Tidal locking

Tidal locking occurs when a celestial body's rotation period matches its orbital period around a star or planet, causing the same face to always point toward its primary. This happens because gravitational forces create differential pulls across the body's radius, gradually dampening spin until equilibrium is reached.

The Moon is tidally locked to Earth, which is why we always see the same lunar face. Many exoplanets in the "Habitable zone" around distant stars are likely locked as well—a crucial consideration for astrobiology. Mercury is locked in a 3:2 ratio with the Sun, rotating three times for every two orbits.

Tidal locking involves complex work done by tidal forces, dissipating energy through friction in the body's interior. The outcome shapes planetary geology, climate, and potential for life. On a locked world, one hemisphere bakes in eternal daylight while the other freezes in darkness—though winds and oceans can redistribute heat.

Understanding tidal locking requires theoretical physics and careful observation, bridging our knowledge of Solar System mechanics and distant worlds.

Related

Gravity, Exoplanet, Habitable zone, Orbital mechanics, Planetary science, Astrobiology