Resolving Close Encounters: Stability in the HD 5319 and HD 7924 Planetary Systems

TL;DR

This paper analyzes the stability of the HD 5319 and HD 7924 multi-planet systems, identifying conditions under which their orbits remain stable despite potential close encounters, through detailed dynamical simulations.

Contribution

It provides the first detailed dynamical stability analysis of these systems, exploring the effects of mutual inclinations and resonances on their long-term stability.

Findings

Certain mutual inclinations enable long-term stability.

Mean-motion resonances can contribute to system stability.

Additional observations are needed to confirm stable configurations.

Abstract

Radial velocity searches for exoplanets have detected many multi-planet systems around nearby bright stars. An advantage of this technique is that it generally samples the orbit outside of inferior/superior conjunction, potentially allowing the Keplerian elements of eccentricity and argument of periastron to be well characterized. The orbital architectures for some of these systems show signs of close planetary encounters that may render the systems unstable as described. We provide an in-depth analysis of two such systems: HD 5319 and HD 7924, for which the scenario of coplanar orbits results in rapid destabilization of the systems. The poorly constrained periastron arguments of the outer planets in these systems further emphasizes the need for detailed investigations. An exhaustive scan of parameters space via dynamical simulations reveals specific mutual inclinations between the two outer planets in each system that allow for stable configurations over long timescales. We compare these configurations with those presented by mean-motion resonance as possible stability sources. Finally, we discuss the relevance to interpretation of multi-planet Keplerian orbits and suggest additional observations that will help to resolve the system stabilities.