Timing Solar System formation The oldest solids that formed in the Solar System are calcium-aluminium–rich inclusions (CAIs), small metallic droplets that were later incorporated into meteorites. The ages of CAIs are conventionally taken as the age of the Solar System, but which exact moment in star formation they correspond to has been unclear. Brennecka et al. measured molybdenum isotope ratios in CAIs and found a wide range of origins in both the inner and outer Solar System. They propose that CAIs formed from heterogeneous material accreting from the presolar nebula and that the ages of CAIs coincide with the Sun's transition from a protostar to a pre–main sequence star. Science, this issue p. 837 Molybdenum isotopes in calcium-aluminum–rich inclusions constrain the early history of the Solar System. Calcium-aluminum–rich inclusions (CAIs) in meteorites are the first solids to have formed in the Solar System, defining the epoch of its birth on an absolute time scale. This provides a link between astronomical observations of star formation and cosmochemical studies of Solar System formation. We show that the distinct molybdenum isotopic compositions of CAIs cover almost the entire compositional range of material that formed in the protoplanetary disk. We propose that CAIs formed while the Sun was in transition from the protostellar to pre–main sequence (T Tauri) phase of star formation, placing Solar System formation within an astronomical context. Our results imply that the bulk of the material that formed the Sun and Solar System accreted within the CAI-forming epoch, which lasted less than 200,000 years.

中文翻译：

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陨石包裹体中钼同位素形成太阳系的天文背景

太阳系形成时间 太阳系中形成的最古老的固体是富含钙铝的内含物 (CAI)，这是后来融入陨石的小金属滴。CAI 的年龄通常被认为是太阳系的年龄，但它们对应的恒星形成的确切时刻一直不清楚。布伦内卡等人。测量了 CAI 中的钼同位素比率，并在内部和外部太阳系中发现了广泛的起源。他们提出，CAI 是由从太阳前星云中吸积的异质物质形成的，并且 CAI 的年龄与太阳从原恒星到主序前恒星的转变相吻合。科学，这个问题 p。837 富含钙铝包裹体中的钼同位素限制了太阳系的早期历史。陨石中富含钙铝的包裹体 (CAI) 是太阳系中最早形成的固体，在绝对时间尺度上定义了其诞生的时代。这提供了恒星形成的天文观测和太阳系形成的宇宙化学研究之间的联系。我们表明，CAI 的不同钼同位素组成几乎涵盖了原行星盘中形成的材料的整个组成范围。我们提出 CAI 是在太阳从原恒星过渡到恒星形成的前主序 (T Tauri) 阶段时形成的，将太阳系的形成置于天文背景中。我们的结果表明，形成太阳和太阳系的大部分物质是在 CAI 形成时期内吸积的，该时期持续了不到 20 万年。