Scientists have completed the first global map of small tectonic ridges scattered across the Moon's surface, revealing fresh evidence that the Moon is still slowly shrinking — and potentially generating new moonquakes.
The research, published in The Planetary Science Journal, was led by scientists from the National Air and Space Museum's Center for Earth and Planetary Studies and their collaborators. The team conducted the first comprehensive study of small mare ridges (SMRs) — subtle surface features found across the Moon's dark plains, known as maria — and determined that many of them are relatively young in geological terms.
Their findings suggest that the Moon remains tectonically active, though in a very different way from Earth.
Unlike Earth, which has shifting tectonic plates that collide, separate and slide past one another, the Moon consists of a single outer shell. As its interior cools over time, the surface contracts, creating compressional stress. That stress produces distinctive landforms when sections of crust are pushed over one another along faults.
For years, scientists have known about lobate scarps — ridges commonly found in the lunar highlands that formed as the Moon contracted. In 2010, earlier research confirmed that the Moon is gradually shrinking as it cools, with these scarps serving as visible evidence of that process.
However, lobate scarps did not fully account for all the Moon's recent contraction features. Small mare ridges, found exclusively in the maria, emerged as another crucial piece of the puzzle.
"Since the Apollo era, we've known about the prevalence of lobate scarps throughout the lunar highlands, but this is the first time scientists have documented the widespread prevalence of similar features throughout the lunar mare," said Cole Nypaver, post-doctoral research geologist at the Center for Earth and Planetary Studies and the study's first author.
"This work helps us gain a globally complete perspective on recent lunar tectonism on the moon, which will lead to a greater understanding of its interior and its thermal and seismic history, and the potential for future moonquakes."
The research team created the first detailed global catalog of SMRs, identifying 1,114 previously unrecognised ridge segments across the near side lunar maria. This raises the total known number of small mare ridges to 2,634.
Their analysis shows that the average SMR is about 124 million years old — closely matching the estimated 105-million-year average age of lobate scarps. These similar ages indicate that both types of features are among the youngest geological formations on the Moon, representing relatively recent tectonic activity.
In some regions, researchers observed highland lobate scarps transitioning directly into small mare ridges within the maria, reinforcing the conclusion that both landforms share a common origin driven by the same compressional forces.
"Our detection of young, small ridges in the maria, and our discovery of their cause, completes a global picture of a dynamic, contracting moon," said senior scientist emeritus Tom Watters.
The implications extend beyond mapping surface features. Previous studies have linked the tectonic forces behind lobate scarps to recorded moonquakes. Because SMRs form through the same faulting processes, the newly mapped ridges could mark additional sources of seismic activity.
Identifying these potential quake zones could help scientists better understand the Moon's interior structure and tectonic evolution. It also has practical importance as space agencies prepare for renewed human exploration.
"We are in a very exciting time for lunar science and exploration," Nypaver said. "Upcoming lunar exploration programs, such as Artemis, will provide a wealth of new information about our moon. A better understanding of lunar tectonics and seismic activity will directly benefit the safety and scientific success of those and future missions."
As interest in returning astronauts to the Moon grows, the new findings serve as a reminder that Earth's nearest neighbour is not as geologically quiet as once thought — and that its surface still bears the marks of a world slowly cooling and contracting.
