Impact crater
Depression formed by hypervelocity impact of a smaller object.
An impact crater is a depression in the surface of a solid astronomical body formed by the hypervelocity impact of a smaller object. Impact craters are the dominant geographic features on many solid Solar System objects including the Moon, Mercury, Callisto, Ganymede, and most small moons and asteroids. They range in size from microscopic craters to vast, complex, multi-ringed impact basins, and are typically circular, though they can be elliptical or irregular due to events such as landslides.
- type
- Geological feature
- formation_cause
- Hypervelocity impact of a smaller object
- common_locations
- Moon, Mercury, Callisto, Ganymede, Earth, and other solid Solar System bodies
- size_range
- Microscopic to about 300 km in diameter on Earth
- known_example
- Meteor Crater on Earth
Lore & Background
Daniel M. In the 1920s, Walter H. Bucher studied several sites now recognized as impact craters in the United States, concluding they were created by some great explosive event, but believed the force was probably volcanic. Boon and Claude C. Albritton Jr. revisited Bucher's studies and concluded the craters were probably formed by impacts.
Reader's Guide
Impact craters are significant because they record the history of collisions in the Solar System, including a period of intense early bombardment around 3.9 billion years ago. The study of impact craters advanced through the work of researchers like Gene Shoemaker, who in 1960, with Edward C. T. Chao, identified coesite at Meteor Crater, proving the crater was formed from an impact generating extremely high temperatures and pressures. This discovery, along with the recognition of shock-metamorphic features, led to a methodical search for impact craters, and by 1970 more than 50 had been tentatively identified. The Apollo Moon landings provided supportive evidence by recognizing the rate of impact cratering on the Moon, making it clear that Earth had suffered far more impacts than could be seen by counting evident craters.
Did You Know?
- Impact craters are typically circular because they are caused by explosions; only very low-angle impacts cause significantly elliptical craters.
- The median impact velocity on Earth is about 20 km/s, with the fastest impacts occurring at about 72 km/s.
- Earth experiences, on average, from one to three impacts large enough to produce a 20-kilometre-diameter crater every million years.
- The Baptistina family of asteroids was once thought to have caused a large spike in the impact rate in the inner Solar System, but this hypothesis has been discredited by subsequent studies.
Frequently Asked Questions
What is an impact crater?
An impact crater is a bowl-shaped depression carved into the surface of a solid body in space when a smaller object slams into it at hypervelocity. Think of it as the geological scar left behind after a cosmic collision.
Where do you find the most impact craters?
They dominate the surfaces of the Moon, Mercury, Callisto, Ganymede, and most small moons and asteroids throughout the Solar System. Earth also has them, though erosion and plate tectonics erase many over time.
How large can an impact crater get?
They span an enormous range, from tiny microscopic pits to vast multi-ringed basins roughly 300 kilometers across on Earth. The scale depends on the size, speed, and angle of the impacting body.
What exactly causes an impact crater to form?
A smaller object—such as a meteorite, comet fragment, or asteroid—strikes a solid surface at hypervelocity, releasing enough energy to excavate a depression and fling material outward. The resulting shape is usually circular, though landslides or oblique angles can make it elliptical or irregular.
What's a well-known impact crater on Earth?
Meteor Crater in Arizona is one of the best-preserved and most studied impact structures on our planet. It gives the public a tangible, visible sense of what these ancient collisions look like.
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