Trace element contents of primitive meteorites; A test of solar system abundance smoothness

Abstract

Elemental abundances from Cl carbonaceous chondrite meteorites are thought to represent the average solar system (“cosmic”) composition, based on the agreement between Cl and solar photospheric abundances and on the smoothness of heavy element abundances of odd mass nuclei when plotted as a function of mass number. To test Cl elemental smoothness, we have analyzed Cl meteorites, using conventional PIXE (proton probe) techniques, where we have good sensitivity for the range of elements: Ni to Mo. Preliminary analyses indicate that elemental smoothness is only approximate, with possible deviations of 30% to perhaps even 50%. This may be due to chemical fractionation. Alternatively, explanations for nonsmooth behavior may be understandable with the aid of general ideas of n-capture nucleosynthesis. As Cl abundances are refined, it could be that the lack of elemental smoothness may provide the strongest argument for the identification of Cl with primordial solar system abundances.