Planet clusters in a 5 Gyr old synthetic planet population with a single planet per system. For all combinations of planet observables a, M_P, and R_P, the differentcolors denote clusters identified by a four-component Gaussian mixture model (GMM). On the diagonal, we show KernelDensity Estimates of the distributions. Without any information about the physics in our formation model, the GMM identified four planet species roughly corresponding to (sub-)Neptunes (blue), icy cores (red), giant planets (yellow), and (super-)Earths (purple).