Why are all meteorite craters round?

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This is exactly the question one of the subscribers asked me recently.

In films, especially old ones, you can often see how a meteoroid, falling to the Earth, literally plows it up, leaving behind a huge ditch, at the end of which there is an irregularly shaped crater. However, in real life, all craters found on Earth, and those that we can see on the Moon, either have a round shape or are close enough to it.

Meteoroids always fall to the Earth at a certain angle and, often quite large, a coincidence of circumstances in which a meteoroid would fall to Earth strictly vertically is practically impossible. Accordingly, the option with plowing the ground when falling, at first glance, looks realistic, because this is how a cannonball plows the ground. But why, then, are all the craters round? Why do we not see substantially elongated craters, if they should be in the absolute majority?

The fact is that the dependence of the shape of the crater on the angle of incidence of the meteoroid is a myth; in fact, the angle of incidence of a celestial body does not affect the shape of the future crater. This is due to the fact that the crater is formed not as a result of plowing and pushing the earth by a meteoroid, but as a result of a powerful explosion that occurs upon impact.

Meteoroids in outer space move at a very high speed, and, therefore, carry with them a huge amount of kinetic energy. When hitting the surface of the planet, the bolide decelerates extremely quickly, and with it a rapid explosive release of its kinetic energy. It leads to an explosion of great force, which forms a crater.

In this case, the shock wave propagates in all directions in almost the same way, and the impact creates a round indentation on the planet’s surface, the dimensions of which are much larger than the size of the falling object itself. If the surface of the soil or rocks at the place of impact has an inhomogeneous structure, then this may slightly affect the propagation of the shock wave and the shape of the crater, however, this influence is very small and is not able to radically change the shape of the crater.

Also, some craters have a rather strange shape — chains of dents overlapping each other. Such craters are formed when, due to the gravitational interaction of a planet or satellite with a cosmic body that flies by, this body collapses. After that, the debris, falling on the surface in a dense formation, form chains of craters that overlap each other, forming one large crater of a bizarre shape.

Author: Fedor Karasenko.

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