New fault map shows moon has shrunk about 45 meters in recent geologic history

By the Everything Space news desk · 15 Oct 2026 · written from the sources below

Image: Phys.org

Mapping over 10,000 young faults reveals the moon is still contracting as its interior cools, with implications for where moonquakes might strike.

A new analysis of lunar surface features suggests the moon has shrunk by roughly 45 meters in radius over the past 400 to 800 million years, according to a study published in The Planetary Science Journal.

Researchers led by Thomas R. Watters of the Smithsonian's National Air and Space Museum used imagery from the Lunar Reconnaissance Orbiter Camera to identify more than 10,000 young tectonic faults across the moon's highlands and dark mare plains. These faults, called lobate scarps and mare ridges, form as the moon's interior cools and contracts, causing its crust to buckle and fracture.

If the contraction rate has stayed steady, the moon has been shrinking by roughly 6 to 11 centimeters per million years, a pace far slower than the tectonic plate motion seen on Earth. Unlike Earth, which distributes most of its tectonic activity along boundaries between more than 15 plates, the moon behaves as a single rigid shell, so contraction-driven faulting is spread broadly across its surface rather than concentrated in specific zones.

That distribution matters because it implies moonquakes tied to fault slippage or new fault formation could happen almost anywhere on the lunar surface, not just in predictable regions.

The study also found that fault density varies by location, with areas of thicker crust showing fewer faults, suggesting these regions may be more structurally stable. The authors propose that widespread faulting didn't occur early in the moon's history because a thick, fractured early crust insulated the interior and slowed cooling, with the contraction becoming more pronounced only in more recent geologic time.

Watters said the number of young faults found was far larger than anticipated, and noted that the moon's interior likely continues to cool and contract today, meaning existing faults may keep growing and new ones may keep forming.

Written in Everything Space’s own words by our news-desk model from the sources above, and checked against them in code: every number in this report appears in its sources, and no sentence is copied from them.