Callisto Base was established in 2109, 11 years after the First Message from Jupiter had given mankind the principles of MEST-Curvature Application, which made it possible for them to travel freely throughout the Solar System.

Callisto Base' function was to monitor Jupiter for further Messages, or signs of life. At first it was a humble Solar Ranger observation outpost with a crew of 30, but conditions on Callisto allowed for expansion: there was water ice available upon the surface. Mining operations went into operation in the 30's and the Base became a town of about 1500 inhabitants, mostly located inside the large ringformed Asgard basin.

Second largest of Jupiter's 17 moons, Callisto was foremost chosen because it lies just beyond range of the far-spanning magnetoshpere which emanates from Jupiter, periodically bombarding the 3 nearer large moons with ferociously deadly radiation that can produce temperatures of 300 to 400 million degrees celcius. Callisto is also a very stable environment among Jovian moons, without the volcanic activity of Io, or Europa's brittle surface of floating ice.

Callisto is 4800 km in diameter and orbits Jupiter at a radius of 1,880,000 km every 16.6 earth days.