The particle column density as a function of time after self-gravity is turned on at t = 20.0   T_orb, for run M2 (256³ grid cells with 8 × 10⁶ particles). Each gravitationally bound clump is labelled by its Hill mass in units of Ceres masses. The insert shows an enlargement of the region around the most massive bound clump. The most massive clump at the end of the simulation contains a total particle mass of 34.9 Ceres masses, partially as the result of a collision between a 13.0 and a 14.6 Ceres mass clump occurring at a time around t = 31.6   T_orb.