Young chondrules in CB chondrites from a giant impact in the early Solar System

Abstract

Chondrules, which are the major constituent of chondritic meteorites, are believed to have formed during brief, localized, repetitive melting of dust (probably caused by shock waves1,2) in the protoplanetary disk around the early Sun. The ages of primitive chondrules3,4,5,6 in chondritic meteorites indicate that their formation started shortly after that of the calcium-aluminium-rich inclusions (4,567.2 ± 0.7 Myr ago) and lasted for about 3 Myr, which is consistent with the dissipation timescale for protoplanetary disks around young solar-mass stars7. Here we report the 207Pb–206Pb ages of chondrules in the metal-rich CB (Bencubbin-like) carbonaceous chondrites Gujba (4,562.7 ± 0.5 Myr) and Hammadah al Hamra 237 (4,562.8 ± 0.9 Myr), which formed during a single-stage, highly energetic event8,9,10,11. Both the relatively young ages and the single-stage formation of the CB chondrules are inconsistent with formation during a nebular shock wave2. We conclude that chondrules and metal grains in the CB chondrites formed from a vapour–melt plume produced by a giant impact between planetary embryos after dust in the protoplanetary disk had largely dissipated. These findings therefore provide evidence for planet-sized objects in the earliest asteroid belt, as required by current numerical simulations of planet formation in the inner Solar System12.

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Figure 1: The CB carbonaceous chondrites Hammadah al Hamra 237 (HH 237) and Gujba.
Figure 2: 204 Pb/ 206 Pb– 207 Pb/ 206 Pb isochron diagram for three Gujba chondrules (numbers 3, 4 and 5).

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Acknowledgements

Financial support for this project was provided by NASA (A.N.K., P.C.) and the Canadian Space Agency (Y.A.). We thank J. A. Wood for comments and suggestions, and E. Twelker for providing samples and images of Gujba and Hammadah al Hamra 237.

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Correspondence to Alexander N. Krot.

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Supplementary Notes

This includes Supplementary Figure Legends, Supplementary Methods and Supplementary Table S1.

Supplementary Figure S1

Polished slabs of Gujba and Hammadah al Hamra 237.

Supplementary Figure 2

Backscattered electron images of chondrules in the Gujba meteorite.

Supplementary Figure 3

Backscattered electron images of inter-chondrule material in the Gujba meteorite.

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Krot, A., Amelin, Y., Cassen, P. et al. Young chondrules in CB chondrites from a giant impact in the early Solar System. Nature 436, 989–992 (2005). https://doi.org/10.1038/nature03830

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