Heterogeneous Accretion of the Sun and the Terrestrial Planets

D. E. Ragland and O. K. Manuel,

(University of Missouri-Rolla)

It has long been suspected that the terrestrial planets accreted heterogeneously, beginning with core formation in a central, iron-rich region of the nebula. It is also commonly assumed that the Sun and meteorites, including IAB iron meteorites, formed at about the same time (4.6E9 yrs ago). In view of the tiny fraction of the solar system's cross-section that encompasses the Sun and the four inner planets, we consider the possibility of heterogeneous accretion of the Sun. We will summarize observations which indicate that the Sun and the inner planets formed heterogeneously, beginning with accretion in a central Fe-rich region. This seems to offer an attractive alternative to the standard solar model's assumption that the Sun began as a fully convective, homogeneous protostar.