Left panel: simulated temperature structures of LTT 3780 c assuming a substantial primary atmosphere. Blue, green, and red curves represent the temperature profiles at different effective temperatures of 350, 400, and 450 K, respectively. Different profiles within each group are caused by different atmospheric metallicity and C/O ratio. There are 27 temperature structures in total. The dashed and solid black vertical lines mark 273.15 K (0 °C) and 373.15 K (100 °C) for reference. Remaining panels: examples of atmospheric abundances of H₂O, CH₄, CO₂, CO, and soot (haze particles), for solar metallicity and C/O ratio, and effective temperature of 400 K, resulting from the photo-chemical simulations at different vertical mixing strengths.