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Nice 2 model
The Nice 2 model is a model of the early evolution of the Solar System. The Nice 2 model resembles the original Nice model in that a late instability of the outer Solar System results in gravitational encounters between planets, the disruption of an outer planetesimal disk, and the migrations of the outer planets to new orbits. However, the Nice 2 model differs in its initial conditions and in the mechanism for triggering the late instability. These changes reflect the analysis of the orbital evolution of the outer Solar System during the gas disk phase and the inclusion of gravitational interactions between planetesimals in the outer disk into the model.
==Description==
The Nice 2 model begins with the outer planets in a stable quadruple resonance with each planet in resonance with its nearest neighbors. One example among several potential stable quadruple resonance configurations is Jupiter and Saturn in a 3:2 resonance, Saturn and Uranus in a 3:2 resonance, and Uranus and Neptune in a 4:3 resonance. Interactions with an outer planetesimal disk that is gravitationally stirred by Pluto-sized objects cause the planets to migrate inward while remaining in resonance.〔 During this migration the eccentricity of the inner ice giant increases, leading to secular-resonance crossings.〔 After several hundred million years, the resonant configuration is destabilized during one of these secular-resonance crossings.〔 Gravitational encounters between the planets similar to those in the original Nice model begin shortly thereafter.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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