[Paper Review] The New Generation Planetary Population Synthesis (NGPPS) I. Bern global model of planet formation and evolution, model tests, and emerging planetary systems

Alexandre Emsenhuber, C. Mordasini+4 more|arXiv (Cornell University)|Jul 10, 2020

Astro and Planetary SciencePhysics and Astronomy9 references25 citations

TL;DR

This paper presents the Generation III Bern planetary formation model (NGPPS), a comprehensive end-to-end simulation that integrates gas disc evolution, planetesimal dynamics, core accretion, N-body interactions, and long-term planetary evolution. It successfully reproduces key features of the Solar System, including the giant impact phase for terrestrial planets and Jupiter-like planets forming just before gas disc dispersal to avoid inward migration.

ABSTRACT

Aims. Comparing theoretical models with observations allows one to make key step forward towards an understanding of planetary systems. It however requires a model able to (i) predict all the necessary observable quantities (not only masses and orbits, but also radii, luminosities, magnitudes, or evaporation rates) and (ii) address the large range in relevant planetary masses (from Mars mass to super-Jupiters) and distances (from stellar-grazing to wide orbits). Methods. We have developed a combined global end-to-end planetary formation and evolution model, the Generation III Bern model, based on the core accretion paradigm. This model solves as directly as possible the underlying differential equations for the structure and evolution of the gas disc, the dynamical state of the planetesimals, the internal structure of the planets yielding their planetesimal and gas accretion rates, disc-driven orbital migration, and the gravitational interaction of concurrently forming planets via a full N-body calculation. Importantly, the model also follows the long-term evolution of the planets on Gigayear timescales after formation including the effects of cooling and contraction, atmospheric escape, bloating, and stellar tides. Results. To test the model, we compared it with classical scenarios of Solar System formation. For the terrestrial planets, we find that we obtain a giant impact phase provided enough embryos (~100) are initially emplaced in the disc. For the giant planets, we find that Jupiter-mass planets must accrete their core shortly before the dispersal of the gas disc to prevent strong inward migration that would bring them to the inner edge of the disc. Conclusions. The model can form planetary systems with a wide range of properties. We find that systems with only terrestrial planets are often well-ordered while giant-planet bearing systems show no such similarity.

Motivation & Objective

• To develop a unified model capable of predicting diverse observable planetary properties, including masses, orbits, radii, luminosities, and evaporation rates.
• To simulate planetary systems across a broad mass range (Mars to super-Jupiters) and orbital distances (from close-in to wide orbits).
• To address the limitations of prior models by incorporating long-term evolution, including cooling, contraction, atmospheric escape, and tidal effects.
• To test the model’s predictive power by comparing its outcomes with classical Solar System formation scenarios.

Proposed method

• The model is based on the core accretion paradigm and solves the underlying differential equations for gas disc structure and evolution.
• It tracks planetesimal dynamics and internal planet structure to compute planetesimal and gas accretion rates directly.
• Orbital migration is modeled using disc-driven migration forces, with full N-body calculations to account for gravitational interactions among forming planets.
• The model includes long-term evolution beyond formation, incorporating planetary cooling, contraction, atmospheric escape, bloating, and stellar tidal effects over gigayear timescales.
• Initial conditions include ~100 planetary embryos in the terrestrial zone to test giant impact outcomes.
• The model is validated by comparing simulated outcomes with known Solar System properties, especially for terrestrial and giant planets.

Experimental results

Research questions

• RQ1 Can a single, self-consistent model reproduce the formation of both terrestrial and giant planets in a way consistent with observed Solar System architecture?
• RQ2 What conditions are required for the formation of a giant impact phase in the terrestrial planet zone?
• RQ3 How does the timing of core formation affect the survival of gas giants against inward migration?
• RQ4 What role does disc dispersal timing play in determining the final orbital configuration of massive planets?
• RQ5 How do long-term evolutionary processes like atmospheric escape and tidal forces influence planetary system stability and observable properties?

Key findings

• The model successfully reproduces the giant impact phase in the terrestrial planet zone when approximately 100 embryos are initially placed in the disc.
• Jupiter-mass planets must accrete their core shortly before gas disc dispersal to avoid strong inward migration that would lead to orbital decay and loss at the disc inner edge.
• Systems composed only of terrestrial planets tend to be well-ordered, while systems hosting giant planets show no such ordering, indicating distinct formation pathways.
• The model captures the full range of observable planetary properties, including radii, luminosities, magnitudes, and evaporation rates, enabling direct comparison with observations.
• The inclusion of long-term evolution processes—cooling, contraction, atmospheric escape, and tidal effects—enables realistic post-formation evolution over gigayear timescales.
• The model demonstrates that planetary system architecture is strongly influenced by the interplay between core formation timing, disc dispersal, and gravitational interactions during formation.