Planetary Desert around Compact Binaries: Dynamical Instability Triggered by Resonance-induced Eccentricity Excitation

Abstract Compact binaries with orbital periods shorter than about seven days show an absence of transiting planets, a feature known as the “circumbinary planet desert.” The physical mechanism behind this desert remains unclear. We investigate its origin by simulating the long-term dynamics of multiplanet circumbinary systems with evolving inner binaries. Our simulations are based on the single-averaged secular equations that average only over the binary orbital period and fully incorporate planet–planet interactions. When an eccentric binary decays via tides, an outer planet can be captured into resonance advection in eccentricity, a state in which its apsidal precession locks with that of the binary, driving extreme eccentricity growth. While such growth can occur in a binary-single planet system, the parameter space is limited and may not necessarily induce instability. In a multiplanet system, however, the excited orbit inevitably crosses those of its neighbors, which triggers violent planet–planet scatterings and produces collisions or ejections. Crucially, these mutual gravitational interactions amplify the “localized” instability of a single planet into a system-wide chain reaction, drastically reshaping the orbital architecture and potentially clearing out the inner regions of planetary systems. Our results suggest that the resonance-induced instability provides a natural explanation for the observed circumbinary planet desert.