planetmigration

Planet migration is the process by which a planet's orbital distance from its star changes after formation, typically due to gravitational interactions with a protoplanetary disk, with remaining planetesimals, or with other planets. In the standard picture, planets grow within a gas-rich disk and can move from their birth locations, shaping planetary systems.

Disk-driven migration occurs when embedded planets exchange angular momentum with the disk. Low-mass planets that do not open a deep gap experience Type I migration, which is usually inward and can be rapid compared with disk lifetimes. The rate depends on disk structure and planetary mass, and under certain conditions additional torques can slow, halt, or even reverse migration, creating outward movement or traps.

More massive planets that open a gap undergo Type II migration, where the planet largely follows the disk’s viscous evolution. This migration is typically slower than Type I but can still move planets substantial distances before the disk dissipates. Inner disk edges or magnetospheric cavities can act as stopping points for migrating giants.

Planetesimal-driven migration can occur after the gas disk disperses, through gravitational scattering with a residual planetesimal disk. This mechanism is usually slower and sensitive to the distribution of material, and it can move planets inward or outward as well as alter eccentricities and inclinations.

Observationally, migration helps explain hot Jupiters, resonant chains in compact multi-planet systems, and the diversity of exoplanetary architectures. While migration is a common explanatory feature, its exact pathways depend on planet mass, disk properties, and timing, and remain areas of active research.