Left: thermal emission spectrum of a planet at 500 K with the Exo-REM atmospheric model (Charnay et al. 2018) downgraded to 1 SHORT band resolution (R ≈ 3500) of MIRI/MRS. Right: PSD of the same spectrum with (blue) and without (red) high-pass filtering. The PSD’s limits are defined by the cutoff resolution, R_c, and the instrumental resolution, R_{in st}. Due to the Gaussian filter, some spectral content may remain below R_c, while no lines exist beyond R_{in st} (see Appendix A).