Look up at a full moon and those dark patches you see? They’re not shadows—they’re the scars of billions of asteroid and comet collisions stretching back more than four billion years. The moon’s surface is a frozen record of violence that Earth has long since erased.
The short answer
The moon has craters because it’s been pummeled by asteroids, meteorites, and comets for over four billion years, and it lacks the atmosphere and geological activity to erase them. Every impact—no matter how small—leaves a permanent mark.
What creates lunar impact craters
When a space rock traveling at roughly 20 kilometers per second slams into the moon, it doesn’t just dig a hole. The impact releases energy equivalent to millions of tons of TNT, vaporizing rock and blasting debris outward in a fraction of a second. A 100-meter asteroid carves out a crater roughly two kilometers across in under a minute. The explosion creates a bowl-shaped depression, throws up a rim of pulverized rock, and scatters ejecta across hundreds of kilometers.
According to NASA’s Lunar Reconnaissance Orbiter data, the moon has approximately 1.3 million craters larger than 10 kilometers in diameter. Zoom in and the count climbs into the hundreds of millions. These are overwhelmingly impact craters—roughly 95% of visible lunar craters formed from collisions, not volcanic activity.
The moon doesn’t discriminate. Without an atmosphere to burn up incoming objects, every meteoroid—whether the size of a grain of sand or a mountain—reaches the surface at full velocity. On Earth, our thick atmosphere incinerates about 99% of small meteoroids before they hit the ground. The moon gets no such protection.
The heavy bombardment: when most craters formed
Here’s what most explanations skip: the moon wasn’t cratered gradually over time. The vast majority of its craters formed during a concentrated period called the Late Heavy Bombardment, roughly 3.8 to 4.1 billion years ago.
During this cosmic shooting gallery, the inner solar system was swept by a storm of asteroids and comets, possibly triggered by the migration of Jupiter and Saturn destabilizing the asteroid belt. The moon—and Earth, and Mars, and Mercury—absorbed an onslaught of impacts that dwarfs anything we see today. Radiometric dating of Apollo lunar samples confirms that ancient rock fragments from this era show widespread evidence of impact-shocked minerals.
After approximately 3.8 billion years ago, the bombardment rate dropped by more than 1,000-fold. The craters you see today are mostly relics of that ancient barrage, frozen in place because the moon lacks the mechanisms to erase them.
The largest scar from this era is the South Pole–Aitken Basin—a staggering 2,500-kilometer-wide impact crater nearly 13 kilometers deep, dated to roughly 4.1 billion years ago. It’s one of the biggest impact structures in the solar system, and it’s still clearly visible because nothing has worn it away.
Why Earth has fewer craters
Earth is hit just as often as the moon—probably more often, since our stronger gravity pulls in more debris. So why doesn’t Earth look like the moon?
The common answer is “Earth has an atmosphere,” and that’s partly true. Our atmosphere does burn up smaller meteoroids before they hit the ground. But atmospheric protection is a minor character in this story. The real crater erasers are plate tectonics and erosion.
Earth’s crust is in constant motion. Tectonic plates drift, collide, and slide beneath one another, resurfacing the planet on timescales of 200 to 300 million years. A crater that formed 500 million years ago has likely been swallowed by a subduction zone, crumpled into a mountain range, or buried under kilometers of sediment. Earth has roughly 190 confirmed impact craters larger than 100 kilometers in diameter, compared to more than 9,000 on the moon.
Add to that rain, wind, rivers, glaciers, and chemical weathering—forces that sculpt Earth’s surface relentlessly. Even a massive impact crater will be eroded beyond recognition in a few million years. The oldest preserved impact crater on Earth is the Vredefort Dome in South Africa, dated to approximately two billion years ago. On the moon, craters more than three billion years old are everywhere.
The moon, by contrast, is geologically dead. No plate tectonics, no water, no wind. The surface you see today looks almost identical to how it appeared a billion years ago. Craters degrade slowly through micrometeorite bombardment and thermal stress, but the process is glacial. A crater can remain sharp-edged for eons.
Craters old and new
Not all lunar impact craters are ancient relics. The moon’s crater population spans an enormous age range, from the primordial basins formed over four billion years ago to fresh impacts detected within the last decade.
Tycho Crater, one of the most prominent features visible from Earth, formed approximately 108 million years ago—practically yesterday in geological terms. You can still see bright rays of ejected material radiating from Tycho across hundreds of kilometers, because nothing has erased them. On Earth, a crater that age would have vanished entirely.
And impacts are still happening. The Lunar Reconnaissance Orbiter has identified hundreds of new craters larger than 10 meters that formed since 2009, proving the moon is still being hit, just at a vastly reduced rate compared to the heavy bombardment era.
The moon as time capsule
The moon’s craters aren’t just scars—they’re a geological archive. Because the surface isn’t constantly recycled like Earth’s, lunar craters preserve a record of the solar system’s early chaos. By dating craters and measuring their density, scientists can reconstruct the bombardment history of the inner planets and test models of planetary formation.
Earth experienced the same pummeling, but the evidence has been scrubbed away. The moon, locked in its airless, tectonically inactive state, kept the receipts.
FAQ
Are lunar craters still forming?
Yes, but at a much slower rate than in the ancient past. Modern impacts create small craters detectable by satellite imaging, but the heavy bombardment that shaped the moon’s appearance ended roughly 3.8 billion years ago. Current impact rates are a tiny fraction of what they once were.
Can we see meteors hitting the moon from Earth?
Not the craters themselves—they form too quickly and are too small to observe directly with telescopes. However, specialized instruments have detected brief thermal flashes from lunar impacts since 2005, caused by the explosive release of energy when an object strikes the surface.
How long does it take a crater to form?
Seconds to minutes, depending on the size and velocity of the impactor. A 100-meter asteroid traveling at typical speeds creates a two-kilometer crater in less than a minute. The ejecta settles over the following minutes to hours, but the crater itself is carved almost instantaneously.
Why doesn’t the moon have valleys and mountains like Earth?
It does—but lunar topography is shaped by impacts and ancient volcanic activity, not by erosion or plate tectonics. The moon’s “mountains” are often the raised rims of massive impact basins, and its “valleys” are rilles carved by lava flows billions of years ago.
The next time you look up at the moon, you’re seeing a surface that hasn’t changed much in billions of years—a cosmic museum of impacts that Earth experienced and forgot.
Written for general interest and accuracy-checked, but not a substitute for specialist sources.