Austar IV
All four books take place on the planet Austar IV, which is the fourth planet of a seven-planet rim system in the Erato Galaxy. It was a Federation penal colony, marked KK29 on the convict map system. It is a semiarid metal-poor world with two moons. During a four hour period in the night the two moons overlap and it becomes so cold that humans cannot remain outside without dying. Also, it has difficult terrain and not many plants or water sources. Such harsh conditions are why Austar IV was chosen as a place to send convicts.
Read more about this topic: The Pit Dragon Trilogy