[tpaine]

And be sure to ignore the fact that some of the planets are 'gas giants'. Methane is a common substance in our solar system, just as it is a common non biological substance on earth.

Methane + heat + pressure = petroleum...

Or, if you favor Golds theory, throw some micro-biological action into the methane soup of the deep hot bio-sphere.

[Cincinatus]

And be sure to ignore the fact that some of the planets are 'gas giants'

In case it's escaped your notice, we don't happen to live on any of those.