Moon Shrinks as Inner Layers Cool Over Millions Years
Lunar radius contraction caused by long-term internal cooling forms thousands of unique surface faults.
Updated on Oct. 20, 2026 in Geology
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Researchers estimate the Moon's radius has decreased by approximately 45 meters over the past 400 to 800 million years. This global contraction is a direct result of the Moon cooling since its formation 4.5 billion years ago.
Why it matters
The continuous cooling of the Moon's interior triggers surface compression that manifests as faults. Understanding this geological process provides insight into the lunar crust and the structural evolution of the Moon.
Researchers identified more than 10,000 young lobate scarps on the lunar surface using images from the Lunar Reconnaissance Orbiter Camera. The study confirms that cooling of the inner layers drives this surface contraction.
The players
Lunar Reconnaissance Orbiter Camera
This instrument is a high-resolution imaging system currently capturing detailed surface data of the Moon.
The Planetary Science Journal
This is a peer-reviewed academic publication that features research on the study of the solar system.
The details
The Moon's outer shell acts as a single plate, which allows compression to create curved surface formations known as lobate scarps. Crust thickness varies across the lunar surface, directly influencing where cracks and faults appear.
Timeline
4.5 billion years ago: The Moon formed and began its cooling process.
400-800 million years ago: The period during which the radius decreased.
October 14, 2026: The study was published in The Planetary Science Journal.
The Big Picture
This discovery updates the paradigm established by the Lunar Reconnaissance Orbiter mission regarding the Moon's geological inactivity. The findings clarify that the Moon is structurally evolving rather than remaining a static, dormant body.
These findings provide a deeper understanding of planetary formation and the long-term cooling of celestial bodies. The data helps scientists model the structural stability of the lunar crust for future exploration planning.
The takeaway
The Moon remains a geologically dynamic environment as its interior continues to cool and contract. Existing faults may continue to grow, and new formations are likely to emerge over time.
Further reading
For more information on the physical evolution of the Moon, see the latest Geology reports.
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