Detection significance of an atmosphere on GJ 3473 b as a function of the eclipse depth in the MIRI F1500W bandpass, with 4 (top) and 10 (bottom) visits. Positive values correspond to the detection significance of an atmosphere, while negative values correspond to the detection significance of a bare rock. At a significance of zero, these two scenarios are equally likely. The four cases are described in Section 4.2, representing different prior considerations. The vertical dashed lines denote the required eclipse depth for a 3σ detection of the eclipse itself, the actual measured eclipse depth, and the eclipse depth of a blackbody, respectively. The light-gray region represents the uncertainty of the present measurement. The horizontal dotted lines show the detection significances at 0 and ±2.5σ.