Example of the genesis of chaos in the giant planets’ orbits and their long-term stability. Top: orbital migration of Jupiter, Saturn, Uranus, and Neptune embedded in the gaseous protoplanetary disk. At the end of the gas disk phase, the planets are locked in a chain of MMRs (2:1, 2:1, 3:2). Bottom: long-term evolution of the Saturn-to-Jupiter orbital period ratio, and the gas giants’ eccentricities and inclinations over the next 500 Myr. This configuration is consistent with a later instability in the orbits of the giant planets (Tsiganis et al. 2005; Levison et al. 2011; Nesvorný & Morbidelli 2012).