How cores grow by pebble accretion

Brouwers, M. G.; Vazan, Allona; Ormel, Chris W.

doi:10.1051/0004-6361/201731824e

Cited by 6 publications

(8 citation statements)

References 3 publications

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“…Indeed, as shown in previous studies (Pollack et al 1986;Brouwers et al 2017;Alibert 2017a;Lozovsky et al 2017) when the core mass is between 1 − 3 M ⊕ solids are expected to dissolve in the gaseous envelope. Therefore, only for the naive scenario in which all the accreted heavy elements are assumed to go to the center the heavy-element mass in the planet is comparable to the core's mass.…”

Section: Introductionsupporting

confidence: 61%

“…The different derived formation timescales when using the various fragmentation models is affected by the mass of the inner compact core. As shown analytically by Brouwers et al (2017) the planetary growth timescale when heavy-element enrichment is considered depends on the heavy-element fraction that is deposited into the envelope relative to the amount that is added to the core. The smaller the inner core is, the faster is the growth of the planet.…”

Section: Planetesimal Accretionmentioning

confidence: 99%

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Jupiter’s heavy-element enrichment expected from formation models

Venturini

Helled

2020

A&A

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Aims. The goal of this work is to investigate Jupiter's growth focusing on the amount of heavy elements accreted by the planet, and its comparison with recent structure models of Jupiter. Methods. Our model assumes an initial core growth dominated by pebble accretion, and a second growth phase that is characterized by a moderate accretion of both planetesimals and gas. The third phase is dominated by runaway gas accretion during which the planet becomes detached from the disk. The second and third phases are computed in detail, considering two different prescriptions for the planetesimal accretion and fits from hydrodynamical studies to compute the gas accretion in the detached phase. Results. In order for Jupiter to consist of ∼20-40 M ⊕ of heavy elements as suggested by structure models, we find that Jupiter's formation location is preferably at an orbital distance of 1 a 10 au once the accretion of planetesimals dominates. We find that Jupiter could accrete between ∼1 and ∼15 M ⊕ of heavy elements during runaway gas accretion, depending on the assumed initial surface density of planetesimals and the prescription used to estimate the heavy-element accretion during the final stage of the planetary formation. This would yield an envelope metallicity of ∼0.5 to ∼3 times solar. By computing the solid (heavy-element) accretion during the detached phase, we infer a planetary mass-metallicity (M P -M Z ) relation of M Z ∼ M 2/5 P when a gap in the planetesimal disk is created, and of M Z ∼ M 1/6 P without a planetesimal gap. Conclusions. Our hybrid pebble-planetesimal model can account for Jupiter's bulk and atmospheric enrichment. The high bulk metallicity inferred for many giant exoplanets is difficult to explain from standard formation models. This might suggest a migration history for such highly enriched giant exoplanets and/or giant impacts after the disk's dispersal.

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Section: Introductionsupporting

confidence: 61%

Section: Planetesimal Accretionmentioning

confidence: 99%

Jupiter’s heavy-element enrichment expected from formation models

Venturini

Helled

2020

A&A

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“…In the scenario of planetesimal accretion, planetary embryos grow from the accretion of kilometer-to hundreds-of-kilometer-sized planetesimals in the early stage of planet formation (e.g., Pollack et al 1996;Hubickyj et al 2005). In contrast, pebble accretion involves the direct accretion of millimeter-to centimeter-sized dust grains that drift past the orbits of the growing protoplanets (e.g., Johansen & Lambrechts 2017;Brouwers et al 2019). An increasing number of studies reveal that both giant and terrestrial-sized planets could form through a combined mechanism that involves both pebble and planetesimal accretion (Alibert et al 2018;Liu et al 2019;Lichtenberg et al 2021); however, the amount of the dominantly accreted solids may vary substantially from one protoplanet to another, sensitively depending on accretion chronology and the local pebble flux.…”

Section: Water Delivered By S-type Asteroids To Earth and Marsmentioning

confidence: 99%

New Evidence for Wet Accretion of Inner Solar System Planetesimals from Meteorites Chelyabinsk and Benenitra

Jin¹,

Bose²,

Lichtenberg³

et al. 2021

Planet. Sci. J.

