Hot Jupiters in Old Wide-Binary Systems

Abstract

Hot Jupiters (HJs) are giant planets with orbital periods shorter than $10$ days, found around $\sim 0.5$-$1\%$ of Sun-like stars. Their origins remain debated despite decades of study. The high prevalence of stellar companions, the eccentricity distribution of 'Cold' Jupiters on longer orbits, and the wide range of stellar spin-orbit misalignments support high-eccentricity migration: planets are excited to eccentric orbits and subsequently circularised via tidal dissipation. Existing high-eccentricity migration models, however, are inefficient in converting the initial population of Cold Jupiters to HJs. Current models reproduce at most $\lesssim 30\%$ of observed HJs, while the resulting Cold/Hot Jupiter ratios ($\gtrsim 30$) overproduce the observed values of $10$-$15$. These models also fail to form HJs around old stars ($\gtrsim 3$ Gyr) on short tidal decay timescales (e.g., $<40$ Myr). Here we show that wide binaries ($a > 10^3$ au) perturbed by the Galactic tidal field produce $1.8\pm 0.14$ more HJs compared to isolated binary systems, accounting for $26$-$40\%$ of the observed population under conservative assumptions. Wide-binaries predominantly produce Gyr-old systems, consistent with the host-age distribution for $t \ge 2.5\ \rm Gyr$. In $\sim 20\%$ of cases, wide-binary perturbations eject giant planets entirely, resolving the Cold/Hot Jupiter ratio discrepancy while naturally seeding the population of free-floating giant planets. In our dynamical framework, wide binaries emerge as active agents that reshape planetary demographics across billions of years. These results will be decisively tested by forthcoming exoplanet and microlensing surveys.