Planetary migration

Planetary migration is a change in a planet’s orbit driven by gravitational interactions with a disk of gas or planetesimals, or with other bodies.

Type I migration: Orbital migration of a low-mass planet driven by gravitational torques from a gaseous disk. This regime describes how disk torques move planets too small to open a substantial gap.
Nice model: A model in which the giant planets began in a compact configuration and later underwent orbital instability. It explains several outer Solar System features through giant-planet migration and instability.
Solar Nebula: The rotating cloud of gas and dust from which the Sun and Solar System formed. The nebula’s gas and solids provided the medium through which early planets migrated.
Orbital resonance: A relationship between orbital periods in which bodies repeatedly align in a fixed pattern. Migrating planets can become trapped in resonances as their orbital periods converge.
In situ formation: The formation of a planet near its present orbit, rather than at a distant birthplace followed by migration. It offers an alternative to migration for explaining close-in planets.
Type II migration: Migration of a planet that opens a gap in a protoplanetary gas disk, often tied to disk evolution. Gap-opening planets can move with the disk’s viscous evolution.
Grand Tack hypothesis: A Solar System formation model in which Jupiter migrated inward, then reversed direction after Saturn became captured in resonance. Its inward-then-outward path offers one explanation for the small mass of Mars.
Protoplanetary disk: A rotating disk of gas and dust surrounding a young star, where planets form. Its gravity and fluid response can drive migration before the gas disperses.
Resonance capture: The process by which converging orbits lock bodies into an orbital resonance. It provides a record of convergent migration in some planetary systems.
Planetary accretion: The growth of planets through collisions and gravitational accumulation of smaller solid bodies. Accretion builds planets, while migration changes the orbits of already forming or formed planets.

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