Certax had no indigenous population, but was colonized by the Federation as a place to incarcerate hardened Human criminals, particularly those who had committed multiple murders. It was described as barren, but outfitted with Grade Alpha medical facilities and engineering workshops. Prisoner work details involved cutting rocks with jackhammers.
In 2267, the Federation starship USS Enterprise diverted to Certax following an engineering disaster. Technician Corcoran was brought to the colony's hospital following exposure to a lethal dose of radiation.
Four convicts took advantage of the starship's predicament by killing a guard and four engineering technicians, then slipping aboard the Enterprise as part of Certax's repair crew. To prevent reprisals after commandeering the Enterprise, the criminals threatened to drop an irradiated warp reactor on the prison from orbit. (TOS comic: "Prison Break")