The dust-to-stellar flux ratio F/F_star at 70   μm as a function of the total mass in terrestrial planets for eight different times from 1 Myr to 3 Gyr. The terrestrial planet mass refers to the final value such that simulations move vertically in time on the plot. The Spitzer observational limit is shown with the dashed line (Trilling et al. 2008). Grey circles represent stable simulations and black circles represent unstable simulations.