Why Study Craters?

An almost perfectly round crater with ejecta radiating outward and a round circle of debris in the center.
Lichtenberg B is a beautifully preserved young impact crater. Rock outcrops in the upper portion of the crater wall are due to the successive thin lava flows that filled Oceanus Procellarum more than 3 billion years ago. Crisp morphology and a highly reflective ejecta deposit make Lichtenberg B stand out from many of the nearby impact craters.
NASA/GSFC/Arizona State University

The Moon’s craters were among the first things Galileo observed upon turning his telescope on the skies, informing the world that the lunar surface was “full of hollows and protuberances, just like the surface of the Earth itself.”

Today’s scientists take a multipronged approach to studying impact craters: orbiting satellites, landers and even robotic explorers. They investigate lunar craters here on Earth through methods like examining and comparing terrestrial craters, computer modeling of impacts, and experiments with NASA’s Vertical Gun Range ― which fires projectiles at 7,000 to 15,000 miles per hour down a 14-foot tube into a dish of material meant to simulate the composition of the cosmic object it’s hitting.

Why all the effort? Because today, centuries after Galileo, we are still learning new things from studying the Moon’s craters.

An orange, tuning-fork shaped device facing a blue tank with a NASA logo on its side.
NASA's Vertical Range Gun fires projectiles to model crater impacts.
NASA Ames Research Center
Two black and white drawings of the Moon, with the right half in shadow, showing depressions and some topography.
A page featuring two of Galileo's original Moon drawings, featured in his famous missive, "The Starry Messenger," published in Venice in 1610.
World Digital Library
plain viewed from above with craters, spacecraft and foot trails visible
This image taken by the Lunar Reconnaissance Orbiter in 2010 depicts the tracks that Apollo 15 astronauts David Scott and James Irwin made 39 years previously. The Moon has no atmosphere, and thus no wind or rain to sweep the footprints away.
NASA/GSFC/Arizona State University
  • Detailed view of the Moon's surface, with sharp-edged craters and regional variations in shades of grey.
    The Moon's far side has thicker crust, is heavily cratered, and lacks the prominent maria of the near side.
    NASA/Arizona State University

    What Can We Learn From a Hole?

    The main story lunar craters tell us is about the history of the Moon’s surface. Typically, an older surface will have more craters, simply because it’s had more time to be pelted with impactors like asteroids and comets. Scientists can tally how many or how few craters are in an area to get an idea of the age of the surface, a technique called crater-counting.

    That’s not the most precise measurement, so scientists combine it with other forms of analysis, like studying Moon rocks and their chemistry, and spectroscopic data, to refine those ages.

    One of the Moon’s big mysteries is why its far side is so much more heavily cratered than its near side. Scientists are still working on that puzzle, but possibilities include the far side’s thicker crust preventing magma from emerging to fill craters; temperature differences between the young Moon’s near and far side allowing lava flows to create basins more easily on the near side; and a massive impact to the far side of the Moon in an area we now call the South Pole-Aitken Basin (SPA) that would have carried certain rare-earth and heat-producing elements to the near side of the Moon, causing increased volcanic activity there. But whatever the answer, the first sign that there was a discovery to be made was the striking presence of the myriad impact craters on the Moon’s far side.

  • A cropped, colorful topographic map of the far side of the Moon, with dark blue in the center (indicating depth), which is the location of the South Pole-Aitken basin. The rest of the image is green, yellow and red, with red indicating highest elevations. Craters are often green surrounded by yellow.
    This Lunar Orbiter Laser Altimeter (LOLA) topographic map centers on the South Pole-Aitken (SPA) basin, the largest impact basin on the Moon and one of the largest impact basins in the solar system.
    NASA/GSFC/MIT

    Excavating Answers

    When impactors carve out portions of the Moon, they can give us a glimpse of the stuff that’s below the surface. Significant impactors explode material out from beneath the Moon’s surface, exposing it for study. For example, the Japanese lunar orbiter Kaguya has detected rings of olivine at the edges of major craters where the crust is thin, possibly a result of impactors breaking through the crust and dredging up material from the mantle or lower crust and pushing it toward the rims of the craters. Olivine is a big part of Earth’s mantle, and this may be evidence that it is a significant component of the Moon’s mantle as well.

