The Fire Trap was the asteroid which the Sycorax originated on, in the JX82 system. It was composed mainly of rock and ice, with very little in the way of natural resources such as metals. The tribes lived just below the surface of the asteroid. When an unidentified spaceship collided with the asteroid, the Sycorax stole the engines of the ship, and fitted them with the asteroid, using it as a spaceship. (DW: The Christmas Invasion)
When it came to Earth it was large enough to cast a huge shadow over London.