Placing Uranus and Neptune

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Science  10 Jun 2011:
Vol. 332, Issue 6035, pp. 1242
DOI: 10.1126/science.332.6035.1242-a

The solar system has two reservoirs of comets: the Kuiper Belt, where Pluto is also located, and the Oort cloud, much further beyond the orbits of the planets. The comets did not necessarily form in the regions they now occupy. In the case of the Oort cloud, computer simulations of its formation suggest that it originated from the region where Uranus and Neptune once were. Based on this constraint and the similarity between the deuterium enrichment in the ice of Oort cloud comets and in Saturn's moon Enceladus, Kavelaars et al. suggest that at the time the Oort cloud formed, Uranus and Neptune were much closer to Saturn than they now are. Deuterium enrichment varies with distance to the Sun and is linked to the time and location at which these ices condensed. The result is consistent with models of the dynamical evolution of the solar system wherein Uranus and Neptune migrate from their formation region to their current location via dynamical interactions.

Astrophys. J. 734, L30 (2011).

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