2026A&A...706A.121A

Context. The presence of a stellar companion can strongly influence the architecture and long-term stability of planetary systems. Motivated by the discovery of exoplanets exhibiting extremely high eccentricities (e ≥ 0.8) in systems with a binary companion, we investigated how planetary orbits around one star (S-type configuration) evolve under the gravitational perturbations of the companion.
Aims. We assess the role of a stellar companion in shaping the orbital evolution of S-type planets and to explore whether dynamical interactions in such environments can account for the formation of highly eccentric planets.
Methods. We performed a suite of N-body simulations, modeling systems initially composed of three Jupiter-mass planets on nearly circular, coplanar orbits around the primary star. We systematically varied the semimajor axis, eccentricity, and inclination of the stellar companion, to characterize the conditions under which extreme eccentricities can be excited.
Results. Our results show that dynamical processes such as planet-planet scattering and secular mechanisms - including the von Zeipel-Kozai-Lidov effect induced by the binary - often act together to produce abrupt and significant changes in planetary orbital evolution, with the outcome strongly dependent on the binary separation. The binary's eccentricity primarily dictates the number of surviving planets, while its inclination not only governs the final eccentricities of those survivors but also drives their orbits to align with the binary plane. Our simulations successfully reproduce the high eccentricities and compact orbits observed in four observed systems, and show close agreement between the modeled configurations and the actual systems.