Letter

Core formation on Mars and differentiated asteroids

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Accepted:
Published online:

Abstract

Meteorite chronometry based on the 182Hf–182W system can provide powerful constraints on the timing of planetary accretion and differentiation1,2,3,4, although the full potential of this method has yet to be realized. For example, no measurements have been made on the silicate-rich portions of planets and planetesimals other than the Earth and Moon. Here we report tungsten isotope compositions for two eucrites, thought to be derived from asteroid 4 Vesta, and from eight other basaltic achondritic meteorites that are widely considered to be from Mars. The eucrites, which are among the oldest differentiated meteorites, yield exceedingly radiogenic tungsten, indicating rapid accretion, differentiation and core formation on Vesta within the first 5–15 Myr of Solar System history, whereas the range of radiogenic tungsten measurements on the martian meteorites points towards tungsten depletion via melting and core formation within the first 30 Myr of the Solar System. The survival of tungsten isotope heterogeneity in the martian upper mantle implies that no giant impacts or large-scale convective mixing took place since this time. These results contrast with those obtained for the Earth–Moon system2,3 for which accretion and core formation related to giant impacts appears to have continued for at least an additional 20 Myr.

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Acknowledgements

We thank M. Lindstrom, L. Nyquist, G. MacPherson, C. Perron and M. Wadhwa for access to their meteorite collections at NASA, Smithsonian Institution of Washington, Museum National d'Histoire Naturelle at Paris, and Field Museum in Chicago. We also thank J. Christensen, E. Essene, H. Pollack, M. Rehkämper, P. van Keken and Y. Zhang for their comments, M. Johnson and C. Hall for their assistance, and K. Righter and M. Drake for access to unpublished papers. This work was supported by NSF, DOE, NASA and the University of Michigan.

Author information

Affiliations

  1. Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan48109-1063, USA

    • Der-Chuen Lee
    •  & Alex N. Halliday

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Corresponding author

Correspondence to Der-Chuen Lee.

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