Grace Alone

Grace Alone was a planetoid 53 AU from Sol, existing in the Kuiper Belt between Neptune and the Oort Cloud.

A prefabricated mining colony existed on the surface, which held a weak but breathable atmosphere due to terraforming. Due to its lower-than-Earth gravity, individuals could bounce about five metres in one step. The First Doctor, Oliver Harper and Steven Taylor encountered the Vardans on Grace Alone when they attempted to invade Earth.

Presumably, the TARDIS travellers were meant to die on Grace Alone as they read that their bodies were found there. Before they could be killed by a Vardan, Oliver absorbed its remaining energy, dispersing himself to save the Doctor and Steven. (AUDIO: The First Wave)