Callisto /kəˈlɪstoʊ/ (Jupiter IV) is a moon of the planet Jupiter. It was discovered in 1610 by Galileo Galilei. It is the third-largest moon in the Solar System and the second largest in the Jovian system, after Ganymede, and the largest object in the Solar System not to be properly differentiated. At 4821 km in diameter, Callisto has about 99% the diameter of the planet Mercury but only about a third of its mass. It is the fourth Galilean moon of Jupiter by distance, with an orbital radius of about 1880000 km. It does not form part of the orbital resonance that affects three inner Galilean satellites—Io, Europa and Ganymede—and thus does not experience appreciable tidal heating. Callisto’s rotation is tidally locked to its revolution around Jupiter, so that the same hemisphere always faces inward; Jupiter appears to stand nearly still in Callisto’s sky. It is less affected by Jupiter’s magnetosphere than the other inner satellites because of its more remote orbit, located just outside the gas giant’s main radiation belt.
Callisto is composed of approximately equal amounts of rock and ices, with a mean density of about 1.83 g/cm3, the lowest density and surface gravity of Jupiter’s major moons. Compounds detected spectroscopically on the surface include water ice, carbon dioxide, silicates, and organic compounds. Investigation by the Galileo spacecraft revealed that Callisto may have a small silicate core and possibly a subsurface ocean of liquid water at depths greater than 100 km.
The surface of Callisto is the oldest and most heavily cratered in the whole Solar System. It does not show any signatures of subsurface processes such as plate tectonics or volcanism, with no signs that geological activity in general has ever occurred, and is thought to have evolved predominantly under the influence of impacts. Prominent surface features include multi-ring structures, variously shaped impact craters, and chains of craters (catenae) and associated scarps, ridges and deposits. At a small scale, the surface is varied and made up of small, sparkly frost deposits at the tips of high spots, surrounded by a low-lying, smooth blanket of dark material. This is thought to result from the sublimation-driven degradation of small landforms, which is supported by the general deficit of small impact craters and the presence of numerous small knobs, considered to be their remnants. The absolute ages of the landforms are not known.
Callisto uses an underwater colony system that heats the surrounding water. Primarily its been used as a gigantic fishery, recreating many of earths undersea wildlife, both for study and consumption. It uses a similar Darkgate tether and docking system that are used with floating stations.
- As a Biocraft organized base, there are always a genetic experiment in the wings.