From Halopedia, the Halo wiki
As part of the Exodus Project, numerous Shaw-Fujikawa Translight Engines were added to the asteroid to facilitate evacuation of the Rubble. The Hollowed-out rock contained miles of corridors, stadium chambers with rows of chairs and restraints for a hundred thousand people, bays, and a bridge near the front. The Exodus' purpose was to carry the one million residents of the Rubble to a location in the galaxy far away from the UNSC and the Covenant.
Circumstances forced the use of the Exodus before the desired number of Slipspace Drives could be installed. Thus, rather than attempting a journey beyond UNSC and Covenant Space, the asteroid was sent toward another human-occupied system. The Exodus reached the 18 Scorpii System and successfully evacuated the ex-Rubble residents to the UNSC colony of Falaknuma. While in orbit around the planet, the asteroid succumbed to damages caused by unanticipated resonances from transitioning such a large body to slipspace, ultimately disintegrating to form a debris ring around Falaknuma.
List of appearances