Chimera is a top-secret human planet used by ONI as a facility to clone and train SPARTAN-IIs in their IMMORTAL-I program. Like Onyx the planet was not on any star map and the staff were not allowed to leave the planet without high level clearance. The planet itself had a breathable air to humans and was mostly covered in thick jungles while its north and south poles were covered in ice and deep snow. In between the icy regions and the jungles were large areas of tundra that separated the two opposite environments.