TOI-216: Resonant Constraints on Planet Migration

TOI-216 is a pair of close-in planets with orbits deep in the 2:1 mean motion resonance. The inner, Neptune-class planet (TOI-216b) near 0.12 au (orbital period $P_{\rm b} \simeq 17$ d) and has substantial orbital eccentricity ($e_{\rm 0.16$), large libration amplitude ($A_\psi 60^\circ$) outer (TOI-216c) gas giant on nearly circular orbit. We carry out $N$-body simulations migration protoplanetary disk to explain configuration planets. find that TOI-216b's must have been halted its current radius allow for convergent two into For inferred damping-to-migration timescale ratio $\tau_e/\tau_a 0.02$, overstable librations resonance lead limit cycle $A_\psi 80^\circ$ $e_{\rm b}<0.1$. system could remained this greater part lifetime. If was removed from inside out, would reduced 60^\circ$ boosted b}$ via resonant interaction TOI-216c. Our results suggest relatively fast inner removal ($\sim 10^5$ yr). Another means explaining stochastic stirring (turbulent) disk. work, need be suppressed, 0.05$, very strong turbulent (or some other source forcing) overcome damping effects gas. Hydrodynamical can performed test these models.