A periodic configuration of the Kepler-25 planetary system?

TL;DR

This paper investigates the Kepler-25 planetary system's proximity to a 2:1 mean motion resonance, revealing challenges in TTV modeling and emphasizing the influence of prior assumptions on inferred system configurations.

Contribution

It demonstrates the system's closeness to a periodic resonant configuration and highlights the impact of prior choices on TTV analysis results.

Findings

Kepler-25 is near a 2:1 MMR, indicating a history of smooth migration.

Standard TTV modeling can misinterpret resonant configurations due to degeneracy.

Priors on eccentricities significantly influence the inferred system architecture.

Abstract

We study proximity of the Kepler-25 planetary system to a periodic configuration, which is known to be the final state of a system that undergoes smooth migration resulting from the planet-disc interaction. We show that the system is close to the periodic configuration of 2:1 mean motion resonance (MMR) what indicates that its past migration was neither disturbed significantly by turbulence in the disc nor the orbits were perturbed by planetesimals that left after the disc dispersal. We show that, because of the TTV model degeneracy, a periodic configuration is difficult to be found when the standard modelling of the transit timing variations (TTVs) is used. The TTV signal of a periodic configuration (with anti-aligned apsidal lines) may be misinterpreted as an aligned non-resonant system. We demonstrate that the standard MCMC modelling of the Kepler-25 TTVs is very sensitive to an a~priori information on the eccentricities (prior probability distributions). Wide priors (of the order of the ones typically used in the literature) result in favouring the aligned non-resonant configurations with small planets' masses and moderate eccentricities, while for the narrower priors the most likely are the anti-aligned resonant systems with larger masses and very low eccentricities.