For most of human history, the Moon was viewed as a silent, frozen world—a geological fossil hanging in the night sky. Earth had volcanoes, earthquakes, drifting continents, and raging storms. The Moon, by comparison, seemed finished.
That picture is changing.
Scientists now know that the Moon is not as geologically dormant as it once appeared. Deep beneath its dusty surface, a slow but relentless process is still unfolding. The lunar interior is cooling. As it cools, it contracts. And as it contracts, the Moon is literally shrinking.
The consequences are dramatic.
This shrinking process is cracking the lunar crust, creating enormous fault systems and triggering powerful moonquakes that can shake the surface with surprising intensity. Some of these seismic events are strong enough to rival moderate earthquakes on Earth, despite occurring on a world often described as “dead.” NASA-backed research suggests that these quakes may still be happening today, raising important questions for future lunar bases and the astronauts who may one day live there.
A World Slowly Getting Smaller
The Moon formed roughly 4.5 billion years ago during a violent period in the Solar System’s history. In its early years, it was far hotter than it is today.
Over billions of years, that heat gradually escaped into space.
As the interior cooled, the Moon began to contract. Scientists estimate that the lunar body has become about 150 feet (50 meters) smaller in diameter over the last several hundred million years. That may not sound like much for an object more than 2,100 miles (3,474 kilometers) across, but on a planetary scale, it is enough to reshape the crust.
NASA scientists often compare the process to a grape turning into a raisin. As the grape loses moisture, its skin wrinkles. The Moon behaves in a similar way, except its crust is rigid and brittle. Instead of forming harmless wrinkles, it breaks.
These fractures create enormous geological structures known as thrust faults, where one section of crust is pushed upward over another. The visible expression of these faults appears as cliff-like features called lobate scarps, some stretching for miles across the lunar landscape.
The Discovery Hidden in Apollo Data
One of the most remarkable aspects of this story is that the evidence was sitting in NASA archives for decades.
During the Apollo missions, astronauts deployed seismometers across the Moon’s surface. Between 1969 and 1977, these instruments recorded thousands of seismic signals, including 28 shallow moonquakes.
For years, scientists knew these quakes existed but struggled to pinpoint their origins accurately.
Then researchers revisited the Apollo data using modern computational techniques. By combining improved quake-location algorithms with high-resolution imagery from NASA’s Lunar Reconnaissance Orbiter (LRO), scientists found something extraordinary: many of the shallow moonquakes occurred suspiciously close to young thrust faults created by the Moon’s contraction.
The pattern was difficult to dismiss as coincidence.
Researchers concluded that the shrinking Moon is likely still generating tectonic activity today. In other words, some of the moonquakes recorded by Apollo astronauts may have been direct evidence of the Moon continuing to contract.
Moonquakes Are Stranger Than Earthquakes
It is tempting to imagine a moonquake as simply a smaller version of an earthquake.
It is not.
Earth’s crust contains water, complex rock layers, and tectonic plates that help absorb and dissipate seismic energy. The Moon lacks many of these features.
As a result, seismic waves can travel through the lunar interior in unusual ways.
Some moonquakes can continue reverberating for more than ten minutes, far longer than many earthquakes on Earth. NASA notes that shrinkage-related moonquakes can reach magnitudes of approximately 5.5 on the Richter scale. While that is not catastrophic by terrestrial standards, it is significant enough to pose engineering challenges on the Moon.
Imagine standing on the lunar surface during one of these events.
There would be no trees swaying, no rattling windows, and no roaring sound traveling through the air. Instead, the ground beneath your boots could continue trembling for an unexpectedly long time while dust and loose material shift across the landscape.
For future explorers, that is a serious concern.
Thousands of Giant Cracks Cover the Moon
When NASA launched the Lunar Reconnaissance Orbiter in 2009, scientists gained the ability to map the Moon in unprecedented detail.
The spacecraft revealed that lunar fault systems are far more common than previously believed.
Researchers have identified thousands of young thrust fault scarps distributed across the Moon’s surface. Some studies have cataloged more than 3,000 such features globally. These structures are among the most widespread tectonic landforms on the Moon.
Many appear geologically young.
Their crisp shapes and limited erosion suggest they formed relatively recently in lunar history. Some researchers even suspect certain faults could still be active today.
This discovery fundamentally changed how planetary scientists think about the Moon.
Rather than being a completely inactive world, the Moon appears to be experiencing slow, ongoing geological evolution.
Earth’s Gravity Is Making Things Worse
The Moon’s shrinking alone does not explain everything.
Earth is also involved.
Our planet exerts powerful tidal forces on the Moon, similar to the way the Moon generates ocean tides on Earth. These gravitational forces subtly flex and distort the lunar crust.
NASA researchers discovered that Earth’s gravitational pull influences the orientation and stress patterns of lunar faults. The effect has been described as Earth “massaging” the Moon. Over immense spans of time, these tidal stresses combine with the stresses created by lunar contraction.
The result is a more complex and active tectonic environment than scientists once expected.
In fact, researchers found that several moonquakes occurred when the Moon was near the farthest point in its orbit from Earth, where changing tidal stresses may help trigger fault movement.
Even hundreds of thousands of miles away, Earth continues to influence the Moon’s geological behavior.
Why Artemis Scientists Are Paying Attention
The discovery has become especially important as NASA prepares for a new era of lunar exploration.
The Artemis program aims to return astronauts to the Moon and eventually establish a sustained human presence there.
Many proposed landing sites are located near the lunar south pole, a region of intense scientific and strategic interest because of its potential water ice reserves.
However, recent NASA-funded studies indicate that active faults and moonquake hazards may exist within or near some candidate landing regions. Researchers have modeled scenarios in which fault movement could generate seismic shaking strong enough to destabilize slopes, trigger landslides, or affect long-term infrastructure.
A brief Apollo mission might face limited risk.
A permanent lunar habitat is a different story.
Engineers designing future bases will need to consider how structures respond to prolonged seismic vibrations, shifting regolith, and potential fault activity over years or decades.
The Moon Is Not Dead
For decades, planetary scientists classified worlds into two broad categories: active and inactive.
Earth was active.
The Moon was inactive.
The latest evidence suggests reality is far more nuanced.
The Moon no longer has giant erupting volcanoes or moving tectonic plates, but it remains a dynamic world. Its interior continues to cool. Its crust continues to deform. Faults continue to shape the landscape. And moonquakes continue to remind us that geological activity does not simply switch off when a planet or moon grows old.
In many ways, the Moon offers scientists a rare opportunity.
Because its geological processes unfold so slowly and preserve themselves so well, the lunar surface acts like a natural archive. Every cliff, fracture, and scarp records part of a story spanning billions of years.
By studying those features, researchers gain insights not only into the Moon’s evolution but also into how rocky worlds throughout the Solar System cool, contract, and change over time.
A Quiet World That Still Moves
Look at the Moon on a clear night and it appears perfectly still.
Nothing about it suggests motion.
Nothing hints at stress building beneath the surface.
Nothing reveals cliffs slowly rising, crustal blocks grinding against one another, or seismic waves rippling through ancient rock.
Yet the evidence tells a different story.
The Moon is shrinking. It has been shrinking for hundreds of millions of years, and it may continue shrinking far into the future. Every small reduction in its size adds stress to the crust, creating fractures that can unleash powerful moonquakes.
The next generation of astronauts may discover that the greatest surprise about the Moon is not how lifeless it looks—but how much geological life remains hidden beneath its silent gray surface.
