  With the Cassini-Huygens Mission in orbit around Saturn, the large moon
Titan, with its reducing atmosphere, rich organic chemistry, and heterogeneous
surface, moves into the astrobiological spotlight. Environmental conditions on
Titan and Earth were similar in many respects 4 billion years ago, the
approximate time when life originated on Earth. Life may have originated on
Titan during its warmer early history and then developed adaptation strategies
to cope with the increasingly cold conditions. If organisms originated and
persisted, metabolic strategies could exist that would provide sufficient
energy for life to persist, even today. Metabolic reactions might include the
catalytic hydrogenation of photochemically produced acetylene, or involve the
recombination of radicals created in the atmosphere by UV radiation. Metabolic
activity may even contribute to the apparent youth, smoothness, and high
activity of the surface of Titan via biothermal energy.
