New data from the Cassini spacecraft show hydrogen is disappearing near Titan's surface. What's more, scientists have not been able to find acetylene, an organic molecule that should be pretty abundant in the moon's thick atmosphere.
...NASA astrobiologist Chris McKay, proposed five years ago that microbial life on Titan could breathe hydrogen and eat acetylene, producing methane as a result.
Scientists emphasize that the findings are not proof of life, and there's plenty of work to do before non-biological causes can be ruled out. Scientific conservatism suggests that a biological explanation should be the last choice after all non-biological explanations are addressed.
What is being observed is hydrogen is disappearing at the surface of the moon and the molecule acetylene appears to be absent when it should be abundant. Further, methane is being produced at the surface. It's possible hydrogen is combining with carbon on the surface to produce methane. But Titan is too cold for that to happen quickly enough to account for all the missing hydrogen.
C2H2 + 3H2 ---> 2CH4 + energy
acetylene + hydrogen → methane + energy
Cassini will be making several more flybys of the moon and will collect more data, but for now, there is no conclusion on the mechanisms involved in the phenomenon.