Abstract
Context. Pebble accretion is an emerging paradigm for the fast growth of planetary cores. Pebble flux and pebble sizes are the key parameters used in the pebble accretion models. Aims. We aim to derive the pebble sizes and fluxes from state-of-the-art dust coagulation models and to understand their dependence on disk parameters and the fragmentation threshold velocity, and the impact of those on planetary growth by pebble accretion. Methods. We used a 1D dust evolution model including dust growth and fragmentation to calculate realistic pebble sizes and mass flux. We used this information to integrate the growth of planetary embryos placed at various locations in the protoplanetary disk. Results. Pebble flux strongly depends on disk properties including size and turbulence level, as well as the dust aggregates’ fragmentation threshold. We find that dust fragmentation may be beneficial to planetary growth in multiple ways. First of all, it prevents the solids from growing to very large sizes, at which point the efficiency of pebble accretion drops. What is more, small pebbles are depleted at a lower rate, providing a long-lasting pebble flux. As the full coagulation models are computationally expensive, we provide a simple method of estimating pebble sizes and flux in any protoplanetary disk model without substructure and with any fragmentation threshold velocity.
Highlights
In the classical paradigm of planet formation, a significant fraction of solids is very quickly converted into kilometer-sized planetesimals
For the first time, we study the growth of a planetary embryo by pebble accretion in connection with a self-consistent dust evolution model, considering the full size distribution obtained in a detailed dust coagulation simulation
In each of the models, we considered the growth of planetary embryos by pebble accretion at 1, 5, 10, 20, 30, 40, and 50 au
Summary
In the classical paradigm of planet formation, a significant fraction of solids is very quickly converted into kilometer-sized planetesimals Some of those planetesimals continue to grow rapidly via runaway growth (e.g., Wetherill & Stewart 1989; Ida & Makino 1993; Kokubo & Ida 1996). The isolation mass may be high enough to reproduce the cores of giant planets, but the core growth timescale in the planetesimal-driven scenario becomes prohibitively long to allow for the accretion of a gaseous atmosphere outside of the Jupiter location (Thommes et al 2002, 2003; Levison et al 2010; Johansen & Bitsch 2019) These drawbacks of the classical planetesimal-driven model motivated the development of the alternative “pebble accretion” scenario. Because pebbles are rapidly drifting through the protoplanetary disk, the size of the feeding zone increases, allowing the embryos to grow to larger sizes before the pebble flux is halted by planet-disk interactions (Lambrechts et al 2014)
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