TITAN AND ENCELADUS : ICY CAULDRONS OF ORGANIC SYNTHESIS

Saturn's giant moon Titan has been of considerable interest since the presence of an atmosphere was hinted at one century ago. The NASA-ESA-ASI Cassini-Huygens mission, at Saturn for the last 6 years, has transformed this curious dot in the sky into a remarkably diverse, complex and interesting world, which is in many ways more Earth-like than anywhere in the solar system. This talk will summarize some of Cassini's recent findings with emphasis on the interactions between Titan's surface, atmosphere, and likely liquid water interior. These include dune-covered sand seas, river channels that attest to violent but perhaps rare downpours and climate change, seas and lakes of liquid hydrocarbons, and possible cryovolcanic features. Evidence for the latter is the subject of ongoing debate, not least because recent or ongoing cryovolcanism introduces a new dimension to organic synthesis on Titan. The hydrocarbons and nitriles drizzling out of the atmosphere, discovered by Cassini to be of remarkable complexity, are an astrobiological dead end given the relative lack of oxygen-bearing compounds. However, hydrolysis on the surface by impact melt or cryovolcanism can yield abundant amino acids, pyrimidines and other compounds of considerable interest. Although tiny, Saturn’s E-ring moon Enceladus provides an intriguing counterpoint to Titan - hosing salty water ice crystals into space in spectacular plumes that also contain organic material. Remarkably these plumes, possibly originating from liquid water beneath the surface, may be the source of much of what little CO₂ and H₂O there is in Titan’s atmosphere.

The recently-approved Cassini Solstice Mission promises to deliver many future discoveries over the next Saturn season, and several proposals for future missions are in work, in many cases (such as airplanes, boats and balloons) exploiting the unique Titan environment. These future prospects will be briefly reviewed.