re: Methan here, methane there?
Hi Doug
Simply the methane breakdown rate on Titan is ~ 60 times less because of the distance and most of it is protected from UV by being at the bottom of the atmosphere. However we know it is breaking down on Titan because of all the photolysis products - smog - that shrouds that moon. Hence reservoirs of methane must exist, probably soaked into the icy soil as "groundwater" as Huygens discovered. On Mars such a reservoir does not and can not exist, hence it needs another origin - either vulcanic or biogenic.
Adam