Core growth as function of time, for different values of the initial dust-to-gas ratio Z₀. Cores are placed on the same orbits as in Fig. 3, and similar labeling is used. Core growth is very sensitive to the initial metallicity: a twice as high value as the canonical dust-to-gas ratio of Z₀ = 0.01 leads to the formation of exclusively gas giants, while lowering the metallicity by a factor 2 leads to systems of small ice giants.