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We investigated the hydrogen isotopic compositions and water contents of pyroxenes in two recent ordinary chondrite falls, namely, Chelyabinsk (2013 fall) and Benenitra (2018 fall), and compared them to three ordinary chondrite Antarctic finds, namely, Graves Nunataks GRA 06179, Larkman Nunatak LAR 12241, and Dominion Range DOM 10035. The pyroxene minerals in Benenitra and Chelyabinsk are hydrated (∼0.018–0.087 wt.% H2O) and show D-poor isotopic signatures (δDSMOW from −444‰ to −49‰). On the contrary, the ordinary chondrite finds exhibit evidence of terrestrial contamination with elevated water contents (∼0.039–0.174 wt.%) and δDSMOW values (from −199‰ to −14‰). We evaluated several small parent-body processes that are likely to alter the measured compositions in Benenitra and Chelyabinsk and inferred that water loss in S-type planetesimals is minimal during thermal metamorphism. Benenitra and Chelyabinsk hydrogen compositions reflect a mixed component of D-poor nebular hydrogen and water from the D-rich mesostases. A total of 45%–95% of water in the minerals characterized by low δDSMOW values was contributed by nebular hydrogen. S-type asteroids dominantly composed of nominally anhydrous minerals can hold 254–518 ppm of water. Addition of a nebular water component to nominally dry inner solar system bodies during accretion suggests a reduced need of volatile delivery to the terrestrial planets during late accretion.

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“…The silicate sublimation front at 2,000 K would under all circumstances destroy pebbles and dust close to the surface of massive protoplanets; however this sublimation is associated with a radiative zone, due to the strong decrease in opacity there (see Figure 1), which would separate the silicate vapour from the bulk envelope. In addition we ignored the latent heat from sublimation and deposition (Brouwers et al 2018(Brouwers et al , 2019Brouwers & Ormel 2020), which may also be important for the thermodynamics of the envelope.…”

Section: Discussionmentioning

confidence: 99%

Transport, destruction and growth of pebbles in the gas envelope of a protoplanet

Johansen,

Nordlund

2020

Preprint

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We analyse the size evolution of pebbles accreted into the gaseous envelope of a protoplanet growing in a protoplanetary disc, taking into account collisions driven by the relative sedimentation speed as well as the convective gas motion. Using a simple estimate of the convective gas speed based on the pebble accretion luminosity, we find that the speed of the convective gas is higher than the sedimentation speed for all particles smaller than 1 mm. This implies that both pebbles and pebble fragments are strongly affected by the convective gas motion and will be transported by large-scale convection cells both towards and away from the protoplanet's surface. We present a simple scheme for evolving the characteristic size of the pebbles, taking into account the effects of erosion, mass transfer and fragmentation. Including the downwards motion of convective cells for the transport of pebbles with an initial radius of 1 millimeter, we find pebble sizes between 100 microns and 1 millimeter near the surface of the protoplanet. These sizes are generally amenable to accretion at the base of the convection flow. Small protoplanets far from the star (> 30 AU) nevertheless erode their pebbles to sizes below 10 microns; future hydrodynamical simulations will be needed to determine whether such small fragments can detach from the convection flow and become accreted by the protoplanet.

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How cores grow by pebble accretion

Cited by 6 publications

References 3 publications

Jupiter’s heavy-element enrichment expected from formation models

Jupiter’s heavy-element enrichment expected from formation models

New Evidence for Wet Accretion of Inner Solar System Planetesimals from Meteorites Chelyabinsk and Benenitra

Transport, destruction and growth of pebbles in the gas envelope of a protoplanet

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