1 Origin and Evolution of Oxygen Isotopic Compositions of the Solar System

On a three-isotope diagram oxygen isotopic compositions of most primitive meteorites (chondrites), chondritic components (chondrules, refractory inclusions, and matrix), and differentiated meteorites from asteroids and Mars deviate from the line along which nearly all terrestrial samples plot. Three alternative mechanisms have been proposed to explain this oxygen isotope anomaly: nucleosynthetic effects, chemical mass-independent fractionation effects, and photochemical self-shielding effects. Presently, the latter two are the most likely candidates for production of the isotopic anomalies. Recent data on solar wind oxygen isotopes lends support to the photochemical self-shielding scenario, but additional solar isotope data are needed. Observations, experiments and modeling are described that will advance our understanding of the complex history of oxygen in the solar system. 1