Earth's gravity may have kept the early moon's volcanic heart beating

The moon's formation is thought to have occurred when another early protoplanet, Theia, collided with Earth, ejecting debris that coalesced into our lunar companion. However, the amount of this debris was relatively small, only about a quarter of Earth's size, which suggests that the moon would have cooled rapidly after its formation, becoming geologically dormant.

Despite this, laboratory analysis of lunar basalts returned by the Chang'e-5 mission indicated they were only around 2 billion years old, which contradicted traditional geological theory. Scientists explored other possibilities, such as radioactive decay and asteroid impacts, but concluded that these sources could not generate enough heat to sustain these basalts.

Therefore, researchers proposed an alternative explanation: tidal heating. This occurs when a celestial body is squeezed, stretched, and kneaded during its elliptical orbit around a larger parent body. Researchers modeled the moon's orbit around Earth 2 billion years ago, noting that it was closer and more eccentric than it is today.

This intense tidal interaction between Earth and the moon would have exerted significant gravitational forces on the lunar interior, particularly in a low-viscosity zone connecting the core and mantle. This energy input generated hundreds of gigawatts of power in specific regions, known as tidal heating anomaly zones (THAZs), located near the core-mantle boundary.

These THAZs were critical in sustaining the moon's core temperature, supporting a magnetic field longer than initially predicted, and driving mantle plumes that formed the lunar basalts seen in Chang'e-5 samples. While this theory provides valuable insights into the moon's geological history, it remains a hypothesis, and future lunar missions may offer further evidence to validate or challenge this explanation.