Born eccentric: Constraints on Jupiter and Saturn’s pre-instability orbits

An episode of dynamical instability is thought to have sculpted the orbital structure outer solar system. When modeling this instability, a key constraint comes from Jupiter's fifth eccentric mode (quantified by its amplitude M55), which an important driver system's secular evolution. Starting commonly-assumed near-circular orbits, present-day giant planets' architecture lies at limit numerically generated systems, and M55 rarely excited true value. Here we perform analysis large batch artificially triggered instabilities, test variety configurations for primordial orbits. In addition more standard setups, motivated results modern hydrodynamical simulations evolution within gaseous disk, consider possibility that Jupiter Saturn emerged nebular gas locked in 2:1 resonance with non-zero eccentricities. We show that, such scenario, Jupiter-Saturn system represents typical simulation outcome, commonly matched. Furthermore, Uranus Neptune's final orbits are determined combination mass Kuiper belt ejected ice giant.