Recent research led by NASA scientist Sander Goossens and his team reveals new insights into the Moon’s deep interior. By studying how Earth and the Sun affect the Moon through tidal forces—similar to the way the Moon’s gravity causes tides on Earth—they discovered a layer within the Moon’s lower mantle that appears to be softer, or less viscous, than expected. This soft layer has important implications for our understanding of the Moon’s formation, evolution, and what lies beneath its surface.
Earth and the Sun create tides on the Moon, pulling on it and causing small, rhythmic changes in its shape. These forces also affect the Moon’s gravity field. Scientists measure the way the Moon’s shape and gravity respond to these forces to learn about its internal structure.
Until now, scientists could only measure these tidal effects for shorter, monthly cycles. In this study, the team was able to measure both monthly and yearly tidal effects on the Moon, providing a more complete picture.
The team used data from two lunar missions:
- GRAIL (Gravity Recovery and Interior Laboratory): This mission measured the Moon’s gravity field with high precision, providing details about its internal structure.
- LRO (Lunar Reconnaissance Orbiter): This orbiter has been tracking the Moon for over eight years, adding more data about its gravity field over time.
By combining information from both missions, the team could observe how the Moon’s gravity and shape change over both monthly and yearly cycles. Using advanced computer modeling techniques, they explored different possible structures for the Moon’s interior and compared these models with their data.
The study revealed that the Moon has a low-viscosity zone (LVZ) in its lower mantle. This means there is a layer deep within the Moon that is relatively soft or partially molten. This LVZ likely consists of materials that are similar to molten rock but may be mixed with solid minerals. The researchers believe that:
- This soft layer is probably located at the boundary between the Moon’s mantle and its core.
- The LVZ could be composed of materials rich in certain minerals, like ilmenite, which is known to be less viscous and could explain the low viscosity of this region.
This layer helps explain why the Moon dissipates energy differently depending on the tidal frequency. The softer, partially molten material absorbs energy and deforms more easily, which fits with the observed data.
This discovery of a soft layer in the Moon’s lower mantle provides important clues about how the Moon has evolved over time. It suggests that there are still heat sources within the Moon, maintaining this layer in a semi-molten state. This has implications for:
- The Moon’s Thermal History: The presence of a soft layer implies that heat is still present within the Moon, possibly from its original formation or from radioactive decay.
- Comparing the Moon to Other Celestial Bodies: The Moon’s LVZ is similar to the partially molten layers found in other planets, like Mars. This similarity can help scientists understand how planets and moons with limited geological activity retain heat over billions of years.
The findings from this study provide a framework for future lunar exploration missions and highlight the importance of precise measurements over time. By understanding the structure beneath the Moon’s surface, scientists can better plan for future missions and potentially uncover more details about the Moon’s past.
These results also open up new questions about the Moon’s interior. Could there be more partially molten zones within the mantle? Are there still active processes, such as volcanic or seismic activity, that we haven’t yet detected? Future lunar missions and continued analysis of the Moon’s gravity and shape will help answer these questions.
The Moon’s tides, caused by the gravitational pull of Earth and the Sun, have revealed a hidden layer in its lower mantle that appears to be softer and likely partially molten. This discovery sheds light on the Moon’s internal structure, suggesting it has a dynamic thermal history. By better Siri understanding the Moon’s interior, scientists are piecing together the story of its formation and evolution, leading to a deeper understanding of Earth’s closest neighbor.
