How Birthplace Shapes the Cores of Gas Giant Planets

Studying gas giant planet formation is crucial for understanding the diversity of planets we observe across the Galaxy. Gas giants represent the most efficient products of planetary accretion, yet the substantial diversity in their observed masses, radii, and compositions suggests that the physical conditions governing their formation vary markedly across planetary systems. We present a theoretical framework for giant planet formation which couples pebble accretion, gas accretion, disk evolution, and migration across different stellar hosts.  

 

We find that the initial embryo formation timescale is a primary bottleneck, and that whether a gas giant ultimately forms is largely controlled by its initial formation location. Two distinct formation pathways emerge depending on the initial orbital distance: At small separations, the core mass is set by the pressure bump the planet opens in the disk, but high midplane temperatures suppress envelope cooling and stall the planet before runaway gas accretion can begin. At larger distances, inward pebble drift depletes the available solid supply before gap opening occurs, yet slow but efficient envelope contraction still allows gas giants to form with anomalously small cores. The resulting core masses range from 0.7 to 20 Earth masses, spanning a much broader interval than is typically assumed in classical models. We also find that the resulting planets differ significantly in masses and compositions depending on their formation conditions and the mass of their host star.  

 

The inferred diversity in core masses, final masses and compositions, and orbital periods, provides a natural explanation for the variety of physical properties observed among giant exoplanets.