Constraints on the birth aggregate of the solar system

Using the observed properties of our Solar System, in particular the isotop ic compositions of meteorites and the regularity of the planetary orbits, w e constrain the star formation environment of the Sun within the scenario o f (external) radioactive enrichment by a massive star. This calculation yie lds a probability distribution for the number of stars in the solar birth a ggregate. The Sun is most likely to have formed within a stellar group cont aining N = (N) approximate to 2000 +/- 1100 members. The a Priori probabili ty of a star forming in this type of environment is p approximate to 0.0085 ; i.e., only about 1 out of 120 solar systems are expected to form under si milar conditions. We discuss additional implications of this scenario, incl uding possible effects from the radiation fields provided by the putative c luster environment and dynamical disruption of the Kuiper Belt. The constra ints of this paper place tight restrictions on the properties of the solar birth aggregate for the scenario of external enrichment by a massive star; alternately, these tight constraints slightly favor a self-enrichment scena rio for the short-lived radioactive species. (C) 2001 Academic Press.