Widespread disruption of resonant chains during protoplanetary disk dispersal

We describe the evolution of low mass planets in a dispersing protoplanetary disk around a Solar mass star. The disk model is based on the results of Yu et al. (2023), which describes a region of the inner disk where the direction of the migration torque is outwards due to the diffusion of the stellar magnetic field into the disk and the resultant gradual increase in surface density outwards. We demonstrate that the magnetospheric rebound phase in such a disk leads to diverging orbits for double and triple planet systems, and the disruption of a high fraction of the initial resonant chains. We present simulations of three planet systems, with masses based on the observed triple planet systems observed by the Kepler satellite, within the context of this model. The final distribution of nearest neighbour period ratios provides an excellent fit to the observations, provided that the initial configurations contain a significant fraction of pairs whose period ratios are less than 2:1. The occurrence rate of planets as a function of orbital period also provides a good match to the observations, for final orbital periods P < 20 days. These results suggest that the period and period ratio distributions of low mass planets are primarily set in place during the disk dispersal epoch, and may not require significant dynamical evolution thereafter.