Shrinking Moon Radius Measured at 148 Feet by Scientists Mapping Ten Thousand Young Lunar Faults
The moon’s radius has decreased by approximately 148 feet (45 meters) over the past 400 to 800 million years as its interior gradually cools from a violent primordial collision roughly 4.5 billion years ago, according to a study published Oct. 14 in The Planetary Science Journal. Researchers examining millions of images captured by NASA’s Lunar Reconnaissance Orbiter Camera (LROC) have identified over 10,000 young faults distributed across the lunar landscape. The celestial body’s ongoing contraction generates active fault lines and moonquakes across an unbroken outer shell.
Unlike Earth, which features a mosaic of about 15 major lithospheric plates concentrating roughly 90% of seismic activity near boundaries, the moon operates as a single-plate body. This unbroken shell lacks tectonic plate boundaries, meaning faults and contractional landforms are scattered widely across the surface. Researchers identified long, curved structures known as lobate scarps alongside small mare ridges, which form when the moon’s surface contracts, cracks, and pushes upward.
Thick Lunar Crust Isolates Interior Warmth and Limits Widespread Cracking
Mapping these thousands of contractional features revealed distinct patterns in where tectonic activity occurs. Areas featuring the thickest lunar crust contain the fewest faults, suggesting those regions possess greater stability than thinner sections. A thick, porous, and heavily fractured crust insulated the moon’s warm interior during its earlier history. This thermal insulation prevented rapid cooling and contraction, meaning a vast majority of the widespread surface cracking developed later in lunar history.
If the rate of radius decrease remains constant, the moon continues shrinking by about 6 to 11 centimeters per million years, or roughly 0.1 micrometers annually. This contraction rate is significantly slower than Earth’s plate movement of about 1.5 centimeters per year, a pace comparable to human fingernail growth driven by terrestrial interior heat loss.
Artemis Landing Sites Sit Near Moonquake Epicenter Candidates
The discovery of thousands of active faults introduces distinct planning challenges for upcoming crewed missions. A 2024 study confirmed that thirteen proposed landing spots for the Artemis 3 (now Artemis 4) missions lie uncomfortably close to potential moonquake epicenters. Because the moon’s single-plate structure allows slips and faults to generate anywhere across the surface rather than along predictable plate boundaries, space agencies must account for seismic risks and potential landslides during lunar exploration.
The Lunar Reconnaissance Orbiter has spent the past 17 years returning millions of images of the lunar surface. Thomas Watters, a scientist emeritus in the Center for Earth and Planetary Studies at the Smithsonian’s National Air and Space Museum and lead author of the study, noted in a statement that the abundance of newly mapped landforms surpassed expectations.
“The number of these young faults revealed in LROC images is much greater than I ever imagined,” Thomas Watters said. “As the interior of the moon continues to cool and contract, it is expected that the growth of existing faults and formation of new faults continues today.”
Frequently Asked Questions About Lunar Contraction
How much is the moon shrinking each year?
Scientists estimate the moon shrinks at a rate of about 6 to 11 centimeters per million years, which breaks down to roughly 0.1 micrometers annually based on contraction data from The Planetary Science Journal.
Why does the moon have faults if it lacks tectonic plates?
The moon acts as a single-plate body with an unbroken outer shell. As its interior cools from its formation 4.5 billion years ago, the entire body contracts, creating scattered faults and lobate scarps across the surface rather than concentrating activity at plate boundaries.
How many young faults have researchers found on the moon?
A study published Oct. 14 in The Planetary Science Journal identified more than 10,000 young faults across the lunar surface, including over 8,900 lobate scarps and more than 2,000 small mare ridges mapped from LROC imagery.
Do lunar faults pose a danger to future astronaut missions?
A 2024 study found several proposed landing sites for NASA’s Artemis program sit near moonquake epicenter candidates, presenting potential risks for landslides that mission planners must evaluate.