The smaller bodies of the Solar System

Abstract

Two kinds of smaller bodies in the Solar System, the minor planets and the comets, are of interest from the point of view of space exploration and of our System's origin; of these the comets are, for the decade that has just begun, without any doubt by far the more important ones. One of the reasons is purely accidental: the return of comet Halley in 1985-86. Being the only case on record of a periodic comet that has remained an easy naked-eye object after some dozen returns, it provides opportunities for in situ studies also, during a fast fly-by mission, which are unlikely to occur again for many years to come. Another reason is that, according to the conviction of almost all workers in the field (cf. the last tri-annual Reports of I.A.U. Commission 15), the comets are among the most pristine objects in the Solar System and most probably closer to the original state than is any other. New insights into their origin have revived the suggestion which had been made already 6 or 7 years ago, that they did not originate in the presolar nebula (ps.n.) itself, but in a satellite nebula or in other nearby fragments of the same parent interstellar cloud, providing another way by which material of a somewhat different early history might have been added to that of the planetary system (Cameron 1973; Biermann 1979). It is my intention to develop this aspect in some more detail.