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Evolution of a Nitrogen Atmosphere on Titan

Photochemical calculations indicate that if NH3 outgassed from Titan it should have been converted to a dense N2 atmosphere during the lifetime of the satellite. A crucial step in the process involves a gas phase reaction of N2H4 with H. The most favorable conditions for this step would be the intermediate production of a CH4-H2 greenhouse capable of raising the gas temperature to 150�K. Subsequently about 20 bars of N2 could have evolved. The pressure-induced opacity of 20 bars of N2 should suffice to explain the recently measured 200�K surface temperature. Unlike the situation on Jupiter, NH3 is not recycled on Titan by reactions involving N2 or N2H4. This may explain the failure of recent attempts to detect NH3 in the upper atmosphere of Titan.