Abstract
Understanding when and how our solar system formed is perhaps one of the most fundamental questions in natural sciences. The prime cosmochemical tools to achieve this goal are the remnants of the earliest stages of planet formation; meteorites and their components. Evidence for the former presence of short-lived radioactive nuclides in these ancient materials is a direct reflection of their recent nucleosynthetic origin prior to or during formation of our young solar system 4.6 Myr ago. Disentangling the origin and distribution of this nucleosynthetic heritage provides a fossil record of the dynamic birth environment of our Sun and a unique time-window into the very earliest history of our solar system.
Ever since the discovery of its decay product, 26Mg, in primitive solar system objects more than 30 years ago, the short-lived radioactive nuclide, 26Al (t1/2 = 0.73 Myr), has been the optimal and most widely used cosmochemical clock for unraveling the infant evolutionary stages of our solar system and for constraining early planetesimal melting and differentiation through 26Al heat production. The accuracy of 26Al-26Mg ages and the validity of current models for planetesimal melting and differentiation, however, relies on the critical assumption that the parent nuclide, 26Al, was uniformly distributed throughout the protoplanetary disk at the time of formation of the first solar system solids. Therefore, we have focused our research on evaluating the initial distribution of 26Al in early-formed meteoritic materials that track the temporal evolution of the solar accretion disk.
Taking advantage of novel chromatographic methods and analytical techniques, we provide unprecedented high-precision Mg isotope data for a wide-range of meteoritic materials and find the existence of small mass-independent anomalies in Mg isotopes, which we interpret as reflecting 26Al heterogeneity. These data questions the validity of using the 26Al-26Mg chronometer under the assumption of 26Al homogeneity and indicates that current 26Al-26Mg ages need re-interpretation. Our analysis shows that large differentiated planetesimals most likely accreted early in the inner solar system characterized by a reduced initial abundance of 26Al, thereby resulting in a low total heat production for planetesimal melting. Planetesimals formed at larger orbital distances from the proto-Sun plausibly accreted from precursor material with higher 26Al abundance. Moreover, our results suggest that the formation of the solar systems oldest solids was brief and recurrent, possibly associated with the earliest evolutionary stages of the proto-Sun. Finally, we propose that physico-chemical mixing and unmixing of presolar dust components inherited from the presolar molecular cloud environment resulted in exotic nucleosynthetic variability, including 26Al heterogeneity, in meteoritic materials.
Our findings are of key importance for understanding of the processes that shaped our solar system. This includes the timing and extent of melting and differentiation within the large planetesimals that eventually served as building blocks for our planetary system. As such, our interpretations require a re-evaluation of our current understanding of solar system chronology.
Ever since the discovery of its decay product, 26Mg, in primitive solar system objects more than 30 years ago, the short-lived radioactive nuclide, 26Al (t1/2 = 0.73 Myr), has been the optimal and most widely used cosmochemical clock for unraveling the infant evolutionary stages of our solar system and for constraining early planetesimal melting and differentiation through 26Al heat production. The accuracy of 26Al-26Mg ages and the validity of current models for planetesimal melting and differentiation, however, relies on the critical assumption that the parent nuclide, 26Al, was uniformly distributed throughout the protoplanetary disk at the time of formation of the first solar system solids. Therefore, we have focused our research on evaluating the initial distribution of 26Al in early-formed meteoritic materials that track the temporal evolution of the solar accretion disk.
Taking advantage of novel chromatographic methods and analytical techniques, we provide unprecedented high-precision Mg isotope data for a wide-range of meteoritic materials and find the existence of small mass-independent anomalies in Mg isotopes, which we interpret as reflecting 26Al heterogeneity. These data questions the validity of using the 26Al-26Mg chronometer under the assumption of 26Al homogeneity and indicates that current 26Al-26Mg ages need re-interpretation. Our analysis shows that large differentiated planetesimals most likely accreted early in the inner solar system characterized by a reduced initial abundance of 26Al, thereby resulting in a low total heat production for planetesimal melting. Planetesimals formed at larger orbital distances from the proto-Sun plausibly accreted from precursor material with higher 26Al abundance. Moreover, our results suggest that the formation of the solar systems oldest solids was brief and recurrent, possibly associated with the earliest evolutionary stages of the proto-Sun. Finally, we propose that physico-chemical mixing and unmixing of presolar dust components inherited from the presolar molecular cloud environment resulted in exotic nucleosynthetic variability, including 26Al heterogeneity, in meteoritic materials.
Our findings are of key importance for understanding of the processes that shaped our solar system. This includes the timing and extent of melting and differentiation within the large planetesimals that eventually served as building blocks for our planetary system. As such, our interpretations require a re-evaluation of our current understanding of solar system chronology.
| Originalsprog | Engelsk |
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| Forlag | Natural History Museum of Denmark, Faculty of Science, University of Copenhagen |
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| Antal sider | 118 |
| Status | Udgivet - 2014 |