Solar System/Planet Formation and Structure

Core Accretion and Disk Instability

The 2 main/most common theories for planet formation are disk instability and core accretion.

Core Accretion

Core Accretion is the theory that planets form from small particles gathering together and forming lumps that accumulate more and more mass. This process is slow, taking millions of years.

Disk Instability

Disk Instability is the theory that planets form from spinning disks of material that accumulates so much mass, it violently collapses on itself and forms a planet. This is a quick process (speaking relatively), taking just thousands of years.