Editing Uranus (section)

== Formation ==
{{main|Formation and evolution of the Solar System}}

{{For|details of the evolution of Uranus's orbit|Nice model}}

It is argued that the differences between the ice giants and the gas giants arise from their formation history.<ref name="Thommes1999" /><ref name="Brunini1999" /><ref name="dangelo2021">{{Cite journal |last1=D'Angelo |first1=Gennaro |last2=Weidenschilling |first2=Stuart J. |last3=Lissauer |first3=Jack J. |last4=Bodenheimer |first4=Peter |date=February 2021 |title=Growth of Jupiter: Formation in disks of gas and solids and evolution to the present epoch |journal=[[Icarus (journal)|Icarus]] |volume=355 |pages=114087 |arxiv=2009.05575 |bibcode=2021Icar..35514087D |doi=10.1016/j.icarus.2020.114087 |s2cid=221654962}}</ref> The Solar System is hypothesised to have formed from a rotating disk of gas and dust known as the [[presolar nebula]]. Much of the nebula's gas, primarily hydrogen and helium, formed the Sun, and the dust grains collected together to form the first protoplanets. As the planets grew, some of them eventually accreted enough matter for their gravity to hold on to the nebula's leftover gas.<ref name="Thommes1999" /><ref name="Brunini1999" /><ref name="dangelo_bodenheimer_2013">{{Cite journal |last1=D'Angelo |first1=Gennaro |last2=Bodenheimer |first2=Peter |date=6 November 2013 |title=Three-dimensional Radiation-hydrodynamics Calculations of the Envelopes of Young Planets Embedded in Protoplanetary Disks |journal=[[The Astrophysical Journal]] |volume=778 |issue=1 |pages=77 |arxiv=1310.2211 |bibcode=2013ApJ...778...77D |doi=10.1088/0004-637X/778/1/77 |issn=0004-637X |s2cid=118522228}}</ref> The more gas they held onto, the larger they became; the larger they became, the more gas they held onto until a critical point was reached, and their size began to increase exponentially.<ref name="dl2018">{{Cite book |last1=D'Angelo |first1=G. |title=Handbook of Exoplanets |last2=Lissauer |first2=J. J. |date=2018 |publisher=[[Springer International Publishing AG]] |isbn=978-3-319-55332-0 |editor-last=Deeg |editor-first=H. |pages=2319–2343 |chapter=Formation of Giant Planets |bibcode=2018haex.bookE.140D |doi=10.1007/978-3-319-55333-7_140 |editor-last2=Belmonte |editor-first2=J. |arxiv=1806.05649 |s2cid=116913980}}</ref> The ice giants, with only a few [[Earth mass]]es of nebular gas, never reached that critical point.<ref name="Thommes1999" /><ref name="Brunini1999" /><ref name="Sheppard Jewitt Kleyna 2006" /> Recent simulations of [[planetary migration]] have suggested that both ice giants formed closer to the Sun than their present positions, and moved outwards after formation (the [[Nice model]]).<ref name="Thommes1999" />