San Helios

San Helios was a planet in the Scorpion Nebula. Before being devoured by Unknown Swarm Creatures 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 doin so by The Doctor. The wormhole was closed forcing the creatures to create another one in order to leave Sna Helios finally. (DW: Planet of the Dead)