[2] Interactions with an outer planetesimal disk that is gravitationally stirred by Pluto-sized objects cause the planets to migrate inward while remaining in resonance.
The first weakness is the artificial selection of the initial orbits of the outer planets to produce an instability that matches the timing of the Late Heavy Bombardment.
[4][5] Investigations focusing on Jupiter and Saturn demonstrated that they can be captured in a 3:2 or 2:1 resonance depending on the characteristics of the protoplanetary disk.
[6][3][7] After capture into resonance, the gaps that Jupiter and Saturn formed in the disk's density distribution may overlap and their inward migration may be halted or reversed.
As a result of this coupling an increase in the average eccentricity of the planetesimal belt driven via the gravitational stirring by Pluto-sized objects yields a decrease in the semi-major axis of the planet.
[1] The increase in the eccentricity of the inner ice giant was found to be due to the varying strengths of the coupling between the planetesimal disk and the planets.
As a result of the conflict between these factors the timing and the occurrence of the instability is fairly independent of the distance to the inner edge of the planetesimal belt.
[1] A study using a numerical simulation that included gravitational interactions among all objects revealed that a dynamical instability occurred in less than 70 million years.
This study used a limited number of planetesimals due to computational constraints so it is as yet unknown whether this result would apply to a more complete disk.
Interactions with this dust disrupts the resonance chain and drive their migration toward the planetesimal disk over a several hundred million years period.
[11] The instability mechanism of the Nice 2 model becomes irrelevant if the dust generated by collisions among the planetesimals disrupts a resonant chain early.