 When the planet exploded, one entire city of Krypton, Argo City, survived the cataclysm.Argo City drifted through space on an asteroid-sized fragment of Krypton, which had been transformed into kryptonite by the explosion.The super-advanced technology of its Kryptonian inhabitants allowed them to construct a life-sustaining dome and a lead shield that protected their city from the kryptonite radiation of the asteroid.