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An asteroid breakup 160 Myr ago as the probable source of the K/T impactor

Abstract

The terrestrial and lunar cratering rate is often assumed to have been nearly constant over the past 3 Gyr. Different lines of evidence, however, suggest that the impact flux from kilometre-sized bodies increased by at least a factor of two over the long-term average during the past 100 Myr. Here we argue that this apparent surge was triggered by the catastrophic disruption of the parent body of the asteroid Baptistina, which we infer was a 170-km-diameter body (carbonaceous-chondrite-like) that broke up Myr ago in the inner main asteroid belt. Fragments produced by the collision were slowly delivered by dynamical processes to orbits where they could strike the terrestrial planets. We find that this asteroid shower is the most likely source (>90 per cent probability) of the Chicxulub impactor that produced the Cretaceous/Tertiary (K/T) mass extinction event 65 Myr ago.

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Figure 1: The orbital and size distribution of the observed Baptistina asteroid family.
Figure 2: Estimates of the initial size–frequency distribution of the Baptistina family.
Figure 3: Collisional evolution of the Baptistina family’s size distribution.
Figure 4: The impact rate of Baptistina fragments on Venus, Earth and Mars.

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Acknowledgements

We thank K. Beatty, C. Chapman, L. Dones, D. Durda, B. Enke, D. Kring, F. Kyte, M. Gounelle, R. Grimm, A. Harris, H. Levison, A. Morbidelli, A. Rubin, E. Scott, A. Stern and M. Zolensky for discussions and comments. We also thank G. Williams of the Minor Planet Center for computing revised H values and observational errors for the Baptistina family. The work of W.F.B. and D.N. on this project was supported by NASA’s Origins of Solar System, Planetary Geology and Geophysics, and Near-Earth Objects Observations programmes. D.V. was supported by the Grant Agency of the Czech Republic.

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Correspondence to William F. Bottke.

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This file contains Supplementary Discussion of several issues that were not addressed in the main text with Supplementary Figures S1-S11 and additional references. (PDF 4096 kb)

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Bottke, W., Vokrouhlický, D. & Nesvorný, D. An asteroid breakup 160 Myr ago as the probable source of the K/T impactor. Nature 449, 48–53 (2007). https://doi.org/10.1038/nature06070

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