Recent studies suggest that the Moon’s interior may still contain a partially molten layer, challenging previous assumptions that it had completely cooled and solidified. Using data from NASA’s GRAIL and Lunar Reconnaissance Orbiter missions, researchers detected changes in the Moon’s gravity, revealing a low-viscosity zone (LVZ) beneath the solid mantle.
Molten Magma May Still Exist Deep within the Moon, New Studies Suggest
By Lydia Amazouz
Published on October 4, 2024 14:00
Recent research points to the existence of a partially molten layer beneath the Moon’s surface, defying long-held assumptions that the lunar interior had cooled and solidified billions of years ago. According to studies from NASA’s Gravity Recovery and Interior Laboratory (GRAIL) and the Lunar Reconnaissance Orbiter, this molten layer lies between the Moon’s rocky mantle and its solid metallic core, suggesting that the Moon's geological activity might not be entirely over. This molten zone, which researchers describe as a low-viscosity zone (LVZ), responds to gravitational pulls from both Earth and the Sun, causing tidal deformations similar to those experienced on Earth.
Evidence from Tidal Distortions and Gravitational Data
The Moon, like Earth, experiences tidal forces caused by gravitational interactions with our planet and the Sun. However, instead of influencing oceans, these tidal forces create physical deformations in the Moon’s surface and its gravitational field. Through precise measurements taken by the GRAIL mission and the Lunar Reconnaissance Orbiter, researchers were able to detect annual fluctuations in the Moon’s gravity for the first time. By analyzing these variations, scientists inferred that there must be a partially molten layer within the Moon’s deep interior. Without such a layer, the changes in gravity could not be explained by existing models of the Moon’s structure.
The study's findings align with earlier hypotheses, but this is the first time the data has provided compelling evidence of a “thick, goopy zone” deep within the Moon. The researchers noted, “Interior modeling indicates that these values can be matched only with a low-viscosity zone (LVZ) at the base of the lunar mantle.” This discovery challenges the long-standing belief that the Moon had fully cooled and solidified, suggesting that its interior is more dynamic than previously thought.
The Mysterious Molten Layer and Its Implications
The existence of this molten layer raises key questions about the Moon’s internal processes, including how this region remains partially molten. Researchers speculate that the heat may be sustained by the presence of ilmenite, a titanium-rich mineral that could be trapping heat in the Moon’s mantle. Ilmenite has been observed in lunar samples collected during the Apollo missions, and its ability to retain heat could explain how the molten zone has persisted for billions of years. The study suggests, “The presence of an LVZ at the lower base of the lunar mantle may be most readily explained by partial melt in an ilmenite-rich layer, which would make the Moon similar to Mars, where partial melt was recently inferred from the analysis of seismic data.”
The idea that the Moon might still have a molten layer, much like Mars, opens new avenues for understanding the evolution of terrestrial planets and moons. If this molten zone plays a role in the Moon’s thermal state and tectonic history, it could also influence other planetary bodies that have similar compositions. Scientists are particularly interested in the potential similarities between the Moon and Mars, as both celestial bodies may still retain some internal heat despite their small sizes and apparent lack of recent volcanic activity.
Future Research and Exploration Prospects
While the current findings are based on remote sensing data, future lunar missions could provide more direct evidence of the Moon’s internal structure. The researchers believe that seismic readings taken from the lunar surface could offer deeper insights into the molten layer’s composition and behavior. Establishing a permanent base on the Moon, a goal of NASA’s Artemis program, would allow scientists to deploy seismic sensors capable of detecting subtle movements and vibrations deep within the Moon’s mantle. Such data could help clarify how thick the partially molten layer is, what materials it contains, and how long it has been active.
Moreover, understanding the Moon’s deep structure has profound implications for lunar exploration. As the study notes, “The existence of this zone has profound implications for the Moon's thermal state and evolution.” If the Moon is still geologically active in some capacity, it could affect how future lunar bases are constructed, particularly in regions near the poles, where ice deposits might be affected by subsurface heat.
This discovery also adds a new dimension to our understanding of planetary bodies that appear geologically inactive on the surface. Like Mars, the Moon may hold hidden reserves of heat that could change how we approach the study of planetary geology. As one researcher noted, “We will learn a whole lot about how the impact process works,” once future missions investigate the Moon’s internal activity in more detail.
The Bigger Picture: Planetary Evolution and Comparisons to Earth
The presence of a partially molten zone beneath the Moon’s surface offers a valuable comparison to Earth’s own interior. While Earth’s mantle is largely molten and drives plate tectonics, the Moon’s much smaller size was thought to have prevented any similar processes from occurring after its early formation. However, the discovery of this low-viscosity zone suggests that the Moon’s mantle might still be evolving, albeit on a much slower timescale than Earth’s. Researchers will now need to revisit older models of lunar formation and cooling to account for this molten layer and its role in shaping the Moon’s interior structure over billions of years.
This study also points to the importance of gravitational interactions between the Earth and the Moon, as the tidal forces exerted by Earth might play a role in sustaining the molten layer. The Moon’s close proximity to Earth means that its interior is continually stressed by tidal forces, potentially keeping parts of its mantle in a partially molten state. This process could be similar to the tidal heating seen in moons around Jupiter and Saturn, such as Io and Enceladus, where gravitational interactions drive internal heating and geological activity.
In conclusion, the discovery of a molten zone within the Moon's mantle not only challenges long-standing assumptions about the lunar interior but also opens new lines of inquiry into how small planetary bodies retain heat over geological timescales. Future missions, equipped with seismic instruments and other advanced sensors, will be critical in confirming the exact nature of this molten layer and understanding its implications for the Moon’s geological history. This discovery marks an important step in our understanding of the Moon and its similarities to other celestial bodies in our solar system.