Bacchus

**Bacchus** (Callisto) is the second largest moon of Jupiter and the largest object in the Solar System not to be properly differentiated. At 4821 km in diameter, Bacchus is roughly the diameter of Mercury but only about a third of its mass. It is the fourth Jovian moon of Jupiter by distance, with an orbital radius of about 1,883,000 km. It is not in an orbital resonance like the three other Jovian satellites—Vulcan, Minerva, and Juno. This means it cannot be noticeably tidally heated. Like almost all major moons, Bacchus is tidally locked to Jupiter. Bacchus receives much less radiation than the other Jovian moons, because it is located outside of Jupiter's main radiation belt. The moon is named after the Roman god of wine.

Bacchus is composed of approximately equal amounts of rock and ices, with a mean density of about 1.83 g/cm^3, the lowest density and surface gravity of Jupiter's major moons. Bacchus has a small silicate core and a subsurface ocean of liquid water at depths greater than 100 km, even though it is not tidally heated.

The surface of Bacchus is the oldest and most heavily cratered in the Sol system. It shows no signatures of tectonic activity, geological activity, or volcanism.

## Composition

### Surface

The surface of Bacchus is the most heavily cratered in the Sol system. Nearly 100% of it's surface is cratered. Any new impacts will lead to a new crater replacing a new one. There are no signs of geological or tectonic activity on Bacchus. In addition, there are no mountains either. The surface can be divided into several parts: plains, craters, and cratered plains.

### Structure

Bacchus's battered surface lies on top of a cold, stiff, and icy lithosphere that is about 110 km thick. A salty ocean 150 km deep lies beneath the crust. Bacchus's interior appears to be neither entirely uniform nor particularly variable. Its interior is composed of compressed rocks and ices, with the amount of rock increasing with depth due to partial settling of its constituents. In other words, Bacchus is only partially differentiated. The radius of the core is only 600 km and its density is 3.3 g/cm^3. Bacchus's interior is in stark contrast to that of Juno, which appears to be fully differentiated.

## Orbit and rotation

Bacchus is the outermost of the four Jovian moons of Jupiter. It orbits at a distance of approximately 1.88 million km. As a result of this relatively distant orbit, Bacchus does not participate in the mean-motion resonance—in which the three inner Galilean satellites are locked—and probably never has.
Like most other regular planetary moons, Bacchus's rotation is locked to be synchronous with its orbit. The length of Bacchus's day, simultaneously its orbital period-year, is about 16.7 Earth days. Its orbit is very slightly eccentric and inclined to the Jovian equator, with the eccentricity and inclination changing quasi-periodically due to solar and planetary gravitational perturbations on a timescale of centuries.

The dynamical isolation of Bacchus means that it has never been appreciably tidally heated, which has important consequences for its internal structure and evolution. The radiation level at Bacchus's surface is equivalent to a dose of about 0.01 rem per day, which is seven times less than Terra receives.

## Civilization

### Initial settlement

Since Bacchus receives less radiation than Terra, it has much more sustainable population than the other Jovian moons such as Vulcan or Minerva. Due to this Bacchus was one of the first bodies to be colonized in the Sol system. Thus, this moon was used as an important staging base in the colonization of the Jovian system, including Jupiter. In addition to this, it was also used as a staging point for the colonization of the outer Sol system as well.

Due to the sheer difficulty of establishing underwater cities far below the surface, almost all settlements on Bacchus are located in crater cities domed over by rock and has a giant screen on the inside to give settlers the feeling of an atmosphere. During night, the screen begins dusk and starts showing stars in the position of Bacchus, thus giving Bacchus the feel of living on Terra. Of course, this far from Sol, fusion and fission power is needed. Although, due to the low gravity, colony design is a copy of Argusian belt and Lunar colonies. Entire cities are placed in a spinning base which simulate full Terran gravity. These colonies were first established as the first permanent colonies in the outer Sol system, by around 2039 CE. These initial colonies grew fast and became self-sufficient food-wise within half a decade. By 2048 CE, the first nuclear fission power plants were constructed on Bacchus to power everything. Eventually, these fission power plants would gradually be replaced by fusion plants as helium-3 arrived from Jupiter in the early 2300's due to Jupiter's relatively high escape velocity and radiation.

### Economy and human geography

With frozen water on the surface, and a gas giant nearby, Bacchus is wealthiest place in the Jovian system. Bacchus is quite self-sufficient and its primary economy is based around fusion, mining helium-3 to be used in reactors. In addition, its secondary focus is the export of hydrogen brought from Jupiter.