Location: Carina Nebula. Byzantium is a large G-class yellow dwarf with 4 planets in its planetary system (all named after Byzantine emperors) including the human colony world of Constantine. The system was first explored by humans in 2153 and colonised a year later.
First planet orbiting Byzantium.
Justinian, by all means can be considered an absolute hell. A large "super earth", it's almost three times the size of Earth with crushing gravity, extemly thick and corossive atmosphere and scortching temperatures. Though the human explorers discovered some sizable heavy metal deposits, the expenses needed to mine the world would bankrupt any corporation. Ever since its initial discovery, Justinian lies alone and forgotten.
Second planet orbiting Byzantium.
Constantine is a two-mooned garden world, orbiting the star Byzatium. It is largey covered by shallow seas, heavily populated with diverse marine life, offering little opportunity in terms of agriculture or mining. Nevertheless the Alliance has established a thriving colony on this world.
Third planet orbiting Byzantium
Theodosius is a standard hydrogen-hellium gas giant. As soon as the colony on Constantine was established, Eldfell-Ashland Energy corporation jumped in, securing the planet's colonization rights from the Alliance. Soon a sizable Helium-3 extraction and refueling facility was built in orbit, drawing many profits for the company as a result of the system's heavy traffic.
Fourth Planet orbitng Byzantium.
Leon is a small blueish ice giant. It's orbit lies far away from the rest of the system. It lacks any remarkable features, which lead to Leon never being developed.