Planet Formation at Cosmic Dawn

Abstract

The first opportunities for rocky planet formation in the early Universe depended on the production and local concentration of heavy elements. Although the mean cosmic metallicity remained low for several gigayears after the Big Bang, local enrichment by Population III supernovae may have produced metal-rich regions capable of forming water-rich protoplanetary disks at Cosmic Dawn. Recent models suggest that such disks can form planetesimals, but their subsequent dynamical evolution remains uncertain. This project explores whether a planetesimal population in a locally enriched Cosmic Dawn disk can survive, migrate, collide, and grow. A coupled numerical framework was developed using AMUSE to simulate the resolvedN-body dynamics of planetesimals and DustPy to provide a viscously evolving one-dimensional gas-and-dust disk background. Three simulations were compared: an N-body-only control run, a run including aerodynamic gas drag and collisions, and a run including gas drag, collisions, and parametrised pebble accretion. The N-body-only control simulation remained dynamically stable over 26 kyr, with no collisions, ejections, or significant radial evolution. When gas drag was included, the disk underwent measurable inward migration and 42 planetesimal mergers over 64 kyr. The strongest growth occurred when pebble accretion was added: within 25 kyr, the number of resolved planetesimals decreased to 636, 348 mergers occurred, and the largest body grew to 2.13 × 10−2 M⊕. These results suggest that gas drag and pebble accretion can substantially accelerate early planetesimal growth in compact, locally enriched disks. The simulations do not fully model terrestrial planet formation, and the results depend on simplified collision physics, a parametrised pebble reservoir, limited particle numbers, and short integration timescales. Nonetheless, they support the conclusion that early protoplanet formation in locally enriched Cosmic Dawn disks is plausible.