Core accretion

Core accretion is a planet-formation model in which solids in a protoplanetary disk build a planetary core that can later capture surrounding gas.

Protoplanetary disk: A rotating disk of gas and dust surrounding a young star, where planets form. Its gas and solids supply the material from which cores and atmospheres grow.
Pebble accretion: A planet-growth process in which small, gas-drag-coupled solids are captured by a growing planetary body. It offers a faster route for building cores than collisions among large planetesimals.
Disk instability: A planet-formation model in which a sufficiently massive, cool disk fragments directly under its own gravity. It forms giant planets by gas fragmentation rather than by first growing a solid core.
Jupiter: The largest planet in the Solar System, a hydrogen- and helium-rich gas giant. Its heavy-element enrichment and inferred interior probe how a giant planet's core formed.
Meter-size barrier: The difficulty of growing solids through intermediate sizes that drift inward rapidly and may fragment in collisions. It threatens the delivery of enough solid material to build cores before the disk disperses.
Dust coagulation: The sticking and growth of dust grains through collisions in a disk. It begins the chain of solid growth that core accretion requires.
Pebble drift: The inward radial migration of solid particles in a gas disk caused by aerodynamic drag. Drifting pebbles can deliver solids to cores but also deplete distant regions.
Gravitational instability: The growth of density perturbations under gravity when pressure or other forces cannot prevent collapse. Disk instability is one planet-forming application of gravitational collapse.
Saturn: The second-largest planet in the Solar System, a gas giant with a prominent ring system. Its composition and interior offer a second test of giant-planet core growth.
Disk dispersal: The removal of gas from a protoplanetary disk through processes such as radiation, winds, and accretion onto the star. Core accretion must build a massive core before its gas supply disappears.

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