Simulations of the in situ formation of Jupiter for Σ_s,0 = 10 g/cm² as a function of the grain opacity reduction factor. The left panel shows the total mass as a function of time. The right panel is the total luminosity (including the intrinsic and the shock luminosity) in units of the intrinsic luminosity of Jupiter today. The curves correspond, from left to right, to f_opa = 10^-4 (black solid), 0.001 (short-dashed green), 0.01 (long-dashed blue), 0.1 (dash-dotted magenta), and 1 (dotted red line). The influence of f_opa on the duration of the plateau phase II is obvious.