Presentation #403.02 in the session Resonant Dynamics and Consequences, Plus Disks!.
The discovery of multi-planet resonant chains such as those in TRAPPIST-1 and Kepler-90, where adjacent planets are in different resonances, has raised questions on the formation of these systems. It is widely accepted that these systems formed through the combination of migration and resonance-capture where migrating planets capture each other in resonances. There is, however, an issue with this scenario as migrating planets tend to capture each other in the same resonance. It has been suggested that tidal forces are the reason that resonant-chain planets are in different commensurabilities. The latter motivated us to examine the validity of this statement. We have carried out extensive simulations of planet formation and migration, and determined the probability of capture for different resonances. Results demonstrate that migrating planets can in fact be captured in different resonances confirming that the diversity of resonances observed in resonant chains is a natural consequence of the formation and resonance capture mechanism, and does not require a secondary process. Results also show that the probability of capture (and, therefore, the final commensurabilities) is highly depended on the characteristics of the systems, especially the planets’ mass-ratio and migration speed. Finally, our simulations indicate that capture in a resonance never occurs at the resonance’s exact commensurability and there is always some deviation. The extent of this deviation also depends on the mass-ratio and orbital characteristics of the planets and the mechanism through which migrating planets lose energy. This also confirms that unlike previous studies, no post-capture mechanism is needed to explain the deviation from exact resonances observed in Kepler (and RV) planet pairs. We present the details of our study and discuss their implications for the formation and orbital architecture of resonant, multi-planet systems.