Image: D.Davis (NASA/NSSDC)

What is an Impact?

An impact is a forceful striking of one body called the impactor (for example a NEO), against another body, called target body (such as a moon or planet).
 

Characteristics of the impactor
How dangerous is an impact depends first of all on some of the impactor's characteristics, such as its mass, its speed, the inclination angle it enters the atmosphere at, or its chemical composition. In fact, all these characteristics are important to evaluate the energy of the impact.


Different types of impacts

Most of the objects that fall on Earth are not bigger than a meter and are therefore destroyed before they reach the ground. The atmosphere of the target body acts as a real shield, burning out small debris, before they reach the ground. From this point of view, the case of meteors deserves some special attention.

Photo: U.S. Geological Survey
When the impactor survives the atmosphere, it can reach the ground with some very evident consequences, such as the formation of impact craters.

Besides the formation of a crater, the worst danger from a NEO impact, comes from the destructive after effects that can range from earthquakes to fires. Climatic after effects due to the enormous amount of dust (or water) released in the atmosphere, are also very dangerous. If the impact happens to be in the oceans, another physical consequence that needs to be examined is the formation of tsunami.


A scientific classification of impacts

Depending on the dimension of the NEO and on some other physical factors (such as the speed of the impactor or whether the target body has an atmosphere) impacts can have very different characteristics. All kinds of impacts take place in a scientific classification called the Torino scale.