The ‘dynamically cold Kuiper belt’ consists of objects on low-inclination orbits between ∼40 and ∼50 au from the Sun. It currently contains material totalling less than a tenth the mass of the Earth1,2, which is surprisingly low because, according to accretion models3,4, the objects would not have grown to their present size unless the cold Kuiper belt originally contained tens of Earth masses of solids. Although several mechanisms have been proposed to produce the observed mass depletion, they all have significant limitations5. Here we show that the objects currently observed in the dynamically cold Kuiper belt were most probably formed within ∼35 au and were subsequently pushed outward by Neptune's 1:2 mean motion resonance during its final phase of migration. Combining our mechanism with previous work6,7, we conclude that the entire Kuiper belt formed closer to the Sun and was transported outward during the final stages of planet formation.
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We are grateful to R. Gomes and M. Holman for acting as referees on this paper. We also thank L. Dones, W. Bottke, J.-M. Petit, and K. Tsiganis for help with an early version of the text and M. Duncan and R. Gomes for discussions. H.F.L. is grateful for funding from NASA. We thank the CNRS and NSF for encouraging friendly relationships between the US and France.
The authors declare that they have no competing financial interests.
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Levison, H., Morbidelli, A. The formation of the Kuiper belt by the outward transport of bodies during Neptune's migration. Nature 426, 419–421 (2003). https://doi.org/10.1038/nature02120
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