The Medician Stars, as Galileo dubbed his discovery in orbit around Jupiter, reimagined as terraformed worlds by 1Wyrmshadow1, on his Deviant Art page. James Oberg discussed their terraforming in his (now classic) “New Earths” (1981), as has Martin Beech in his more recent “Terraforming: The Creating of Habitable Worlds” (2009) and Martyn Fogg in “Terraforming: Engineering Planetary Environments” (1995). The first, semi-serious discussion, was fictional – Robert Heinlein’s “Farmer in the Sky” (serialised as “Satellite Scout” in 1950, then novelised in 1953.) Heinlein’s tale began with Ganymede being given an oxygen atmosphere busted out of ice on the ground, via total-annihilation powered systems. Heinlein is vague on details – he knew the ingredients, not the details. So he had the moon being kept warm via “the Heat-Trap” and the ice being lysed by some energy delivery system. The story begins long after the process had progressed to a colony of 15,000 dirt-farmers slowly converting the place into living room for an over-flowing Earth.
Of course Heinlein had to fudge a few details. Even in 1950 Ganymede was suspected to be rather too low density to be as rocky as Heinlein describes. The real Ganymede is half ice. Not a total disaster. If only the outer-layers melted and the topography was kind, then water would pool in the lower parts and the meteoritic dust in the crust would form a layer of soil over it. Such a world would need to stay, on average, cool, but parts would be warm enough for water and vegetation. Ice warms slowly – witness the permafrost under the tundra of northern Europe. Given a low enough average temperature and enough salts in the ice and the stuff will remain stable. But beware TOO MUCH Global Warming…