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Contamination of the asteroid belt by primordial trans-Neptunian objects


The main asteroid belt, which inhabits a relatively narrow annulus 2.1–3.3 au from the Sun, contains a surprising diversity of objects ranging from primitive ice–rock mixtures to igneous rocks. The standard model used to explain this assumes that most asteroids formed in situ from a primordial disk that experienced radical chemical changes within this zone1. Here we show that the violent dynamical evolution of the giant-planet orbits required by the so-called Nice model2,3,4 leads to the insertion of primitive trans-Neptunian objects into the outer belt. This result implies that the observed diversity of the asteroid belt is not a direct reflection of the intrinsic compositional variation of the proto-planetary disk. The dark captured bodies, composed of organic-rich materials, would have been more susceptible to collisional evolution than typical main-belt asteroids. Their weak nature makes them a prodigious source of micrometeorites—sufficient to explain why most are primitive in composition and are isotopically different from most macroscopic meteorites5,6.

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Figure 1: The orbital element distributions of real and modelled asteroids.
Figure 2: The beginning and end states of the SFDs in the three regions studied.


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H.F.L., W.F.B., A.M. and D.N. are grateful to NASA’s Origins of Solar Systems and Outer Planet Research programmes. D.N. is also grateful to the US National Science Foundation’s Astronomy & Astrophysics Grants programme for funding. M.G. wishes to thank Centre National de la Recherche Scientifique, Programme National de Planétologie and the European Community for funding. We thank S. Stewart and Z. Leinhardt for discussions and S. Weidenschilling and A. Harris, who acted as referees.

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Correspondence to Harold F. Levison.

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Supplementary Information

This file contains Supplementary Notes (incorporating Figures 1-6 and Tables 1-2): (1) The Orbital Dynamics Calculations, (2) Collisional and Dynamical Depletion Evolution Model (CoDDEM) Calculations, (3) The Micrometeorite Origin Problem, (4) The Collisional Evolution of the Primordial Cometary Disk; and Supplementary References. (PDF 1644 kb)

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Levison, H., Bottke, W., Gounelle, M. et al. Contamination of the asteroid belt by primordial trans-Neptunian objects. Nature 460, 364–366 (2009).

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