Abstract
We run numerical simulations to study the accretion of gas and dust grains onto gas giant planets embedded into massive protoplanetary discs. The outcome is found to depend on the disc cooling rate, planet mass, grain size and irradiative feedback from the planet. If radiative cooling is efficient, planets accrete both gas and pebbles rapidly, open a gap and usually become massive brown dwarfs. In the inefficient cooling case, gas is too hot to accrete onto the planet but pebble accretion continues and the planets migrate inward rapidly. Radiative feedback from the planet tends to suppress gas accretion. Our simulations predict that metal enrichment of planets by dust grain accretion inversely correlates with the final planet mass, in accordance with the observed trend in the inferred bulk composition of Solar System and exosolar giant planets. To account for observations, however, as much as ~30-50% of the dust mass should be in the form of large grains.
Highlights
The formation mechanisms of gas giant planets can be constrained by studying their metallicities (e.g., Guillot 2005; Miller & Fortney 2011; Helled et al 2014)
In this paper we study pebble accretion onto gas giant planets embedded in massive protoplanetary discs at large (∼ 100 AU) separations from the host star
While the downward trend in the pebble enrichment of planets with mass Mp is clear from our simulations, much more work is necessary to determine the exact dependence of ZP on planet mass and other parameters, such as mass of the star, M∗
Summary
The formation mechanisms of gas giant planets can be constrained by studying their metallicities (e.g., Guillot 2005; Miller & Fortney 2011; Helled et al 2014). In GI, the outer regions of gravitationally unstable protoplanetary discs may fragment into Jupiter mass and larger clumps that were previously believed to share the composition of their parent discs (e.g., Boss 1997). These clumps may undergo further collapse and cooling and evolve into gas giant planets. Planetesimal accretion can alter the composition of such planets (Boley et al 2011)
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