Greenhouse models of the atmosphere of titan

The greenhouse effect is calculated for a series of model atmospheres of Titan containing varying proportions of methane, hydrogen, helium, and ammonia. The pressure induced transitions of hydrogen and methane are the major sources of infrared opacity. For each model atmosphere we first computed its temperature structure with a radiative-convective equilibrium computer program and then generated its brightness temperature spectrum to compare with observed values. This comparison indicates that the methane-to-hydrogen ratio is 1_?.67⁺², the surface pressure is at least 0.4atm, and the surface temperature at least 150°K. In addition, except possibly close to the surface, the amount of ammonia is far less than the saturation vapor value. Large amounts of helium may also be present. Many of the successful model atmospheres have methane condensation clouds in the upper troposphere, which help reconcile spectroscopic gas abundances and the observed ultraviolet albedo of Titan with the gas amounts required for the greenhouse effect. The occurrence of large amounts of hydrogen may be a prerequisite for the occurrence of large amounts of methane in the atmosphere and vice versa. This hypothesis may help explain why Titan is the only satellite in our solar system known to have an atmosphere.