Possible Dynamical Pathways to the Misalignment of the VHS 1256–1257 System

Circumbinary planets (CBPs) provide a unique window into planet formation and dynamical evolution in complex gravitational environments. Their orbits are shaped not only by the protoplanetary disk but also by the perturbations from two stellar hosts, making them sensitive probes of both early- and late-stage dynamical processes. In this work, we investigate the unusual architecture of the VHS J125601.92−125723.9 system, where a retrograde, nearly polar tertiary orbits an extremely low-mass substellar binary in a hierarchical triple configuration. We find that triple-body dynamics can naturally reproduce the observed high eccentricity of the inner binary and the tertiary's near-polar obliquity. However, this configuration alone cannot account for the observed mutual inclination, which is both near-polar and retrograde. This tension suggests two possible formation pathways: either the planet formed in an aligned, protoplanetary disklike configuration and was later tilted by an additional, undetected fourth companion (below current Gaia limits), or the system formed close to its current state. Stellar flybys, in contrast, are unlikely due to their long timescales. Our results highlight both the explanatory power and the limitations of triple dynamics, and the potential role of hidden companions in shaping extreme planetary architectures.

We would like to thank the anonymous referee, Gongjie Li, Rebecca Martin, Michael Poon, and Hannao Rein for fruitful discussions and comments. L.H. and S.N. thank Howard and Astrid Preston for their generous support. C.S. acknowledges support from the Department of Energy Computational Science Graduate Fellowship supported by the U.S. Department of Energy, Office of Science, Office of Advanced Scientific Computing Research, under Award No. DE-SC0026073. We would like to thank UCLA Office of Advanced Research Computing’s Research Technology group for the computational and storage services provided by the Hoffman2 Shared Cluster, and the UCLA Department of Physics and Astronomy for their continued support.