Masses (M_p∕M_J) for the systems with two and three equal-mass planets on circular orbits: red circles represent a system with two planets that are detectable, while green and blue circles represent three planets detectable and undetectable, respectively. Since the equations are not fully correct for more massive planets, for the two-planet case we show only systems for which M_P ≤ 50 M_J whereas for the three-planet case we show only systems for which M_P ≤ 15 M_J.