If you're going to say goodbye to Earth and all its conveniences, perhaps forever, and make the 500+ million mile move to one of the moons of Jupiter, you might want to know a few things about it.
Jupiter has 79 moons in all, but only four are large enough to see through an ordinary telescope or binoculars from Earth. These four "Galilean" moons were first observed in the early 1600s and named for four of Zeus's "lovers". (If you're familiar with the mythology "victims" might be a better term for them). Io, with its unique sulfur yellow surface, orbits closest to Jupiter. The tidal forces exerted by Jupiter's gravity causes significant volcanic activity on Io. Next is Europa, whose subterranean liquid ocean is considered one of the best candidates to find life elsewhere in the Solar System. Unfortunately the proximity of Europa and Io to Jupiter's radiation belt mean both moons would not make great places for humans to spend time. Safer would be Ganymede, the largest moon in the Solar System, larger even than the planet Mercury. But even here an unprotected moon grunt would get a lifetime's worth of radiation in less than two weeks.
Callisto on the other hand orbits far enough from Jupiter that this wouldn't be an issue. As long as your attire shields you from the thin cold atmosphere you are free to walk around on Callisto's cratered surface of rock and ice. While the size of the moon's craters greatly varies, a diameter of twenty-five miles is pretty typical. The rim of such a crater could be up to five miles above the crater floor. Try to picture being in a bowl smaller in area than metropolitan Los Angeles, with sides rising up nearly as much as Everest does from the sea. And if you happened to be on the side of the moon that perpetually faces Jupiter you would be treated to an even more impressive sight. While the Sun and Jupiter's other moons would regularly pass in and out of view, the marbled gas giant would be forever locked above the horizon, taking up about seventeen times more sky than the Earth's moon does from Earth.
Valhalla is the largest impact crater in the Solar System. It is known as a multi-ring crater, which resembles something like ripples on a pond emanating from a cast stone. Indeed the rings are evidence of a subterranean liquid ocean on Callisto. Like many of the larger and older craters Valhalla contains newer and smaller ones such as Mimir, Sarakka, and Nár. Settlements in and around these craters would require habitat structures and rovers that could cover the distances between them. Being about the size of Mercury, Callisto's gravity is only one eighth as strong as Earth's. This would allow for some unique habitat design that might not be structurally sound on Earth. "Tenting" clusters of habitats inside an insulating dome would make operations in a crater much easier, as workers could freely move about between habitats in a controlled climate without the need for cumbersome space suits.
Energy would come primarily from two sources. The Jupiter system is just close enough to the Sun that solar power would be feasible. A "day" on Callisto lasts about seventeen Earth days, which means a particular outpost would have sunlight for half that time before nightfall. To get through the equally long period of darkness nuclear power would be necessary. Radioisotope Thermoelectric Generators, or RTGs, are portable nuclear sources that could supplement the energy needs of an outpost during these long nights, but operations would still be curtailed until the next day.
Artificially intelligent robotics would be an important aspect of building a civilization on a moon like Callisto. Such AIs could be sent out in advance of human beings to create rover paths and "seed" craters with materials and equipment. Even after humans arrive in a crater these AIs could continue to operate there, carrying out day to day operations in factories and other facilities. Settlers on Callisto could also benefit from partnerships with any parallel settlements on nearby Ganymede. For instance shipments of needed goods and supplies could be sent via drones to Callisto from Ganymedean factories.
But how would it feel to live on Callisto? If you were one of the earliest arrivals it would be arduous. You would be working hard to establish a basic settlement, confined to cramped habitats huddled on a harsh barren moonscape, constantly anxious about resources needed for survival like air, electricity, food and water, and probably growing weary of being around the same people all the time. But suppose you came later, after the colony had grown more populous and self sufficient, into something resembling a real town. Monotony and spartan living might give way to optimism, maybe even an exhilaration over the prospect of building a fresh civilization. At least for a time you may be able to forget about the ideological baggage that so often drags societies on Earth into injustice, waste and destruction. Life on Callisto could be an opportunity. You might decide to make a name for yourself in this nascent paradise, by expanding out to new craters, founding new outposts, and building factories that fill the demand for luxuries. A person of your ambition arriving on Callisto at the right moment just might be remembered as the one who transformed the moon from an interplanetary backwater into a vibrant civilization.
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