Left: 15 μm band secondary eclipse depth as a function of fO₂ across the surface pressure grid space with main graphite activity a_c = 10⁻⁶. Dashed circles indicate stable atmospheres, as approximated using the methodology described in Section 5. Symbols in black indicate the stable atmospheres of all surface pressure scenarios for the main graphite activity value, while all other colors indicate the variability in graphite content for a 100 bar atmosphere. Right: 15 μm band for the bare-rock with various surface material scenarios, plotted on the same vertical scale as the left panel.