JWST simulations for NIRISS SOSS (top), NIRSpec G395H (middle), MIRI LRS (bottom) with no noise floor. Each simulation is done for 100 transits in each observing mode. One transit observation consists of 1 hr in-transit and 1 hr out-of-transit. All simulations are for a GJ 1214-type host star with J = 8, for the same planet parameters as in Figure 1. The only difference between the simulations is the gravity and metallicity (H₂O/H₂), indicated in the color legend. All spectra are binned to R = 100. The red error bars represent the proposed ±20 ppm noise floor for NIRISS/NIRSpec and ±50 ppm noise floor for MIRI (Greene et al. 2016).