1. Southwest Research Institute, 1050 Walnut Street, Suite 300,
2. Center for Lunar Origin & Evolution, NASA Lunar Science Institute, Boulder, Colorado 80302, USA
3. Laboratoire de Minéralogie et de Cosmochimie du Muséum, CNRS & Muséum National d'Histoire Naturelle, 75005 Paris, France
4. Observatoire de la Côte d'Azur, Nice, Cedex 4, F-06304, France
5. Department of Physics, Aristotle University of Thessaloniki, Thessaloniki, 54006 Hellas, Greece

Correspondence to: Harold F. Levison^1,2 Correspondence and requests for materials should be addressed to H.F.L. (Email: hal@boulder.swri.edu).

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 model^{2, 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 meteorites^{5, 6}.

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