A time-dependent photochemical model for Titan’s atmosphere and the origin of H2O

Context. Titan’s stratosphere contains oxygen compounds (CO, CO2, and H2O), implying an external source of oxygen whose nature is still uncertain. Recent observations from the Herschel Space Observatory using the HIFI and PACS instruments and the Cassini/CIRS, as well as steady-state photochemical modeling indicate that the amounts of CO2 and H2O in Titan’s stratosphere may imply inconsistent values of the OH/H2O input flux, and that the oxygen source is time-variable.