Time between sticking collisions. The figure shows the three 128² runs from Fig. 11 plus two higher-resolution runs. In all runs the particle size is τ_f = 0.003 and Z = Σ_solid/ Σ_total = 0.074. We fit a Maxwellian distribution to to all particle pairs with separation less than D. Extrapolating the fit toward small D we estimate the time between sticking collisions. The points on the figure appear to follow a power law t_stick ∝ D². The region in green corresponds to the 1σ confidence region marked in Fig. 10. The figure shows that t_stick< 10⁵ years is a robust upper bound on t_stick.