Hf-182-W-182 age dating of a Al-26-poor inclusion and implications for the origin of short-lived radioisotopes in the early Solar System

作者：Holst Jesper C; Olsen Mia B; Paton Chad; Nagashima Kazuhide; Schiller Martin; Wielandt Daniel; Larsen Kirsten K; Connelly James N; Jorgensen Jes K; Krot Alexander N; Nordlund Ake; Bizzarro Martin^*

来源：Proceedings of the National Academy of Sciences of the United States of America, 2013, 110(22): 8819-8823.

DOI：10.1073/pnas.1300383110

• meteorite inclusions
• short-lived radionuclides
• Solar System formation

Refractory inclusions [calcium-aluminum-rich inclusions, (CAIs)] represent the oldest Solar System solids and provide information regarding the formation of the Sun and its protoplanetary disk. CAIs contain evidence of now extinct short-lived radioisotopes (e.g., Al-26, Ca-41, and Hf-182) synthesized in one or multiple stars and added to the protosolar molecular cloud before or during its collapse. Understanding how and when short-lived radioisotopes were added to the Solar System is necessary to assess their validity as chronometers and constrain the birthplace of the Sun. Whereas most CAIs formed with the canonical abundance of Al-26 corresponding to Al-26/(27)l of similar to 5 x 10(-5), rare CAIs with fractionation and unidentified nuclear isotope effects (FUN CAIs) record nucleosynthetic isotopic heterogeneity and Al-26/Al-27 of %26lt; 5 x 10(-6), possibly reflecting their formation before canonical CAIs. Thus, FUN CAIs may provide a unique window into the earliest Solar System, including the origin of short-lived radioisotopes. However, their chronology is unknown. Using the Hf-182-W-182 chronometer, we show that a FUN CAI recording a condensation origin from a solar gas formed coevally with canonical CAIs, but with Al-26/Al-27 of similar to 3 x 10(-6). The decoupling between Hf-182 and Al-26 requires distinct stellar origins: steady-state galactic stellar nucleosynthesis for Hf-182 and late-stage contamination of the protosolar molecular cloud by a massive star(s) for Al-26. Admixing of stellar-derived Al-26 to the protoplanetary disk occurred during the epoch of CAI formation and, therefore, the Al-26-Mg-26 systematics of CAIs cannot be used to define their formation interval. In contrast, our results support Hf-182 homogeneity and chronological significance of the Hf-182-W-182 clock.

• 出版日期2013-5-28