# Resonant structure, formation and stability of the planetary system HD155358

## TL;DR

This paper re-analyzes the HD155358 planetary system using Bayesian models, demonstrating the importance of planet-planet interactions for understanding system stability, resonance, and formation history.

## Contribution

It introduces a Bayesian framework that compares models with and without gravitational interactions, revealing the significance of PPI in orbital configuration and migration modeling.

## Key findings

- PPI models favor mean motion resonance (MMR) configuration.
- NoPPI models are consistent with previous non-interacting analyses.
- Stable orbital configurations are identified through long-term simulations.

## Abstract

Two Jovian-sized planets are orbiting the star HD155358 near exact mean motion resonance (MMR) commensurability. In this work we re-analyze the radial velocity (RV) data previously collected by Robertson et al. (2012). Using a Bayesian framework we construct two models - one that includes and one that excludes gravitational planet-planet interactions (PPI). We find that the orbital parameters from our PPI and noPPI models differ by up to $2\sigma$, with our noPPI model being statistically consistent with previous results. In addition, our new PPI model strongly favours the planets being in MMR while our noPPI model strongly disfavours MMR. We conduct a stability analysis by drawing samples from our PPI model's posterior distribution and simulating them for $10^9$ years, finding that our best-fit values land firmly in a stable region of parameter space. We explore a series of formation models that migrate the planets into their observed MMR. We then use these models to directly fit to the observed RV data, where each model is uniquely parameterized by only three constants describing its migration history. Using a Bayesian framework we find that a number of migration models fit the RV data surprisingly well, with some migration parameters being ruled out. Our analysis shows that planet-planet interactions are important to take into account when modelling observations of multi-planetary systems. The additional information that one can gain from interacting models can help constrain planet migration parameters.