Found confirmation of the rapid formation of large asteroids in the solar system

Modern concepts of the formation of the solar system include two competing hypotheses about the mechanisms of the occurrence of asteroids-planetesimals, which eventually became embryos of future planets.
According to one of the hypotheses, the future asteroids for quite some time were small accumulations of matter. Their merging and the formation of large celestial bodies, a meter and kilometer in size, required considerable time – about hundreds of millions of years or more. As a result, now in the asteroid belt between Mars and Jupiter (the main belt), we can observe a picture close to that which was during the initial formation of asteroids.
According to another version, it happened much faster. The disorganized substance under the action of gravity gathered immediately into objects measuring tens and hundreds of kilometers. What we see now is the result of their subsequent collisions with each other, when most of the original planetoids collapsed with the formation of many small fragments.
A group of astronomers, led by Kevin Walsh of the Southwest Research Institute in Boulder, Colorado, USA, decided to look into this issue in more detail.
The study was subjected to asteroids located at a distance of 2.1-2.5 astronomical units from the Sun. Now the parameters of the orbit of all the registered asteroids of the main belt are known, and the chemical composition of most of them. On the basis of these data, asteroids are united into families – groups of fragments of larger celestial bodies formed once in their collisions with each other, or, alternatively, groups of small fragments and a large asteroid from which they were once knocked out. Several dozens of such families are known.

Diagram of the distribution of asteroids depending on the inclination of the orbit and eccentricity. The cluster of points visible in the diagram is a family of asteroids. / © Wikipedia
Walsh and his colleagues managed to open another asteroid family, which arose in a collision about 4 billion years ago. This in itself is a valuable scientific result.
But the key point of the work is the allocation of the total mass of those asteroids, which neither in its composition nor in the parameters of the orbit can be attributed to any known family. This means that they can not be debris of larger bodies.
Such asteroids were found, and it turned out that their size is at least 35 kilometers. Approximately estimating the mass, “knocked out” of them during the existence of the solar system, the authors came to the conclusion that once these asteroids measured at least hundreds of kilometers.
This result is a serious argument in favor of the hypothesis of rapid formation (and subsequent destruction) of large asteroids. It is likely, however, that the discussion on this will not end.