Migration of a Neptune-mass planet (panel a) and disk surface density evolution (panel b) in simulation run-fid. In panel a. the solid curve shows the time evolution of the planet’s semimajor axis. The gray circle marks the planet position at the time shown in Figs. 2 and 3. The planet undergoes a reversal in migration direction (termed “rebound migration”) as the inner photo-evaporative cavity expands from the inside out. The video can be downloaded from: https://github.com/bbliu-astro/movies/blob/main/hydrodynamic_rebound/Neptune.gif and online.