Realization of the CO and water gas masses by the MonteCarlo approach. On the top panel, 10 realizations are done (i.e., 10 targets), while on the bottom panel, 30 realizations are performed. Statistical identification of the non-monotonic behavior is very likely possible if N ≳ 10 and if the mass sensitivities of CO gas and water gas are an order of 10^–4M_⊕ and of 10^–9 – 10^–8M_⊕ or lower, respectively.