Some speculations on Titans past, present and future

The solar systems second largest natural satellite is shrouded by a thick nitrogen atmosphere, rich in methane, within which sunlight- and cosmic-ray-driven organic chemistry has gone on for some 4.5 billion years. The earliest history of Titans atmosphere, and specifically its origin, remains unclear until the Cassini–Huygens probe measures the ratio of argon to nitrogen and the abundances of other noble gases and isotopes. However, the abundance of deuterated methane in the atmosphere today is consistent with an atmosphere that originated in the chemically-processed sub-nebula around Saturn, rather than in cometary material. Titans overall atmospheric history is driven by the depletion of methane, and the mechanisms by which methane might be resupplied from surface or external sources. Remote sensing data mitigate against a large reservoir of methane at Titans surface, leaving open the possibility that methane is periodically depleted from Titans atmosphere on timescales of 107–108 years; under such conditions Titan might oscillate between thin and thick atmospheric epochs. Titans surface may provide a repository for complex organic molecules that were synthesized during times when liquid water was temporarily available on the surface, such as after impacts or cryo-volcanic eruptions. Such molecules might provide clues to the resolution of some difficult issues associated with the origin of life. Identifying the presence and nature of such molecules is a difficult exploration problem that must be left to missions which follow-on from the Cassini–Huygens exploration of Titan.