Jupiter

Europa

Ganymede

Callisto

King of the planets, Jupiter occupies the fifth orbit from the Sun and is the largest planet in the Solar System, notable for its iconic Red Spot and beautiful banded appearance.

## Overview

Jupiter sits at around 5.20 AU from the Sun, and takes 12 years to complete a full orbit. In contrast to its long orbital period, the planet rotates only every 10 hours, making it have the shortest days in the Solar System.

There are at least 95 moons circling the planet, with more possibly still waiting to be discovered. The largest of these, the Galilean moons, are the largest and most iconic with one of them, Europa, having its own native life, the first to be found beyond Earth. They also serve as home to the Jovian Protectorate, the capital being on Callisto.

Its atmosphere is mostly hydrogen and helium, along with trace amounfs of methane and ammonia. Jupiter's mass is more than 2 and half times of all the other planets combined, theoretically, it would be possible to fit all the other planets within with room to spare.

## Observation and Exploration

Jupiter has been observed since prehistoric times, due to being the third brightest object in Earth's night sky, after the Moon and Venus, being named after the chief deity of the Roman religion.

The main Galilean moons were discovered by Galileo Galiliei in 1610, with more being found the following centuries. It wasn't until 1973 that we'd see this giant world and its moons up-close, when Pioneer 10 performed a flyby of the planet, followed by Pioneer 11 in 1974.

Not long after that, Voyager 1 would pass by the planet in March, 1979, followed by Voyager 2 in July of that year. Later on in 1995, the Galileo space probe would be the first to properly orbit the planet, studying the climate and intense thunderstorms on the planet, even sending down a small atmospheric probe in the process. Sadly, unlike the Pioneers and Voyagers, Galileo didn't continue any further, ending its mission by plummeting into the jovian atmosphere.

The 21st Century is when interest in Jupiter took a rise, when Europa was found to harbour life in the 2030s thanks to the Jupiter Icy Moons Explorer (or JUICE for short). This revolutionary new discovery prompted several new missions to explore the newly discovered biosphere existing next-door, as well as the other Galiliean moons for signs of any life.

The first manned mission, the *Vanguard 1,* as part of the Outer Solar System Exploration Program (OSSEP) was commenced in the 2050s, to further study Europa as well as map out future colony sites on Ganymede and Callisto.

## Colonisation

After decades of intensive exploration, the 2080s saw the eventual colonisation of the Jovian system under the *Galilean Initiative,* having been spearheaded from Mars and Ceres. Of course, only the moons were colonised, as technology was not yet advanced enough for atmosphere cities on Jupiter itself.

Atmospheric mining officially began on Jupiter during the 26th century, with dirigible cities being built at the time. Sky tours are also conducted on specially designed zeppelins in the upper atmosphere, giving magnificent views of the clouds and aurorae.

People living on Jupiter or its moon system are referred to as *Jovians*, affectionately called *Jovies*, by other planets. Alternatively, those on the moons can also be called *Galileans,* to distinguish themselves from those living in Jupiter's atmospheric cities.

## Moons

### Io

Io was the only major moon that wasn't colonised due to its extremely volcanic nature as well as high radiation levels. The tidal pull combined with how geologically active it is results in a constantly changing surface, making a stable settlement impossible. Only a small robotic lander was sent, however it only lasted a couple minutes before sinking into the surface.

It is most notable for its hyper-eruptions, large enough to be seen from orbit, creating magnificent, umbrella-shaped clouds. The Jovian Protectorate has stationed observation decks in orbit, to allow for citizens to witness these hyper-eruptions for themselves. These eruptions can usually be predicted thanks to probes monitoring tectonic activity in orbit.

### Europa

Famous for harbouring life in its subsurface ocean, Europa was what ultimately prompted exploration of the Galiliean moons in the first place. Only research bases have been built to study Europa's ecosystems, as full-fledged colonisation or even terraforming is strictly prohibted by the Jovian Protectorate, so the native life isn't disturbed.

The underground biosphere of Europa is among some of the most diverse eved found, primarily kept warm my Jupiter's radiation as well as hydrothermal vents. The discovery of this life proved to be a game changer for Humanity, telling us more about our place in the universe and how life comes to be elsewhere.

### Ganymede

The largest of the Galilean moons, unique for possessing its own magnetic field, generating ribbon-like aurorae at its north and south poles. It also contains a subsurface ocean of saltwater, though unlike its sister Europa, does not contain life. Although in Jupiter's radiation belt, its magnetic field works to shield away some of it, making radiation resistant domes fairly easy to build. Ganymede is the main mining hub for the Galilean system, thanks to its size, even being larger than the planet Mercury. As such, Ganymede exports most of its resources for usage elsewhere in the Jovian system and beyond. This has caused some Ganymedeans to feel animosity towards Calisto, viewing them as "self centered" due to the Protectorate having its capital there.

### Callisto

Callisto serves as the capital of the Jovian Protectorate, as well as the Galilean moons in general. Thanks to its position outside Jupiter's radiation belt, it was arguably the easiest to colonise, with colonists being free to walk about the surface in regular space suits. Tourists and residents alike use this to their advantage, venturing outside their domed colonies to admire the views of Jupiter and its moons in the sky. Geographically Callisto is heavily cratered, giving it an almost sparkly/spotty appearance from orbit, with its capital city, *Valhalla*, being built in the biggest crater, bearing the same name.

The quality of life on Callisto is arguably the highest as settlements were built without worry of shielding from Jupiter's radiation, allowing for more artistic architecture.

### Amalthea

Noted for being the reddest object in the Solar System, likely a result of ash from Io covering it when falling to Jupiter. Amalthea is the fifth largest moon after Europa, its appearance making it more noteworthy then its other irregular siblings. Because of this, it is often visited during Jovian moon tours.