One of the most challenging problems of natural science is the question of how our solar system was formed some 4,6 billion years ago. The main difficulties encountered in trying to find any definite answer to this problem are twofold. In the first place we cannot design direct experiments which could give us clues to the relative importance of the various physical processes. In fact, we are restricted to try to gather all available pieces of information we can get from the present day solar system about its origin. Secondly, we could look for an entire sample of different objects in the universe with similar properties, which again could provide us with important insights into the physical processes relevant for the formation of planetary systems.