Instability-Driven Dynamical Evolution Model of a Primordially 5 Planet Outer Solar System

TL;DR

This paper presents a new 5-planet instability model for the early outer solar system, showing it can reproduce observed dynamics and avoid Kuiper belt excitation, expanding understanding of planetary formation scenarios.

Contribution

It introduces a novel 5-planet multi-resonant initial state model that successfully explains the outer solar system's current configuration and dynamics.

Findings

5-planet models can reproduce outer solar system dynamics

Ejection of an ice giant is consistent with observed orbital configurations

Short ejection timescales prevent Kuiper belt excitation

Abstract

Over the last decade, evidence has mounted that the solar system's observed state can be favorably reproduced in the context of an instability-driven dynamical evolution model, such as the "Nice" model. To date, all successful realizations of instability models have concentrated on evolving the four giant planets onto their current orbits from a more compact configuration. Simultaneously, the possibility of forming and ejecting additional planets has been discussed, but never successfully implemented. Here we show that a large array of 5-planet (2 gas giants + 3 ice giants) multi-resonant initial states can lead to an adequate formation of the outer solar system, featuring an ejection of an ice giant during a phase of instability. Particularly, our simulations demonstrate that the eigenmodes which characterize the outer solar system's secular dynamics can be closely matched with a 5-planet model. Furthermore, provided that the ejection timescale of the extra planet is short, orbital excitation of a primordial cold classical Kuiper belt can also be avoided in this scenario. Thus the solar system is one of many possible outcomes of dynamical relaxation and can originate from a wide variety of initial states. This deems the construction of a unique model of solar system's early dynamical evolution impossible.