7. Relationship Between Meteorites, Asteroids and Comets

Abstract

There seem to be no objection any more to regard the asteroid belt as the past and present source of initial and intermediate parent-bodies of meteorites. Initial parent bodies were of the size of the present-day largest asteroids; the irregular size of medium sized asteroids suggests intermediate parent bodies fragmented by collisions. Finally, most of the terminal parent bodies can be identified with Earth-crossing or grazing objects. In contrast, icy planetesimals of the outer zone of the primeval nebula underwent almost no thermal evolution, but only a complicated orbital evolution leading to the comets observed now. This does not exclude the possibility that some extinct comets end up on asteroid-type orbits, although their nuclei might still contain ices covered by an insulating crust that can preserve them for a very long time. These could be the parent bodies of bolides, as opposed to meteorites.