On The Orbital Evolution of Multiple Wide Super-Jupiters: How Disk Migration and Dispersal Shape the Stability of The PDS 70 System

TL;DR

This paper investigates the long-term dynamical fate of a multi-wide giant-planet system, using PDS 70 as a case study. The authors couple 2D hydrodynamic simulations that include disk photoevaporation with subsequent N-body integrations to track orbital evolution after gas dispersal, and they contrast disk-driven outcomes with those inferred from disk-free orbit fits. They find that disk-driven evolution can yield stability for more than a gigayear, while disk-free posteriors show only a small fraction (less than a few percent) of configurations remaining stable for 100 Myr. In a three-planet scenario including a proposed inner planet d, higher photoevaporation leads to instability within tens of Myr, underscoring the critical role of disk processes in shaping the architecture and longevity of wide-separation giant planets.

Abstract

Direct imaging has revealed exoplanet systems hosting multiple wide-orbit Super-Jupiters, where planet-planet interactions can shape their long-term dynamical evolution. These strong perturbations may lead to orbital instability, raising questions about the long-term survival of such systems. Shortly after formation, planet-disk interactions can shepherd planets into mean-motion resonances, which may promote long-term stability as seen in HR 8799. However, early-stage processes such as disk photoevaporation and viscosity can influence these outcomes. The $\sim$5 Myr-old PDS 70 system offers a unique laboratory to investigate these processes: its two massive ($>$4 $M_{Jup}$), wide-orbit ($>$20 AU) giants are still embedded in their natal disk. We perform 2D hydrodynamic simulations of the system, allowing the disk to disperse via photoevaporation. Once the disk dissipates, we continue to track the planets' orbital evolution over Gyr timescales using N-body simulations. We find that the system is likely to remain stable for $>$ 1 Gyr. To assess the importance of disk-driven evolution, we compare these results with disk-free N-body simulations using orbital parameters constrained by orbit fits that include recent relative astrometry and radial velocities from the literature. In this case, we find that only $\lesssim 4\%$ of posterior is stable for 100 Myr, highlighting the importance of considering disk-driven evolution for long-term dynamics stability of exoplanetary systems. We also simulate two three-planet configurations including the proposed inner candidate "PDS 70 d", finding that a higher photoevaporation leads the system to become unstable in $<$ 10 Myr.