Nice model

• 1. Origins And Development

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  Scientists at the Côte d'Azur Observatory in Nice, France published a triplet of papers in the general science journal Nature during 2005. This international collaboration proposed that four giant planets once occupied near-circular orbits with radii between 5.5 and 17 astronomical units. These initial positions placed Jupiter, Saturn, Uranus, and Neptune much closer to the sun than they reside today. A dense disk of small rock and ice planetesimals extended from the outermost giant planet out to some distance beyond 30 astronomical units. The total mass of this primordial disk reached approximately 35 Earth masses. This configuration differed sharply from earlier models which assumed the planets formed near their current locations.

• 2. Planetary Migration Mechanics

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  Planetesimals at the inner edge of the disk occasionally passed through gravitational encounters with the outermost giant planet. Uranus or Neptune scattered these icy bodies inward while moving outward themselves to conserve angular momentum. Each exchange shifted planetary orbits by minute amounts until cumulative effects caused significant migration over several hundred million years. Jupiter and Saturn eventually reached their mutual 1:2 mean-motion resonance where Saturn's orbital period became twice that of Jupiter. This resonance increased orbital eccentricities and destabilized the entire system. Jupiter then shifted Saturn toward its present position while mutual encounters propelled Neptune and Uranus onto highly eccentric paths. These ice giants plowed into the planetesimal disk scattering tens of thousands of objects from stable orbits in the outer Solar System. The disruption removed 99% of the primordial disk mass almost entirely.

• 3. Late Heavy Bombardment Debate

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  The main motivation for introducing the Nice model was explaining a hypothetical surge in asteroid impacts on the lunar surface around 600 million years after formation. Icy planetesimals scattered onto planet-crossing orbits when the outer disc disrupted causing sharp spikes in impacts. Mean-motion resonances swept through the inner Solar System driving asteroids into intersecting orbits with terrestrial planets. However newer studies show no peak in the cratering record but rather an exponential decay of craters over time. Recent measurements using laser ablation microprobe on the argon-40 to argon-39 isotope ratio on Vesta's surface contradict the bombardment timeline. Statistical artifacts combining finite uncertainty in age determination with the moon's cutoff age may create an apparent peak known as the Late Heavy Bombardment. Strong doubts about this unique phase weaken the credibility of the original Nice Model predictions regarding impact flux.

• 4. Minor Body Populations

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  Running dynamical models with different initial conditions produced various distributions of minor bodies across the Solar System. Objects captured in Jupiter's mean motion resonances formed the Hilda family while others escaped onto stable orbits beyond 2 astronomical units. These objects underwent collisional erosion grinding populations into progressively smaller fragments subject to the Yarkovsky effect and Poynting, Robertson drag. Simulated size-frequency distributions matched observations suggesting Jupiter Trojans, Hildas, and spectral D-type asteroids are remnant planetesimals from capture processes. The dwarf planet Ceres may be a Kuiper-belt object captured by this mechanism. Neptune's migration created both resonant and non-resonant populations forming plutinos and other groups with higher inclinations. Cold classical objects originated primarily from the outer disk while hot populations resulted from scattering events. The cold population remains markedly redder than the hot group indicating differing compositions and formation regions.

• 5. Satellite Capture Scenarios

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  Original populations of irregular satellites captured by traditional mechanisms were lost during planetary encounters at the time of global instability. Uranus and Neptune encountered large numbers of planetesimals after entering and disrupting the planetesimal disk. A fraction of these planetesimals were captured via three-way interactions during encounters between two planets like Uranus and Neptune. The probability for a particular planetesimal to be captured by an ice giant reached several times one in ten thousand. New satellites could form at almost any angle unlike regular satellites which orbit within equatorial planes. Some irregulars exchanged positions between planets creating suspected collisional families seen today. Triton the largest moon of Neptune can be explained if it was captured in a three-body interaction involving binary disruption. However insufficient interactions existed between Jupiter and other planets to explain its retinue of irregulars in initial simulations.

• 6. Model Modifications And Variants

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  Hydrodynamical models indicated that giant planet orbits would converge resulting in capture into series of resonances before instability. The slow approach of Jupiter and Saturn to their 2:1 resonance altered inner Solar System objects due to sweeping secular resonances. The first modification involved initial positions where gas disk migration led to quadruple resonant configurations with Jupiter and Saturn in 3:2 resonance. Gravitational encounters with Pluto-massed objects stirred outer disk orbits causing inward migration of giant planets. This late instability triggered by long-distance interactions became known as the Nice 2 model. The second modification required one ice giant to encounter Jupiter causing its semi-major axis to jump. In this jumping-Jupiter scenario an ice giant scattered inward onto a Jupiter-crossing orbit then outward after encountering Jupiter. Step-wise separation avoided slow sweeping of secular resonances across the inner solar system. A five-planet hypothesis hypothesized an early Solar System with five giants where one was ejected during instability. David Nesvorný and others proposed this variant beginning with resonant chains breaking sequentially. Simulations found statistically small likelihoods for reproducing terrestrial planet orbits under these conditions.