Thick black line: spectrum of Mars between 1232.6 and 1234.2 cm⁻¹, integrated over the Martian disk, recorded on May 7, 2016 (Ls = 148.5°, normalized radiance). Synthetic spectra of Mars: CO₂ alone (blue),H₂O₂ alone with H₂O₂/CO₂ = 100 ppbv (red). Thin black line (in absolute units shifted by −0.05): transmission from the terrestrial atmosphere, as measured by the TEXES instrument. “Atm” indicates terrestrial absorption.