"This is almost as odd to imagine as an alien biology," McKay told me. "It would require some unknown mineral acting as the catalyst on Titan's surface that converts hydrogen molecules and acetylene back to methane."
Settling the mystery would require a Titan lander to conduct experiments on surface material. "We possibly could measure metabolism but (as with the Mars Viking experiments) there could be confusion between chemical reactions and biological metabolism," says McKay. "Detection of biomolecules would be easier and more definitive." This would require a gas chromatograph mass spectrometer (GCMS), as is being flown on upcoming Mars Science Laboratory and was flown on the twin Viking Mars landers, and ESA Huygens Titan lander (which carried a GCMS for atmospheric studies.)
"The distinction between microbial activity and a non-biological catalysis would be the accumulation of complex and non-equilibrium organic molecules, the alien equivalent of ATP and Ribisco," says McKay.
If exotic alien life were someday confirmed on Titan, it would further dilute the idea of a precise "habitable zone" around stars. Various manifestations of life could evolve under a wide range of temperature and chemical environments. This would unfold on a variety of moons and planets throughout a planetary system.