    None of the Apollo samples were definitively identified as being pieces of the Moon’s mantle, but scientists believe such rocks should be found on the surface due to impacts, and have suggested regions to find these samples during future missions. The South Pole-Aitken Basin, the largest and deepest basin on the Moon, is a particularly attractive target because the impact that created it was so tremendous that scientists expect it to have pierced through the crust and into the mantle.

  • A gif of two images. The first image shows a region of the cratered surface of the Moon. The second picture shows the same region, but a pale dot has appeared, surrounded by many faint, dark rays that stretch far away from it.
    This duo of images show the birth of a new crater on the Moon. An impactor created a 39-foot-wide crater with rays of ejecta radiating away from it.
    NASA/GSFC/Arizona State University

    Look Out Above ― And Below

    The study of lunar craters tells us much about problems astronauts may encounter when human beings return to the Moon. Scientists analyzing before and after pictures taken by NASA’s Lunar Reconnaissance Orbiter found new craters forming on the Moon at a rate 33 percent higher than expected. This means that any equipment placed on the Moon for a long time ― like a lunar base ― would have to be able to withstand damage caused when nearby impacts spray debris that can move as fast as 1,600 feet per second (500 meters per second).

    These images from the Lunar Reconnaissance Orbiter show the birth of a new crater. The before and after pictures capture a 39-foot (12 meter) wide crater and its rays of ejecta appearing on the surface of the Moon.

Writer: Tracy Vogel; Science Advisors: Daniel P. Moriarty (University of Maryland at College Park), Natalie M. Curran (NASA's Goddard Space Flight Center)

Get The Basics

All About Lunar Craters

Craters are the mark the passing universe leaves on the Moon, a cosmic guestbook. They tell us the history not only of the Moon, but of our solar system.

Learn More
Aristarchus crater has slumping terraced walls and peaks in its center. The terrain looks rubble-covered and pitted.
This view of Aristarchus crater from the Lunar Reconnaissance Orbiter shows clearly terraced walls and central peaks.
NASA/GSFC/Arizona State University

Explore Further

Expand your knowledge about lunar craters.

Craters riddle the moons North Pole with the largest creating large dark grey pits. The darkest colors are at the poles, since there is less sunlight that illuminates it. The further you move out from the poles to the edge of the captured image, the lighter it becomes.

Why Study Craters

Lunar craters are about more than just the Moon.

Read More
An illustration of meteorites bombarding a landscape. The ground is bare rock, molten in places and smoking. Pools of molten rock and fires dot the terrain. Three meteorites streak through a cloudy, smoky sky.

What is the Late Heavy Bombardment?

Lunar craters give scientists a peek into our solar system’s asteroid-pummeled past.

Read More
The far side of the Moon is colored in blues, purples, greens, yellows and reds. Blue and purple, indicating lower elevations, are centered in a rough oval in the middle of the far side. This is the location of the South Pole-Aitken Basin. Craters are blue surrounded by green, yellow is scattered around the image, and red is mostly located in the upper area of the Moon. A dotted circle roughly in the center of the South Pole-Aitken Basin shows the location of the mysterious mass.

What is the South Pole-Aitken Basin?

The Moon's largest basin holds many secrets.

Read More
A photo of the Moon's Orientale impact basin. It is colored in to show free-air gravity differentiations. There are yellow areas (average gravity), green and blue areas (below average) and red areas (above average).

The Explosive History of Orientale Basin

The Moon’s Orientale basin demonstrates the violence of a tremendous lunar impact.

Read More