Predicting the long-term stability of compact multiplanet systems

TL;DR

This paper introduces SPOCK, a machine learning classifier that rapidly predicts the long-term stability of compact multi-planet systems using physically motivated features, significantly outperforming previous methods and aiding in exoplanet characterization.

Contribution

The paper presents SPOCK, a novel machine learning model that efficiently predicts system stability over billion-orbit timescales, generalizes across diverse configurations, and enhances exoplanet system analysis.

Findings

SPOCK achieves speed-ups of up to 10^5 over full simulations.

It outperforms previous stability prediction methods.

Provides stronger eccentricity constraints than radial velocity or transit duration measurements.

Abstract

We combine analytical understanding of resonant dynamics in two-planet systems with machine learning techniques to train a model capable of robustly classifying stability in compact multi-planet systems over long timescales of $10^9$ orbits. Our Stability of Planetary Orbital Configurations Klassifier (SPOCK) predicts stability using physically motivated summary statistics measured in integrations of the first $10^4$ orbits, thus achieving speed-ups of up to $10^5$ over full simulations. This computationally opens up the stability constrained characterization of multi-planet systems. Our model, trained on $\approx 100,000$ three-planet systems sampled at discrete resonances, generalizes both to a sample spanning a continuous period-ratio range, as well as to a large five-planet sample with qualitatively different configurations to our training dataset. Our approach significantly outperforms previous methods based on systems' angular momentum deficit, chaos indicators, and parametrized fits to numerical integrations. We use SPOCK to constrain the free eccentricities between the inner and outer pairs of planets in the Kepler-431 system of three approximately Earth-sized planets to both be below 0.05. Our stability analysis provides significantly stronger eccentricity constraints than currently achievable through either radial velocity or transit duration measurements for small planets, and within a factor of a few of systems that exhibit transit timing variations (TTVs). Given that current exoplanet detection strategies now rarely allow for strong TTV constraints (Hadden et al., 2019), SPOCK enables a powerful complementary method for precisely characterizing compact multi-planet systems. We publicly release SPOCK for community use.