Mars geothermal adiabat (brown) superimposed on phase diagrams of: water (blue), methane (orange), and carbon dioxide (yellow), based on Figures 3, 5, and 6. The solid, dashed, and dashed–dotted lines represent the L–V line, S–L line, and ζ₂ = 0 loop, respectively. The triple point (TP), CP, and DP are represented by diamonds, circles, and squares, respectively.