Hi All

Some geophysical modelling suggests that methane in Titan's atmosphere is due to three distinct episodes of heat loss from the rocky core...

Titan's Methane Mystery May Be Solved

...first was in the time of initial segregation of the core from the icy mantle, then about 2 billion years ago heat built up enough for the silicate core to convect, then again 500 million years ago. Jonathan Lunine says that was probably the last convection episode and the methane that remains is tied up in clathrates between the icy crust and the ammonia/water mantle. In a few megayears the methane will be photolysed away and the sky will clear. Quite possibly without a methane greenhouse the nitrogen will chill out and a thin nitrogen atmosphere will remain, a bit like Triton today.

Adam