Why is Venus 460°C, Earth comfortable and Mars freezing? The atmosphere. T_eq = T_☉·√(R_☉/2a)·(1−A)^¼ sets the no-atmosphere baseline. Greenhouse: T_surface = T_eq·(1+¾τ)^¼. Earth τ≈0.78 (+33K). Venus τ≈120: runaway greenhouse. Jeans escape: atmosphere retained if v_thermal < v_escape/6 — small hot planets lose H₂/He first. The simulator covers 7 planets including TRAPPIST-1e.
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