Comparison of transit spectra for three atmospheric types. Type A atmospheres spectra stand out with high transit depth, CH₄ features at 3.3 μm, and lack of CO₂ features. Spectra originating from atmospheres of type B lack CH₄ features. Spectra obtained from type C can (if they display oxygen-rich features) resemble type B spectra or resemble type A spectra if they are hydrogen-rich and show CH₄ features.