Ganymede is larger than Mercury, about the same size as Mars, but has very low density. It may have a liquid water atmosphere 60 miles thick (holding more water than found on earth. If we could drive Ganymede into Venus, we might get something habitable (after everything cooled down).
I’ve often thought that the next moon of Saturn to be discovered should be named Mutthead, to go with Mimas. Maybe it’s just me.
Wow, Mars is small!