## The Nice Model The **Nice Model** is a scenario for the dynamical evolution (i.e. the migration) of the planetary and non-planetary bodies in the Solar System . It is characterized by the migration of the giant planets from a more initial, compact configuration into their present positions, after the dissipation of the initial protoplanetary disk. ![[niceModel.svg|align:center|500]] ## The Steps of the Nice Model 0) Following the [[Standard Model of Planetary Formation]] and dissipation of the primordial Solar System disk, the four giant planets (Jupiter, Saturn, Uranus, and Neptune) were originally found on near-circular orbits between $\sim 5.5 - 17 \; {\rm AU}$, and there remained a large, dense disk of small rock and ice planetesimals from $\sim 17 - 35 \; {\rm AU}$. 1) Planetesimals at the disk's inner edge have gravitational encounters with the outermost giant planet, exchanging angular momentum. ([[Planetary Migration#Planetesimal-Driven Migration]]) - The icy planetesimals scatter inwards. - The planet migrates outwards. - The scattered planetesimals encounter the other giant planets, moving each outwards by the same process. - This process continues until the planetesimals interact with the innermost giant planet, Jupiter, whose gravity sends them into highly elliptical orbits or ejects them from the Solar System. - Jupiter moves slightly inward while planetesimals contribute to the future [[Kuiper Belt]] and [[Oort Cloud]] 2) After long, gradual migration, Jupiter and Saturn cross their mutual 1:2 mean-motion resonance, increasing their orbital eccentricities and destabilizing the entire planetary system. - Leads to development of generation of the Trojans, Greeks, and Hildas groups in the [[asteroid belt]] - The giant planets are shifted very quickly and dramatically. - Jupiter shifts Saturn to its present position, pushing Neptune and Uranus into more eccentric orbits. (potentially causing them to switch places) - The ice giants then plough through the planetesimal disk, scattering the planetesimals causing... 1) **Late Heavy Bombardment** - a sharp spike of impacts by icy objects on the lunar surface and terrestrial planets after their formation 2) **Irregular Satellites** - Saturn, Uranus, and Neptune have many smaller satellites on with high inclinations ([[Planetary Migration#Kozai Mechanism]]) 3) **Adding to Oort Cloud & Kuiper Belt** - the scattered bodies sent further out and on highly eccentric and inclined orbits - This disruption scatters the primordial disk, removing 99% of its mass and explaining the absence of a dense [[Smaller Non-Planetary Bodies#Trans-Neptunian Object (TNO)]] population. 3) The giant planets reach their final orbital semi-major axes through dynamical friction with the remaining planetesimal disc, removing eccentricity in the planetary orbits. ## Problems - Does not seem to produce enough low-eccentricity objects in [[Kuiper Belt]] - Maybe the [[Kuiper Belt#Hot & Cold Population|cold population]] formed in situ?