Top: atmospheric model of HR8799 b calculated with petitRADTRANS and simulated MRS data using MIRISIM with realistic observation parameters, including all available noise sources. After the whole simulation chain and pipeline calibration steps we recover the input flux (see inset) by subtracting the stellar PSF with a simulation of HR8799 A without the planets. The error bars indicate the 3σ estimates from apertures with no planet signal at the same separation from the star as HR8799 b. Bottom: opacity of different molecules as a function of wavelength in the mid-IR. Many molecules provide modulation in their opacityr which will translate to detectable molecular features in their spectra.