Orbital migration

Orbital migration is a change in an astronomical body's orbit caused by gravitational interactions or exchanges of momentum with surrounding material. It can alter orbital size, shape, or orientation over time.

Planet–disk interaction: Gravitational exchange between a planet and a surrounding disk of gas or solid material. Disk torques can transfer angular momentum and drive a planet inward or outward.
Hot Jupiter: A gas giant planet orbiting very close to its star, typically completing an orbit in days. Their close orbits are often explained by migration from farther out.
Orbital elements: Parameters that specify the size, shape, orientation, and position of an orbit. Migration is described through changes in these measurable orbital parameters.
Orbital perturbation: A deviation in an orbit caused by gravitational influences beyond an ideal two-body interaction. Perturbations may oscillate or accumulate without producing sustained migration.
Type I migration: Migration of a low-mass planet driven by gravitational torques from a gaseous protoplanetary disk. This torque-driven regime can move small planets rapidly before the disk disperses.
Grand Tack hypothesis: A model in which Jupiter migrated inward and then outward through the early Solar System. It proposes a specific migration path that helps explain the inner planets' small masses.
Angular momentum: A conserved physical quantity describing rotational motion and orbital motion. Exchanging angular momentum is a central way disks and companions change orbits.
Orbital decay: A gradual decrease in orbital size caused by energy loss from an orbiting system. Decay is inward evolution specifically, while migration can be inward or outward.
Type II migration: Migration of a planet massive enough to open a gap in a protoplanetary disk, coupled to the disk's evolution. Gap-opening planets migrate through a different disk regime than low-mass planets.
Nice model: A model of Solar System evolution in which giant planets migrated as they interacted with a planetesimal disk. It links giant-planet migration to the Solar System's later orbital arrangement.

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