What is tidal locking?

You may have never heard of tidal locking before and may wonder, what exactly is tidal locking? What does it look like, and what does it even mean?

Tidal locking is when a body in space orbits another body in a way that the body’s year and day are equal in length. This means that the body spins around its own axis once for each time it orbits around another, specific body in space. By having equal years and days, this orbiting body shows the same side of its face to those looking at it from the other body, or the body that being rotated around.

Think about Earth and its moon. We see the same side of the moon, never getting a glimpse of its other side from Earth. This is because the moon is tidally locked to the Earth. The moon orbits around Earth every 28 days, and the moon rotates completely around its axis in 28 days.

Tidal locking happens because both bodies, the moon and the Earth in the previous example, exert force on each other. The force that is exerted will always be stronger on the sides facing each other, meaning the force exerted on the moon and Earth is stronger where they face each other. This force causes the bodies to stretch and distort, which actually causes Earth’s tides.

The moon is pulled and stretched, which causes it to slow down. The slowing of the moon eventually causes the orbit to match its rotation. Other planets have tidally locked moons too. Pluto’s moon, Charon, is tidally locked to its primary body (Pluto). However, Pluto and Charon are a special case because they are both tidally locked to each other. This means that Pluto always shows the same side to Charon, and Charon always shows the same side to Pluto. This would be like the Earth showing the same side of the planet to the moon, and the moon showing the same side to us.

Tidal locking does influence how our planet moves, because tidal locking slows down the spin of our planet. That means millions of years from now that we may be like Pluto and Charon, meaning we may only see one side of the moon and the moon only sees one side of Earth.

Tidal locking doesn’t have to only exist between a moon and planet; it can happen with other bodies in space too! Astronomers often say that binary stars, or star systems that have two stars at their center, are most likely tidally locked to each other. A Canadian telescope may have also confirmed that a star is tidally locked with a nearby planet. Therefore, more can be tidally locked than just planets and their moons.

Now, whenever anyone asks you what tidal locking is, you now know what to tell them: It is when one body in space orbits another in way that causes its day and year to be the same in length.