Exactly what the Noumenon is, has been the subject of considerable debate among Covenant scholars for centuries. Some believe that it is a part of the Halo Array, while others insist that it is separate, but equally important. Even its purpose is unknown, and speculation ranges from a massive Forerunner shipyard to a research facility, and even to a rival to the Ark. For a long time, even it's existence was uncertain - the only sources were obscure engravings copied from destroyed Forerunner relics from the Sangheili world of Ketesh, known for producing historical theologians who have been rejected by the Covenant as legitimate.