at planetary gap edges

A low accretion efficiency of planetesimals formed at planetary gap edges

A low accretion efficiency of planetesimals formed at planetary gap edges

Composition of giant planets: The roles of pebbles and planetesimals

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