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Surface shows signs of recent tectonic activity, raising questions about future lunar missions

COLLEGE PARK, Md. — When Apollo astronauts first walked on the Moon, they stepped onto what many believed was a geologically dead world. Now, research from the Smithsonian Institution reveals that parts of the lunar surface have been moving and changing within the last few hundred million years – a finding that could significantly impact where we build future lunar bases.

For scientists, this discovery challenges decades of assumptions about lunar geology. Previously, researchers thought major geological activity on the Moon stopped billions of years ago, leaving behind only ancient evidence like the large, arching ridges visible on the Moon’s near side (the hemisphere we can see from Earth).

“Many scientists believe that most of the Moon’s geological movements happened two and a half, maybe three billion years ago,” said Jaclyn Clark, an assistant research scientist in the University of Maryland’s Department of Geology, in a statement. “But we’re seeing that these tectonic landforms have been recently active in the last billion years and may still be active today. These small mare ridges seem to have formed within the last 200 million years or so, which is relatively recent considering the Moon’s timescale.”

The research team from UMD and the Smithsonian Institution’s National Air and Space Museum discovered 266 previously unknown ridges on the far side of the Moon — the hemisphere perpetually hidden from Earth’s view. These ridges, which scientists call “small mare ridges” or SMRs, are found in the Moon’s dark patches known as maria. To understand maria, imagine ancient impact basins that were later filled with dark lava, creating the vast dark “seas” we can see on the Moon’s surface today.

Each ridge is typically about 100 meters wide (about the length of a football field) and 1,000 meters long (roughly ten football fields). While these dimensions might sound large by human standards, they’re actually quite small compared to other lunar features, which is why scientists classify them as “small” mare ridges. These ridges typically appear in groups of 10 to 40, like a series of parallel wrinkles in the lunar surface.

The research team used an ingenious method to determine the age of these ridges: they counted craters. This technique, described in The Planetary Science Journal, works because the Moon’s surface accumulates impact craters over time, much like a car collecting dents and scratches as it ages.

“Essentially, the more craters a surface has, the older it is; the surface has more time to accumulate more craters,” Clark explained. “After counting the craters around these small ridges and seeing that some of the ridges cut through existing impact craters, we believe these landforms were tectonically active in the last 160 million years.”

The team focused their investigation on three main areas: the South Pole-Aitken Basin, Bolyai Crater, and Aitken Crater. The South Pole-Aitken Basin is particularly noteworthy. It’s one of the largest known impact craters in our solar system, spanning about 2,500 kilometers (roughly the distance from Los Angeles to Chicago). Within these areas, researchers found evidence of recent geological activity that tells us the Moon isn’t as dormant as once thought.

Understanding how these ridges form requires thinking about several forces working together. Imagine the Moon as a very slowly deflating balloon. As it gradually cools over millions of years, it shrinks slightly, causing its surface to wrinkle — similar to how a grape’s skin wrinkles as it becomes a raisin. Additionally, the Moon is slowly moving away from Earth at a rate of about 3.8 centimeters per year, while also experiencing regular tugs from Earth’s gravity. These combined forces create stresses that can cause the lunar surface to buckle and form ridges.

The discovery becomes even more intriguing when connected to historical data from the Apollo missions. Those missions detected shallow moonquakes decades ago, and scientists now believe these newly discovered ridges might be connected to similar seismic activity happening today. Using sophisticated computer modeling, researchers determined that the faults creating these ridges are remarkably shallow – extending only 52-100 meters below the surface, about the height of a 15-30 story building.

“We hope that future missions to the Moon will include tools like ground penetrating radar so researchers can better understand the structures beneath the lunar surface,” Clark said. “Knowing that the Moon is still geologically dynamic has very real implications for where we’re planning to put our astronauts, equipment and infrastructure on the Moon.”

As space agencies worldwide prepare for long-term lunar presence, including NASA’s Artemis program, this research highlights the need to carefully consider geological activity when choosing sites for future lunar bases. Just as we wouldn’t build a settlement on an active fault line on Earth, we need to understand and account for the Moon’s geological activity when planning future lunar infrastructure. These small ridges, invisible to casual observation from Earth, could have outsized implications for humanity’s future on the Moon.