Dynamical Evolution of Closely Packed Multiple Planetary Systems Subject to Atmospheric Mass-Loss

A gap in exoplanets' radius distribution has been widely attributed to the photo-evaporation threshold of their progenitors' gaseous envelope. Giant impacts can also lead to substantial mass-loss. The outflowing gas endures tidal torque from the planets and their host stars. Alongside the planet-star tidal and magnetic interaction, this effect leads to planets' orbital evolution. In multiple super-Earth systems, especially in those which are closely spaced and/or contain planets locked in mean motion resonances (MMRs), modest mass-loss can lead to dynamical instabilities. In order to place some constraints on the extent of planets' mass-loss, we study the evolution of a series of idealized systems of multiple planets with equal masses and a general scaled separation. We consider mass-loss from one or more planets either in the conservative limit or with angular momentum loss from the system. We show that the stable preservation of idealized multiple planetary systems requires either a wide initial separation or a modest upper limit in the amount of mass-loss. This constraint is stringent for the multiple planetary systems in compact and resonant chains. Perturbation due to either impulsive giant impacts between super-Earths or greater than a few percent mass-loss can lead to dynamical instabilities.