Editing Planetary migration (section)

== In the Solar System ==
{{main|Nice model}}
[[Image:Lhborbits.png|thumb|upright=2|Simulation showing outer planets and Kuiper belt: (a)&nbsp;Before Jupiter/Saturn 2:1 resonance. (b)&nbsp;Scattering of Kuiper belt objects into the Solar System after the orbital shift of Neptune. (c)&nbsp;After ejection of Kuiper belt bodies by Jupiter<ref name="Gomes">{{cite journal |url=http://www.nature.com/nature/journal/v435/n7041/pdf/nature03676.pdf |title=Origin of the cataclysmic Late Heavy Bombardment period of the terrestrial planets |author=Gomes, R. |author2=Levison, H.F. |author3=Tsiganis, K. |author4=Morbidelli, A. |journal=Nature |date=2005 |volume=435 |pages=466–469 |doi=10.1038/nature03676 |pmid=15917802 |issue=7041 |bibcode=2005Natur.435..466G |s2cid=4398337 |access-date=2008-06-08 |archive-url=https://web.archive.org/web/20110525101220/http://www.nature.com/nature/journal/v435/n7041/pdf/nature03676.pdf |archive-date=2011-05-25 |url-status=live |doi-access=free }}</ref>]]
The migration of the outer planets is a scenario proposed to explain some of the orbital properties of the bodies in the Solar System's outermost regions.<ref name=Levinson2007>{{cite journal |author1=Levison, Harold F. |author2=Morbidelli, Alessandro |author3=van Laerhoven, Christa |display-authors=etal | title=Origin of the structure of the Kuiper Belt during a dynamical instability in the orbits of Uranus and Neptune |date=2007 |arxiv=0712.0553 |doi=10.1016/j.icarus.2007.11.035 |journal=Icarus |volume=196 |issue=1 |page=258 |bibcode=2008Icar..196..258L|s2cid=7035885 }}</ref> [[Trans-Neptunian object|Beyond Neptune]], the Solar System continues into the [[Kuiper belt]], the [[scattered disc]], and the [[Oort cloud]], three sparse populations of small icy bodies thought to be the points of origin for most observed [[comet]]s. At their distance from the Sun, accretion was too slow to allow planets to form before the [[solar nebula]] dispersed, because the initial disc lacked enough mass density to consolidate into a planet. The Kuiper belt lies between 30 and 55&nbsp;AU from the Sun, while the farther scattered disc extends to over 100&nbsp;AU,<ref name=Levinson2007/> and the distant Oort cloud begins at about 50,000&nbsp;AU.<ref>{{cite arXiv |title=Origin and dynamical evolution of comets and their reservoirs |author=Alessandro Morbidelli |eprint=astro-ph/0512256 |date=2005}}</ref>

According to this scenario the Kuiper belt was originally much denser and closer to the Sun: it contained millions of planetesimals, and had an outer edge at approximately 30&nbsp;AU, the present distance of Neptune. After the [[formation of the Solar System]], the orbits of all the giant planets continued to change slowly, influenced by their interaction with the large number of remaining planetesimals. After 500–600&nbsp;million years (about 4&nbsp;billion years ago) Jupiter and Saturn divergently crossed the 2:1 [[orbital resonance]], in which Saturn orbited the Sun once for every two Jupiter orbits.<ref name="Levinson2007" /> This resonance crossing increased the eccentricities of Jupiter and Saturn and destabilized the orbits of Uranus and Neptune. Encounters between the planets followed causing Neptune to surge past Uranus and plough into the dense planetesimal belt. The planets scattered the majority of the small icy bodies inwards, while moving outwards themselves. These planetesimals then scattered off the next planet they encountered in a similar manner, moving the planets' orbits outwards while they moved inwards.<ref>{{cite web |url=http://www.psrd.hawaii.edu/Aug01/bombardment.html |title=Uranus, Neptune, and the Mountains of the Moon |work=Planetary Science Research Discoveries |date=21 August 2001 |author=Taylor, G. Jeffrey |publisher=Hawaii Institute of Geophysics & Planetology |access-date=2008-02-01 |df=dmy-all |archive-url=https://web.archive.org/web/20181022075509/http://www.psrd.hawaii.edu/Aug01/bombardment.html |archive-date=22 October 2018 |url-status=live }}</ref> This process continued until the planetesimals interacted with Jupiter, whose immense gravity sent them into highly elliptical orbits or even ejected them outright from the Solar System. This caused Jupiter to move slightly inward. This scattering scenario explains the trans-Neptunian populations' present low mass. In contrast to the outer planets, the inner planets are not believed to have migrated significantly over the age of the Solar System, because their orbits have remained stable following the [[Late Heavy Bombardment|period of giant impacts]].<ref name="sciam">{{cite magazine |title=The Chaotic Genesis of Planets |author=Lin, Douglas N.C. |magazine=Scientific American |issue=5 |volume=298 |date=May 2008 |pages=50–59 |url=http://www.sciam.com/article.cfm?id=the-genesis-of-planets |url-access=subscription |doi=<!-- does not actually have one --> |pmid=18444325 |bibcode=2008SciAm.298e..50C |access-date=2008-06-08 |archive-url=https://web.archive.org/web/20081119112817/http://www.sciam.com/article.cfm?id=the-genesis-of-planets |archive-date=2008-11-19 |url-status=live }}</ref>