What if an asteroid struck the Moon?

Look at the Moon. Can you see the dark and light patches? Up close, it has lots of round holes called craters.

Space rocks made them. What happens when a new rock lands?

Through binoculars or a telescope, the Moon is covered in craters, from tiny pits to huge bowls. NASA says the Moon's surface is cratered and pitted by impacts from asteroids, meteorites and comets.

So what actually happens when a space rock hits the Moon? And could it change the Moon itself? This is a thought experiment built on real observations: scientists have watched rocks hit the Moon and found the new craters they made. Choose a path and explore.

The Moon's craters preserve billions of years of impact history for the inner solar system, NASA notes: with no liquid water or wind and relatively little erosion, the Moon keeps them well preserved. Impacts still happen: meteoroids strike it every day.

This thought experiment follows a single impact, from the flash of light to the new crater, the material thrown out, and what observers on Earth would see. Facts here come from impact monitoring, orbital imaging and meteorite studies; anything beyond them is labeled an idea.

The Moon has almost no air. So space rocks do not slow down or burn up before they land.

They make craters. The craters stay for a very long time.

The Moon has only a very thin layer of gas around it, far too thin to slow down rocks from space. So meteoroids, small rocky pieces, reach the surface every day, traveling at 12 to 40 kilometers per second.

There is no rain or wind on the Moon to wear craters away, so they can last for billions of years. Tycho Crater, for example, is more than 85 kilometers wide. Over billions of years, impacts have ground the surface into a gray, powdery dust.

The Moon's exosphere is too sparse to impede impacts, so a steady rain of asteroids, meteoroids and comets reaches the surface (NASA). Washington University's meteorite site gives typical meteoroid speeds of 12–40 km/s.

Over billions of years these impacts have pulverized the surface into regolith, a rubble pile of powdery dust and rocky debris above fractured bedrock. The dark maria are impact basins later filled with lava between 4.2 and 1.2 billion years ago.

A space rock hits the Moon. There is a quick flash of light!

Then there is a brand-new crater. Bits of Moon dust and rock fly up.

On March 17, 2013, a NASA telescope recorded the brightest flash it had ever seen on the Moon. Later, NASA's Lunar Reconnaissance Orbiter photographed the spot and compared pictures from before and after. A brand-new crater, about 18 meters across, had appeared.

When a rock hits the Moon, it throws out dust and rock. Any piece thrown fast enough escapes the Moon's gravity. Some of those pieces have traveled all the way to Earth.

NASA's Lunar Impact Monitoring Program at Marshall Space Flight Center has recorded over 300 flashes since 2005, assumed to be meteoroid impacts. The brightest, on 17 March 2013, was followed up by LRO's Narrow Angle Camera, and comparing before-and-after images revealed a new crater 18 m across. Hundreds of other surface changes appear in such image pairs.

Impact ejecta launched faster than the Moon's average escape velocity of 2.38 km/s leave its gravity; most of that material is captured into orbit around Earth or the Sun.

The Moon has no wind and no rivers or rain.

So its craters stay for a very, very long time. They show where space rocks landed long ago.

On the Moon, craters are kept for billions of years, so its surface is like a history book of space rocks. NASA explains that, with no liquid water or wind, the Moon has kept a record of space-rock impacts for billions of years, a record of how our whole solar system was built and shaped.

Every new crater adds a page. Scientists watch for new impacts by looking for flashes and by comparing spacecraft pictures taken before and after.

Because lunar craters are preserved for billions of years, NASA notes, they provide an impact history for the Moon and other bodies in the inner solar system; NASA attributes their preservation to the relative lack of erosion and other surface processes.

Tracking present-day impacts, through flash monitoring and before-and-after orbital imaging, connects that ancient record to the rate of impacts happening now. The LROC team describes systematically searching its growing set of image pairs for such changes.

Scientists watch the Moon with telescopes. Sometimes they see a tiny flash where a rock lands.

Pieces of the Moon have even landed on Earth. Scientists keep them in collections.

From Earth, scientists watch the Moon with telescopes for the flashes made by impacts, and spacecraft later find the new craters.

Pieces of the Moon have also reached Earth by themselves. Rocks knocked off the Moon by impacts have landed here as lunar meteorites, often found in Antarctica and in deserts. By 2024, scientists had classified nearly 150 separate groups of them. Their total mass is more than all the Moon rock the Apollo astronauts brought back.

Lunar meteorites are rocks ejected from the Moon by impacts of asteroidal meteoroids or possibly comets; those captured into Earth orbit fall to Earth over years to tens of thousands of years (Washington University in St. Louis). NASA's Lunar Meteorite Compendium counted nearly 150 classified groups by January 2024, totaling more than 417 kg, against about 382 kg returned by Apollo.

NASA also follows asteroids that pass near the Moon. In June 2025 it estimated a 4.3% chance that asteroid 2024 YR4 would hit the Moon on 22 December 2032, adding that such an impact would not alter the Moon's orbit. Webb observations in February 2026 then sharpened the orbit, and on 5 March 2026 NASA ruled out a lunar impact: the asteroid should pass about 21,200 km from the lunar surface. NASA concluded it poses no significant impact risk to Earth either.