Why is the Moon in a synchronous orbit around Earth, always keeping the same face toward Earth?
A) There is a strong magnetic attraction between the two bodies that keeps the Moon turned toward Earth.
B) The Moon must rotate on its axis at the same rate it orbits Earth to conserve angular momentum.
C) As the Moon rotates, friction between the Moon's large liquid interior and its mantle has slowed the rate of rotation until it just matches the orbital rate. Over time it will slow further, and then the Moon will no longer be in a synchronous orbit.
D) When the Moon was molten and experienced chemical differentiation, the gravitational pull of Earth caused large tides. The friction created as Earth's gravity attempted to keep the high tide bulge pointed toward Earth resulted in the Moon's rotation being slowed, causing it always to face Earth.

Question

Quizplus · Accepted Answer

The correct explanation is that the gravitational pull of Earth on the Moon, especially when the Moon was still partially molten, created significant tidal forces. These forces acted to slow the Moon's rotation until it matched its orbital period, resulting in the synchronous orbit we observe today. This process is known as tidal locking.

Why Is the Moon in a Synchronous Orbit Around Earth