Mercury is soid rock. the gases beingt blow away by strong solar wind and radiations.

If we get rid of the gases on ganymede, like a large furry dog which got it's hair clipped not much would be left.

Merc is rocky, Ganymede is gassy. There is no empirical, rational comparison. Mercury is WAY denser than Ganymede. Besides 'gany fooled around with Jove.