Kolkokron

Kolkokron was a junk planet orbiting a dying star, (AUDIO: Time in Office) uninhabited, with nothing but rocks and boulders on it in the far future. (TV: Frontios)

After a brief and unintentional stop on Queth, (PROSE: Life After Queth) the Fifth Doctor and Tegan Jovanka left the Gravis on Kolkokron, separating him from the rest of the Tractators back on Frontios. (TV: Frontios)

Professor Stream later retrieved the Gravis from Kolkokron and brought it to 20th century Earth to use with the other Tractators in his quantum gravity engine. (AUDIO: The Hollows of Time)