Warm Jupiter Tidal Migration Can Spare Inner Planets; Hot Jupiter Tidal Migration May Not

TL;DR

This study explores how the high-eccentricity tidal migration of giant planets affects the survival of inner planets, revealing conditions under which inner planets can remain stable and providing a framework to differentiate migration mechanisms.

Contribution

It offers a combined analytic and simulation-based analysis of inner planet survival during giant planet tidal migration, identifying key stability thresholds and applying findings to observed exoplanet systems.

Findings

Inner planets survive if periastron exceeds ~14 mutual Hill radii.

Systems with known hot Jupiters and inner companions likely did not form via high-eccentricity migration.

Warm Jupiters with larger periastron distances can coexist with inner planets.

Abstract

In this work, we investigate the dynamical survival of short-period inner planets during the high-eccentricity tidal migration of companion exterior giant planets. Using a combination of analytic arguments and N-body simulations including equilibrium tides and general relativistic precession, we find the boundary in parameter space where an inner companion can remain dynamically stable. We find that survival requires a periastron separation exceeding roughly 14 mutual Hill radii at closest approach. Below this threshold, secular eccentricity exchange, orbit crossing, and/or tidal evolution can lead to the destruction of the inner planet. We apply our methodology to the current exoplanet sample and find that none of the known systems containing a short-period giant and an inner companion could have assembled via high-eccentricity tidal migration. However, warm Jupiters with larger periastron distances ($q_{\mathrm{out}} \sim 0.05-0.08$ AU, corresponding to final observed semi-major axis values $a_{\mathrm{out}} \sim 0.10-0.16$ AU) can allow the survival of short-period inner planets while potentially also circularizing on $\lesssim 1$ Gyr timescales. Our results provide a framework for distinguishing disk migration from tidal migration in observed multi-planet systems containing close-in gas giants.