Internal density evolution at r = 30 AU in the minimum mass solar nebula model (see Kataoka et al. 2013b, for more details). The solid line represents the evolution. The black, green, blue, and red lines are in the coagulation phase of hit-and-stick, collisional compression, gas compression, and self-gravitational compression, respectively. The dotted lines show the af = (constant) lines, where af = 0.1 μm, 10 μm, 1 mm, and 10 cm, respectively.