1.2Locking of the larger body. 1.3Eccentric orbits. 2Occurrence. Toggle Occurrence subsection. 2.1Moons. 2.1.1Earth's Moon. 2.2Planets.

This phenomenon, called “synchronous tidal locking,” sounds like a weird coincidence ― but it’s actually quite common. All the solar system’s large moons are tidally locked with their planets. The bigger moons synchronize early in their existence, within hundreds of thousands of orbits.

Tidal locking explained in 3D — see why the Moon always shows the same face to Earth, how tidal bulges create torque, and discover mutual locking. Interactiv...

Tidal locking explained in 3D — see why the Moon always shows the same face to Earth, how tidal bulges create torque, and discover mutual locking. Interactive animation on Unseel.

Given enough time, this would create a mutual tidal locking between Earth and the Moon. The length of Earth's day would increase and the length of a lunar month would also increase.

The same tidal forces that locked the Moon are gradually slowing Earth's rotation, increasing the length of a day. A future state of mutual tidal locking would require Earth's day to lengthen to match the Moon's orbital period, which is currently about 27 days.

Learn how tidal locking happens, why it affects moons and planets, and what it reveals about gravity, rotation, and orbital evolution.

Tidal locking is a spin matching an orbit, so one face stays toward the planet. The Moon’s far side still has day and night.

This mutual locking is the final equilibrium state for any two-body tidal system, given enough time. The tidal torques Charon raises on Pluto and Pluto raises on Charon were both strong enough, relative to the bodies’ small sizes, to bring the whole system to a standstill.

Given enough time, this would create a mutual tidal locking between Earth and the Moon, where the length of a day has increased and the length of a lunar month has shortened until the two are the same.