Material ablated from the planetesimal surfaces re-condense and grows to mm-sized pebbles in the disk’s midplane. Top: Mass flux of pebbles as a function of time and semimajor axis for the nominal Solar System simulation. The solid lines take into account the formation and ablation of newer generations of planetesimals forming at the gap edges from this flux of pebbles, while the dotted lines do not. Bottom: Corresponding pebble-to-gas surface density ratios.