Mechanism of collisions

Collisions among the very numerous asteroids that inhabit the Main Belt, happen very often. The physics behind these collisions is very complicated, and the consequences depend on the conditions (in particular their relative speed or their kinetic energy) and on the physical characteristics of the bodies involved in the collision (mainly, their chemical composition).
Basically, two main phenomena can take place after a collision between asteroids: fragmentation and accretion.

When two bodies collide with a sufficiently small relative speed (smaller than 100 m/s for two asteroids of the Main Belt) they can stick together, forming a new, bigger body. This phenomena is called accretion and has been very important in the formation of the solar system (click here to know more about the accretional phases of the solar system)


Different mechanisms of fragmentation
If the collision between the two bodies happens with a higher relative speed (or if the chemical composition of the two asteroids is more fragile) the two bodies will undergo a collisional fragmentation giving birth to smaller bodies.
The destiny of the fragments produced in a collision can be very different: these new fragments can either escape toward a new life, as single asteroids, either give birth to dynamical families of asteroids. Normally, the first hypothesis is not very usual and the collisions between the asteroids of the Main Belt are not enough energetic to make these objects become NEOs.

A laboratory experiment on fragmentation: the impact between
two bodies is simulated with a contact explosive charge.
(Image courtesy of Ian Giblin, Ph.D Thesis, 1994
Click here for more information)