The original environment of the solar system can be inferred by studying the oxygen isotope ratios in the Sun as well as in primitive meteorites and comets. The oxygen isotopic fractionation measured in primitive meteorites is mass-independent, which can be explained by the isotopic-selective photodissociation of CO. The isotopic-selective photodissociation model in a collapsing cloud by Lee et al. (2007) imply the birth of the Sun in a stellar cluster with an enhanced radiation field, which is consistent with the inferred presence of 60Fe.

• JEONG-EUN LEE(Department of Astronomy and Space Science, Sejong University) Corresponding Author
• EDWIN A. BERGIN(Department of Astronomy, The University of Michigan)
• JAMES R. LYONS(Institute of Geophysics and Planetary Physics, Department of Earth and Space Sciences, University of California)