Changes in the metallicity of gas giant planets due to pebble accretion

TL;DR

This study uses numerical simulations to explore how gas and pebble accretion influence the metallicity and mass of gas giant planets, revealing dependencies on cooling rates, feedback, and grain size, and aligning with observed planetary compositions.

Contribution

It provides new insights into how pebble accretion affects planetary metallicity and mass, considering radiative feedback and cooling efficiency, which was not thoroughly modeled before.

Findings

Metal enrichment inversely correlates with planet mass.

Efficient cooling leads to rapid gas and pebble accretion, forming massive brown dwarfs.

Large dust grains are necessary to match observed planetary compositions.

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.