Binary tidal evolution as a sculptor of circumbinary planet architectures
Year: 2026
Type: article
Abstract: Circumbinary planets (CBPs) are expected to form in circumbinary discs and migrate towards the disc inner cavity, often close to the dynamical stability boundary of the binary. Yet, the observed transiting and radial-velocity population is not strictly marginally stable. Excluding extreme systems, the typical offset from the stability limit is Δ ≡ a_ ̊m p /a_ ̊m crit =1.22^ +0.18 _ -0.07 , suggesting that post-formation evolution may have shaped the present-day architecture. We investigated whether the secular evolution of close binaries can contribute to the observed displacement of CBPs from marginal stability. We tested how prescribed binary contraction and eccentricity damping move the stability boundary, a_ ̊m crit (t), thereby modifying Δ=a_ ̊m p /a_ ̊m crit as well as the orbital response, survival, and loss of near-boundary planets as a function of binary mass ratio. We performed controlled, high-accuracy N-body simulations of single coplanar CBPs initially placed near a_ (t) modifies the planets' final offsets, orbital response, survival, and loss. crit. The planets evolve under Newtonian gravity, while the central binary follows a prescribed contraction and eccentricity damping track that approximately conserves orbital angular momentum. We measured how the resulting motion of a_ crit The retreat of a_ ̊m crit (t) filters the initially near-boundary population, adding a contraction-driven loss component dominated by ejections. Surviving planets remain quasi-fossilised, with median changes in a_̊m p and e_̊m p close to zero and typical semi-major axis drifts of only a few per cent. Considering all valid synthetic survivors, the final offset reaches a global median value of Δ_f = 1.86^ +0.18 _ -0.26 . Applying the same fiducial damping prescription to the observed sample shifts the median offset from Δ_ ̊m now =1.22^ +0.18 _ -0.07 to Δ_ ̊m damp =1.44^ +0.32 _ -0.10 . Near-equal-mass binaries undergo stronger dynamical filtering, with enhanced ejections and collisions. Binary tidal evolution offers a plausible internal pathway for shaping non-marginal circumbinary architectures. By displacing or removing planets initially close to marginal stability, the inward retreat of a_ crit (t) can widen the inner circumbinary gap and move surviving planets towards larger offsets from the present-day stability boundary. This mechanism links binary orbital evolution, dynamical filtering, and the detectability of transiting CBPs, supporting a multi-channel interpretation of the CBP desert in which physical sculpting and geometric selection act together.
Source: Astronomy and Astrophysics
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
Awards: G143927386, G7689440551
OpenAlex ID: W7214959423