Period–radius diagram of planets selected from the synthetic population at 2 Gyr after applying the detection selection similar to PAST III (Chen et al. 2022). Planets with different compositions are plotted in different colours: red for H/He-rich envelopes, blue for waterrich envelopes, and green for purely rocky (Silicate+Fe) planets. The dashed lines represent the boundaries of planet radii between different subsamples: Neptune-sized planets, sub-Neptune, valley planet, and super-Earth. Histograms of planetary radius and orbital period are shown in the right panel and the top panel, respectively.