Figure 2. Concentration of solid particles in a turbulent disk and onset of gravitational instability. The x- and y-axes represent, respectively, the radial and the azimuthal directions in the disk. The colors illustrate the local density of solids, relative to their mean density (black stands for no concentration, yellow for high concentration). The time in orbital periods is reported above each panel. Notice the progressive local concentration of the solid particles with time. The box inside the panels magnifies the density structure in the vicinity of the most massive self-gravitating clump of solids, whose total mass eventually exceeds the mass of Ceres.