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Tidal migration is a type of planetary migration or moon orbital migration in which tides on/within an astronomical object play a role in changing the orbit of an object orbiting it, e.g., changing the orbit of a planet (or binary companion) orbiting a star or the orbit of a moon orbiting a planet. Depending upon directions and periods of rotation and orbit, the migration may be inward or outward. The Moon's orbit around the Earth is undergoing an outward tidal migration.
If host rotation and the orbit are in the same direction (prograde) and an orbit takes longer than a host rotation (orbital period is longer than the host rotation period), then the host's rotation grows slower, its rotation period increasing. The orbit enlarges, the orbiting body's orbital period also increasing, but growing more slowly than the host rotation period, and without other influences, the periods are eventually the same (tidal locking). The mechanism is the host's tidal deformation (and subsequent return to normal) not responding instantly, so the shifted mass is rotated in front of the orbiting body's position giving the gravitational force on the orbiting body a small forward component, increasing its orbital speed (tidal acceleration). Such a slightly-faster orbital speed shifts the orbiting body onto the outward portion of a slightly more eccentric orbit moving away from the host, and its orbital speed falls as it moves further from the host. This push is constant, pushing result in a growing orbit and orbital period. The "equal and opposite reaction" of the constant push slows the host's rotation. In addition to the Moon, the major moons of Saturn and Jupiter are undergoing this kind of outward migration, both of which rotate faster than Earth.
On the other hand, if the host's rotation period is longer than the orbital period, then the host's rotation increases (decreasing its rotation period), and the orbiting body migrates inward; the host's tidal deformation lags behind the orbiting body, so it is dragged forward, increasing the rotation, and the orbital speed is slowed, resulting in a smaller orbit and shorter orbital period. This can eventually lead to tidal locking, unless the orbiting object first collides with the host or is torn apart by tidal forces.
If the host's rotation and the orbit are in opposite directions (retrograde), the situation is somewhat similar to the latter: the orbiting body migrates inward for similar reasons, and will collide with the host or be torn apart, but in this case, the host's rotation is slowing and in theory, it could reverse.
The host's tides, i.e., constant deformation or rearrangement of the host's material, generates heat through friction, heating the host (tidal heating), in some cases, significantly. The disturbance caused by the tide can trigger waves such as in the sizeable atmospheres of gas planets, and resonances between the orbit and the waves can drastically change the effects of the tide, e.g., speed up the orbital migration. This is termed resonance locking. If such waves within a host star produce changes in its luminosity, they are termed tidally excited oscillations.
Since both bodies are orbiting around each other, these effects apply to both bodies, including tendency to migrate, changes in the rotation period, and tidal heating. The larger body has more effect on the smaller body, and if there is a large size difference (e.g., the Sun and a planet, or Jupiter and one of its moons), then the effect on the larger is minor. The smaller object is typically the earlier to be tidally locked (always the same side facing its host), such as the Moon with the Earth, and some of Jupiter's moons. Pluto and its moon, Charon, which are much closer in mass, are each tidally locked to the other, each always with the same side facing the other.