182Hf-182W age dating of a 26Al-poor inclusion and implications for the origin of short-lived radioisotopes in the early Solar System
182Hf-182W age dating of a 26Al-poor inclusion and implications for the origin of short-lived radioisotopes in the early Solar System
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DOI：
10.1073/pnas.1300383110
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发表时间：
2013-05-28
影响因子：
11.1
通讯作者：
Bizzarro, Martin
中科院分区：
文献类型：
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作者：
Holst, Jesper C.;Olsen, Mia B.;Bizzarro, Martin
难熔包裹体[富钙铝包裹体，CAIS]是太阳系最古老的固体物质，提供了有关太阳及其原行星盘形成的信息。CAI包含现已灭绝的短寿命放射性同位素(如Al-26、Ca-41和Hf-182)的证据，这些放射性同位素是在一颗或多颗恒星中合成的，并在原太阳系分子云坍塌之前或期间被添加到原太阳系分子云中。了解短暂的放射性同位素是如何以及何时被添加到太阳系中，对于评估它们作为计时器的有效性和限制太阳的诞生地是必要的。而大多数CAI的典型丰度对应于Al-26/(27)L的5×10(-5)，具有分馏和未知核同位素效应的罕见CAI记录了核合成的同位素不均一性和Al-26/Al-27的5×10(-6)，可能反映了它们在典型CAI形成之前的形成。因此，有趣的CAIS可能为了解最早的太阳系提供了一个独特的窗口，包括短寿命放射性同位素的起源。然而，他们的年表是未知的。利用HF-182-W-182天文计时器，我们发现了一个记录凝聚起源的FUN-CAI，该凝聚起源于一个与正则CaI通常形成的太阳气体，但Al-26/Al-27类似于3×10(-6)。HF-182和Al-26之间的脱钩需要不同的恒星起源：HF-182的稳态银河系恒星核合成和Al-26的后期大质量恒星(S)对原太阳系分子云的污染。原行星盘中混合了来自恒星的Al-26，是在CaI形成时期发生的，因此，不能用Al-26-Mg-26系统学来确定它们的形成间隔。相反，我们的结果支持了HF-182-W-182时钟的同质性和年代学意义。
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 < 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.