Ernesto Vieira | Searcharxiv

arXiv2026

Dynamical formation of long-period exoplanets systems in evolving binary stars

The dynamical formation and evolution of long-period giant exoplanets have not been well constrained due to the few observational parameters. In this study, we explore the dynamical effects in a multi-planetary system around one star of an evolving wide binary system. We used an interpolated result of a MESA stellar evolution inside REBOUND N-body integrations to perform simulations with a range of distinct planetary masses in a circumstellar configuration (S-type orbit), centered on a primary star that evolves from the main sequence star to a white dwarf. Control simulations without stellar evolution were performed to isolate the effects of mass loss. Although few exoplanets are currently known to possess long-period and moderate eccentricities, we investigated the evolution mechanisms of long-period gas giants within this specific regime. Although these exoplanets often remain undetected due to their wide orbits and long periods, we propose that their formation pathways are robust throughout the evolution of binary systems. We also simulated an evolved single star in a multi-planetary system and concluded that the secondary star made the exoplanets more unstable and concentrated the survivors within a semi-major axis of 50 au.

astro-ph.EP↗

arXiv2025

The resilience of the sailboat stable region

Binary systems host complex orbital dynamics where test particles can occupy stable regions despite strong gravitational perturbations. The sailboat region, discovered in the Pluto-Charon system, allows highly eccentric S-type orbits at intermediate distances between the two massive bodies. This region challenges traditional stability concepts by supporting eccentricities up to 0.9 in a zone typically dominated by chaotic motion. We investigate the sailboat region's existence and extent across different binary system configurations. We examine how variations in mass ratio, secondary body eccentricity, particle inclination, and argument of pericenter affect this stable region. We performed 1.2 million numerical simulations of the elliptic three-body problem to generate four datasets exploring different parameter spaces. We trained XGBoost machine learning models to classify stability across approximately $10^9$ initial conditions. We validated our results using Poincaré surface of section and Lyapunov exponent analysis to confirm the dynamical mechanisms underlying the stability. The sailboat region exists only for binary mass ratios $μ= [0.05, 0.22]$. Secondary body eccentricity severely constrains the region, following an exponential decay: $e_{s,\mathrm{max}} \approx 0.016 + 0.614 \exp(-25.6μ)$. The region tolerates particle inclinations up to $90^\circ$ and persists in retrograde configurations for $μ\leq 0.16$. Stability requires specific argument of pericenter values within $\pm 10^\circ$ to $\pm 30^\circ$ of $ω= 0^\circ$ and $180^\circ$. Our machine learning models achieved over 97\% accuracy in predicting stability. The sailboat region shows strong sensitivity to system parameters, particularly secondary body eccentricity. Among Solar System dwarf planet binaries, Pluto-Charon, Orcus-Vanth and Varda-Ilmarë systems could harbor such regions.

astro-ph.EP↗