Why did volcanic activity continue on the Moon long after its formation? Part of the answer may lie deep beneath the lunar surface, where tidal forces could have generated concentrated regions of internal heating.
A new study published in Planet explores how tidal heating may have been distributed within the Moon. Using numerical simulations, Miao Chen and colleagues from Chengdu University of Technology show that an ultralow-viscosity zone near the lunar core-mantle boundary could concentrate tidal energy dissipation, creating localized heat sources with potentially important implications for the lunar thermal evolution.
How Tides Generate Heat Inside the Moon
Tides are most familiar as the rise and fall of Earth's oceans. But tidal forces also act on solid planetary bodies. As the Moon orbits Earth, Earth's gravitational pull causes the Moon to deform periodically. Because the Moon’s interior is not perfectly elastic, some of the energy involved in tidal deformation is converted into heat. This process is known as tidal heating.
However, tidal heating is not distributed uniformly throughout the Moon. Its intensity depends on both the Earth-Moon orbital configuration and the physical properties of the lunar interior. In particular, materials with different viscosities respond differently to tidal forces, potentially producing substantial variations in heat generation.
Understanding where tidal heating occurs therefore requires more than reconstructing the Moon's ancient orbit. It also requires knowledge of the viscosity structure deep within the Moon.
A Hidden Heat Source Near the Core-Mantle Boundary
Previous studies have suggested the presence of an ultralow-viscosity zone near the lunar core-mantle boundary. Based on this evidence, the researchers incorporated this deep structure into their tidal heating calculations and used 3D numerical simulations to investigate its heating effects.
The results reveal a striking pattern: tidal heating can become strongly concentrated near the equatorial region of the core–mantle boundary, forming two symmetrically distributed regions of enhanced heating in model cross sections. The researchers refer to this feature as the Tidal Heating Anomaly Zone (THAZ).
The significance of this finding lies not simply in the presence of tidal heating, which has long been recognized, but in how the deep viscosity structure of the moon may control where that heat is generated. Rather than being distributed evenly, tidal energy dissipation could produce localized heat sources within the deep lunar mantle.
How Much Heat Could Be Generated?
To estimate the potential strength of this deep heat source, the researchers examined orbital conditions relevant to approximately 3.2 billion years ago, assuming a lunar orbital period of about 16 present-day Earth days and testing different orbital eccentricities.
Under a high-eccentricity scenario (e = 0.5), the model predicts that a strongly heated region occupying only about 2.5% of the lunar mantle volume could generate approximately 150 GW of tidal heating power. This is about 4.3 times the radiogenic heating power estimated for the same region.
By comparison, when orbital eccentricity is reduced to 0.05, the predicted tidal heating power falls to just 1.5 GW.
This hundredfold difference highlights the strong influence of orbital conditions on deep tidal heating. Importantly, the high-eccentricity case represents a model scenario illustrating the potential strength of this mechanism, rather than evidence that such intense heating persisted throughout lunar history.
What Could This Mean for Lunar Evolution?
The three-dimensional simulations further suggest that concentrated tidal heating could alter temperatures in the deep lunar mantle and influence the upward movement of mantle material. Such processes may provide an additional pathway for transporting heat from the Moon's interior toward shallower regions.
These findings offer a possible explanation for how localized deep heating might have contributed to the prolonged magmatic activity of the moon. However, identifying a potential heat source does not establish a direct connection to volcanic eruptions at the surface.
Several processes must be considered before such a connection can be demonstrated, including partial melting, magma generation and transport, and heat loss during magma ascent. The present simulations do not fully account for the latent heat associated with melting or heat loss during magma transport, leaving important questions for future research.
Nevertheless, the study provides a new perspective on lunar thermal evolution. It suggests that the interaction between tidal forces and the deep viscosity structure of the moon could have produced localized heating near the core-mantle boundary, potentially influencing mantle dynamics and the redistribution of internal heat.
Further modeling, together with constraints from lunar observations and returned samples, will be needed to determine how strongly this mechanism contributed to the Moon's magmatic history.
DOI: 10.15302/planet.2026.26014