San Helios

San Helios was a planet in the Scorpion Nebula. Before being devoured by a Metallic Swarm and turned into a desert planet, the civilisation there had a population of 100 million, centred at San Helios City. The Swarm Creatures arrived there via a Wormhole they opened via the velocity of their movement. They opened one on San Helios after devouring everything in an attempt to move on put were prevented from doing so by The Doctor. The wormhole was closed forcing the creatures to create another one in order to leave San Helios finally. Interestingly, the similarly sounding Sanghelios is another fictional planet in the Halo series of games, from which the Elite race originate.

(DW: Planet of the Dead)