Could asteroids still be forming in the Solar System?
Originally asteroids formed in the early phases of the Solar System when the Sun was surrounded by a disc of gas and dust particles, which collided together to form larger bodies. These objects are the leftovers of the planetary building blocks that now mostly reside in the asteroid belt between Mars and Jupiter. There is no creation of asteroids by this mechanism anymore because the relative speeds between existing asteroids are too high; therefore when they collide with each other the outcome cannot be an accretion anymore, but rather a disruption.
However, collisions occurring between asteroids sometimes cause the disruption of a large asteroid. Asteroid families, which are identified groups of asteroids sharing the same orbital characteristics and composition, are evidence of such disruptions. Each family is the product of the disruption of a parent body, and family members are the fragments produced by such a disruption. In this sense asteroids are still forming as fragments of larger ones that are disrupted by a collision. In fact, based on our current understanding, most asteroids smaller than 50 kilometres (31 miles) in diameter are believed to be at least of the second generation.