"Rodney Kelp" wrote in message
...
How do you get a nitrogen atmosphere from a moon that has methane oceans?

Ask the same question of Earth, how do we have a nitrogen atmosphere with
liquid water oceans?

Briefly, there's every reason to expect materials with similar boiling
points (and more importantly, molecular masses) to be present on a given
body. Loss mechanisms for the atmosphere can be absorptive (like the CO2
that was soaked up to form carbonates on Earth) or 'exhaustive' where the
material is lost from the planet by exoatmospheric escape.

So, if Titan accreted a shedload of methane in its early life (maybe...)
then there's nothing to have stopped a comparable cosmic-abundance-worth of
nitrogen being trapped too. Do a trawl for 'Lunine' and 'J.S.Lewis' for
papers (NASA ADS for starters) and ideas.

-James Garry
(ex Huygens payload tweaker)