These illustrations show the asteroid belt in the present day and in the early solar system, located between the Sun (at center) and four terrestrial planets (near the Sun) and Jupiter. The top image shows the conventional model for the asteroid belt, largely composed of rocky material. The middle image shows the proposed model, with a small number of active comets and a dormant cometary population. The lower diagram shows how the asteroid belt might have looked in the early solar system, with vigorous cometary activity. // Ignacio Ferrin/University of Antioquia