Ganymede and Callisto

Nearly as large in size as Luna, but darkly colored and not as heavily cratered, Ganymede and Callisto are very similar worlds. Neither is as dense (nor has as much gravity), as their mantles consist of more ice than iron rock. Both possess abundant volatiles and water (albeit frozen), making them ideal candidates for habitation. Ganymede, with its differentiated surface of rocky and icy terrain, has an iron core and thus a faint magnetic field. Callisto, the smaller of the two, is composed mostly of icy silicate clays. As on Luna, most cities on Ganymede and Callisto are built below ground to shield them from meteor impacts (and, on Ganymede, from Jupiter’s radioactive bombardment).

While within the “protection” of the Jovian Republic, both moons are a patchwork of city-states. Some are full members of the Jovian polity, while others are only tolerated. Ganymede tends to swing more heavily toward the Junta, as its citizens still see the Junta-maintained infrastructure—accurately or not—as necessary in such a hostile environment. Callisto, outside the worst radioactive effects of the Jovian magnetosphere, is an easier place for technoprogressivism to gain a foothold.


The nucleus of this city-state was a research station founded by a coalition of Pacific Rim nations in Callisto’s Valhalla region, a massive primordial impact zone where the icy subsurface lies exposed, simplifying extraction of clean water. When the Fall came, Hyoden, which had long faced labor shortages, opened itself to those refugees who could make it to Jupiter. Now Hyoden has two million inhabitants, making it the largest city-state on Callisto and the largest non-Junta state in the Jovian system. Hyoden is itself heavily militarized, as the tendency of the local authorities to turn a blind eye toward operatives using their territory for forays against the Junta makes for uneasy relations with their powerful neighbor.


Situated along the southern edge of the vast, rocky plain called Galileo Regio, almost on Ganymede’s equator, Liberty (population 7 million) is the Junta’s largest planetary city-state. It is closely tied to Liberty Station, a major shipyard and defense installation in geosynchronous orbit. Major industries include shipbuilding, space construction, fabrication, and security products and services. The Castle, the central security network point from which all surveillance data collected in the Junta is monitored and processes, is rumored to be in or near Liberty. Liberty is mostly underground, but it boasts a number of parks in armored surface domes. If one were to spend enough time topside, one would see the deceleration torches of incoming metal asteroids from the belt bound for the shipyards lighting up the sky several times a day.

Ganymede and Callisto

Beyond the Black questionable