Earth's Moon is Still Hot Inside: Tidal Forces Heat Lunar Interior

The inside of the moon may not be the frozen chunk of rock that scientists once thought it was. Researchers have discovered that there is an extremely soft layer deep inside the moon and that the heat is effectively generated in the layer by the gravity of Earth, revealing that the moon may just have a hot interior.

In order to better understand the moon and its interior, the researchers compared the deformation of the moon by using Kayuga (SELENE, Selenological and Engineering Explorer) and other probes. These tools suggested that the interior of the moon still hasn't cooled and hardened. Instead, it's kept warm by the effect of the Earth on the moon due to tidal forces.

Understanding the internal forces that work inside the moon is an important step when it comes to understanding how it came to be in the first place. By learning how it internally functions, scientists can then infer how it came into being.

The scientists learned about the interior of the moon by studying its deformation. This deformation is caused by how gravity acts on the moon and deforms its surface; a celestial body will react differently depending on the type of interior structure that it has. The researchers found that the tidal forces of the moon could be explained if it's assumed that there is a soft layer in the deepest parts of the lunar mantle. As the moon orbits the Earth, gravity causes this mantle flexes and generates heat. This heat generation is most likely what softens this interior layer. That said, scientists aren't done with studying the moon.

"I believe that our research results have brought about new questions," said Yuji Harada, the principle investigator in the new study, in a news release. "For example, how can the bottom of the lunar mantle maintain its softer state for a long time? To answer this question, we would like to further investigate the internal structure and heat-generating mechanism inside the moon relative to the Earth, and heat-generating mechanism inside the moon in detail."

The findings are published in the journal Nature Geoscience.