How Craters Are Formed
When solar system objects (meteoroids, comets, or asteroids) crash into planets, the energy of the impact creates a hole: a crater.
All of the bodies in the solar system have been bombarded throughout time, including Earth. When passing through Earth’s atmosphere, a fast-moving meteoroid compresses the air in front of it, heating up both the air and the meteoroid. This heat vaporizes small impactors before they reach the surface.
Larger meteoroids reach the Earth’s surface and can produce craters. The record of larger impact events has been altered or erased as a result of tectonic activity, erosion, and volcanism, which change the Earth geologically. But the solid surfaces of other planetary bodies retain an impact record, sometimes spanning more than 4 billion years!
The “Hole” Story
Crater formation goes through several stages before the final crater is made. When the excavation process is complete, the resulting craters are categorized as simple or complex.Simple craters are bowl-shaped, while complex craters may exhibit other characteristics, including a central peak, rings, or terraces.
The 68-km-diameter crater Calvino, on Mercury. Taken by the MESSENGER spacecraft in November of 2011. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington. More info