Oort cloud

The Oort cloud, also known as the cometary cloud, was a region on the edge of the Solar system filled with asteroids in constant orbit around Sol. It was the point of origin of many of the solar system's comets. Counting this cloud, the solar system extended to a distance of about 1 and a half light-years or 40 billion miles from the Sun. (PROSE: To the Slaughter, AUDIO: Origins of the Cybermen)

History
An alien probe searching for signs of life used it as a base of operations. (AUDIO: Murmurs of Earth) By the 24th century, it had become a navigational hazard. To fix that and improve the system's feng shui, Robart Falsh and Aristotle Halcyon sold all the asteroids in the cloud to the Kilomons, Draconians and other alien races. (PROSE: To the Slaughter)

After the Dalek Time Squad had been defeated in the Dark Times with their ship falling apart in the Time Vortex, (AUDIO: Mutually Assured Destruction), a Dalek drone under their command found itself in the Oort cloud, (PROSE: The Last Message) sometime before 2985 where it was found by the Starship Future. (AUDIO: Genetics of the Daleks)

The Other appeared in the Oort cloud. (PROSE: Eternity Weeps)