Jupiter is the fifth planet from Sol and the largest planet in the Sol system. It is a gas giant without a solid surface and its mass is greater than that of all the other planets in the Solar System combined. The planet is named after Jupiter, the king of the gods in ancient Roman religion. Although the planet itself is uninhabitable, a number of its moons are inhabited by approximately forty-five million inhabitants in total. As a planetary system, it is de jure governed by both the United Nations and the Martian Congressional Republic.
It is a gas giant with a mass more than 2.5 times that of all the other planets in the Sol system combined and slightly less than one-thousandth the mass of the Sun. Its diameter is eleven times that of Earth, and a tenth that of the Sun. Jupiter orbits the Sun at a distance of 5.20 AU (778.5 Gm), with an orbital period of 11.86 years. It is the third brightest natural object in the Earth's night sky, after the Luna and Venus, and has been observed since prehistoric times.
Ganymede is the seventh satellite of Jupiter and the largest moon in the Sol System. It is one of the "Galilean moons", the four largest moons of Jupiter that Galileo Galilei discovered. It is the only moon with any magnetosphere, the ability to deflect charged ionizing radiation, making it the only place where dome-grown crops stood a chance in Jupiter's harsh radiation belt besides Callisto. It can be thought of as a place of harvest, and definitely a lynch pin in the food economy in the belt. Large mirrors were placed around the moon, most likely to supply the Sun's light to the surface for crop growth. The magnetosphere helps claim the Jovian moon has the lowest amount of birth defects and stillbirths. This being the case, many women come to Ganymede to deliver. It is the center of what made human expansion to the outer planets possible.
Ganymede Station was one of the first permanent human settlements in the outer planets, built as a long-term colony with large domes filled with food crops. It was known as the safest station in the Jovian system, and many humans from other colonies traveled to Ganymede to deliver their babies. During the Eros Incident, a revolt ended with sixteen dead.
Callisto, also Jupiter IV, is the second-largest moon of Jupiter and the third-largest in the Sol System. It houses the Martian Congressional Republic Navy (MCRN) Callisto Shipyards, the MCR's (Martian Congressional Republic) primary military shipyards.
The moon has a moderate subterranean population as the moon does not enjoy the protection from Jupiter's radiation belts in contrast to Ganymede. The colony has a mining industry but also boasts shipyards, including the MCRN Callisto shipyards and the United Nations (UN) owned UN Callisto shipyards. Additionally, a respected university with affiliations to Mars's technical institutes is located in the colony. The hemisphere facing Jupiter includes an observatory focused on Jovian research.
At some point prior to the Eros Incident, Callisto was the site of a proxy war between Earth and Mars, the Callisto Insurrection. As tensions rose over union negotiations, the UN sent in increasing numbers of private security forces while the MCR sent in advisors. The groups inflamed the tensions, resulting in Belter groups they backed fighting each other in the stead of Earth and Mars. This led to the death of Charanpal Avasarala, the son of UN Secretary-General Chrisjen Avasarala.
Io is one of the moons of Jupiter and the fourth-largest moon in the Sol System, slightly larger than Luna. It is the innermost of the "Galilean moons", the main group of Jupiter's moons that were discovered first.
Unlike some of Jupiter's moons, Io isn't shielded from the gas giant's massive radiation, with a standard vac suit being insufficient to protect its user. This, combined with its tectonic instability, makes it rather unsuitable for human habitation. There are numerous volcanoes across the moon that spew molten silicate into the atmosphere. Io houses research labs and supplies power cells to the Belt.
Europa, also "Jupiter II", is the sixth closest moon of Jupiter, and the smallest of its four Galilean satellites, but still the sixth-largest moon in the Sol System. Europa is slightly smaller than Luna and is primarily made of silicate rock with a water-ice crust. It has a very thin atmosphere, composed primarily of oxygen. The Tereshkova missions were the first long-term crewed surveys of Europa, whose mission was the search for extraterrestrial life. These missions, however, failed to discover alien life. Europa has a human settlement, which grows vegetables and beef in big mirror-fed greenhouses and supplies food to the Belt. There exists a Methodist church named St. John's United Congregation on Europa Station.