Large enough that it could almost have formed the nucleus of a protostar in its own right, Jupiter’s massive size makes the Jovian system one of the most challenging places in the system to colonize. Jupiter’s powerful magnetic eld means that its inner moons— and the outer ones, when their orbits pass through its immense magnetotail—are bombarded with enough ionizing radiation to kill transhumans not protected by the heaviest of shielding within a matter of hours. There are sixty-three moons and moonlets in the Jovian system, but only the well-explored, populous, regular moons are described here.

Resources and Economy

Jupiter’s powerful gravity well is a major hindrance to gas mining in the planet’s atmosphere, as even craft that do not succumb to the violent, centuries-long atmospheric storms can only achieve escape velocity with the most powerful propulsion systems. Given the need for heavy shielding on such craft, gas mining on Jupiter is not nearly as efficient as on Saturn. Jupiter has a tenuous ring system, much less dense than Saturn’s, which extends out for 20,000 kilometers around the planet, encompassing the orbits of its two closest moonlets.

Jupiter’s gravity, however, is also a valuable resource. Craft bound for Saturn and beyond can slingshot themselves outward by circling the planet to pick up velocity, cutting months or years off their trips. The heavily militarized Jovian Republic levies tolls against all spacecraft using Jupiter’s gravity to pick up velocity, including asteroids under propulsion. This protection money is the Junta’s primary source of revenue. Planetary Consortium ships generally accept the payment as part of operating expenses. Other factions are not so cooperative, and the Junta regularly seizes or destroys blockade runners.

Habitat Amalthea

The largest of the moonlets, hollow Amalthea is probably the most livable sarcophagus habitat due to the large lake created from its icy core. Living on Solano carries some prestige among Junta citizens. Rumor has it that most of the residents are well-placed RAND think tank personnel, most of whom work on defense projects. A fusion-powered axial light tube illuminates the 30-kilometer diameter central cavern, whose landscape is patterned after the subdivisions and of ce parks of an early 21st-century suburb.

Body Europa

Europa has no atmosphere and lies within the fear- some magnetosphere of Jupiter. Its surface is bombarded with enough radiation for an unshielded transhuman to receive an irrevocably fatal dosage within a few days—much faster when Europa’s orbit passes through Jupiter’s immense magnetotail. As a result, transhumans on Europa dwell beneath the icy crust, largely in the ocean below, adopting a variety of aquatic and amphibious morphs for survival.

Body Ganymede and Callisto

Larger in size than 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 eld. Callisto, the smaller of the two, is composed mostly of icy silicate clays.

Habitat Hyoden

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 2 million inhabitants, making it the largest city-state on Callisto and the largest non-Junta state in the Jovian system.

Body Io

Beneath Io’s tenuous, patchy atmosphere of volcanic gases and neutral atomic dust lies a barren, grayish yellow, rocky surface coated with a thin frost of sulfur dioxide. Tidal heating caused by gravitational interaction with Jupiter makes Io the most volcanically active body in the system—so active that the meteor cratering found on every other planet and moon is completely absent on Io. Massive volcanic calderas, lakes of molten rock, and geysers of sulfur dot the surface, with eruptions and accompanying seismic activity lasting months or years.

Habitat Liberty

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 processed, is rumored to be in or near Liberty.

Region The Trojans

The Trojans and Greeks are two 600 million kilometer-long arcs of scattered, icy-rock asteroids sharing the orbit of Jupiter. They orbit in the stable L4 and L5 points sixty degrees ahead of and behind the giant planet. Mars and Neptune also have Trojan asteroids, but when someone speaks of “the Trojans” they’re normally talking about the Jovian groups. In the early days, L4 asteroids (ahead of Jupiter) were named after Greek heroes of Homer’s Iliad; L5 asteroids (trailing Jupiter) were named after heroes of Troy.