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Published November 11, 2018 | Published + Accepted Version
Journal Article Open

A balanced budget view on forming giant planets by pebble accretion

Abstract

Pebble accretion refers to the assembly of rocky planet cores from particles whose velocity dispersions are damped by drag from circumstellar disc gas. Accretion cross-sections can approach maximal Hill-sphere scales for particles whose Stokes numbers approach unity. While fast, pebble accretion is also lossy. Gas drag brings pebbles to protocores but also sweeps them past; those particles with the largest accretion cross-sections also have the fastest radial drift speeds and are the most easily drained out of discs. We present a global model of planet formation by pebble accretion that keeps track of the disc's mass budget. Cores, each initialized with a lunar mass, grow from discs whose finite stores of mm–cm-sized pebbles drift inward across all radii in viscously accreting gas. For every 1 M_⊕ netted by a core, at least 10 M_⊕ and possibly much more are lost to radial drift. Core growth rates are typically exponentially sensitive to particle Stokes number, turbulent Mach number, and solid surface density. This exponential sensitivity, when combined with disc migration, tends to generate binary outcomes from 0.1 to 30 au: either sub-Earth cores remain sub-Earth, or explode into Jupiters, with the latter migrating inward to varying degrees. When Jupiter-breeding cores assemble from mm–cm-sized pebbles, they do so in discs where such particles drain out in ∼10^5 yr or less; such fast-draining discs do not fit mm-wave observations.

Additional Information

© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model) Accepted 2018 August 5. Received 2018 July 31; in original form 2018 May 22. We thank Bertram Bitsch, Jeffrey Fung, Anders Johansen, Michiel Lambrechts, Wladimir Lyra, Ruth Murray-Clay, Chris Ormel, Diana Powell, Michael Rosenthal, Julia Venturini, and an anonymous referee for comments that helped to improve the manuscript. JWL and EC acknowledge support from the National Science Foundation and a Berkeley Excellence Accounts for Ressearch (BEAR) grant. EJL is supported by the Sherman Fairchild Fellowship from Caltech. This research used the Savio computational cluster resource provided by the Berkeley Research Computing program at the University of California, Berkeley (supported by the UC Berkeley Chancellor, Vice Chancellor for Research, and Chief Information Officer).

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Additional details

Created:
August 19, 2023
Modified:
October 19, 2023