The Moon Is Shrinking and Scientists Clocked the Speed

The moon is shrinking, and scientists have finally measured how fast. A study published on Oct. 14, 2026, maps more than ten thousand young thrust faults across the lunar surface and estimates that the moon's radius has contracted by about forty-five meters over the past four hundred to eight hundred million years, according to the Smithsonian Institution. It is the most detailed accounting yet of a slow-motion squeeze driven by the gradual cooling of the lunar interior, and it confirms the Moon Is Shrinking on a schedule researchers can now describe with real numbers.

The research was led by Thomas R. Watters, scientist emeritus at the Smithsonian's Center for Earth and Planetary Studies, working with colleagues at the National Air and Space Museum. Using imagery from the Lunar Reconnaissance Orbiter Camera, the team catalogued thousands of contractional landforms known as lobate scarps and small mare ridges across both the bright lunar highlands and the dark volcanic plains. The survey drew on seventeen years of orbiter images, giving the authors the most complete global picture of recent lunar tectonics ever assembled. "The number of these young faults revealed in LROC images is much greater than I ever imagined," Watters said in a statement, adding that existing faults are expected to keep growing and new ones to keep forming as the interior continues to cool. His reaction was reported by Popular Science alongside the study's release.

Breaking the total down, the map holds roughly eight thousand nine hundred curved, cliff-like scarps plus more than two thousand smaller ridges threading the dark maria. If the contraction has proceeded at a steady pace, the numbers imply the moon has been losing about six to eleven centimeters of radius per million years. Expressed on a human timescale, that is roughly a tenth of a micrometer each year, a movement far too small for any instrument on the surface to notice day to day. By comparison, the plates of Earth creep along at around one and a half centimeters a year, about the rate fingernails grow, driven by heat escaping from our planet's interior. The Moon Is Shrinking far more slowly, yet the cumulative effect over geologic time is written across its entire face.

A single eggshell, cracking everywhere

The reason the shrinking matters has less to do with the moon getting smaller and more to do with where it breaks. Earth spreads most of its tectonic violence along the boundaries between more than fifteen moving plates; about ninety percent of all seismic activity on our planet happens near those edges. The moon has no such system. It behaves as one rigid shell, so the stress of a cooling, contracting interior has nowhere to concentrate and instead fractures the crust almost everywhere. A moonquake tied to a slipping fault or a brand-new break could therefore strike with little warning in regions no one would have flagged as dangerous.

The study also offers a clue about why the contraction seems to be a late-stage story rather than an ancient one. The authors propose that a thick, heavily fractured early crust acted as an insulating blanket, trapping heat inside and holding off serious cooling for a long stretch of lunar history. Only as that heat finally began leaking away did the crust start buckling in earnest. The map supports the idea: regions with thicker crust show noticeably fewer faults, which suggests those areas may be structurally steadier ground. For engineers sketching the first permanent habitats, that pattern could eventually help separate the safest building sites from the shakiest, a question explored in depth by Phys.org's coverage of the fault survey.

What it means for the bases we keep planning

None of this changes the view from your backyard. The moon will look exactly the same tonight as it did last year, and the difference over a human lifetime is effectively zero. But the timing of the finding lands right as crewed lunar plans are accelerating, with the first hardware for a permanent moon base potentially touching down as soon as this December. Knowing that shallow moonquakes can originate almost anywhere, rather than clustering along predictable seams, gives mission planners a new variable to design around, from where to anchor habitats to how to route power and communications lines.

There are still open questions, and the authors are upfront about them. The shrinkage rate assumes the contraction has been roughly constant across the whole period, while the real cooling history of the interior may have sped up or slowed down along the way. Fault counts also depend on what the camera can resolve, so future, sharper surveys could push the tally higher still. Continued observation should tighten the estimates, and the orbiter camera that made this census possible is still collecting images. The deeper point is that our nearest neighbor is not the dead, static rock of old textbook diagrams. Between this slow tectonic breathing and the recent discovery of two asteroids slipping inside the moon's orbit, the lunar neighborhood keeps proving more dynamic than it looks. The moon you see tonight is a touch smaller than the one the dinosaurs saw, and scientists finally know the pace at which it got there.