Dark Matter Reefs

The Dark Matter Reefs were a collection of similar astronomical phenomena in close proximity to each other.

Based on the way that Professor Yana described their general location to the the Tenth Doctor, Martha and Jack in about the year 100,000,000,000,000, they were quite remote from the planet Malcassairo. He suggested that the planet Utopia was between the Condensate Wilderness, on the near side of Malcassairo, and "the Wild Lands" and the Reefs, on the far side. (DW: Utopia)